Aldosterone as a factor of extracellular volume regulation: mechanism of action

The key role assumed by aldosterone in the regulation of extracellular volumes, requires that chloride moves along with sodium when active transport of the later ion is stimulated. In the mammalian nephron, aldosterone promotes reabsorption of sodium by the principal cells of the cortical portion of the collecting ducts. This results from hormone-induced increase in conductance for sodium at the apical pole of the target cells, and later on, from associated increased density of the sodium "pump" units at the basolateral pole. Studies carried out on amphibian epithelia indicate that chloride permeability - of mitochondria-rich cells, in all likelihood - is concurrently increased by aldosterone. It therefore looks as though this steroid hormone influences in a concerted way 2 cell populations, one being involved in transepithelial sodium transport, the other one representing the route of passage for the accompanying anion.