Nonpeptide and peptide growth hormone secretagogues act both as ghrelin receptor agonist and as positive or negative allosteric modulators of ghrelin signaling.

Holst B, Brandt E, Bach A, Heding A, Schwartz TW

Molecular endocrinology (Baltimore, Md.)19 May 2005Cited by 101 (Europe PMC)

PMID15905359DOI10.1210/me.2005-0059PepBankPUB-15905359

Summary

The text of this summary is not shown here, because the article license does not allow reuse. Read it at the source (opens in a new tab)

Text rights: Publisher copyright. Results still quote short attributed sentences.

Results from this study10

8 results from studies that gave the peptide. No result from this study comes from people.

01LabIn vitro (cells)Activity measurement
In ghrelin receptor assays, the potency of GHRP‑6 varied 600-fold (0.1-61 nm) depending on the signal transduction assay.
In plain wordsIn lab tests, GHRP‑6 was 600 times more potent in some ghrelin receptor assays than in others.
Peptide
GHRP-6
Outcome
Not applicablePotency across signal transduction assays
Study
n: not reported in source
Outcome group
Receptor activity and mechanism · Pharmacology
Studied dose
Dose not stated
Measurements
Potency
0.1 to 61 nm
depending on signal transduction assay
Source sentences
Summary
In contrast, the potency of GHRP-6 varied 600-fold (0.1-61 nm) depending on the signal transduction assay, and it acted as a negative allosteric modulator of ghrelin signaling.
1 context sentence(design, population, supporting numbers)
Summary · context
Two nonpeptide (L692,429 and MK-677) and two peptide [GH-releasing peptide (GHRP)-6 and ghrelin] agonists were compared in binding and in signal transduction assays: calcium mobilization, inositol phosphate turnover, cAMP-responsive element (CRE), and serum-responsive element (SRE) controlled transc…
Report a problemFND-1590535901
02LabIn vitro (cells)Mechanism
In ghrelin receptor assays, GHRP‑6 acted as a negative allosteric modulator of ghrelin signaling.
In plain wordsIn lab tests, GHRP‑6 weakened the signal that ghrelin produces at its receptor.
Peptide
GHRP-6
Outcome
Not applicableAllosteric modulation of ghrelin signaling
Study
n: not reported in source
Outcome group
Receptor activity and mechanism · Pharmacology
Studied dose
Dose not stated
Source sentences
Summary
and it acted as a negative allosteric modulator of ghrelin signaling.
1 context sentence(design, population, supporting numbers)
Summary · context
Two nonpeptide (L692,429 and MK-677) and two peptide [GH-releasing peptide (GHRP)-6 and ghrelin] agonists were compared in binding and in signal transduction assays: calcium mobilization, inositol phosphate turnover, cAMP-responsive element (CRE), and serum-responsive element (SRE) controlled transc…
Report a problemFND-1590535902
03LabIn vitro (cells)Activity measurement
In receptor assays, MK‑677 acted as an agonist with an affinity of 6.5 nm.
In plain wordsIn lab tests, MK‑677 acted as a receptor agonist with an affinity of 6.5 nm.
Peptide
MK-677 (ibutamoren)
Outcome
Not applicableReceptor affinity
Study
n: not reported in source
Ghrelin receptor signaling assays
Outcome group
Receptor activity and mechanism · Pharmacology
Studied dose
Dose not stated
Measurements
Affinity
6.5 nm
MK-677
Source sentences
Summary
MK-677 acted as a simple agonist having an affinity of 6.5 nm
1 context sentence(design, population, supporting numbers)
Summary · context
Two nonpeptide (L692,429 and MK-677) and two peptide [GH-releasing peptide (GHRP)-6 and ghrelin] agonists were compared in binding and in signal transduction assays: calcium mobilization, inositol phosphate turnover, cAMP-responsive element (CRE), and serum-responsive element (SRE) controlled transc…
Report a problemFND-1590535904
04LabIn vitro (cells)Activity measurement
In receptor assays, MK‑677 activated calcium mobilization within the reported signaling potency range of 0.2-1.4 nm.
In plain wordsIn lab tests, MK‑677 activated calcium signaling within the reported potency range of 0.2-1.4 nm.
Peptide
MK-677 (ibutamoren)
Outcome
IncreaseCalcium mobilization
Study
n: not reported in source
Ghrelin receptor signaling assays
Outcome group
Receptor activity and mechanism · Pharmacology
Studied dose
Dose not stated
Source sentences
Summary
MK-677 acted as a simple agonist having an affinity of 6.5 nm and activated all signal transduction systems with similar high potency (0.2-1.4 nm).
1 context sentence(design, population, supporting numbers)
Summary · context
