Time course of development of transtubular sodium concentration differences in proximal surface tubules of the rat kidney. Micropuncture experiments in intact and adrenalectomized rats.

Int the proximal and distal surface tubules isotonic Na reabsorption (Φ Naout) is impaired by adrenalectomy. In the present experiments the time course of development of transtubular Na concentration differences (Na)P−(Na)TF was studied in the proximal convolution. 1. Na concentration was measured in free flow mannitol diuresis. Endproximal (Na)P−(Na)TF averaged 23.0±0.5 meq/l after 8.5±0.6 sec (controls) and 15.2±1.7 meq/l after 13.6±0.5 sec (adrenalectomized rats). 2. In modified stopped flow experiments tubular fluid, aspirated at the beginning of the proximal convolution in mannitol diuresis, was injected between two oil columnes and reaspirated after 28–36 sec of contact time. (Na)P−(N…