Evidence for a positive inotropic effect of aldadiene (-K, -Na) on the isolated ventricular myocardium.

Abstract

The effect of Aldadiene (-K, -Na) was studied in the isolated cat papillary muscle preparation. At doses of 500–2000 µg/ml, significant increases are observed in the extent of shortening, in the velocity of isotonic shortening and relaxation and in the rate of isometric tension development. Force-velocity relations are shifted upwards and to the right with increases of both the preload velocity and the maximum isometric tension. The maximum increases of cardiac mechanics are observed 3–4 min after Aldadiene incubation. In most of the experiments there is a late decrease of cardiac mechanics compared with the controls, approximately 20 to 30 min after Aldadiene incubation, which is most probably due to the elevation of extracellular potassium concentration associated with Aldadiene-K incubation. Using Aldadiene-Na, this late decrease of cardiac mechanics was largely reduced. The results demonstrate a direct positive inotropic action of Aldadiene (-K, -Na) on the isolated ventricular myocardium.