title: Effect of estrogen on calcium and sodium transport by the nephron luminal membranes.
abstract: Estrogens are widely used for contraception and osteoporosis prevention. The aim of the present study was to investigate the effect of 17 beta-estradiol on calcium (Ca(2+)) transport by the nephron luminal membranes, independently of any other Ca(2+)-regulating hormones. Proximal and distal tubules of rabbit kidneys were incubated with 17 beta-estradiol or the carrier for various periods of time, and the luminal membranes of these tubules were purified and vesiculated. Ca(2+) uptake by membrane vesicles was measured using the Millipore filtration technique. Incubation of proximal tubules with the hormone did not influence Ca(2+) 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 Ca(2+) from 0.34+/-0.04 (s.e.m. ) to 0.17+/-0.04 pmol/microg per 5 s (P<0.05). In the presence of 100 mM Na(+), 0.5 mM Ca(2+) uptake was strongly diminished and the effect of 17 beta-estradiol disappeared (0.17+/-0.01 and 0.21+/-0.07 pmol/microg per 5 s in vesicles from the control and treated tubules). Direct incubation of the membranes with 17 beta-estradiol, however, failed to show any influence of the hormone on Ca(2+) transport. The action of 17 beta-estradiol was dose-dependent, with a half-maximal effect at approximately 10(-9) M. Ca(2+) uptake by the distal 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/microg per 10 s (P<0.02). In contrast with the effect of the hormone on Ca(2+) transport, estradiol increased Na(+) uptake by both the proximal and distal tubule luminal membranes. In conclusion, incubation of proximal and distal tubules with estrogen decreases Ca(2+) reabsorption by the high-affinity Ca(2+) channels of the distal luminal membranes, and enhances Na(+) transport by the membranes from proximal and distal nephrons.
authors.affiliation: Maisonneuve-Rosemont Hospital, Research Center and University of Montreal, Quebec, Canada. visionfrsq@hmr.qc.ca
authors.forename: M G
authors.initials: MG
authors.lastname: Brunette
authors.forename: M
authors.initials: M
authors.lastname: Leclerc
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D046508:Culture Techniques / Q000379:methods; D003864:Depression, Chemical; D004958:Estradiol / Q000494:pharmacology*; D007686:Kidney Tubules, Distal / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000378:metabolism; D009399:Nephrons / Q000187:drug effects / Q000378:metabolism*; D011817:Rabbits; D012964:Sodium / Q000378:metabolism*
chemical_list: D004958:Estradiol; D012964:Sodium; D002118:Calcium