Ipamorelin

Ipamorelin is a five-residue synthetic peptide that acts as an agonist at the growth hormone secretagogue receptor type 1a (GHS-R1a), the same G protein-coupled receptor targeted by endogenous ghrelin. Receptor occupancy in somatotroph cells of the anterior pituitary drives Gq-coupled phospholipase C signalling, intracellular calcium mobilisation, and exocytotic release of stored growth hormone. Because the peptide acts at the pituitary rather than at the growth hormone-releasing hormone receptor, its secretory profile is pulsatile and preserves the episodic architecture of endogenous growth hormone output.

The property that distinguishes ipamorelin within its class is selectivity. In the original characterisation work, doses more than 200-fold above the ED50 for growth hormone release produced adrenocorticotropic hormone and cortisol responses no different from those following growth hormone-releasing hormone stimulation — a separation not seen with earlier growth hormone-releasing peptides such as GHRP-6, which elevate corticotropic and lactotropic axes alongside growth hormone. For experimental work, that selectivity narrows the number of confounding endocrine variables an investigator has to control for.

Receptor pharmacology beyond the pituitary is an active area. GHS-R1a is expressed in the hypothalamic arcuate nucleus, the enteric nervous system, and peripheral sensory neurons, and comparative agonist and antagonist studies have been used to separate the central appetite and growth hormone effects of the receptor from its peripheral gastrointestinal and nociceptive effects.

The published record on ipamorelin spans skeletal, gastrointestinal, endocrine and sensory endpoints. Findings below are from preclinical and early-phase work and are presented for research context only.

• Receptor selectivity. Raun and colleagues established ipamorelin as the first growth hormone secretagogue with a release profile comparable in selectivity to growth hormone-releasing hormone itself, without the concurrent corticotropin release characteristic of earlier peptides in the class.

• Longitudinal bone growth. In hypophysectomised rats, ipamorelin produced a dose-dependent rise in longitudinal growth rate from 42 µm/day in vehicle controls to 44, 50 and 52 µm/day across escalating dose groups, alongside a dose-dependent effect on body weight gain.

• Bone mineral content. A separate study in adult female rats compared ipamorelin with GHRP-6 and reported increased bone mineral content by in vivo DXA, notably without measurable change in total IGF-I, IGF binding proteins, or serum markers of bone formation and resorption — suggesting an effect that is not fully accounted for by the systemic IGF-I axis.

• Glucocorticoid antagonism. Ipamorelin counteracted glucocorticoid-induced reduction in bone formation in adult rats, and a companion study found that methylprednisolone did not suppress the growth hormone release evoked by the peptide — a pairing that has made it a useful probe in steroid-catabolism models.

• Gastrointestinal motility. In a rodent model of postoperative ileus, repeated dosing at 0.1 and 1 mg/kg significantly increased cumulative faecal pellet output, food intake and body weight gain, implicating peripheral GHS-R1a in the recovery of gut transit.

• Visceral and somatic nociception. More recent work characterised ipamorelin as a peripherally restricted ghrelin receptor agonist in models of non-inflammatory visceral hypersensitivity and somatic mechanical allodynia, extending interest in the receptor beyond endocrine endpoints.

• Pathway dissection. Comparative agonist and antagonist studies along the ghrelin/GHS-R axis have separated growth hormone secretion from appetite and central cFos activation, clarifying which downstream readouts track receptor occupancy and which do not.

This section describes laboratory handling. It is not clinical guidance, and no safety claim for human or veterinary administration is made or implied.

• Handle as a research chemical of undetermined hazard. Use gloves, eye protection and a laboratory coat; weigh and reconstitute lyophilized material in a controlled environment.

• Keep the sealed vial protected from light. Storage temperature and reconstitution conditions are stated on the item specification sheet and the lot Certificate of Analysis, which take precedence over general guidance.

• Reconstituted peptide solutions have materially shorter working stability than lyophilized powder. Prepare working aliquots and avoid repeated freeze-thaw cycles.

• Preclinical tolerability does not establish safety in any other context.

• Dispose of unused material and consumables in accordance with the institutional chemical waste policy.

