CDB15:0000365 CORT — GHSR

ABSTRACT: Antagonism between GH secretagogues (GHS) and somatostatin (SRIH) has been postulated and demonstrated, but SRIH does not bind to GHS receptors (GHS-R) and potent synthetic peptidyl GHS (GHRP6, hexarelin) do not displace radiolabeled SRIH from its receptors. However, non-natural SRIH octapeptide agonists (mainly lanreotide and vapreotide) displace 125I-Tyr-Ala-hexarelin from pituitary binding sites suggesting that an endogenous factor related to SRIH might exist and interact with GHS-R. Our aims were to investigate the ability of different SRIH-like peptides such as various SRIH fragments (SRIH 3-14, SRIH 7-14, SRIH 3-10, SRIH 7-10, SRIH 2-9) and a natural neuropeptide that shows a high structural homology with SRIH such as cortistatin-14 (CST) to compete with 125I-Tyr-Ala-hexarelin for human pituitary binding sites and to compare their binding affinity with that of hexarelin and ghrelin, a gastric-derived peptidyl GHS that has been proposed as a natural ligand of GHS-R. While the binding of 125I-Tyr-Ala-hexarelin to pituitary membranes was completely displaced by unlabelled hexarelin, ghrelin and CST, none of the SRIH fragments tested inhibited this binding. Ghrelin and CST exhibited a similar affinity (4.6-5.4 x 10(-7) mol/l) for the binding while hexarelin was more effective by about four orders of magnitude in displacing 125I-Tyr-Ala-hexarelin. Our data demonstrate for the first time that cortistatin, a natural peptide related to SRIH, binds to GHS-R and suggest that this factor may play a role in modulating the activity of these receptors.