Evidence for the histamine-mediated myotropic effect of angiotensin II in the rabbit aorta

Histamine H1-receptor antagonist mepyramine and H2-receptor antagonist metiamide, respectively diminished and potentiated angiotensin II(A II)-induced myotropic responses in the rabbit aortic strips. The responses of the octapeptide were also inhibited in the presence of histidine decarboxylase inhibitor, 2-hydroxy-5-carbomethoxybenzoxyamine and restored when subcontractile quantities of histamine are added to the inhibitor-containing medium. Inhibition of histamine degradation by aminoguanidine potentiates A II's responses. These results are taken as evidences indicating A II-induced histamine synthesis in the test preparation.