Tubular action of diuretics: distal effects on electrolyte transport and acidification

We used clearance and free-flow micropuncture techniques to evaluate the influence of several diuretic agents, given both individually and in various combinations, on transport of sodium, potassium, and fluid, and on acidification and ammonium transport, within the distal tubule of the rat kidney. The loop diuretics, furosemide and piretanide, sharply increased fractional delivery of fluid, sodium, and potassium into the distal tubule, and, as a result, sodium reabsorption and potassium secretion were enhanced in this nephron segment. These two drugs also stimulated urinary acidification and increased urinary phosphate, titratable acid, and ammonium excretion. These effects took place both within the loop of Henle and along the distal tubule. Amiloride and triamterene alone inhibited distal tubular sodium reabsorption and potassium secretion, and, when given with one of the loop diuretics, suppressed both the kaliuresis and the increased acid and ammonium excretion induced by the latter agents. Hydrochlorothiazide and tizolemide inhibited sodium reabsorption within the distal tubule, and were associated with a stimulation of potassium secretion within this segment. Addition of one of these two latter distally acting agents to either of the loop diuretics led to a further augmentation of sodium excretion, but to a reduction of potassium excretion, compared to the responses seen after the loop diuretics alone.