[Cardiac effects of antikaliuretic diuretics-clinical and biochemical investigation (author's transl)].
Recently direct myocardial effects of antikaliuretic diuretics with respect to contractility parameters and prevention of digitalis-induced arrhythmias were published. In order to test the value of these reports we measured the effect of potassium-canrenoate and triamterene on cardiac output and on digitalis-induced arrhythmias in patients during diagnostic and the therapeutic flow directed right heart catheterization (Swan-Ganz) in our intensive care unit. In addition the influence of these drugs on (Na+ + K+)-ATPase and on (3H)g-strophanthin binding to human cardiac cell membranes was investigated to gain information on the mechanism of their action. Triamterene (100-200 mg p.o.) was without any effect on cardiac output, the same was found true for potassium-canrenoate given in a single dose (200-1000 mg intravenously). However, when applied in two doses (200 mg i.v. and 60 min later 400 mg i.v.), potassium-canrenoate increased cardiac output by 11 percent (p less than 0.05). Only in 2 out of 14 patients potassium-canrenoate (200-400 mg i.v.) suppressed digitalis-induced ventricular ectopic beats. Canrenone, the active metabolite of potassium-canrenoate displaces [(3H)]g-strophanthin from its binding sites in human cardiac cell membranes and inhibits (Na+ + K+)-ATPase activity. These in vitro effects were measured at the same concentrations as found in vivo after "therapeutical" doses. The effects of triamterene in this respect were found only in extremely high concentrations. Our results imply that canrenone has cardiac glycoside-like effects in human cardiac cell membranes.