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.