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 pho sphate (P-i) in proximal tubules of the kidney. We investigated the ef fect of beta-estradiol (E(2)) injected to thyropanthyrodectomized and ovarectomized rats upon Na+-cotransport of P-i and other solutes acros s renal brush border membrane (BBM). In BBM from kidneys of E(2)-treat ed rats the capacity for Na+-P-i cotransport was considerably suppress ed (Delta 8% - 42; P < 0.01) whereas Na+-cotransports of L-proline D-g lucose and SO4 across the same BBM did not differ from controls. We su rmise that E(2) inhibits selectively Na+-P-i cotransport by direct int eraction with E(2) receptors in proximal tubular cells. These results indicate the existence of the inhibitory effect of estrogens upon rena l proximal tubular Na+-P-i cotransport and, by extention, proximal Pi reabsorption. We suggest that this modulatory action of E(2) plays a r ole in pathophysiology of mineral metabolism due to estrogen deficienc y and should be considered when estrogens are used for pharmacotherapy of postmenopausal osteoporosis and some types of cancer. (C) 1996 Aca demic Press, Inc.