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This Article Full Text Full Text (PDF) All Versions of this Article: 292/3/E723    most recent 00445.2006v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via ISI Web of Science (4) Citing Articles via Google Scholar Google Scholar Articles by Zhang, Y. Articles by Wong, M.-S. Search for Related Content PubMed PubMed Citation Articles by Zhang, Y. Articles by Wong, M.-S.

Ovariectomy worsens secondary hyperparathyroidism in mature rats during low-Ca diet

¹State Key Laboratory of Chinese Medicine and Molecular Pharmacology, Shenzhen; ²School of Pharmacy, Shenyang Pharmaceutical University, Shenyang; and ³Central Laboratory of the Institute of Molecular Technology for Drug Discovery and Synthesis, Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China; ⁴The University of Chicago, Pritzker School of Medicine, Chicago, Illinois; and ⁵Department of Orthopaedics and Traumatology, the Chinese University of Hong Kong, Hong Kong, China

Submitted 24 August 2006 ; accepted in final form 24 October 2006

Estrogen deficiency impairs intestinal Ca absorption and induces bone loss, but its effects on the vitamin D-endocrine system are unclear. In the present study, calciotropic hormones levels, renal vitamin D metabolism, 1,25-dihydroxyvitamin D₃ [1,25(OH)₂D₃]-dependent intestinal calcium absorption, and bone properties in 3-mo-old sham-operated (sham) or ovariectomized (OVX) rats fed either a normal-Ca (NCD; 0.6% Ca, 0.65% P) or a low-Ca (LCD; 0.1% Ca, 0.65% P) diet for 2 wk were determined. LCD increased serum 1,25(OH)₂D₃ levels in both sham and OVX rats. Serum parathyroid hormone [PTH(1–84)] levels were highest in OVX rats fed LCD. Renal 25-hydroxyvitamin D1-hydroxylase (1-OHase) protein expression was induced in both sham and OVX rats during LCD, while renal 1-OHase mRNA expression was highest in OVX rats fed LCD. Renal vitamin D receptor (VDR) and mRNA expressions in rats were induced by ovariectomy in rats fed NCD but suppressed by ovariectomy in rats fed LCD. The induction of intestinal calcium transporter-1 and calbindin-D9k mRNA expressions by LCD were not altered by ovariectomy. As expected, bone Ca content, cancellous bone mineral density, and bone strength index in proximal metaphysis of rat tibia were reduced by both ovariectomy and LCD (P < 0.05) as analyzed by two-way ANOVA. Taken together, the data demonstrate that ovariectomy alters the responses of circulating PTH levels, renal 1-OHase mRNA expression, and renal VDR expression to LCD. These results suggest that estrogen is necessary for the full adaptive response to LCD mediated by both PTH and 1,25(OH)₂D₃.

parathyroid hormone; renal vitamin D receptor; renal 25-hydroxyvitamin D1-hydroxylase; dietary Ca restriction