PTH independent sex difference in renal handling of inorganic phosphate in the rat: effect of oophorectomy.

In order to evaluate the sex difference in the renal handling of inorganic phosphate (Pi) in the rat we performed clearance experiments using intact, thyroparathyroidectomized (TPTX), oophorectomized (OophX) and orchiectomized (OrchX) rats. During stepwise elevation of the Pi concentration in plasma (Pi-titration) to about 6 mmol/l the reabsorptive mechanism of Pi was saturated. The ratio Pi-reabs./GFR in intact males was higher than in females. A significant difference in this parameter was also observed in thyroparathyroidectomized rats: in females this value was 3.47 +/- 0.13, and in males it was 4.54 +/- 0.37 mumol/ml (P less than 0.001). Oophorectomy in the absence of parathyroid hormone (PTH) increased Pi-reabs./GFR from 3.18 +/- 0.36 to 4.12 +/- 0.24 mumol/ml (P less than 0.001); however, orchiectomy did not significantly change the reabsorption of Pi. In conclusion, the present results demonstrate a PTH independent sex difference in the renal handling of inorganic phosphate and are consistent with the hypothesis that estrogens may play a dominant role in this differentiation.