Endogenous inotropic substance from heart tissue has digitalis-like properties.

In the past few years, we developed an extraction procedure which we successfully used to isolate a crude fraction containing digitalis-like substance (DLS) from porcine left ventricular tissue. In this study, the crude fraction was found to cross-react with digoxin antibodies and showed immunoreactivity of 4.25 +/- 0.6 ng digoxin equivalent/ml. On further purification of the crude fraction using silica gel G column chromatography, a fraction C was obtained, which was highly positive inotropic on canine trabeculae and it dose-dependently inhibited ouabain sensitive 86Rb+ uptake in rat heart slices. A 50% inhibition of uptake was obtained by 25 microliters of fraction C. Fraction C also inhibited canine kidney Na+, K(+)-ATPase (Sigma, U.S.A.) dose-dependently and a 50% inhibition of this enzyme required 17 microliters of fraction C. Ashing of the fraction C at 500 degrees C resulted in loss of inotropic and enzyme inhibitory activities, indicating an organic nature of the unknown digitalis-like substance.