Hexarelin is a new hexapeptide (His-D-2-methyl-Trp-Ala-Trp-D-Phe-Lys-NH2) that stimulates the release of growth hormone both in vitro and in vivo. In this double-blind, placebo-controlled, rising-dose study we evaluated the growth hormone releasing activity of hexarelin in healthy human subjects. Twelve adult male volunteers received single intravenous boluses of 0.5, 1 and 2.micrograms.kg-1 hexarelin as well as placebo. For safety, drug doses were given in a rising-dose fashion with placebo randomly inserted into the sequence. Plasma growth hormone concentrations increased dose-dependently after the injection of the peptide, peaking at about 30 min and then decreasing to baseline values within 240 min with a half-life of about 55 min. The mean peak plasma growth hormone concentrations (Cmax) were 3.9, 26.9, 52.3, 55.0 ng.ml-1 after 0, 0.5, 1 and 2 micrograms.kg-1, respectively. The corresponding areas under the curve of growth hormone plasma levels from drug injection to 180 min (AUC0-180) were 0.135, 1.412, 2.918 and 3.695 micrograms.min.ml-1. The theoretical maximum response (Emax) and the dose that produces half of the maximum response (ED50) were estimated using logistic regression. The calculated ED50 values were 0.50 and 0.64 microgram.kg-1 for Cmax and AUC0-180, respectively. The corresponding Emaxs were 55.1 ng.ml-1 and 3936 ng.min.ml-1, thus indicating that the effect after the 2 micrograms.kg-1 dose is very close to the maximal response. Plasma glucose, luteinising hormone, follicle-stimulating hormone, thyroid-stimulating hormone and insulin-like growth factor I were unaffected by hexarelin administration, while the peptide caused a slight increase in prolactin, cortisol and adrenocorticotropic hormone levels. Hexarelin was well tolerated in all subjects. The results of this study indicate that intravenous administration of hexarelin in man produces a substantial and dose-dependent increase of growth hormone plasma concentrations.
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Eur J Clin Pharmacol (1994) 46:421-425
© Springer-Verlag 1994
Growth hormone-releasing activity of hexarelin in humans
A dose-response study
B. P. Imbimbo 1, T. Mant 2, M. Edwards 2, D. Amin 2, N. Dalton ~, E Boutignon 3, V. Lenaerts 3, P. Wiithrich 3, R. Deghenghi s
1 Medical Department, Mediolanum Farmaceutici, Milan, Italy
2 Drug Research Unit, Guy's Hospital, London, UK
3 Europeptides, Argenteuil, France
Received: 1 August 1993 / Accepted in revised form: 8 December 1993
Abstract.
Hexarelin is a new hexapeptide (His-D-2-
methyl-Trp-Ala-Trp-x)-Phe-Lys-NH2) that stimulates the
release of growth hormone both in vitro and in vivo. In this
double-blind, placebo-controlled, rising-dose study we
evaluated the growth hormone releasing activity of hexa-
relin in healthy human subjects. Twelve adult male vol-
unteers received single intravenous boluses of 0.5, 1 and
2 .gg-kg -1 hexarelin as well as placebo. For safety, drug
doses were given in a rising-dose fashion with placebo ran-
domly inserted into the sequence. Plasma growth hor-
mone concentrations increased dose-dependently after
the injection of the peptide, peaking at about 30 rain and
then decreasing to baseline values within 240 min with a
half-life of about 55 min. The mean peak plasma growth
hormone concentrations (Cmax) were 3.9, 26.9, 52.3,
55.0 ng. ml -~ after 0, 0.5, 1 and 2 ~tg. kg -~, respectively. The
corresponding areas under the curve of growth hormone
plasma levels from drug injection to 180 min (AUCc~180)
were 0.135, 1.412, 2.918 and 3.695 ~tg-min-m1-1. The the-
oretical maximum response (Emax) and the dose that pro-
duces half of the maximum response (EDs0) were esti-
mated using logistic regression. The calculated EDs0
values were 0.50 and 0.64 pg-kg -~ for Cm~ and AUC0_~s0,
respectively. The corresponding ErnaxS were 55.1 ng. mk 1
and 3936 rig. min-m1-1, thus indicating that the effect after
the 2 gg. kg ~ dose is very close to the maximal response.
Plasma glucose, luteinising hormone, follicle-stimulating
hormone, thyroid-stimulating hormone and insulin-like
growth factor I were unaffected by hexarelin administra-
tion, while the peptide caused a slight increase in prolac-
tin, cortisol and adrenocorticotropic hormone levels.
Hexarelin was well tolerated in all subjects. The results of
this study indicate that intravenous administration of
hexarelin in man produces a substantial and dose-depen-
dent increase of growth hormone plasma concentrations.
Key words:
Hexarelin, Growth hormone; growth hor-
mone releasing peptides
Correspondence to: B.R Imbimbo, Medical Department, Mediola-
num Farmaceutici, Via S. G. Cottolengo 15,1-20143 Milan, Italy
Growth hormone-releasing peptides (GHRPs) are a new
class of small peptides, consisting of six or seven amino
acids, that release growth hormone (GH) in several animal
species including man [1]. Chemically, GHRPs are unrelat-
ed to growth hormone-releasing hormone (GHRH), the
natural 44-amino acid peptide that releases GH from the
pituitary [2]. The first GH-releasing hexapeptide, GHRP-
6, was described in 1984 [3]. Other GH releasing hexa- and
hepta- peptides were described later [1]. All of these
GHRPs stimulate GH release from the pituitary level [4, 5]
acting at receptor sites which are different from those of
GHRH [6, 7]. Indeed, when administered with GHRH,
GHRPs have a synergistic effect [8]. In addition to their pi-
tuitary action, GHRPs also act on the hypothalamus where
GHRP binding sites have been reported [9,10].
Recently, a new hexapeptide (hexarelin) has been de-
scribed [11]. Its chemical structure (His-I>2-methyl-Trp-
Ala-Trp-D-Phe-Lys-NH2) is similar to that of GHRP-6,
with the substitution of D-tryptophan with its 2-methyl
derivative. Hexarelin is less susceptible to degratation
than GHRP-6 [12]. Preliminary studies in rats have indi-
cated that the drug is more potent and less toxic than
GHRP-6 [13].
This study reports the pharmacodynamic, safety and
tolerability results of the first administrations of hexarelin
to humans. The dose-response curve of the GH-releasing
activity of hexarelin in healthy male human subjects was
assessed.
Subjects and methods
Study design
The protocol of the study was approved by the Lewisham and North
Southwark Committee on Ethical Practice. The study was carried
out according to a double-blind, placebo-controlled, rising-dose de-
sign, Twelve adult male volunteers received single intravenous bo-
luses of 0.5, 1 and 2 ~tg. kg ~1 hexarelin as well as placebo. For safety,
drug doses were given in a rising-dose fashion with placebo inserted
into the sequence according to a random allocation schedule. Doses
were separated by one-week washout periods.
422
Hexarelin was synthesized by Bachem (Bubendorf, Switzer-
land). Vials containing 100 p,g lyophilized hexarelin or placebo (lac-
tose) were prepared by Europeptides (Argenteuil, France).
