Does the hormone "endogenous ouabain" exist in the human circulation?

Studies in the early 1990s suggested that a hormone identical to ouabain or an isomer of ouabain is secreted by the adrenal glands into the circulation and plays a role in the regulation of arterial pressure and cardiac and renal function. This hormone, known as endogenous ouabain (EO), was claimed to contribute to the pathophysiology of a number of disorders including heart failure, renal failure, pregnancy-induced, and essential hypertension. However, some research groups have been unable to confirm the presence of EO in the human circulation and the issue remains in dispute. In that the implications are of considerable importance to clinicians who, like the authors, lack biochemical expertise, it would be useful if the dispute could be addressed by disinterested scientists with long-standing and acknowledged expertise in analytical chemistry who could opine as to whether the evidence is, or is not, sufficient to state categorically that EO does (or does not) exist in the circulation in man. This brief review does not present new data but, rather, recommends that adjudication is needed regarding this important issue.