Somatostatin octapeptides (lanreotide, octreotide, vapreotide, and their analogs) share the growth hormone-releasing peptide receptor in the human pituitary gland

The binding affinity of somatostatin-14 (SRIF), various SRIF derivatives, a nd some peptides belonging to the growth hormone-releasing peptide (GHRP) f amily to specific receptors for SRIF and GHRP in the human pituitary gland has been measured. GHRP receptors have been identified using [I-125]Tyr-Ala -hexarelin, a peptide that thas been demonstrated to be a potent growth hor mone (CH) releaser in humans. Tyr-Ala-hexarelin binding was displaced in a dose-dependent manner by different GHRPs (hexarelin, GHRP-2, and EP-51216). Surprisingly, some SRIF octapeptide derivatives such as vapreotide, lanreo tide, octreotide, and their analogs were also able to displace the GHRP lig and. By contrast, no inhibition of Tyr-Ala-hexarelin binding was observed i n the presence of SRIF or SRIF derivatives (SRIF H-2186, H-2485, and H-3382 ) that are known to have a weak SRIF-like activity. When [I-125]Tyr(1)-SRIF -14 was used as a ligand, we observed displacement with SRIF and the octape ptide SRIF analogs but not with GHRPs and other SRIF derivatives. The resul ts point to a sharing of the GHRP receptor with the octapeptide SRIF analog s, but not SRIF, Our data are consistent with the hypothesis that the putat ive natural CH secretagogue ligand may be a growth hormone release inhibiti ng factor that is different from SRIF and that is antagonized by GHRP.