Lyophilized hexarelin or placebo was dissolved in i ml isotonic
saline and administered in appropriate volumes according to body
weight. If eligible at the screening visit, subjects were admitted to the
unit on the afternoon before each dosing day for a limited physical
examination (cardiac, pulmonary, abdominal), 12-lead ECG, labor-
atory safety and drug screening. Each dose of the study drug was
given after an overnight fast, and fasting was maintained for 4 h post-
dose. Clinical monitoring and plasma collection continued for 24 h
after each dose, and subjects were confined in the unit during this
period.
Blood sampling
About 30 min before drug injection, a 18-G catheter was inserted
into a cubital vein to allow repeated blood sampling. The vein was
kept patent by a slow infusion of isotonic saline. At time 0, each sub-
ject received the treatment according to the randomization sche-
dule. Blood for haematology and clinical chemistry was collected at
approximately 0,1 and 24 h after each dose. Plasma samples for GH
assay were collected at 10 rain before the dose and 0,10, 20, 30, 40, 50,
60 and 90 rain and 2, 3, 4 and 24 h after. Plasma samples for assay of
glucose, prolactin, cortisol, adrenocorticotropic hormone (ACTH),
luteinizing hormone (LH), follicle-stimulating hormone (FSH), thy-
roid-stimulating hormone (TSH) and insulin-like growth factor I
(IGF-I) were collected at 0, 30 and 60 min and 24 h after each dose.
Urine was collected for 24 h after drug injection for assay of free cor-
tisol. The volume of each fraction was recorded, and 20-ml aliquots
were frozen at -20 °C for subsequent assay.
Assays
Plasma GH levels were measured in duplicate by a chemilumi-
nescence immunometric assay (HGH, Nichols Institute, San Juan
Capistrano, Calif.). The sensitivity of the assay was 0.02 ng-m1-1.
The ranges of inter- and intra-assay coefficients of variation were
7.9-9.2 % and 4.0-5.4 %, respectively. All samples taken from an in-
dividual subject were simultaneously analysed in the same assay
Plasma glucose concentrations were assayed with a Beckman
system timed endpoint method using hexokinase.
Plasma prolactin concentrations were assayed by immunoassay
(All6gro-PRL, Nichols Institute). The sensitivity of the assay was
1
0.14 ng- ml-. The inter- and intra-assay coefficients of variation were
6.7-8.0 % and 3.5-4.6 %, respectively.
Plasma and urine cortisol concentrations were assayed by fluo-
rescence polarization immunoassay (TDx Cortisol, Abbott Labora-
tories, Chicago, Ill.). The sensitivity of the assay was 1.6 nmol-1-1.
The inter- and intra-assay coefficients of variation were 1.0-7.2 %
and 2.7-8.4 %, respectively.
Plasma LH concentrations were assayed by an immunochemi-
luminometric assay (Magic Lite LH, Ciba, Basel, Switzerland). The
1
sensitivity of the assay was 0.07 IU-1-, The inter- and intra-assay
coefficients of variation were 2.8-8.8 % and 2.2-8.4 %, respectively
Plasma FSH concentrations were assayed by an immunochemi-
luminometric assay (Magic Lite FSH). The sensitivity of the assay
was 0.1 IU. 1 q. The inter- and intra-assay coefficients of variation
were 5.0-8.8 % and 2.7-7.3 %, respectively
Plasma TSH concentrations were assayed by a microparticle
enzyme immunoassay (IMx Ultrasensitive hTSH, Abbott Labora-
tories, Abbott Park, Ill.). The sensitivity of the assay was 0.03 mIU-
1 -~. The inter- and intra-assay coefficients of variation were 4.0-
7.2 % and 3,0-5,2 %, respectively.
Plasma ACFH concentrations were assayed by immunoassay
(Alldgro HS-ACTH, Nichols Institute). The sensitivity of the assay
was 1 pg-m1-1. The inter- and intra-assay coefficients of variation
were 6.8-7.8 % and 3.0-3.2 %, respectively.
Plasma IGF-I concentrations were assayed by radioimmuno-
assay (Department of Chemical Endocrinology, St. Bartholomew's
Hospital, London, UK). To avoid interference by bindings proteins,
the assay was performed after ffomic acid-acetone extraction. The
sensitivity of the assay was 0.1 ng- ml 1. The inter- and intra-assay
coefficients of variation were 10.1-15.7 % and 10.3-12.0 %, respec-
tively. All samples taken from an individual subject were analysed
with the same kit.
Safety and tolerability
Electrocardiac (ECG) monitoring was started i h before drug injec-
tion and continued for 4 h thereafter. Rhythm strips were collected
at time -1, 0.5, 1, 3 and 24 h. Supine blood pressure and heart rate
were recorded at time 0, 20, 40 and 60 min and 2, 4 and 24 h after in-
jection. Blood for complete haematology and clinical chemistry
were collected at 1 and 24 h postdose. Urine was also collected at 1
and 24 h for complete urinalysis. Adverse events were carefully
monitored.
Statistical analysis
The maximum GH plasma concentration observed (Cmax) and the
time of its occurrence (tmax) were obtained from individual data. The
areas under the GH plasma levels versus time curves from 0 to
60
[/3
0 Placebo i.v.
2
v
Hexarelin 0.5 /~g/kg i.v,
,,>, 5O
._l ~ ~-z~/ I:3 Hexarelin 1.0 g,g/kg
i.v.
z~ Hexarelin 2.0 ,u,g/kg i.v.
<
4o
g
o
n- "~ 20
eo 10
%
0
, , , , i
//// .
0 1 2 3 4 24
TIME AFTER INJECTION (h)
Fig.
l. Time-course of growth hormone plasma concentrations after
different intravenous doses of hexarelin in 12 healthy young male
volunteers
Table
1. GH responses (mean with SEM) to different intravenous
doses of hexarelin in 12 healthy young male volunteers
Hexarelin Cm~ Tm~x AUC0-180
Dose (ng-ml- 1) (min) (ng. rain- ml- 1)
(~g.kg-1)
0.0 3.9 +__ 1.3 168 __+ 28 135 + 51
0.5 26.9 _____ 4.3 a 32 +__ 28 1442 + 260 a
1.0 52.3__+5.08 33__+3 ° 2918+309"
2.0 55.0__+4.5 a 33+2 a 3695+337 ~
*P < 0.05 vs 0.0 gg- kg 1
+ 180 min (AUCc~ls0) were calculated with the linear trapezoidal
method. Statistical comparisons were performed with non-parame-
tric tests. The Friedman test was employed to simultaneously com-
pare medians of the four treatment groups and Dunnett's test for
multiple pairwise comparisons. The significance level was P < 0.05
(two-sided test).
A dose-response curve was constructed for Cr~ and AUC0_ls0 of
GH. The theoretical maximum response (Emax) and the dose that
produces half of the maximum response (EDs0) were estimated
using logistic regression.
