Renal excretion of para-aminosalicylic acid: a two-way transport system in the dog.

Abstract

The renal excretion of free para-aminosalicylic acid (PAS) was studied in dogs. With increasing loading and sustaining infusion of the compound alone, a negative T (rate of urinary excretion minus the rate of filtration of PAS) was observed, but a positive T was obtained during added sodium bicarbonate or sodium acetate infusion. While the positive T values were greater during acetate than in bicarbonate infusion, urinary pH was higher in the latter. Studies with intrarenal arterial injection and stop-flow techniques showed evidence of a bidirectional transport of free PAS. The reabsorption of PAS was influenced by the urinary pH. Sodium bicarbonate infusion reduced the reabsorption; lactic acid infusion increased it. Secretion of the free PAS does not require a high urinary pH and is augmented by acetate and blocked by probenecid. This suggests that the secretion of free PAS involves an active process, analogous, though not necessarily identical to the system for PAH and for other related substances.