On the mechanism of action of aldosterone.

Studies to elucidate the mode of action of aldosterone have been carried out in the amphibian urinary bladder. The following previously reported hypotheses were evaluated: (1) aldosterone stimulates sodium transport by increasing the amount of sodium available to the sodium pump; (2) aldosterone enhances energy production for the sodium pump; and (3) aldosterone-stimulated sodium transport is obligatorily coupled to aerobic metabolism. In the present experiments, aldosterone potentiated the effect of vasopressin on sodium transport in the absence of aerobic metabolism or oxidative phosphorylation. This effect was not due to enhanced energy supply. Thus both hypotheses 2 and 3 appear not to be valid. In addition, aldosterone-stimulated sodium transport exhibited increased sensitivity to the specific inhibitor, ouabain, and this inhibition was readily reversed by K(+). These findings, as well as previously reported work, have led us to propose that aldosterone stimulates sodium transport by inducing a change either in the sodium pump itself, i.e., synthesis or activation, or in its environment in the serosal plasma membrane of the responsive cells.