H1- and H2-receptors in the guinea-pig heart: an electrophysiological study.

The mechanical and electrophysiological effects of 2-pyridylethylamine (PEA) and 4-methylhistamine (4MeH) in different sections of guinea-pig heart were examined. 4MeH produced a dose-dependent increase in contractility in the right ventricle and the right atrium, and a decrease in functional refractory period (FRP) in all the sections studied; the action potential duration was decreased and the plateau phase was usually heightened in both atria and the ventricle. These effects were consistently antagonized by cimetidine. PEA-induced changes in contractility, FRP and the action potential profile were studied in the presence of cimetidine. Triprolidine antagonized PEA effects on FRP and the action potential profile only in the left atrium. The results obtained are discussed in terms of the functional role of both H1 and H2 receptors in the various guinea-pig heart sections.