4500
4000
~m 35o0
~ 3000
z
°
2500
o E
I
J 2000
E
o ,E 1500
E
& 1000
o
,
500
< 0
J AUCma x = 3936 ± 540 ng.min/mL
60
50
40
44
E
E 20
=
10
I
I
0 ,4- 0.05 p.g/kg
Crnox = 55.1 4- 4.5 ng/mL
I I I [ I I I
0.0 0.5 1.0 1.5 2.0 2.5 3.0
HEXARELIN INTRAVENOUS DOSE (#g/kg)
Fig.2.
Dose-response curve on AUC~180
(upper panel)
and maxi-
mum growth hormone plasma concentrations
(lower panel)
after
different intravenous doses of hexarelin in 12 healthy young male
volunteers
423
Rate of disappearance of GH from plasma was estimated with
log-linear regression of the postabsorption mean concentrations.
The slopes of the regression lines represent the elimination rate con-
stants (ke) from plasma. The corresponding elimination half-lives
(tl/2) were defined as In 2. ke -1.
Calculations were performed with the SigmaStat statistical pack-
age [14]. Although non parametric tests were adopted for statistical
comparisons, results are expressed as mean -+ SEM.
Results
Pharmacodynarnics
Figure 1 shows the GH plasma level profiles after placebo
and the different doses of hexarelin. The placebo injection
had little or no effect on plasma GH concentrations (GH
< 5 ng-ml 1). After hexarelin, a dose-dependent increase
in plasma GH was observed. Doses of 05, 1 and 2 gg-kg -1
of the peptide consistently increased plasma GH concen-
trations, peaking at 30-40 min and then decreasing to ba-
seline values within 240 min, with a half-life of 50, 51 and
58 min, respectively. Mean
Cma x
and AUCcqs0 increased
dose dependently (Table 1 and Fig. 2). The calculated
EDs0 values were 0.50 (0.05) gg.kg -1 and 0.64 (0.13)
gg-kg -1 for Cmax and AUC0_180, respectively. The corre-
sponding Em~x values were 55.1 (4.5) ng.m1-1 and 3936
(540) ng. min. ml 1, thus indicating that the effect after the
2 ~tg-kg i dose is very close to the maximum response.
Plasma concentrations of glucose, LH, FSH, TSH and
IGF-I were unaffected by hexarelin administration
(Table 2). Plasma levels of prolactin were moderately in-
creased by drug injection (Table 2). The peak plasma cor-
tisol concentrations also tended to be higher in response
to hexarelin than in response to placebo (Table 2). How-
ever, urinary excretion of cortisol remained unchanged.
Plasma ACTH concentrations changed little during hexa-
relin or saline administration. Although peak ACTH
levels were significantly higher after hexarelin compared
to placebo, individual values on hexarelin were always
within the normal range. The only exception was one sub-
ject who received 2 gg. kg -1 for which a value of 72 pg- ml -~
was observed 30 min after injection.
Safety and tolerability
There were no clinically significant adverse events. Three
subjects on placebo, five on hexarelin 0.5 gg. kg -1, four on
1 gg- kg 1 and seven on 2 gg. kg -1 reported minor adverse
Table 2. Peak plasma concentrations (mean with SEM) of prolactin, cortisol, glucose, LH, FSH, TSH, ACTH and IGF-I after different
intravenous doses of hexarelin in 12 healthy young male voluhteers
Hexarelin Glucose Prolactin Cortisol Urinary LH
Dose (mg-dl 1) (ng.ml-1) (ng.ml-1) Cortisol (IU.1-1)
( gg. kg-1) (gg. day-~)
0.0 95.5+1.5 11.7+1.5 140_+16 402+5,9 6.62_+0.48
0.5 96.1_+1.2 15.3 + 1.5 a 190±14 a 43.7-+6.0 6.96_+0.66
1.0 93.5-+1.3 20.1+2.4 a 201_+12 a 40.4-+3,7 6.48±0.62
2.0 94.4-+1.2 25.4+2.3 a 206_+12 a 45.6-+8.1 6.13-+0.56
normal range 70-110 3.0-14.7 55-236 10-91 1.3-19.8
*P < 0.05 vs 0.0 gg. kg -1
FSH TSH ACTH IGF-I
(IU. 1-1) (mIU. 1- ~) (pg. ml- 1) (ng. ml- 1)
5.51_+0.69 1.78+0.22 19.3+2.2 228+16
5.94-+0.79 1.79+0.30 24.3 + 3.P 221+18
5.57+0.68 1.52+0.19 25.8+2.5" 256+13
5.30 + 0.70 1.63 + 0.22 33.4 + 3.9" 258 + 17
2.0-12.8 0.32-5.00 ~ 9-52 40-316
424
events. The most frequent adverse event believed to be
drug-related was transient flushing and was observed in
two subjects receiving 0.5 ~tg-kg -~, one receiving i gg-kg -~
and five receiving 2 gg kg -1. One additional subject re-
ceiving I gg. kg ~ experienced sweating.
There were no clinically significant changes in heart
rate, blood pressure or ECG tracings at any dose level.
There were no drug-related abnormalities in clinical
chemistry or haematology.
Discussion
This study demonstrates that intravenous administration
of hexarelin results in substantial dose-dependent in-
creases in plasma GH concentrations. The effect is maxi-
mal with 2 gg. kg -1. In general, the pattern of GH release
induced by hexarelin is similar to that reported for
GHRP-6 [15-20]. However, the maximal effective dose of
other GHRPs by the intravenous route has never been
fully evaluated [15-20]. The dose most studied has been
1 gg. kg -1. To our knowledge, only two subjects have re-
ceived intravenous doses of 1.6 and 2.5 gg. kg -1 GHRP-6
[15]. The extent of GH response obtained in the present
study with I gg. kg -~ hexarelin by the intravenous route is
similar to that recently reported for GHRP-1, considered
more potent than GHRP-6 [1].
The estimated EDs0 of intravenous hexarelin in man
was found to be around 0.5 gg- kg -~. Of the species tested
so far, man is the most sensitive to the effects of the drug
on GH release [11-13]. Indeed, the estimated EDs0 in
rats and dogs was approximately 20 and 100 gg. kg -~, re-
spectively [11-13]. This seems to indicate that the activity
of hexarelin is species-specific. Hexarelin may mimic the
action of endogenous GHRP-like substances which
could have, especially in man, a crucial role in the regula-
tion of GH secretion [21]. If this hypothesis is correct, the
physiology of GH secretion in man may have to be re-
defined.
As with other GHRPs [15-20], the action of hexarelin
is not completely specific for GH release. We found a
slight dose-related increase in prolactin levels in com-
parison to placebo. Stress may have had an influence on
this variable since the prolactin levels of three of the sub-
jects who received placebo were higher than the upper
limit of the normal range. There was also a slight dose-re-
lated effect on cortisol levels, although they generally re-
mained within normal limits after all hexarelin treat-
ments.
Hexarelin was generally safe and well tolerated at
the doses administered (0.5-2 gg-kg-1). Flushing epi-
sodes appeared to be more frequent in the highest dose
group. The only subject who had ACTH concentrations
above normal limits following intravenous injection of
2 gg. kg -~ hexarelin also experienced flushing that lasted
10 min.
