Hormonal control of distal nephron function.

The distal tubule and collecting tubules are important control sites of fluid and electrolyte excretion. In our presentation we consider the cell mechanisms of transport of sodium and potassium ions and the effects of several hormones. Aldosterone and antidiuretics stimulate potassium secretion directly, and the available evidence strongly suggests that this effect involves the principal cell population. Epinephrine inhibits potassium secretion at sites beyond the distal tubule. In addition to such direct effects, secondary factors such as hormone-induced changes in flow rate along the distal tubule and changes in the plasma potassium level play an important modifying role. Several examples are presented to demonstrate that interaction of several control components uncouples potassium secretion from distal flow rate and tends to stabilize urinary potassium excretion during changes in sodium and water balance.