beta-Estradiol inhibits Na+-P-i cotransport across renal brush border membranes from ovarectomized rats

Estrogens play a major role in mineral homeostasis, however it remains unclear whether they exert regulatory action upon reabsorption of phosphate (P-i) in proximal tubules of the kidney. We investigated the effect of beta-estradiol (E(2)) injected to thyropanthyrodectomized and ovarectomized rats upon Na+-cotransport of P-i and other solutes across renal brush border membrane (BBM). In BBM from kidneys of E(2)-treated rats the capacity for Na+-P-i cotransport was considerably suppressed (Delta 8% - 42; P < 0.01) whereas Na+-cotransports of L-proline D-glucose and SO4 across the same BBM did not differ from controls. We surmise that E(2) inhibits selectively Na+-P-i cotransport by direct interaction with E(2) receptors in proximal tubular cells. These results indicate the existence of the inhibitory effect of estrogens upon renal proximal tubular Na+-P-i cotransport and, by extention, proximal Pi reabsorption. We suggest that this modulatory action of E(2) plays a role in pathophysiology of mineral metabolism due to estrogen deficiency and should be considered when estrogens are used for pharmacotherapy of postmenopausal osteoporosis and some types of cancer. (C) 1996 Academic Press, Inc.