In conclusion, the results of this study demonstrate
that hexarelin is safe and well tolerated when given as
single intravenous doses of up to 2 gg. kg I in healthy
male subjects. The drug produces a substantial and dose-
dependent increase in GH plasma concentrations. Hexa-
relin could possibly be used in the diagnosis of GH defi-
ciency and in the treatment of patients with insufficient
somatotrophic secretion due to hypothalamic dysfunc-
tion.
Acknowledgements'. The study was supported by a grant from
Mediolanum Farmaceutici, Milan, Italy and from Europeptides, Ar-
genteuil, France. Part of this study was presented at the Interna-
tional Symposium on Growth Hormone II: Basic and Clinical As-
pects, held in Tarpon Springs, Florida, on 3-6 December 1992. Ab-
stract book: p. 37 (abstract 22).
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Abstract book: p. S-28
... doses of 2.0 /ig o f GHRP per kg of body weight administered to normal adults were compared with 1.0 ytig/kg doses, the increase in peak serum GH concentration was slight and statistically not significant (Ghigo et a l, 1994a). A dose-response study of hexarelin by Imbimbo et al (1994) showed this increase to be approximately 6%. The S.C., i n. and oral dosages have been based largely on comparisons with the responses to the i.v. ...
... The majority of the studies were conducted using an intravenous hexarelin dose o f 1.0 /ig of peptide per kg of body weight. The rationale for doing so was that this dose of hexarelin had been shown to produce near-maximal / maximal GH release whilst avoiding any side effects (Ghigo et al., 1994a;Imbimbo et al., 1994). Most o f our studies were planned with a view to comparing the GH-releasing effect of intravenous hexarelin with that of GHRH. ...
... The GH dose-response curve (cubic model) showed a plateau at a hexarelin dose of 1.0 //g/kg, suggesting that such a dose was near-maximal. A dose-response study by Imbimbo et al (1994), where hexarelin doses of up to 2.0 //g/kg were administered to normal adults, showed that increasing the dose o f hexarelin from 1 . 0 to 2 . ...
Ahmed F. Massoud
This work describes physiological studies of the growth hormone releasing peptide (GHRP) hexarelin. Four groups of studies were conducted on young, healthy, adult male volunteers, as follows; 1. Studies which demonstrated that hexarelin is a potent growth hormone (GH) secretagogue, capable of inducing GH release after two successive administrations. GHRP acts synergistically with growth hormone releasing hormone (GHRH) to induce massive GH release. However, this synergistic action is lost on repeated administration. 2. Studies which showed that GH itself attenuates the GH response to GHRP. 3. Studies which showed that the GH-releasing activity of GHRP, alone or in combination with GHRH, is attenuated but not abolished by increasing somatostatin (SS) tone. The large GH release induced by GHRP plus GHRH despite the presence of high SS tone suggests that combined therapy may be utilised to produce GH release in conditions where SS tone is unknown. 4. Studies which established GH dose-response curves for hexarelin. This group of studies also showed that hexarelin is non-specific for GH release, inducing prolactin (PRL) and cortisol release in a dose-related manner. These studies showed that at low doses of hexarelin it is possible to induce adequate GH release with minimum concomitant rise in PRL and cortisol. Moreover, combined GHRH plus low dose hexarelin is synergistic for GH release with no additive effect on PRL and cortisol release. The actions of GHRPs and their interaction with the two main endogenous regulators of GH secretion, namely, GHRH and SS, strongly suggests that an endogenous GHRP ligand exists and plays an important role in the regulation of GH release. The specific GH release induced by low doses of GHRP, alone or in combination with GHRH, together with the oral activity of these peptides, holds a great promise for future therapeutic use.
... Generally well tolerated with no serious adverse events reported; Alteration of sleep architecture (reduced slow−wave sleep); stimulation of multiple endocrine axes (ACTH, cortisol, prolactin) beyond GH; non−specific pituitary/adrenal activation observed (90,138,140 The distribution phase is approximately 7,6 +/-1,9 min, and the elimination phase is 2,5 +/-1,1 h, resulting in an effective half-life of around 2.5 h. *Evidence base coding (per Section 3.5 stratification): A, randomized controlled trial evidence within an approved clinical indication; A*, historical regulatory approval (FDA approval for paediatric GHD historically held; commercially withdrawn 2008), with no current regulatory approval for performance/body-composition indications; B, phase I/II human studies (PK/PD, endocrine, or paediatric GHD-related), without controlled efficacy data for body-composition or performance endpoints; C, limited human data, predominantly shortterm or indirect; D, no peer-reviewed human studies, with claims resting on preclinical extrapolation and grey-literature user narratives. ...
Aleksander Dominikowski
Zofia Rękoś
Michał Olejarz Marek Ruchała
Performance-enhancing drugs (PEDs) marketed as “research compounds” include unregulated peptides intended to modulate the growth hormone–insulin-like growth factor-1 (GH–IGF-1) axis. The agents most commonly encountered in clinical practice and online self-administration protocols include growth hormone-releasing hormone (GHRH) analogues (e.g., sermorelin, tesamorelin, CJC-1295 with Drug Affinity Complex [DAC], CJC-1295 without DAC), growth hormone secretagogues (GHS; e.g., growth hormone-releasing peptide-2 (GHRP-2), growth hormone-releasing peptide-6 (GHRP-6), hexarelin, ipamorelin), the growth hormone (GH) fragment - AOD9604 (hGH 176–191), and insulin-like growth factor-1 (IGF-1) analogues (e.g., pegylated mechano growth factor (PEG-MGF), IGF-1 Long R3 (IGF-1 LR3)). Reported adverse effects span endocrine and metabolic disturbances (including prolactin and cortisol elevations, appetite changes, and dysglycaemia), fluid retention syndromes, musculoskeletal symptoms (myalgia/arthralgia), and injection-site reactions. Given the absence of regulatory approval for physique- or performance-related indications and the uncertainty surrounding product composition, dose, and stacking practices in unregulated supply chains, clinicians increasingly require a pragmatic framework to interpret symptoms and laboratory abnormalities in patients using these compounds. This narrative review contrasts peer-reviewed pharmacokinetic/pharmacodynamic and clinical evidence with commonly encountered online self-administration protocols, stratifying peptides into evidence tiers from regulatory-grade randomized trial data to a complete absence of human studies, and highlights the resulting uncertainty around putative performance and recomposition benefits. We summarise structural characteristics, pharmacologic effects, and commonly reported dosing patterns, and we synthesise clinically relevant adverse effects with particular attention to hormonal imbalance, endocrine–metabolic risk, and biologically plausible but unproven mitogenic concerns. Finally, we propose a clinically oriented assessment algorithm to support exposure history taking, triage of symptom domains, and risk communication without legitimising off-label peptide regimens.
