The involvement of histamine receptor subtypes in gastric acid secretion and mucosal blood flow in the anaesthetized rabbit.

1. The involvement of histamine receptor subtypes in the gastric acid secretory and mucosal blood flow responses of the pentobarbitone-anaesthetized rabbit to histamine were investigated. 2. Histamine produced a dose-related increase in gastric acid secretion and mucosal blood flow. Maximal effects were stimulated further by mepyramine and inhibited by metiamide. Mepyramine had no effect on methacholine- or impromidine-stimulated gastric acid secretion or mucosal blood flow. 3. Impromidine also produced a dose-related increase in gastric acid secretion and mucosal blood flow. The maximal effect produced depended on the method of administration. The H1-receptor agonist 2-TEA inhibited impromidine-stimulated blood flow but not gastric acid secretion. 4. It is concluded that, in addition to stimulating acid secretion by an action on H2-receptors, histamine also exerts an inhibitory effect which is mediated by H1-receptors and that this inhibitory effect operates via reduced blood flow resulting from vasoconstriction in the stomach.