Biological actions of aldosterone

Aldosterone exerts its effect by binding to type I corticosteroid receptors in the cytoplasm, translocating to the nucleus, and binding to an acceptor site in the chromatin, which results in gene activation and synthesis of a specific protein (see Chapter 30). Aldosterone induces the synthesis of aldosterone-induced protein (AIP), which is involved in transcellular Na+,K+-ATPase. 

The type I corticosteroid receptor (mineralocorticoid receptor) binds cortisol and aldosterone with equal affinity. Because the circulating level of cortisol normally exceeds that of aldosterone by about 1000-fold (Table 32-1), activation of the receptor by aldosterone would probably not occur, were it not for the presence of a cortisolinactivating enzyme in cells responsive to aldosterone. This enzyme, llySHSD (Chapter 30), catalyzes the conversion of cortisol to cortisone, a metabolite that is not recognized by the receptor. Inhibition or absence of this enzyme leads to excessive aldosterone-like effects due to receptor activation by cortisol, a condition referred to as apparent mineralocorticoid excess (AME). AME can 

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