A technique for perfusing the isolated rat kidney with heparinized whole blood is described. Numerous aspects of renal function are evaluated. Blood and urine flows approximated normal limits occasionally but diminished and increased, respectively, with time. The reabsorption rates of osmoles, sodium, chloride, potassium, lactate, and phosphate were proportional to the filtered loads. Variations in filtered load were due mainly to changes in glomerular filtration rate (GFR). Tubular secretion of p-amino hippuric acid varied with the GFR, and TmPAH per milliliter GFR was 60% of in vivo values. Glucose reabsorption was practically complete. Urine osmolalities, initially in the range 400–1,000 mosmoles/liter, fell during a perfusion, often to values well below plasma levels. Postperfusion histologic studies usually showed slight to moderate tubular dilatation. It was concluded that: 1) The handling of individual ions approximated in vivo function. 2) Changes in GFR and in the rate of excretion of PAH represented changes in the number of active nephrons. 3) Low urine osmolalities were due to decreasing ability of the nephrons to reabsorb water.
blood and urine flow; electrolyte excretion
Submitted on February 25, 1963
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