Gastric inhibitory polypeptide and glucagon-like peptide-1(7-36) amide exert similar effects on somatostatin secretion but opposite effects on gastrin secretion from the rat stomach.

Previous studies on the isolated perfused stomach have shown that gastric inhibitory polypeptide (GIP) and glucagon-like peptide-1(7-36) amide (GLP-1(7-36) amide) stimulate release of somatostatin (somatostatin-like immunoreactivity, SLI). GIP produced a paradoxical increase in gastrin secretion, whereas GLP-1(7-36) was inhibitory. In the current study, the actions of synthetic (sp) and native (np) porcine and synthetic human (sh) GIP, GLP-1(7-36), and GLP-1(7-37) on SLI and gastrin secretion were compared using a gradient perfusion of peptide. All peptides increased SLI secretion at a threshold concentration of approximately 50 pmol/L (p < 0.05). The initial rate of increase in response to spGIP (119 +/- 39 pg/min) was greater than with other forms of GIP or GLP-1. Maximal increases obtained with the two porcine peptides did not differ. Gastrin secretion was increased by concentrations of spGIP and npGIP similar to those increasing SLI secretion, but the maximal response to shGIP was lower. In contrast to GIP-induced increases, both GLP-1(7-36) and GLP-1(7-37) suppressed gastrin secretion. It is concluded that human and porcine GIP, GLP-1(7-36), and GLP-1(7-37) all stimulate SLI secretion but with different maximal effects, and GIP stimulates gastrin secretion whereas both forms of GLP-1 inhibit gastrin secretion.