Circulating digitalis-like factors.

The ability of extracts of mammalian plasma and tissue to mimic the biologic activities of the digitalis glycosides has suggested the existence of endogenous regulators for Na, K ATPase. Purification of plasma extracts has identified several classes of circulating lipids with digitalis-like activity including free fatty acids, lysophospholipids, and arachidonic acid metabolites of the lipoxygenase pathway. Circulating steroids with digitalis-like activity include dehydroepiandrosterone sulfate and hydrocortisone. Evidence for other, more unique compounds has also been published although their structure has not yet been determined. Analysis of tissue suggests that hypothalamus contains a unique, low molecular digitalis-like factor (DLF) which also circulates in plasma. Some studies suggest that the hypothalamic factor is also present in other parts of the brain and in the adrenal. Some of these endogenous DLF may function as modulators of cardiovascular function by regulating renal sodium excretion and peripheral vascular resistance in both physiological and pathophysiological situations.