Somatostatin receptors and the effect of somatostatin on histamine-stimulated adenylate cyclase activity in isolated gastric glands of guinea pigs

To investigate the mechanism of the suppressive action of somatostatin on gastric acid secretion, we determined the somatostatin binding and adenylate cyclase activity on crude membrane fractions of isolated gastric glnads of gunea pigs. The binding studies using125I-Tyr11 somatostatin showed the presence of somatostatin receptors with a single high affinity on crude membrane fractions. The dissociation constant (KD) for somatostatin was 1.05±0.13 nM, and the number of binding sites (Bmax) was 6.98±1.27 fmol/mg protein (mean±SE, n=6). The adenylate cyclase activity was increased by histamine, which was completely inhibited by 10-3M cimetidine. Somatostatin non-competitively suppressed the histamine-stimulated adenylate cyclase activity in the presence of guanosine 5′-triphosphate (GTP). These results suggest that somatostatin inhibits histamine-stimulated acid secretion throught the inhibition of the adenylate cyclase system, via somatostatin receptor and guanine nucleotide binding protein, which is activated by GTP binding.