Urea and inulin clearances in undisturbed, unanesthetized rats

Abstract

Inulin and urea clearances were determined simultaneously on unanesthetized, undisturbed rats with catheters permanently inserted in the abdominal aorta, jugular vein, and urinary bladder. The rats were fed a) a normal Purina chow diet; b) a high-protein diet with normal salt content; or c) a high-protein diet with 2% NaCl added. Some rats on the high-protein, high-salt diet were given additional infusions of either urea or 5% amino acid solution. In the control animals, inulin clearances averaged 0.59 ml/min per 100 g body wt, and urea clearances averaged 0.39 ml/min per 100 g body wt. Significantly higher urea and inulin clearances were obtained on the other diets. Of 79 clearances determined on normal rats given the high-protein, high-salt diet, a total of 17 urea-to-inulin clearance ratios greater than one were obtained No urea-to-inulin clearance ratios greater than one were obtained with any of the other diets. Reasons are given in support of urea production or active secretion by the kidneys as the probable explanations for these results.