... This GH-releasing peptide does not have sequence similarity with ghrelin but acts as an agonist of the ghrelin receptor and mimics ghrelin (Wang and Tomlinson 2009). Hexarelin peptide dose-dependently increases growth hormone (GH) plasma concentrations in humans and is functionally stronger than ghrelin (Imbimbo et al. 1994). In addition, hexarelin has the ability to enhance serum nitric oxide (NO) levels in atherosclerotic rats (Pang et al. 2010). ...
Tayfun Baser
Ercan Ozdemir
Ahmet kemal Filiz Sinan Gursoy
Ghrelin, a peptide hormone released from the gastric endocrine glands, shows analgesic activity apart from its various physiological effects. Nevertheless, the effects of ghrelin receptor (GHS-R) agonists on morphine analgesia and tolerance have not yet been elucidated. The purpose of this study was to evaluate the effects of the ghrelin receptor agonist hexarelin and antagonist [d-Lys3]-GHRP-6 on morphine antinociception and tolerance in rats. A total of 104 Wistar albino male adult rats (weighing approximately 220–240 g) were used in the experiments. To induce morphine tolerance, a three-day cumulative dose regimen was used in the rats. Then, randomly selected rats were evaluated for morphine tolerance on day 4. The analgesic effects of hexarelin (0.2 mg·kg–1), [d-Lys3]-GHRP-6 (10 mg·kg–1), and morphine (5 mg·kg–1) were measured at 30-min intervals (0, 30, 60, 90, and 120 min) by tail-flick and hot-plate analgesia tests. The findings suggest that hexarelin in combination with morphine attenuates analgesic tolerance to morphine. On the other hand, ghrelin receptor antagonist [d-Lys3]-GHRP-6 has no significant analgesic activity on the morphine tolerance in analgesia tests. Furthermore, co-administration of hexarelin and morphine increases the analgesic effect. In conclusion, these data indicate that administration of GHS-R agonist hexarelin with morphine enhances the antinociception and attenuates morphine tolerance.
... 8,9 In healthy male adults, intravenous examorelin increased plasma GH values, which reached their peak value at approximately 30 min and decreased to baseline levels within 240 min with a half-life of~55 min. 10 Examorelin was well tolerated, while examorelin experiences reversible diminished efficacy by 50-75% over the course of weeks to months. 11 Examorelin reached Phase II clinical testing for the treatment of GH deficiency, but the results have not been officially reported yet. ...
Junichi Ishida
Masakazu Saitoh Nicole Ebner
Stephan von Haehling
Growth hormone secretagogues (GHSs) are a generic term to describe compounds that increase growth hormone (GH) release. GHSs include agonists of the growth hormone secretagogue receptor (GHS‐R), whose natural ligand is ghrelin, and agonists of the growth hormone‐releasing hormone (GHRH) receptor, to which the GHRH binds as a native ligand. Several GHSs have been developed with a view to treating or diagnosing of GH deficiency, which causes growth retardation, gastrointestinal dysfunction, and altered body composition, in parallel with extensive research to identify GHRH, GHS‐R, and ghrelin. This review will focus on the research history and the pharmacology of each GHS, which reached randomized clinical trials. Furthermore, we will highlight the publicly disclosed clinical trials regarding GHSs.
... Hexarelin (His-D-2MeTrp-Ala-Trp-D-Phe-Lys-NH 2 ) differs from GHRP-6 by having D-Trp substituted by D-2-methyl-Trp, making hexarelin biologically more stable with greater GH release activity than GHRP-6 and the first orally active GHRP. Studies in humans have shown that hexarelin was efficient and well tolerated, eliciting a substantial and dose-dependent elevation in plasma GH concentrations, while causing minor sleep problems as side effects [33,39]. Because of the highly vascularized nasal cavity, intranasal administration was also implemented for hexarelin that further improved its bioavailability and efficacy as a therapeutic tool for GH deficiency [40]. ...
Loïze Maréchal Maximilien Laviolette Amélie Rodrigue-Way
André Tremblay
Uncovering the biological role of nuclear receptor peroxisome proliferator-activated receptors (PPARs) has greatly advanced our knowledge of the transcriptional control of glucose and energy metabolism. As such, pharmacological activation of PPARγ has emerged as an efficient approach for treating metabolic disorders with the current use of thiazolidinediones to improve insulin resistance in diabetic patients. The recent identification of growth hormone releasing peptides (GHRP) as potent inducers of PPARγ through activation of the scavenger receptor CD36 has defined a novel alternative to regulate essential aspects of lipid and energy metabolism. Recent advances on the emerging role of CD36 and GHRP hexarelin in regulating PPARγ downstream actions with benefits on atherosclerosis, hepatic cholesterol biosynthesis and fat mitochondrial biogenesis are summarized here. The response of PPARγ coactivator PGC-1 is also discussed in these effects. The identification of the GHRP-CD36-PPARγ pathway in controlling various tissue metabolic functions provides an interesting option for metabolic disorders.
Zeeshan Khan Saima Ikram
Jamshaid Ahmad
Muhammad Alaa Eldeen
Background: Cancer remains a significant global health challenge, with ongoing research focused on identifying effective therapeutic targets. Human agmatinase (AGMAT), a binuclear manganese enzyme, has been associated with cancer progression through its role in polyamine production and its involvement in the NO/MAPK/PI3K signaling pathway in lung tissue. Objective: This study aimed to identify potential inhibitors of AGMAT from a library of FDA-approved drugs using computational methods, intending to find novel therapeutic agents for cancer treatment. Methods: The three-dimensional structure of AGMAT was determined using homology modeling, with Pseudomonas guanidinobutyrase (GbuA) serving as the template due to its 74% sequence similarity to AGMAT. The model was validated using PROCHECK, Verify3D, ProSA and ERRAT software. High-throughput virtual screening was conducted on a chemical library of approximately 7922 FDA-approved drugs to identify potential AGMAT inhibitors. Molecular docking simulations assessed the binding affinities of these drugs. Results: The virtual screening identified ten lead FDA-approved molecules: Nemifitidum, Examorelin, Pralmorelin hydrochloride, Nonathymulin, Ebiratide, Lypressin, Histrelin, Agripressin, Cetrorelix and Ornipressin that exhibited significant binding affinities to AGMAT. Conclusion: The identified lead compounds represent promising candidates for further investigation as potential cancer therapeutics targeting AGMAT. These findings provide a basis for future experimental validation and the development of new drugs toward cancer treatments.
