6533b857fe1ef96bd12b4510

RESEARCH PRODUCT

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

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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−(Na)TF was 30.1±1.4 meq/l and 24.7±2.5 meq/l in the controls and adrenalectomized rats respectively. 3. (Na)P−(Na)TF in steady state (i. e. after 60 sec of contact time) were 33.6±0.8 meq/l and 41.8±1.2 meq/l in the 2 groups. From the results we derive at the conclusion that in adrenal insufficiency proximal sodium reabsorption is not only affected by an impairment of the intrinsic transport capacity but also by a proportional decrease of leak permeability for sodium. 4. Due to an increased transit time in adrenal insufficiency fractional reabsorption of sodium and of potassium was unchanged in the proximal convolution. Therefore it seems likely that the same compensation mechanism as for sodium holds for potassium and the reabsorption of potassium is impaired in adrenal insufficiency also in the proximal convolution.