Proximal tubular reabsorption of inorganic phosphate in adrenalectomized rats

Micropuncture studies have been performed in adrenalectomized (Adr.X) and sham-adrenalectomized (Sham-Adr.X) rats in order to examine the effects of acute adrenalectomy on the inorganic phosphate (Pi) transport in the convoluted proximal tubule of superficial nephrons under free flow conditions. Adrenalectomy diminished single nephron glomerular filtration rate from 27.0 +/- 12.4 (Sham-Adr.X) to 10.9 +/- 7.1 nl/min (mean +/- S.D., P less than 0.001), increased the inulin ratio (tubular fluid-to-plasma) at the end of the proximal convolution from 2.14 +/- 0.60 (Sham-Adr.X) to 3.62 +/- 1.67 (P less than 0.001) and decreased both the (TF/P)Pi ratio from 0.87 +/- 0.20 (Sham-Adr.X) to 0.46 +/- 0.28 (P less than 0.001) and the fractional delivery of inorganic phosphate onto the loop of Henle from 44 +/- 18 (Sham-Adr.X) to 15 +/- 10% (P less than 0.001). Thus the fractional reabsorption of inorganic phosphate in the convoluted proximal tubule in acutely Adr.X rats was higher than in Sham-Adr.X animals. It is concluded that glucocorticoid hormones play an important role in the regulation of the fractional reabsorption of Pi in the proximal tubule. The mechanism of this regulation is discussed.