The effects of 2,4,6-triaminopyrimidine (TAP) on sodium and potassium excretion by the rat kidney: comparison with amiloride.

2,4,6-Triaminopyrimidine (TAP) has been reported to be a blocker of the cation-specific paracellular conductance pathways of several epithelia. The compound is also known to inhibit sodium transport in the frog skin. Its effects on renal function were studied in clearance experiments in anesthetized rats and in isolated perfused rat kidneys and compared with the effects of amiloride. The effects of both compounds on electrical resistance of the frog gallbladder were also evaluated. Both TAP and amiloride caused modest natriuresis and a marked reduction in potassium excretion. Amiloride is approximately 1000 times more potent than TAP when compared on the basis of drug concentration in the urine. The concentrations of both substances in urine (at effective doses) correspond to concentrations reported to be effective against sodium transport in amphibian membranes. The urinary concentrations of TAP also correspond to the concentrations required to inhibit paracellular cation movement in the gallbladder. Amiloride at the level tested (10(-3) M) did not seem to influence the paracellular pathway. The results neither establish nor disprove a role of the paracellular pathway in potassium secretion. Both TAP and amiloride are secreted by the renal tubules.