Endogenous factors with immunological and biological activity similar to cardiac glycosides: biochemical and pathophysiological implications.

Abstract

Endogenous factors with properties similar to digitalis drugs (Endogenous Digitalis-Like Factors, EDLF) have been found in several tissues and body fluids of animals and humans. Detectable EDLF concentrations were found in blood and urine extracts of adults (normal healthy controls, hypertensive patients and salt loaded healthy subjects), while higher levels were generally observed in plasma samples of pregnant women, newborns and patients with renal insufficiency. The chemical characteristics of this endogenous factor are, at the present, unknown, although it has been suggested that EDLF could be a substance with low molecular weight. Experimental studies and theoretical considerations suggest that EDLF, in addition to the ability to react with antibodies anti-digitalis drugs (such as digoxin and ouabain), might also bind to the specific cellular receptor of the cardiac glycosides and thus inhibit the membrane Na+/K+-ATPase (sodium pump). Therefore, it has been suggested that EDLF is an endogenous modulator of the membrane sodium-potassium pump and it could play a role in the regulation of fluids and electrolytes, muscular tone of myocardium, and also in pathogenesis of hypertension.