Abstract
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.