Action of H1 and H2 inhibitors on the response of histamine sensitive adenyly cyclase from guinea-pig mucosa.

In the guinea-pig, it has been shown that homogenates of mucosa from the fundus contain an adenylyl cyclase system that is activated by histamine as well as by prostaglandins PGE1 and PGA1. The effects of burimamide, an H2-inhibitor, and mepyramine and chlorpheniramide, both H1-inhibitors, were tested. Both H1 and H2 inhibitors behaved kinetically as competitive inhibitors of histamine, but the Km derived for burimamide (2.5 - 4.1 . 10(-5)) was significantly lower than that for either chlorpheniramine (0.9 - 1.9 . 10(-4)) or mepyramine (1.3 - 1.4 . 10(-4)). On the other hand none of the three inhibitors influenced the cyclase activation by PGE1 and PGA1. These results suggest that there are at least two types of receptors in the preparation studied, one responsive to histamine and the other to the prostaglandins, and that the specificity of H1- and H2-receptors is not absolute in the broken cell preparation.