Cardiac histamine ouabain interaction: potentiation by ouabain of the arrhythmogenic effects of histamine
Cardiac effects of histamine include stimulation of sinus rate and ventricular contractile force, impairment of atrioventricular conduction and increase in ventricular automaticity. Atrioventricular block and increase in ventricular automaticity are common features of digitalis toxicity. The purpose of the present investigation was to study the influence of low concentrations of ouabain on the cardiac effects of immunologically released and administered histamine. Hearts excised from guinea pigs passively sensitized to penicillin antigens responded to antigen with sinus tachycardia, atrioventricular conduction block, increase in ventricular automaticity, decrease in coronary flow rate and histamine release. During anaphylaxis in the presence of ouabain, 10-9 and 3 times 10-9 M, the duration of conduction arrhythmia and the incidence of ventricular automaticity were greatly increased. Dose-response studies for the cardiac effects of exogenous histamine were conducted in vitro in the presence of ouabain 10-9 and 3 times 10-9 M. Ouabain, in a concentration-dependent fashion, potentiated histamine-induced prolongation of the P-R interval, but not the increases in sinus rate and in ventricular contractile force. Oution block and idioventricular also greatly increased the incidence of histamine-induced atrioventricular conduction block and idioventricular rhythms. Our results clearly identify a histamine-Ouabain interaction leading to severe disruption of atrioventricular conduction and to increased ventricular automaticity.