Tubular reabsorption of phosphate after release of complete ureteral obstruction in the rat

Tubular reabsorption of phosphate after release of complete ureteral obstruction in the rat. The excretion of phosphate was studied in rats after release of complete unilateral ureteral obstruction of 24 hours' duration. Marked differences were observed in the rate of excretion of phosphate between the control and the postreleased kidney. After release of unilateral ureteral obstruction, the fractional excretion of phosphate by the control kidney was greater than in normal rats, while the fractional excretion of phosphate by the experimental kidney was markedly decreased. The increased excretion of phosphate by the control kidney was abolished by prior parathyroidectomy and was attributed to an increase in the concentration of circulating parathyroid hormone. The low urinary excretion of phosphate by the experimental kidney could not be attributed to refractoriness of the renal tubule to the action of parathyroid hormone or to changes in the intrinsic capacity of the tubule to reabsorb phosphate. A marked decrease in the filtered load of phosphate is the most likely factor responsible for the low phosphate excretion by the experimental kidney. Support for this concept was obtained from studies in rats in which the filtered load of phosphate was decreased unilaterally by partially constricting the aorta proximal to the left renal artery. In these rats the fractional excretion of phosphate was considerably less in the constricted than in the contralateral normal kidney both before and after the administration of exogenous parathyroid hormone. In addition, a marked dissociation was observed between the rate of excretion of salt and water and the rate of excretion of phosphate in rats studied after release of unilateral ureteral ligation. Fractional excretion of sodium and water was greater in the experimental than in the control kidney whereas fractional excretion of phosphate was greater in the control than in the experimental kidney. These findings are consistent with the hypothesis that in the postobstructed kidney there is increased phosphate reabsorption in the proximal tubule and decreased sodium and water reabsorption in the distal tubule. Reabsorption tubulaire des phosphates apres levee d'une occlusion complete de l'uretere chez le rat. L'excretion des phosphates a ete etudiee chez rats apres levee d'une occlusion unilaterale de l'uretere pendant 24 heures. Des differences importantes ont ete observees dans les debits d'excretion de phosphate entre le renin controle et le renin libere. Apres la levee de l'occlusion unilaterale l'excretion fractionnelle des phosphates par le rein controle est plus grande que chez l'animal normal, alors qu'elle est tres diminuee du cote experimental. L'augmentation de l'excretion des phosphates par le rein controle est abolie par une parathyroidectomie prealable et elle est attribuee a une augmentation de la concentration circulante d'hormone parathyroidienne. L'excretion de phosphates faible par le rein experimental ne peut pas etre mise au compte d'une insensibilite du tube renal a l'action de l'hormone parathyroidienne ou de modifications de la capacite intrinseque du tube a reabsorber les phosphates. Une diminution importante de la charge filtree de phosphates est plus probablement le facteur responsable de la diminution de l'excretion de phosphates par le rein experimental. Des arguments en faveur de cette hypothese ont ete obtenus par l'etude de rats dont la charge de phosphates filtres a ete diminuee unilateralement par une constriction partielle de l'aorte en amont de l'artere renale gauche. Chez ces rats l'excretion fractionnelle de phosphates est tres inferieure du cote subissant la constriction a ce qu'elle est par le rein normal controlateral, aussi bien avant qu'apres l'administration d'hormone parathyroidienne. De surcroit, une dissociation nette a ete observee entre le debit d'excretion de sel et d'eau et le debit d'excretion de phosphates chez les rats etudies apres l'ablation de la ligature ureterale. L'excretion fractionnelle de sodium et d'eau est plus grande par le rein experimental que par le rein temoin alors que l'excretion fractionnelle de phosphates est plus grande par le rein controle que par le rein experimental. Ces constatations sont compatibles avec l'hypothese d'une reabsorption proximale de phosphate accrue et d'une reabsorption distale d'eau et de sodium diminuee dans le rein qui a subi l'obstruction.