Two nonpeptide (L692,429 and MK-677) and two peptide [GH-releasing peptide (GHRP)-6 and ghrelin] agonists were compared in binding and in signal transduction assays: calcium mobilization, inositol phosphate turnover, cAMP-responsive element (CRE), and serum-responsive element (SRE) controlled transc…
Report a problemFND-1590535905
05LabIn vitro (cells)Activity measurement
In receptor assays, MK‑677 activated inositol phosphate turnover within the reported signaling potency range of 0.2-1.4 nm.
In plain wordsIn lab tests, MK‑677 activated inositol phosphate signaling within the reported potency range of 0.2-1.4 nm.
Peptide
MK-677 (ibutamoren)
Outcome
IncreaseInositol phosphate turnover
Study
n: not reported in source
Ghrelin receptor signaling assays
Outcome group
Receptor activity and mechanism · Pharmacology
Studied dose
Dose not stated
Source sentences
Summary
MK-677 acted as a simple agonist having an affinity of 6.5 nm and activated all signal transduction systems with similar high potency (0.2-1.4 nm).
1 context sentence(design, population, supporting numbers)
Summary · context
Two nonpeptide (L692,429 and MK-677) and two peptide [GH-releasing peptide (GHRP)-6 and ghrelin] agonists were compared in binding and in signal transduction assays: calcium mobilization, inositol phosphate turnover, cAMP-responsive element (CRE), and serum-responsive element (SRE) controlled transc…
Report a problemFND-1590535906
06LabIn vitro (cells)Activity measurement
In receptor assays, MK‑677 activated CRE-controlled transcription within the reported signaling potency range of 0.2-1.4 nm.
In plain wordsIn lab tests, MK‑677 activated CRE-controlled transcription within the reported potency range of 0.2-1.4 nm.
Peptide
MK-677 (ibutamoren)
Outcome
IncreaseCRE-controlled transcription
Study
n: not reported in source
Ghrelin receptor signaling assays
Outcome group
Receptor activity and mechanism · Pharmacology
Studied dose
Dose not stated
Source sentences
Summary
MK-677 acted as a simple agonist having an affinity of 6.5 nm and activated all signal transduction systems with similar high potency (0.2-1.4 nm).
1 context sentence(design, population, supporting numbers)
Summary · context
Two nonpeptide (L692,429 and MK-677) and two peptide [GH-releasing peptide (GHRP)-6 and ghrelin] agonists were compared in binding and in signal transduction assays: calcium mobilization, inositol phosphate turnover, cAMP-responsive element (CRE), and serum-responsive element (SRE) controlled transc…
Report a problemFND-1590535907
07LabIn vitro (cells)Activity measurement
In receptor assays, MK‑677 activated SRE-controlled transcription within the reported signaling potency range of 0.2-1.4 nm.
In plain wordsIn lab tests, MK‑677 activated SRE-controlled transcription within the reported potency range of 0.2-1.4 nm.
Peptide
MK-677 (ibutamoren)
Outcome
IncreaseSRE-controlled transcription
Study
n: not reported in source
Ghrelin receptor signaling assays
Outcome group
Receptor activity and mechanism · Pharmacology
Studied dose
Dose not stated
Source sentences
Summary
MK-677 acted as a simple agonist having an affinity of 6.5 nm and activated all signal transduction systems with similar high potency (0.2-1.4 nm).
1 context sentence(design, population, supporting numbers)
Summary · context
Two nonpeptide (L692,429 and MK-677) and two peptide [GH-releasing peptide (GHRP)-6 and ghrelin] agonists were compared in binding and in signal transduction assays: calcium mobilization, inositol phosphate turnover, cAMP-responsive element (CRE), and serum-responsive element (SRE) controlled transc…
Report a problemFND-1590535908
08LabIn vitro (cells)Activity measurement
In receptor assays, MK‑677 activated arrestin mobilization within the reported signaling potency range of 0.2-1.4 nm.
In plain wordsIn lab tests, MK‑677 activated arrestin signaling within the reported potency range of 0.2-1.4 nm.
Peptide
MK-677 (ibutamoren)
Outcome
IncreaseArrestin mobilization
Study
n: not reported in source
Ghrelin receptor signaling assays
Outcome group
Receptor activity and mechanism · Pharmacology
Studied dose
Dose not stated
Source sentences
Summary
MK-677 acted as a simple agonist having an affinity of 6.5 nm and activated all signal transduction systems with similar high potency (0.2-1.4 nm).
1 context sentence(design, population, supporting numbers)
Summary · context
Two nonpeptide (L692,429 and MK-677) and two peptide [GH-releasing peptide (GHRP)-6 and ghrelin] agonists were compared in binding and in signal transduction assays: calcium mobilization, inositol phosphate turnover, cAMP-responsive element (CRE), and serum-responsive element (SRE) controlled transc…
Report a problemFND-1590535909

