The chronotropic effect of histamine, prometasin and cimetidin on rat heart.

The effect of histamine, prometasin (the blocker of histamine H-1 receptor) and cimetidin (the blocker of histamine H-2 receptor) on the frequency of the isolated right atrium of rat was studied. Histamine, prometasin and cimentidin were applied cumulatively in concentrations of 5.4 X 10(-6) to 16.3 X 10(-3) mmol/l so that each new concentration was 3.3 times higher than the preceding one. The positive chronotropic effect of histamine was shown to be strongest with a concentration of 5.4 X 10(-3) mmol/l. Prometasin and cimentidine applied in increasing concentrations gave a negative chronotropic effect. Prometasin and cimetidin applied in a concentration of 5.4 X 10(-3) mmol/l before histamine, decreased the positive chronotropic effect of histamine to more than 60% no matter whether prometasin and cimetidin were applied alone or together. This finding suggests that the effect of histamine on rat heart is mainly realized via histamine H-1 and H-2 receptors and partly through releasing catecholamines from the adrenergic nerve terminal.