Histamine H1-and H2-receptors in coronary arteries of pigs.

Histamine exerts its action in smooth muscle via in two types of receptors. In coronary arteries of pigs both types of receptors are also involved in responses to histamine. Histamine initiates by an interaction with H1-receptors a contraction and with H2-receptors a relaxation. The histamine-induced contraction is reduced by the competitively antagonistic action of mepyramine. Metiamide potentiates dose-dependently the histamine-caused contraction in the absence and presence of mepyramine. The proportion of H2-receptors in relation to H1-receptors is calculated.