The dependence of cardiac eicosanoid effects on changes of calcium concentration

Investigations were performed in isolated heart preparations of guinea pigs to prove the dependence of myocardial eicosanoid effects (PGE1, PGF2a, PGI2, U 46619) on concentration and fluxes of calcium ions. In auricles the increase of cardiac performance by eicosanoids was more evident, when calcium ions were reduced in the medium. In isolated perfused hearts a continuous perfusion of eicosanoids showed a cardiodepressive effect. The coronary flow was increased by PGE1 and PGI2, but decreased by U 46619. The actions of prostaglandins were diminished, but the U 46619 influence increased with rising calcium concentrations. The antiaggregatory effect of PGI2 was decreased by calcium. Furthermore the calcium antagonist verapamil opposed Ca2+-fluxes and the cardiac and coronary effects of prostaglandins. The results indicate that eicosanoids induce cardiac and vascular effects by changes in the membrane calcium fluxes and/or the intracellular concentration and distribution of calcium ions.