Nina Balthasar
The synthetic growth hormone secretagogues (GHS) exert their growth hormone (GH) releasing effects by activating their receptor (GHS-R) in hypothalamic neurones and pituitary GH cells. The aim of this study was to investigate hypothalamic and pituitary GHS physiology by in vitro studies and transgenesis, over-expressing the GHS-R in hypothalamic GH releasing hormone (GHRH) neurones or pituitary GH cells. Initially, to analyse transgene expression driven by two targeting cosmids - a rat GHRH or a human GH cosmid - transgenic mice expressing enhanced green fluorescent protein (eGFP) were generated. In rGHRH-eGFP transgenic mice eGFP protein was visible in brightly fluorescing GHRH neurone cell bodies and median eminence nerve terminals. hGH-eGFP transgenic mice showed high levels of eGFP fluorescence limited to GH expressing pituitary cells. These mice provide useful new tools to study GHRH and GH cell physiology. In vitro studies with a stably GHS-R transfected GH cell line showed that processing of the GHS-R cDNA resulted in a functionally active receptor. In transgenic mice overexpression of the GHS-R in GHRH neurones caused alteration of the GH axis with increased pituitary GH content and body weight. GH responses to a GHS injection seemed enhanced. However, prolonged GHS exposure did not cause enhanced body weight gain compared to WT littermates. These studies suggested that enhancement of GHS-R abundance in GHRH neurones caused alteration of the GH and GHS axis, implicating GHRH neurones as an important GHS target in GH release. In contrast, transgenic mice with 50-fold GHS-R over-expression in GH cells showed reduced pituitary GH content, body weight and GH responses to GHRH. These data suggest that somatotroph function might be compromised by high levels of GHS-R over-expression. Crossing the hGHS-R over-expressing mice with their eGFP counterpart mice will facilitate the further investigation of their physiological phenotype by enabling in vivo analysis of GHS effects directly in identified cells.
Jamshaid Ahmad
Saima Ikram Fawad Ahmad Maryam Mushtaq
The outbreak of SARS-CoV-2 in December 2019 in China subsequently lead to a pandemic. Lack of vaccine and specific anti-viral drugs started a global health disaster. For a sustained control and protection, development of potential anti-viral drugs is one of the targeted approach. Although, designing and developing a panel of new drugs molecules are always encouraged. However, in the current emergency, drug repurposing study is one of the most effective and fast track option. The crystal structure of a SARS-CoV-2 (Severe acute respiratory syndrome coronavirus 2) RNA Dependent RNA Polymerase (RdRp) has recently been deciphered through X-ray crystallography. The single-chain of core RNA Dependent RNA Polymerase relies on virus-encoded cofactors nsp7 and two units of nsp8 for its optimum function. This study explored the FDA approved database of 7922 molecules and screened against the core polymerase along with cofactors. Here we report a panel of FDA approved drugs that show substantial interactions with key amino acid residues of the active site. Interestingly, some of the identified drugs (Ornipressin, Lypressin, Examorelin, Polymyxin B1) bind strongly within the binding pockets of both forms of RdRp. Besides, we found strong candidates for the complex form as well which include Nacortocin, Cistinexine, Cisatracurium (among others). These drugs have the potential to be considered while contriving therapeutic options.
John T. Sigalos
Alexander W Pastuszak
Introduction: Growth hormone (GH) increases lean body mass, decreases fat mass, increases exercise tolerance and maximum oxygen uptake, enhances muscle strength, and improves linear growth. Long-term studies of GH administration offer conflicting results on its safety, which has led to strict Food and Drug Administration criteria for GH use. The potential drawbacks of exogenous GH use are believed to be due in part to impaired regulatory feedback. Aim: To review the literature on GH secretagogues (GHSs), which include GH-releasing peptides and the orally available small-molecule drug ibutamoren mesylate. Methods: Review of clinical studies on the safety and efficacy of GHSs in human subjects. Main outcome measure: Report on the physiologic changes from GHS use in human subjects including its safety profile. Results: GHSs promote pulsatile release of GH that is subject to negative feedback and can prevent supra-therapeutic levels of GH and their sequelae. To date, few long-term, rigorously controlled studies have examined the efficacy and safety of GHSs, although GHSs might improve growth velocity in children, stimulate appetite, improve lean mass in wasting states and in obese individuals, decrease bone turnover, increase fat-free mass, and improve sleep. Available studies indicate that GHSs are well tolerated, with some concern for increases in blood glucose because of decreases in insulin sensitivity. Conclusion: Further work is needed to better understand the long-term impact of GHSs on human anatomy and physiology and more specifically in the context of a diversity of clinical scenarios. Furthermore, the safety of these compounds with long-term use, including evaluation of cancer incidence and mortality, is needed. Sigalos JT, Pastuszak AW. The Safety and Efficacy of Growth Hormone Secretagogues. Sex Med Rev 2017;X:XXX-XXX.
Miklos Góth
Charles E. Lyons
Benedict J Canny
Michael O Thorner
GH secretion has been thought traditionally to be regulated by the two hypothalamic hormones, GH-releasing hormone (GHRH) and somatostatin (SRIF). Recent evidence has suggested that other factors may be involved. These factors include the natural ligand for the synthetic hexapeptide GH-releasing peptide (GHRP) and the putative hypophysiotropic factor pituitary adenylate cyclase-activating polypeptide (PA-CAP). Accordingly, we examined the effects of GHRP and PACAP on GH secretion at the single cell level using the reverse hemolytic plaque assay which allows distinction of effects on the number of secreting cells and the amount of hormone each cell secretes. Both factors stimulated GH secretion in a dose-dependent fashion, with PACAP being more effective. PACAP increased both the number of cells secreting and the mean amount of hormone secreted per cell. In contrast, GHRP increased the number of secreting cells, although it had no effect on the amount of secretion per cell. GH secretion induced by GHRH, GHRP, and PACAP was inhibited by SRIF, but the effect was predominantly on the number of cells secreting rather than the amount secreted per cell. Specific antagonists to GHRP and GHRH inhibited GH secretion induced by the respective agonist but not that induced by the other factor nor by PACAP. These findings confirm the complex nature of the regulation of GH secretion at the level of the somatotrope. At least three factors, operating via distinct receptors, are able to increase GH secretion. In addition, they ascribe a potential physiological role for the hitherto putative hypophysiotropic factor PACAP.
