Effect of histamine on the gastric smooth muscles of guinea pig.

The responses to histamine were studied in circular smooth muscles of three different regions of the guinea pig stomach: the fundus, the antrum and the pylorus. Histamine elicited contractions in all three regions. The contractile responses to histamine were completely abolished by mepyramine (10(-3) g/l). These results showed the presence of H1 receptors, which mediate contractile response, in all regions of the stomach. In the presence of mepyramine, histamine caused marked relaxation in the preparations from the fundus contracted by acetylcholine. This relaxation was noticeably suppressed by cimetidine, indicating the existence of H2 receptors in the fundus.