The site of action of antidiuretic hormone in the mammalian nephron



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Regional unidirectional fluxes of water and sodium were determined by use of high ureteral pressures and a modified stop-flow technique. Fluxes are best demonstrated in the proximal and distal regions. The magnitude of Na net fluxes in the proximal and distal tubules are respectively 180 and 220 mueq/cm[raised 2]/min. Water net fluxes in the proximal and distal tubules are approximately 1160 and 1310 mul/cm[raised 2]/min. Unidirectional fluxes of Na and water were also quantitated. This is the first report for the magnitude of ion and water fluxes in the intact canine kidney. Low concentrations of ADH at both the contraluminal and luminal nephron surface increase distal water outflux and K net flux, and decrease distal Na outflux. ADH at the contraluminal nephron surface also increases distal Na influx and proximal water influx, and decreases proximal Na outflux and net flux; these directional changes in ion and water flux are counteracted by ADH at the luminal nephron surface. Higher concentrations of ADH at the luminal surface decrease the magnitude of all fluxes altered by ADH at the contraluminal surface only. Low concentrations of ADH cause natriuresis and kaliuresis. The natriuresis is due to a stimulation of proximal and distal Na influx and to a stimulation of distal water outflux. The kaliuresis is due to a decrease in proximal water influx. These effects occur when ADH is in contact with the serosal membrane of the nephrons.