Digoxin Transport in the Distal Nephron of Rats during Saline Diuresis

AbstractThe nephron segments involved in the renal tubular transport of digoxin and the direction of transport in each segment were evaluated using renal micropuncture techniques in 11 rats made diuretic by i.v. infusion of .85% saline. Tubular fluid was collected from 4 different sites along the nephron: late proximal, early distal, late distal, and ureter. The concentrations of 3H-digoxin and 14C-inulin were measured in each sample and the reab-sorption of water and efflux or influx of digoxin were calculated. Water was removed from the lumen along the entire length of the nephron and only 2.53 ± 0.3% of the filtrate was excreted in the urine. Digoxin was also absorbed in the proximal convoluted tubule and in the loop of Henle. About 1/3 of the filtered drug exited in these early nephron segments probably by passive diffusion. In the distal convoluted tubule, digoxin was added to the tubular fluid. The fraction of digoxin present in the lumen increased from 64 ± 3.8% of the filtered load at early distal...