Gastrin releasing peptide: endocrine functions in the rat.

The effect of porcine gastrin releasing peptide (GRP), a heptacosapeptide with potent gastrin releasing activity which has recently been isolated from porcine non-antral gastric tissue, on pituitary function was investigated in the rat. Graded doses of synthetic porcine GRP were injected intravenously and the animals were killed at various intervals after injection. Prolactin, growth hormone, luteinizing hormone (LH), follicle-stimulating hormone (FSH) and thyroid-stimulating hormone (TSH) were measured in serum by specific radioimmunoassays. GRP had no significant effect on prolactin, growth hormone or FSH serum concentrations at any dose or sampling time studied. In contrast, the heptacosapeptide significantly stimulated LH release and suppressed TSH secretion with injection of low doses. There are striking structural and some functional similarities between GRP and bombesin, an amphibian skin tetradecapeptide which shows amino acid homology with the C-terminal region of GRP. This suggests that the endocrine effects of GRP may be mediated by its bombesin-like residue.