H 1 and H 2 histamine receptors in rat gastric submucosal arterioles

Abstract

The types and functions of histamine receptors in the gastric submucosal arterioles of the rat were studied using an image-splitting in vivo microscopy technique. Histamine, 10 −5 to 10 −3 M, applied topically to the exposed submucosa, caused dose-dependent increases in arteriolar diameter in both the corpus and antrum. Both the H 1 receptor antagonist, mepyramine, and the H 2 receptor antagonist, metiamide, inhibited the response to 10 −5 and 10 −4 M histamine, displacing the dose-response curve to the right. In the corpus the two antagonists were equally potent, but in the antrum, the H 1 antagonist caused much greater inhibition than the H 2 antagonist. When the antagonists were administered together, there was still further displacement of the dose-response curve to the right. However, 10 −3 M histamine surmounted this inhibition. The H 1 receptor agonists aminoethyl thiazole and aminoethyl pyridine, and the H 2 receptor, dimaprit, dilated the submucosal arterioles in the corpus and antrum. This effect was inhibited by the respective specific receptor antagonists. In conclusion, independent H 1 and H 2 receptors, both subserving vasodilatation, are present in the gastric submucosal arterioles.