Azasteroids and heart adenosine triphosphatase

Azasteroids, some known to be active, others to be inactive as inotropic and antishock agents, were tested as inhibitors of a metal-stimulated heart ATPase. In every instance the biologically active azasteroids inhibited catalysis just as did ouabain and the erythrophleum alkaloids. Biologically inactive azasteroids had no effect upon the enzyme. The in vitro enzyme system appears to hold promise as a preliminary assay method for inotropic activity. The relationship of azasteroid action in vivo to that of the cardiac glycosides and to the transport enzyme has been discussed.