M L Hartman
Giovanni Farello S S Pezzoli
Michael O Thorner
Intravenous infusions of the synthetic hexapeptide GH-releasing peptide (His-DTrp-Ala-Trp-DPhe-Lys-NH2; GHRP) specifically stimulate GH release in man. To determine whether orally administered GHRP stimulates GH secretion, 10 normal men received oral doses of placebo, 30, 100, and 300 micrograms/kg GHRP, and an iv injection of 1.0 micrograms/kg GHRP at weekly intervals in a single blind, randomized design. Serum GH concentrations were measured in blood samples obtained at 5-min intervals for 1 h (0700-0800 h) before and 4 h (0800-1200 h) after each dose. Mean (+/- SE) peak GH concentrations were 4.0 +/- 1.5, 5.2 +/- 1.6, 9.2 +/- 3.3, 18 +/- 3.7, and 26 +/- 5.6 micrograms/L for placebo; 30, 100, and 300 micrograms/kg oral GHRP; and 1 micrograms/kg iv GHRP, respectively; mean 4-h (0800-1200 h) integrated GH concentrations were 312 +/- 109, 406 +/- 159, 698 +/- 284, 1264 +/- 303, and 1443 +/- 298 min.micrograms/L, respectively. To analyze changes in the pulsatile pattern and amount of GH secretion after the administration of GHRP, a waveform-independent deconvolution method was used to estimate GH secretion rates. Variable increases in GH secretion after placebo and GHRP treatments were observed. Despite this variability, weighted least squares linear regression revealed that increasing doses of oral GHRP progressively stimulated GH secretion (P less than 0.005); similar relationships were observed for the peak GH concentration and 4-h integrated GH concentrations. The GH responses to oral GHRP (300 micrograms/kg) and iv GHRP (1 microgram/kg) were significantly greater than that to placebo (P less than 0.05) and were comparable in magnitude. Pairwise comparisons revealed that increases in GH concentrations and secretion rates after the 30 and 100 micrograms/kg oral doses of GHRP were not significantly different from those after placebo. The increase in GH secretion after GHRP treatment was accounted for entirely by an increase in the amplitude of GH secretory events, as no significant increase in the number of GH secretory pulses was observed. The onset and duration of action of GHRP were analyzed by a proportional hazards general linear regression model. Intravenous GHRP had a more rapid onset of action than all doses of oral GHRP (P less than 0.02). Increasing doses of oral GHRP resulted in earlier GH responses (P = 0.006). However, the duration of the GH response was similar for iv GHRP and all doses of oral GHRP, averaging 120-150 min.(ABSTRACT TRUNCATED AT 400 WORDS)
Allan Blake
Roy G Smith
The hexapeptide His- d -Trp-Ala-Trp- d -Phe-Lys-NH 2 (GHRP-6) and GH-releasing factor (GHRH) produced a rapid release of GH upon perifusion of dispersed rat pituitary cells. In contrast to the native hormone GHRH, GHRP-6 elicited a response of short duration. When perifusion of each secretagogue was continued until the cells no longer released GH, a challenge by the alternative secretagogue immediately resulted in a secondary release of GH. These results are consistent with each secretagogue causing desensitization of discrete receptor-linked second messenger pathways. Cells which were perifused for 1 min with GHRP-6 required continued perifusion with culture medium alone for 60 min before they completely regained responsiveness to a subsequent challenge with GHRP-6. Somatostatin (SRIF) was able to inhibit the action of either secretagogue completely. However, when both GHRH and GHRP-6 were perifused together, SRIF attenuated but did not block GH secretion. These perifusion data add support to conclusions derived from static cell culture studies, that GHRH and GHRP-6 act through different receptor sites and that through discrete signalling pathways their individual effects on GH release are amplified Journal of Endocrinology (1991) 129, 11–19
Cyril Bowers D K Alster J M Frentz
It has been shown that iv GH-releasing peptide (GHRP; His-DTrp-Ala-Trp-DPhe-Lys-NH2) specifically releases GH in man. Because of the clinical value of having an orally active peptide to release GH, five normal men were given GHRP orally at dosages of 100 and 300 micrograms/kg. At the 300 micrograms/kg dosage, the GH rise was detectable at 30 min, peaked between 60-75 min, and gradually declined to the baseline level between 150-180 min. Peak GH levels rose 63- and 202-fold above the baseline after administration of 100 and 300 micrograms/kg GHRP, respectively. Nine short stature children with varying degrees of GH deficiency were also included in this study. All children had short stature, slow growth, and delayed bone age and were being treated with biosynthetic human GH. The studies were performed after stopping GH treatment for 2-3 weeks. The oral GHRP dose administered to all of the children was 300 micrograms/kg, because this dosage was found to consistently increase GH levels in adults. The magnitude and pattern of the GH response to oral GHRP in four of the nine children were essentially the same as those in the five normal men. In the other five children, the GH responses were low but still measurable in three and undetectable in two of the children. Serum immunoreactive GHRP (irGHRP) levels were measured before and at 15- to 30-min intervals 3-5 h after oral as well as iv bolus GHRP administration. For comparison of serum irGHRP and GH levels, results were included after iv bolus administration of 0.1, 0.3, and 1.0 micrograms/kg GHRP to normal men. Since 300 micrograms/kg oral GHRP released about the same amount of GH as 1 microgram/kg, iv, in normal men, it was calculated that oral GHRP has about 0.3% the activity of iv GHRP. After iv GHRP, the peak serum irGHRP levels were immediate and proportional to the dosage, and the disappearance rate decreased exponentially. Between 100-240 min, the mean serum irGHRP level was essentially the same and remained slightly elevated. After administration of 300 micrograms/kg GHRP orally to normal men, serum irGHRP was measurable within 15 min, the peak serum irGHRP level coincided with the GH rise at 60 min, and serum irGHRP levels fell more slowly than serum GH levels. The serum half-life was 20 min, and the distribution volume was 2.5 L after both oral and iv administration.(ABSTRACT TRUNCATED AT 400 WORDS)
Satoko Hayashi
Yasuhiko Okimura Hiroji Yagi Kazuo Chihara
The effects of intranasal and iv administration of His-D-Trp-Ala-Trp-D-Phe-Lys NH2 (GHRP) on plasma GH, PRL, LH, FSH, TSH, cortisol, insulin, IGF-I as well as GHRH-like immunoreactivity (LI) levels were examined in 6 healthy male subjects. An iv bolus injection of GHRP (lμg/kg BW) caused a remarkable increase in plasma GH levels with a mean (±SE) peak of 54.9±4.2μg/L. In addition an intranasal administration of GHRP resulted in a significant, dose-related increase in plasma GH with peaks of 39.6±15.3μg/L at a dose of 30μg/kg BW, 14.1±5.0μg/L at 15μEg/kg BW and 7.5±5.7μg/L at 5μg/kg BW. Plasma PRL and cortisol levels were slightly but significantly increased after iv administration of GHRP, whereas GHRP totally failed to affect plasma TSH, LH, FSH, insulin, blood sugar and GHRH-LI levels. Seven consecutive, intranasal administrations of 15μg/kg BW GHRP every 8h were well tolerated in all subjects examined. During this treatment, GH responsiveness to GHRP was not attenuated by desensitization and plasma IGF-I was increased from 94.5±5.8μg/L before GHRP to 125.8±6.0μg/L after repeated GHRP administration. These findings indicate that intranasal administration of GHRP stimulates GH secretion and consequently enhances IGF-I production in normal subjects. If GHRP is demonstrated to be beneficial in the treatment of some patients with GH deficiency, the intranasal route of administration may be more useful than the painful injections because a prolonged period is required for the treatment.
Cyril Bowers A.O. SARTOR
Gemma Reynolds T M Badger
GH-releasing peptide (His-DTrp-Ala-Trp-DPhe-Lys-NH2 or GHRP) releases GH by a unique and complementary dual site of action on the hypothalamus and pituitary. These effects are mediated via non-GH-releasing hormone (non-GHRH) and nonopiate receptors in rats. Select types of opiates are known to release GH by a hypothalamic site of action, and thus, the dermorphin heptapeptide and benzomorphan opiate agonist 2549 used in this study presumably act on the hypothalamus to release GH. Neither dermorphin nor 2549 released GH or augmented the GH responses of GHRP or GHRH in vitro by a direct pituitary action, while GHRH antiserum inhibited the GH response of both dermorphin and 2549 in vivo. Evidence indicates that these opiates and GHRP administered together synergistically release GH, demonstrating the independent action(s) of GHRP and the opiates. Present data indicate that one of the major differences in the actions of dermorphin, 2549, and GHRP is the inhibition of somatostatin (SRIF) release by the opiates but not by GHRP. Although the actions of dermorphin, 2549, and GHRP on GH release are GHRH dependent, release of endogenous GHRH does not explain how GH is released synergistically by the combination of these peptides. It is proposed that dermorphin/2549 synergistically release GH with GHRP or GHRH because these opiates inhibit SRIF release. Since the GHRP plus GHRH synergistic GH release was not explained by inhibition of SRIF or stimulation of GHRH, an alternative mechanism is proposed to explain how GHRP synergistically release GH in combination with GHRH. The complementary, rather dramatic synergistic interaction of GHRP, GHRH, and dermorphin or GHRP, GHRH, and 2549 in releasing GH again strongly supports the independent actions of these compounds.
