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      Estradiol-17β Stimulates Phosphate Uptake and Is Mitogenic for Primary Rabbit Renal Proximal Tubule Cells

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          The direct effects of estradiol-17β (E<sub>2</sub>) on phosphate (P<sub>i</sub>) uptake and on DNA synthesis in the primary rabbit kidney proximal tubule cells (PTCs) have been investigated. In the present study, E<sub>2</sub> (>10<sup>–9</sup> M, over 9 days) causes an increase both in [<sup>3</sup>H]thymidine incorporation and the number of PTCs. The anti-estrogen tamoxifen completely prevented the E<sub>2</sub>-induced increase in [<sup>3</sup>H]thymidine incorporation, and ameliorated the stimulatory effect of E<sub>2</sub> on growth. E<sub>2</sub> (>10<sup>–9 </sup> M, over 5 days) also stimulated the P<sub>i</sub> uptake and its effect was due to the V<sub>max</sub> values but not to the K<sub>m</sub> value for P<sub>i</sub> uptake. Estriol and estrone also exerted significant stimulatory effects on P<sub>i</sub> uptake. Progesterone, tamoxifen, actinomycin D and cycloheximide prevented the E<sub>2</sub>-induced stimulation of P<sub>i</sub> uptake. In conclusion, estrogens at physiological concentrations stimulate P<sub>i</sub> uptake and DNA synthesis in the renal proximal tubule cells, and these effects are estrogen receptor mediated.

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          Most cited references 7

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          Characterization of primary rabbit kidney cultures that express proximal tubule functions in a hormonally defined medium

          Primary cultures of rabbit-kidney epithelial cells derived from purified proximal tubules were maintained without fibroblast overgrowth in a hormone-supplemented serum-free medium (Medium RK-1). A hormone- deletion study indicated that the primary cultures derived from purified rabbit proximal tubules required all of the three supplements in Medium RK-1 (insulin, transferrin, and hydrocortisone) for optimal growth but did not grow in response to EGF and T3. In contrast, the epithelial cells in primary cultures derived from an unpurified preparation of rabbit kidney tubules and glomeruli grew in response to EGF and T3, as well as insulin, transferrin, and hydrocortisone. These observations suggest that kidney epithelial cells derived from different segments of the nephron grow differently in response to hormones and growth factors. Differentiated functions of the primary cultures derived from proximal tubules were examined. Multicellular domes were observed, indicative of transepithelial solute transport by the monolayers. The proximal tubule cultures also accumulated alpha- methylglucoside (alpha-MG) against a concentration gradient. However, little or no alpha-MG accumulation was observed in the absence of Na+. Metabolic inhibitor studies also indicated that alpha-MG uptake by the primaries is an energy-dependent process, and depends upon the activity of the Na+/K+ ATPase. Phlorizin at 0.1 mM significantly inhibited 1 mM alpha-MG uptake whereas 0.1 mM phloretin did not have a significant inhibitory effect. Similar observations have been made concerning the Na+-dependent sugar-transport system located on the lumenal side of the proximal tubule, whereas the Na+-independent sugar transporter on the peritubular side is more sensitive to inhibition by phloretin than phlorizin. The cultures also exhibited PTH-sensitive cyclic AMP synthesis and brush-border enzymes typical of proximal cells. However, the activities of the enzymes leucine aminopeptidase, alkaline phosphatase, and gamma-glutamyl-transpeptidase were lower in the cultures than in purified proximal-tubule preparations from which they are derived.
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            Parathyroid hormone leads to the lysosomal degradation of the renal type II Na/Pi cotransporter.

            We have studied the involvement of proteolytic pathways in the regulation of the Na/Pi cotransporter type II by parathyroid hormone (PTH) in opossum kidney cells. Inhibition of lysosomal degradation (by leupeptin, ammonium chloride, methylamine, chloroquine, L-methionine methyl ester) prevented the PTH-mediated degradation of the transporter, whereas inhibition of the proteasomal pathway (by lactacystin) did not. Moreover it was found (i) that whereas lysosomal inhibitors prevented the PTH-mediated degradation of the transporter they did not prevent the PTH-mediated inhibition of the Na/Pi cotransport and (ii) that treating opossum kidney cells with lysosomal inhibitors led to an increased expression of the transporter without any concomitant increase in the Na/Pi cotransport. Further analysis by subcellular fractionation and morphological techniques showed (i) that the Na/Pi cotransporter is constitutively transported to and degraded within late endosomes/lysosomes and (ii) that PTH leads to the increased degradation of the transporter in late endosomes/lysosomes.
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              The effect of estrogen deficiency on bone mineral density, renal calcium and phosphorus handling and calcitropic hormones in the rat


                Author and article information

                Nephron Exp Nephrol
                Cardiorenal Medicine
                S. Karger AG
                09 October 2002
                : 10
                : 5-6
                : 355-364
                aDepartment of Veterinary Physiology, College of Veterinary Medicine, Hormone Research Center, Chonnam National University, Kwangju, Korea and bDepartment of Biochemistry, School of Medicine, State University of New York at Buffalo, N.Y., USA
                65300 Exp Nephrol 2002;10:355–364
                © 2002 S. Karger AG, Basel

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                Page count
                Figures: 6, Tables: 1, References: 46, Pages: 10
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                Original Paper

                Cardiovascular Medicine, Nephrology

                Kidney, Phosphate, Na/Pi cotransport, Estradiol-17β


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