Two Receptor Families, One Goal

Growth hormone releasing peptides (GHRPs) such as GHRP-6 and hexarelin, as well as ipamorelin, activate the ghrelin receptor (GHS-R1a) in the pituitary and hypothalamus. GHRH analogs such as sermorelin and tesamorelin, by contrast, act via a completely different receptor, the GHRH receptor.

Why Ipamorelin Is Different

GHRP-6 was developed in the 1980s by Cyril Bowers at Tulane University – the first synthetic growth hormone releasing peptide. It and its more potent successor hexarelin, however, also bind CD36 in cardiac tissue in addition to the ghrelin receptor, a pathway independent of the pituitary axis.

Ipamorelin, developed by Novo Nordisk, activates the ghrelin receptor considerably more selectively. Unlike older GHRPs, it showed no significant effects on cortisol or prolactin in studies.

GHRH Analogs: Sermorelin and Tesamorelin

Sermorelin corresponds to the first 29 of the 44 amino acids of native human GHRH and was FDA approved under the name Geref as early as 1997 – production was discontinued in 2008 for commercial, not safety, reasons.

Tesamorelin carries a chemical modification at the N-terminus that protects it from degradation by the enzyme DPP-4. It has been approved since 2010 under the name Egrifta for treating visceral fat in HIV-associated lipodystrophy.

Sources

  • Raun K, et al. Eur J Endocrinol. 1998;139(5):552–561. PMID 9849822
  • Bodart V, et al. Circulation Research. 1999;85(9):796–802. PMID 10532947
  • Walker RF. Clin Interv Aging. 2006;1(4):307–308. PMID 18046908
  • Falutz J, et al. J Acquir Immune Defic Syndr. 2010;53(3):311–322. PMID 20101189

References without a PMID can be located via the respective publisher.