Hyperresponsiveness of Cardiac Muscles to Histamine in Reserpine-Treated Guinea Pigs.

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The hyperresponsiveness of cardiac tissue to histamine following treatment with reserpine was pharmacologically characterized. Guinea pig hearts were isolated 24 hours after intraperitoneal administration of 5mg/kg reserpine. This treatment resulted in a complete depletion of tissue norepinephrine. Reserpine treatment potentiated the positive inotropic response of isolated perfused hearts to histamine at doses ranging from 0.3 to 3μg (23 to 57% increase for reserpine-treated animals vs. 14 to 32% increase for control animals). Isolated left ventricular papillary muscle of reserpine-treated guinea pig hearts also showed hyperresponsiveness to histamine at concentrations of 0.1μM or greater. The hyperresponsiveness of the papillary muscle contraction of the reserpine-treated animals to histamine was abolished in the presence of 1μM cimetidine, but not attenuated in the presence of 1μM diphenhydramine. This hyperresponsiveness was not modified by 1μM bunazosin or 1μM propranolol. The results suggest that H2-receptor mediated action plays a role in the hyperresponsiveness of cardiac muscles to histamine.