Effect of parathyroid hormone on phosphate reabsorption in rat distal convolution

Abstract

The sites and magnitude of Pi reabsorption were determined in acutely thyroparathyroidectomized rats with volume expansion before and during infusion of highly purified bovine hormone (PTH), 2 U [units] h-1. Pi reabsorption was found in the distal convolution in all 13 animals studied before PTH replacement. The mean filtered Pi remaining in the lumen decreased from 24.6 .+-. 3.5% in the early distal convolution to 13.6 .+-. 2.7% in the late distal convolution (P < 0.001). Similarly, Pi reabsorption occurred in the loop of Henle in 12 of 13 rats studied. PTH infusion increased the Pi load delivered to the late proximal, early distal, and late distal convolutions. Pi reabsorption during PTH infusion decreased from 71 .+-. 5 to 54 .+-. 5 pmol min-1 in the proximal tubule (P < 0.001); from 13 .+-. 3 to 5 .+-. 2 pmol min-1 in the loop of Henle (P < 0.01); and from 13 .+-. 2 to 6 .+-. 2 pmol min-1 in the distal convolution (P < 0.01). In acutely thyroparathyroidectomized rats with volume expansion Pi reabsorption occurs not only in the proximal tubule and loop of Henle but also in the distal convolution. The results apparently provide the 1st direct demonstration of an effect of PTH on Pi reabsorption in the distal convolution and loop of Henle. These effects of the hormone occurred in the absence of measurable changes in renal tubular permeability and Na reabsorption.