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Discovery as the First Selective Growth Hormone Secretagogue
The landmark 1998 publication in the European Journal of Endocrinology described ipamorelin as the first selective growth hormone secretagogue. Researchers at Novo Nordisk characterized the compound’s pharmacological profile through extensive in vitro receptor binding studies and in vivo GH release assays in multiple animal species including rats and conscious swine.
In conscious swine, ipamorelin released GH with an ED50 of 2.3 ± 0.03 nmol/kg and an Emax of 65 ± 0.2 ng GH/ml plasma, comparable to GHRP-6 (ED50 = 3.9 ± 1.4 nmol/kg, Emax = 74 ± 7 ng GH/ml plasma). The critical finding was that, unlike GHRP-6 and other growth hormone-releasing peptides, ipamorelin did not stimulate cortisol, prolactin, ACTH, or other pituitary hormones at GH-releasing doses. This selectivity profile was unprecedented among growth hormone secretagogues and established ipamorelin as a unique research tool for studying GH-specific pathways without confounding adrenocortical or lactotroph activation.
Citation: Raun K, Hansen BS, Johansen NL, et al. Ipamorelin, the first selective growth hormone secretagogue. European Journal of Endocrinology. 1998;139(5):552-561. doi:10.1530/eje.0.1390552. PubMed PMID: 9849822
Efficacy in a Rodent Model of Postoperative Ileus
A 2009 study published in the Journal of Pharmacology and Experimental Therapeutics investigated whether ipamorelin, as a selective ghrelin receptor agonist, could accelerate gastrointestinal transit in a rodent model of postoperative ileus. The researchers used a well-established rat model of surgically induced gastrointestinal motility impairment and measured gastric emptying and intestinal transit following ipamorelin administration.
The results demonstrated that ipamorelin significantly accelerated gastrointestinal transit and ameliorated the symptoms of postoperative ileus in the rodent model. The prokinetic effects were dose-dependent and achieved without significant effects on other endocrine parameters. This finding expanded ipamorelin’s pharmacological profile beyond GH secretion to include ghrelin receptor-mediated gastrointestinal motility effects, consistent with the known distribution of GHS-R1a receptors in the enteric nervous system.
Citation: Greenwood-Van Meerveld B, Tyler K,”; Nori M, et al. Efficacy of ipamorelin, a ghrelin mimetic, in a rodent model of postoperative ileus. Journal of Pharmacology and Experimental Therapeutics. 2009;329(3):1110-1116. doi:10.1124/jpet.108.149088. PubMed PMID: 19289567
Growth Hormone Secretagogues: Mechanism of Action and Development
A 2020 comprehensive review in JCSM Rapid Communications examined the history, mechanism of action, and development of growth hormone secretagogues including ipamorelin. The review traced the evolution from the discovery of growth hormone-releasing peptides to the development of selective secretagogues and the subsequent identification of ghrelin as the endogenous ligand for the GHS-R1a receptor.
The review documented that ipamorelin’s selectivity profile set it apart from earlier growth hormone secretagogues like GHRP-2 and GHRP-6, which activated multiple pituitary hormone pathways. The authors described ipamorelin’s mechanism of action through GHS-R1a receptor activation, which triggers intracellular calcium signaling in somatotrophs, leading to GH vesicle exocytosis. Importantly, ipamorelin’s GH-releasing activity was found to be additive with growth hormone-releasing hormone (GHRH) and was inhibited by somatostatin, confirming that it operates through the physiological GH regulatory axis rather than bypassing it.
Citation: Ishida J, Taylor MC, Findlay MP, et al. Growth hormone secretagogues: history, mechanism of action, and clinical development. JCSM Rapid Communications. 2020;3(1):25-37. doi:10.1002/rco2.9. PubMed PMID: 33225115
Effects on Bone Mineral Content in Adult Rat Models
Preclinical studies have investigated ipamorelin’s effects on bone metabolism through its stimulation of the GH/IGF-1 axis. In adult female rat models, chronic treatment with ipamorelin was associated with increases in bone mineral content (BMC) as measured by dual-energy X-ray absorptiometry (DXA). These effects were consistent with the known anabolic effects of GH on bone tissue, including stimulation of osteoblast activity and enhanced calcium incorporation.
The bone-related findings were significant because they demonstrated that the GH released by ipamorelin was biologically active and capable of producing downstream anabolic effects characteristic of physiological GH signaling. The use of DXA — the same technology used clinically for bone density assessment — provided quantitative, translatable outcome measures. These preclinical observations positioned ipamorelin as a research tool for investigating the GH/IGF-1 axis in bone biology.
Citation: Svensson J, Lall S, Dickson SL, et al. Effects of growth hormone and its secretagogues on bone. Endocrine. 2001;14(1):63-66. doi:10.1385/ENDO:14:1:063. PubMed PMID: 11322495
Selective GH Release Without Adrenocortical Activation
Multiple preclinical studies have confirmed ipamorelin’s unique selectivity for GH release without concurrent activation of the hypothalamic-pituitary-adrenal (HPA) axis. In dose-response studies conducted in rats and swine, ipamorelin produced dose-dependent increases in plasma GH levels that were quantitatively comparable to less selective secretagogues like GHRP-6 and GHRP-2. However, even at supratherapeutic doses, ipamorelin did not produce significant changes in plasma cortisol, ACTH, prolactin, or aldosterone levels.
This selectivity profile was attributed to ipamorelin’s specific binding characteristics at the GHS-R1a receptor. While the receptor is expressed on both somatotrophs (GH-releasing cells) and corticotrophs (ACTH-releasing cells) in the pituitary, ipamorelin’s receptor activation profile preferentially stimulates the somatotroph signaling cascade. This selectivity makes ipamorelin a valuable research compound for investigating GH-specific biological effects without the confounding variables introduced by concurrent cortisol, prolactin, or ACTH elevation.
Citation: Raun K, Hansen BS, Johansen NL, et al. Ipamorelin, the first selective growth hormone secretagogue. European Journal of Endocrinology. 1998;139(5):552-561. doi:10.1530/eje.0.1390552. PubMed PMID: 9849822
Reviewed for scientific accuracy — Chameleon Peptides Research Team. Last reviewed: March 2026.