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Box 4.32Aldosterone actions in the kidney

In the circulation aldosterone (A) is mainly bound to cortisol-binding globulin (CBG) or albumin. Free aldosterone enters the tubule cells of the kidney and binds to the mineralocorticoid receptor (MR). This induces release of a heat shock protein (hsp), dimerization of two MRs and translocation to the nucleus where it binds to a glucocorticoid response element (GRE) on the DNA and, along with other transcription factors, initiates protein synthesis. The aldosterone-induced proteins include factors that regulate the luminal Na⁺ channel and components of the Na⁺/K⁺ ATPase pump. There is also evidence for rapid membrane effects of aldosterone on tubular cells.