Effects of histamine and the histamine antagonists mepyramine and cimetidine on human coronary arteries in vitro.

The effects of histamine have been studied on human isolated coronary artery preparations taken from hearts ranging in age from 9 to 73 years. Histamine in large concentrations (100 microM) contracted arteries which were without tone or spontaneous activity and sometimes induced rhythmic contractile activity. If spontaneous rhythmic activity was present it was enhanced by histamine. The contractile effects of histamine were inhibited by mepyramine but not by cimetidine. Arteries which were contracted by depolarization responded with relaxation to histamine concentrations lower than those required to evoke a contraction; arteries from younger hearts were more sensitive than those from older hearts. Mepyramine potentiated the maximal relaxant effect of histamine in arteries from hearts of all ages but cimetidine had very little effect. In the presence of mepyramine, cimetidine antagonized the relaxant effect of histamine, shifting the concentration-effect curve to the right. It is concluded that human coronary arteries contain both H1- and H2-type receptors, the H1-receptors mediating contraction. The relaxant effects of histamine can only be inhibited by a combination of both H1- and H2-receptor antagonists.