Study wrapper · #227
Ipamorelin, the first selective growth hormone secretagogue.
Editor's note
This is the foundational characterisation of ipamorelin (Raun and colleagues) and the source of its central selling point: selectivity. Across rat pituitary cells, anaesthetised rats, and conscious swine, ipamorelin released GH with potency and efficacy similar to GHRP-6, acting through the GHRP/GHS receptor. The distinguishing result is what it did not do: unlike GHRP-6 and GHRP-2, ipamorelin did not raise ACTH or cortisol even at doses more than 200-fold above its GH-releasing dose, giving it a GH-selectivity profile resembling GHRH. That clean separation is the reason ipamorelin is often preferred over earlier GHRPs. The evidence here is robust for what it is, multi-model preclinical pharmacology, but it is preclinical and in-vitro, characterising receptor behaviour and hormone release, not clinical outcomes. For Ipamorelin, this establishes the mechanism and selectivity story; human efficacy data remain the missing piece.
Plain-language abstract
This paper introduced ipamorelin and explained how it works. Ipamorelin is a five-amino-acid peptide. In lab dishes of rat pituitary cells, it triggered growth-hormone release about as strongly as the established peptide GHRP-6, and tests with blocking drugs showed it works through the same receptor as GHRP-6, not through the separate GHRH pathway. It also raised growth hormone in rats and in pigs, again with strength similar to GHRP-6. The key difference emerged when the researchers checked other hormones: GHRP-6 and GHRP-2 both raised the stress hormones ACTH and cortisol, but ipamorelin did not, even at doses more than 200 times higher than the dose needed to release growth hormone. It also did not disturb reproductive or thyroid hormones. The researchers concluded that ipamorelin was the first peptide of its type to release growth hormone as selectively as the body's own GHRH, making it an interesting candidate for future development. This is laboratory and animal research, not a study in people.