Sermorelin and tesamorelin vs ipamorelin, GHRP-2 and hexarelin: two receptor classes compared

The GHRH receptor is a class B G-protein-coupled receptor. Sermorelin is the shortest fully active fragment of human GHRH; tesamorelin is the full 44-residue sequence with an N-terminal modification that resists enzymatic cleavage.

The growth hormone secretagogue receptor (GHS-R1a) is the receptor for the gut hormone ghrelin. Ipamorelin, GHRP-2 and hexarelin are short synthetic peptides containing D-amino acids that were developed as agonists of this receptor before ghrelin itself was identified.

Because the families act at different receptors, an in-vitro study usually needs a cell system that expresses the relevant receptor (GHRH-R or GHS-R1a). Comparisons across families are comparisons of different pathways, not of potency at one target.

The size difference is large: the GHRH analogs are 3.3 to 5.1 kDa, the secretagogues 0.7 to 0.9 kDa. That affects LC-MS charge states, HPLC retention and the molarity of a stock solution made from a given mass.

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