BACKGROUND Both secretin and cholecystokinin (CCK) inhibit gastric acid secretion. However, their mode of action has yet to be determined. A newly developed primary culture of human antral epithelial cells has been used to examine the effect of secretin and cholecystokinin on somatostatin release. METHODS Normal human antral epithelial cell cultures enriched for D cells were maintained in culture for 2 days before release studies. RESULTS Native human secretin at 10(-8) mol/L stimulated somatostatin release threefold. Porcine secretin and the secretin analogs, Tyr10 human secretin, Tyr13 porcine secretin, and Tyr10,13 porcine secretin were equipotent to native human secretin. CCK stimulated somatostatin release with the greatest response (eight times basal) at 10(-7) mol/L. The response to CCK was inhibited in a competitive manner by the addition of the benzodiazepine analog, MK-329. Addition of secretin in the presence of 10(-8) mol/L CCK resulted in a potentiation of somatostatin release, with the greatest response at 10(6) mol/L secretin, resulting in a 12-fold increase above basal. CONCLUSIONS The stimulation observed after the addition of CCK was the result of activation of the CCK-A receptor subtype. The secretin receptor resembles that of the pancreatic D cells and acts through increasing intracellular cyclic adenosine monophosphate levels. Finally, these data indicate that the inhibitory action of CCK and secretin on gastric acid secretion may result from a synergistic action on antral D cells to release somatostatin, which in turn decreases antral gastrin release.