Effect of amiloride, ouabain, and furosemide on distal tubular function in the rat.

DUARTE, CRISTOBAL G., FRANCOISE CHOMETY, AND GERHARD GIEBISCH. Effects of amiloride, ouabain, and furosemide on distal tubular function in the rat. Am. J. Physiol. 221(Z) : 632-639. 1971 .-Freeflow samples of tubular fluid (TF) were collected from superficial distal rat tubules and analyzed for inulin-14C, sodium (Na), and potassium (K). The effects of the three diuretic agents, a,miloride, ouabain, and furosemide, were studied. Amiloride completely suppressed K secretion at the distal tubular level with only small modifications of distal tubular Na reabsorption. Ouabain induced distal kaliuresis and natriuresis in animals kept on a low-potassium diet. The effects of ouabain upon distal tubular electrolyte transport consisted in depression of both tubular Na and K reabsorption. The distal potassium effects of ouabain were independent of any increase in distal sodium delivery and are thought to be due to depression of active potassium uptake across the luminal cell membrane of distal tubule cells. The main kaliuretic effect of furosemide on distal potassium transport is related to the delivery to the distal tubule of a much greater than normal fraction of fluid. After furosemide administration, despite a very significant elevation of distal tubular sodium concentration, fractional Na reabsorption rate control values. along this tubular segment greatly exceeded