Dissociation of cimetidine effects on inotropic and chronotropic action in cardiac anaphylaxis

The changes of heart rate (HR) and dP/dtmax elicited by challenging the sensitized heart and by a bolus injection of histamine in the presence of cimetidine were observed. The results showed that cimetidine did not completely inhibit the positive chronotropic effect in cardiac anaphylaxis. The increase in HR elicited by exogenous histamine on sensitized heart was completely abolished. Cimetidine inhibited the positive inotropic and chronotropic effect of histamine on normal heart in a dose-dependent manner. It is suggested either an H2 receptor subtype or concomitant with the release of histamine, other mediators eliciting positive chronotropism in cardiac anaphylaxis may exist.