For laboratory research use only. Not for human or veterinary use. Not a drug, food, cosmetic or dietary supplement.

Ipamorelin is a pentapeptide agonist of GHS-R1a used as a reference compound in growth hormone secretagogue research. Its defining characteristic is selectivity: it evokes pituitary growth hormone release while leaving adrenocorticotropic hormone, cortisol and prolactin largely unchanged at doses far above the growth hormone ED50, which makes it a cleaner experimental probe than the earlier growth hormone-releasing peptides it descends from.

The preclinical literature covers longitudinal bone growth and bone mineral content in rodents, antagonism of glucocorticoid-induced suppression of bone formation, restoration of gastrointestinal transit in postoperative ileus models, and more recent work on peripherally restricted antinociception. Several of these effects appear to be at least partly independent of the systemic IGF-I axis, which is itself an open question in the field.

Peptonova Labs supplies ipamorelin as a lyophilized powder with a lot-specific Certificate of Analysis recording compound identity and measured purity. Material is intended for in-vitro research and analytical reference by laboratories and institutional purchasers.

1. Raun K, Hansen BS, Johansen NL, Thøgersen H, Madsen K, Ankersen M, Andersen PH. Ipamorelin, the first selective growth hormone secretagogue. European Journal of Endocrinology. 1998;139(5):552-561.

2. Johansen PB, Nowak J, Skjaerbaek C, Flyvbjerg A, Andreassen TT, Wilken M, Orskov H. Ipamorelin, a new growth-hormone-releasing peptide, induces longitudinal bone growth in rats. Growth Hormone & IGF Research. 1999;9(2):106-113.

3. Svensson J, Lall S, Dickson SL, Bengtsson BA, Rømer J, Ahnfelt-Rønne I, Ohlsson C, Jansson JO. The GH secretagogues ipamorelin and GH-releasing peptide-6 increase bone mineral content in adult female rats. Journal of Endocrinology. 2000;165(3):569-577.

4. Andersen NB, Malmlöf K, Johansen PB, Andreassen TT, Ørtoft G, Oxlund H. The growth hormone secretagogue ipamorelin counteracts glucocorticoid-induced decrease in bone formation of adult rats. Growth Hormone & IGF Research. 2001;11(5):266-272.

5. Malmlöf K, Johansen PB, Haahr PM, Wilken M, Oxlund H. Methylprednisolone does not inhibit the release of growth hormone after intravenous injection of a novel growth hormone secretagogue in rats. Growth Hormone & IGF Research. 1999;9(6):445-450.

6. Venkova K, Mann W, Nelson R, Greenwood-Van Meerveld B. Efficacy of ipamorelin, a novel ghrelin mimetic, in a rodent model of postoperative ileus. Journal of Pharmacology and Experimental Therapeutics. 2009;329(3):1110-1116.

7. Mohammadi EN, Louwies T, Pietra C, Northrup SR, Greenwood-Van Meerveld B. Attenuation of visceral and somatic nociception by ghrelin mimetics. Journal of Experimental Pharmacology. 2020;12:267-274.

8. Hassouna R, Labarthe A, Zizzari P, Videau C, Culler M, Epelbaum J, Tolle V. Actions of agonists and antagonists of the ghrelin/GHS-R pathway on GH secretion, appetite, and cFos activity. Frontiers in Endocrinology. 2013;4:25.

9. Sinha DK, Balasubramanian A, Tatem AJ, Rivera-Mirabal J, Yu J, Kovac J, Pastuszak AW, Lipshultz LI. Beyond the androgen receptor: the role of growth hormone secretagogues in the modern management of body composition in hypogonadal males. Translational Andrology and Urology. 2020;9(Suppl 2):S149-S159.

10. Giorgioni G, Del Bello F, Quaglia W, Botticelli L, Cifani C, Micioni Di Bonaventura E, Micioni Di Bonaventura MV, Piergentili A. Advances in the development of nonpeptide small molecules targeting ghrelin receptor. Journal of Medicinal Chemistry. 2022;65(4):3098-3118.