[Milrinone decreases the positive inotropic response of heart muscle to izadrin].

The interaction of the cAMP-phosphodiesterase inhibitor milrinone and the beta-adrenoceptor agonist isoproterenol was studied on guinea-pig isolated hearts. Milrinone, (10 microns) caused a positive inotropic response which differed from that of isoproterenol (7 nM) and decreased cardiac inotropic responses to the subsequent administration of isadrin despite a significant great rise in cAMP. The interaction of the drugs is assumed to be associated with the milrinone-induced increase in cGMP which is able to restrict myocardial cAMP-activated processes.