Ouabain, a new steroid hormone of adrenal gland and hypothalamus.

Ouabain has been isolated and identified as a constituent of human blood, bovine adrenal glands and hypothalamus. This water soluble inhibitor of the sodium pump (Na+/K+-ATPase) circulates in elevated concentrations in blood plasma of 50% of Caucasians with elevated blood pressure. It is released from adrenal cortical cells in tissue culture by angiotensin II. A ouabain antagonist, PST2238, lowers blood pressure in hypertensive rats. Hence, ouabain is most probably a new steroid hormone formed in adrenal glands and hypothalamus. Consistent therewith is the demonstration of a specific binding globulin for cardiac glycosides in blood plasma.