Studies that did not test the peptide alone2

In this study, the peptide was a lab tool or a carrier, part of a mix, or the subject of a lab method. These results are not evidence about taking the peptide.

09LabNot a test of GHRP-6 aloneIn vitro (cells)Mechanism
In ghrelin receptor assays, coadministration of the nonendogenous agonists (pooled, including GHRP‑6) raised the maximal signaling efficacy of ghrelin above ghrelin alone.
In plain wordsIn lab tests, giving ghrelin together with the non-natural agonists, pooled, raised the largest ghrelin signal above ghrelin alone.
Peptide
GHRP-6
Outcome
IncreaseMaximal ghrelin signaling efficacy during coadministration
Study
n: not reported in source
Outcome group
Receptor activity and mechanism · Pharmacology
Source sentences
Summary
Unexpectedly, the maximal signaling efficacy for ghrelin was increased above what was observed with the hormone itself during coadministration with the nonendogenous agonists.
1 context sentence(design, population, supporting numbers)
Summary · context
Two nonpeptide (L692,429 and MK-677) and two peptide [GH-releasing peptide (GHRP)-6 and ghrelin] agonists were compared in binding and in signal transduction assays: calcium mobilization, inositol phosphate turnover, cAMP-responsive element (CRE), and serum-responsive element (SRE) controlled transc…
In this study, GHRP-6 was a lab tool or a carrier, part of a mix, or the subject of a lab method. This result is not evidence about taking GHRP-6.
Report a problemFND-1590535903
10LabNot a test of MK-677 (ibutamoren) aloneIn vitro (cells)Mechanism
In receptor assays, ghrelin coadministration with nonendogenous agonists including MK‑677 increased maximal signaling efficacy compared with ghrelin alone.
In plain wordsIn lab tests, ghrelin with nonendogenous agonists including MK‑677 increased maximal signaling compared with ghrelin alone.
Peptide
MK-677 (ibutamoren)
Outcome
IncreaseMaximal ghrelin signaling efficacy
Study
n: not reported in source
Ghrelin receptor signaling assays
Comparator
Ghrelin alone
Outcome group
Receptor activity and mechanism · Pharmacology
Source sentences
Summary
Unexpectedly, the maximal signaling efficacy for ghrelin was increased above what was observed with the hormone itself during coadministration with the nonendogenous agonists.
1 context sentence(design, population, supporting numbers)
Summary · context
Two nonpeptide (L692,429 and MK-677) and two peptide [GH-releasing peptide (GHRP)-6 and ghrelin] agonists were compared in binding and in signal transduction assays: calcium mobilization, inositol phosphate turnover, cAMP-responsive element (CRE), and serum-responsive element (SRE) controlled transc…
In this study, MK-677 (ibutamoren) was a lab tool or a carrier, part of a mix, or the subject of a lab method. This result is not evidence about taking MK-677 (ibutamoren).
Report a problemFND-1590535910

AI wrote and checked these results. AI can make mistakes, so check important results against the source.

Version history

PepBank keeps every version of the data on this study. Status changes from Retraction Watch, Europe PMC and Crossref are listed with their source.

Versions 4 to 14Current
28 Oct 2026, 02:02 UTC
The same notice was added 11 times, first on 14 Oct 2026, 05:02 UTC. The status did not change between them.
Study results updated
Version 3
14 Oct 2026, 01:46 UTC
Study data updated · source update from Europe PMC
Version 2
12 Oct 2026, 12:58 UTC
Study results updated
Version 1
9 Oct 2026, 03:13 UTC
First added · source update from Europe PMC

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Nonpeptide and peptide growth hormone secretagogues act both as ghrelin receptor agonist and as positive or negative allosteric modulators of ghrelin signaling.

Summary

Results from this study10

Studies that did not test the peptide alone2

Version history

Subjects

Publication types

MeSH terms