Effect of estrogen on calcium and sodium transport by the nephron luminal membranes

Estrogens are widely used for contraception and osteoporosis prevention. Th e aim of the present study was to investigate the effect of 17 beta -estrad iol on calcium (Ca2+) transport by the nephron luminal membranes, independe ntly of any other Ca2+-regulating hormones. Proximal and distal tubules of rabbit kidneys were incubated with 17 beta -estradiol or the carrier for va rious periods of time. and the luminal membranes of these tubules were puri fied and vesiculated. Ca2+ uptake by membrane vesicles was measured using t he Millipore filtration technique. Incubation of proximal tubules with the hormone did not influence Ca2+ uptake by the luminal membranes, In contrast , incubation of distal tubules with 10(-8) M 17 beta -estradiol for 30 min decreased the initial uptake of 0.5 mM Ca2+ from 0.34 +/- 0.04 (S.E.M.) to 0.17 +/- 0.04 pmol/mug per 5 s (P <0.05). In the presence of 100 mM Na+, 0- 5 mM Ca2+, uptake was strongly diminished and the effect of 17 beta -estrad iol disappeared (0.17 +/- 0.01 and 0.21 +/- 0.07 pmol/mug per 5 s in vesicl es from the control and treated tubules). Direct incubation of the membrane s with 17p-estradiol, however, failed to show any influence of the hormone on Ca2+ transport. The action of 17 beta -estradiol was dose-dependent, wit h a half-maximal effect at approximately 10(-9) M. Ca2+ uptake by the dista l tubule membranes presents dual kinetics. 17 beta -Estradiol decreased the V-max value of the high-affinity component from 0.42 +/- 0.02 to 0.31 +/- 0.03 pmol/mug per 10 s (P <0.02). In contrast with the effect of the hormon e on Ca2+ transport, estradiol increased Na+ uptake by both the proximal an d distal tubule luminal membranes. In conclusion, incubation of proximal an d distal tubules with estrogen decreases Ca2+ reabsorption by the high-affi nity Ca2+ channels of the distal luminal membranes, and enhances Na+ transp ort by the membranes from proximal and distal nephrons.