Histamine-mediated hyposmotic stimulation of gastric acid secretion

Gastric glands incubated in hyposmotic medium (200 mOsm) accumulated aminopyrine, a measure of acid secretion, to the same extent as that of paired glands in isomotic medium containing histamine (10(-4) M). These maximal responses to hyposmolality and histamine were not additive. The hyposmotic response peaked earlier than the histamine response. Hyposmotic stimulation was nearly abolished by preincubation of the glands with metiamide and cimetidine, H-2 histamine antagonists. In the presence of histaminase, no hyposmotic stimulation occurred. The response to forskolin, a stimulant of adenylate cyclase, was equivalent in hyposmotic and isosmotic media. These results indicate that hyposmolality releases histamine from a paracrine cell in the gastric gland and that histamine binds to H-2 receptors on the parietal cell to initiate a cyclic AMP-mediated stimulation of acid secretion.