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<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<0.001) and decreased both the (TF/P)_Pi ratio from 0.87±0.20 (Sham-Adr.X) to 0.46±0.28 (P<0.001) and the fractional delivery of inorganic phosphate into the loop of Henle from 44±18 (Sham-Adr.X) to 15±10% (P<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.Supported by the Deutsche Forschungsgemeinschaft (Fr239/7). Parts of this work 6] have been presented at the 52th Meeting of the German Society of Physiology, Kiel. FRG, 1979, and at the XIIIth Symposion of the German Society of Nephrology, Berlin, 1979