Aldosterone: a telling case of fruitful interplay between biological and clinical research

Aldosterone, discovered thirty years ago, has rapidly gained an enviable status among clinicians as well as biologists: this hormone is the main regulator of extracellular fluid volume--essentially through its effect on sodium retention in the distal parts of the nephron. This aspect has been fruitfully approached by means of (amphibian) epithelia carrying out transcellular sodium transport and resembling in this respect the distal renal tubule. Recent results suggest that, at least after prolonged incubation, not only is sodium entry (at the apical border) facilitated by aldosterone, but the latter steroid also somehow improves the handling of the ions by the "pump" located at the basal-lateral border. As a consequence, the target cells exposed to aldosterone are optimally geared for enhanced transcellular sodium transport. Biochemically, both processes depend on the standard pattern of steroid hormone action: after interaction of aldosterone with protein receptors(s) present in the cytoplasm of target cells, and migration of the resulting complex to their nucleus, synthesis of specific messenger ribonucleis acid is stimulated which leads to increased synthesis of proteins eventually responsible for the physiological response. An intriguing aspect of the concerted response to aldosterone documented in amphibian sodium-transporting epithelia, is that both cell borders of target cells are not influenced simultaneously: this is currently investigated [Beauwens et al. 1982b].