Cyril Bowers
Gemma Reynolds Debra A. Durham
Michael O Thorner
The acute GH release stimulated by the synthetic hexapeptide, His-DTrp-Ala-Trp-DPhe-Lys-NH2 [GH releasing peptide (GHRP)], was determined in 18 normal men and compared with the effects of GH-releasing hormone, GHRH-(1-44)-NH2. Specificity of effect was assessed by measurement of serum PRL, LH, TSH, and cortisol. GHRP was administered at doses of 0.1, 0.3, and 1.0 microgram/kg by iv bolus. GHRH at a dose of 1.0 microgram/kg was administered alone and together with various does of GHRP. No adverse clinical effects of laboratory abnormalities were observed in response to GHRP. A side-effect of mild facial flushing of 1- to 3-min duration occurred in 16 of the 18 subjects who received GHRH-(1-44)-NH2. Mean (+/- SEM) peak serum GH levels after injection of placebo and 0.1, 0.3, and 1.0 microgram/kg GHRP were 1.2 +/- 0.3, 7.6 +/- 2.5, 16.5 +/- 4.1, and 68.7 +/- 15.5 micrograms/L, respectively. The submaximal dosages of 0.1 and 0.3 microgram/kg GHRP plus 1 microgram/kg GHRH stimulated GH release synergistically. Serum PRL and cortisol levels rose about 2-fold above basal levels only at the 1 microgram/kg dose of GHRP, and there were no changes in serum LH and TSH over the first hour after administration of the peptide(s). GHRP is a potent secretagogue of GH in normal men. Since GHRP and GHRH together stimulate GH release synergistically, these results suggest that GHRP and GHRH act independently. This supports our hypothesis that the GH-releasing activity of GHRP reflects a new physiological system in need of further characterization in animals and man.
K Cheng Wanda W.-S. Chan Albert Barreto
Roy G Smith
His-D-Trp-Ala-Trp-D-Phe-Lys-NH2 (GHRP-6) stimulated GH release from rat primary pituitary cells in a time- and dose-dependent manner. Stimulation was observed after a 15-min, but not a 4-h, incubation. The concentrations of GHRP-6 required for half-maximal and maximal stimulation were 7 x 10(-9) and 10(-7) M, respectively. GH release induced by GHRP-6 was not affected by the addition of either naloxone or the GRF antagonist [N-Ac-Tyr1,D-Arg2]GRF-(1-29)-NH2. The latter inhibited GRF-stimulated GH release by shifting the dose-response curve to the right. His-D-Trp-D-Lys-Trp-D-Phe-Lys-NH2, an analog of GHRP-6, inhibited GH release stimulated by GHRP-6 without affecting that induced by GRF. When present together at maximal concentrations, GHRP-6 and GRF produced a synergistic effect on GH release. GHRP-6 had no effect on intracellular cAMP levels, whereas GRF increased intracellular cAMP concentrations by 3-fold. Combined treatment of pituitary cells with GRF and GHRP-6 resulted in a potentiation of the GRF-induced increase in cAMP levels. Basal GH release was reduced by 30% after pretreatment with GHRP-6 (10(-7) M) for 1 h. Pretreatment with GHRP-6 also decreased the subsequent response to GHRP-6, but not GRF. In contrast, pretreatment with GRF for 1 h had no effect on the subsequent action of GHRP-6 or GRF on GH release. The desensitization induced by GHRP-6 was completely reversed within 1 h after removal of the peptide. Results from this study indicate that GHRP-6 and GRF stimulated GH release from somatotrophs via different receptors and through discrete mechanisms.
Bernard Ilson
Diane Jorkasky R T Curnow R M Stote
Growth hormone-releasing peptide (GHRP, SK&F 110679) is a hexapeptide (His-DTrp-Ala-Trp-DPhe-LysNH2) that selectively stimulates the release of growth hormone (GH) but not other pituitary hormones in vitro and in vivo in a variety of animal species. GHRP was administered to 17 normal men at doses of from 0.05 to 2.5 micrograms/kg as a 30 min intravenous infusion. Eight of the men were infused with saline as a control. Serum GH increased consistently at doses of 0.25 microgram/kg and above during the infusion of the peptide, peaked at 45 min and then decreased to baseline values by 210 min. The mean peak serum GH concentrations (+/- SE) in response to GHRP infusion were 17.8 +/- 6.1 micrograms/L at a dose of 0.25 microgram/kg (n = 4, p = .03 vs saline), 38.3 +/- 9.2 micrograms/L at 0.5 microgram/kg (n = 4, p = .04 vs saline) and 63.0 +/- 5.4 micrograms/L at 1.0 microgram/kg (n = 4, p = .002 vs saline). Serum LH, FSH, TSH and ACTH were unaffected by GHRP administration. GHRP was safe and well-tolerated in all men. GHRP infusion resulted in a dramatic, selective and dose-dependent increase in serum GH concentrations.
Ellen E. Codd A.Y.L. Shu
Roger F. Walker
The drug SK&F 110679 (His-D-Trp-Ala-Trp-D-Phe-LysNH2), is an enkephalin-derived hexapeptide, which specifically releases growth hormone in a wide variety of species in vivo and in vitro. Previous binding studies, using ligands which are specific for mu and delta opioid binding sites, demonstrated an inverse relationship between the opioid binding potency and the potency in releasing growth hormone of a series of peptides related to SK&F 110679. In an attempt to understand its mode of action better, a binding assay for the peptide was established using a ligand which had been tritium labelled at the D-Trp2 residue. Membrane fragments from both the hypothalamus and anterior pituitary tissue were found to contain sites to which [3H]SK&F 110679 reversibly and saturably bound. The binding curves for [3H]SK&F 110679 to membrane fragments of both hypothalamus and anterior pituitary were resolved into two binding components with the computer program LIGAND. The Kd's obtained were in the 10(-8) M and 10(-5) M range. The relationship of these binding sites to the growth hormone-releasing activity of the peptide was explored by examining the relationship between the binding and potency in releasing growth hormone of a series of peptides related to SK&F 110679. For sites in both the hypothalamus and pituitary, a significant correlation between binding and the release of growth hormone was obtained. Thus, these binding sites appeared to be involved in the release of growth hormone by SK&F 110679-related peptides.(ABSTRACT TRUNCATED AT 250 WORDS)