CHARACTERIZATION OF VASCULAR HISTAMINE-RECEPTORS IN THE RAT

In the rat the decrease in blood pressure caused by histamine involves activation of both H1‐ and H2‐receptors. Since arterial pressure measurements alone do not permit the separation of responses into cardiac and vascular components, the following experiments were undertaken to study vascular histamine receptors. Vascular responses were studied in the autoperfused hindquarters of anaesthetized rats. Intra‐arterial histamine caused vasodilatation which was only partially attenuated by treatment with mepyramine, an H1‐receptor antagonist. Treatment with metiamide, the H2‐receptor antagonist, did not affect vasodilatation caused by histamine but did attenuate vasodilatation which persisted after mepyramine. Intra‐arterial 4‐methylhistamine, an H2‐receptor agonist, caused vasodilatation which was reduced by metiamide. The H1‐receptor agonist, 2‐(2‐pyridyl)ethylamine also caused vasodilatation which was blocked by mepyramine. It is concluded that in the rat, histamine causes vasodilatation mediated by both H1‐ and H2‐receptors. 1979 British Pharmacological Society