Positive inotropic drugs--digitalis.

Digitalis glycosides inhibit Na+K+-ATPase in the cells and have been used for scientific studies of cation transport over cell membranes. Furthermore, digitalis has a positive inotropic and antiarrhythmogenic effect. Specific binding sites for digitalis glycosides have been observed in erythrocytes, the myocardium and the central nervous system. Transcellular transport of digoxin has been found in the kidney, since digoxin is excreted by tubular secretion. Recent studies have discovered an endogenous digitalis-like substance both inhibiting Na-K-ATPase and displacing digoxin from specific binding sites at the erythrocytes. The concentration of this component in plasma seems to be higher in hypertension than in normotension. Future studies will have to disclose other effects of this substance in order to evaluate whether it can be used as a drug in heart failure.