Effects of dietary calcium restriction on 1,25-dihydroxyvitamin D3 net synthesis by rat proximal tubules

Craig B. Langman*, Murray J. Favus, David A. Bushinsky, Fredric L. Coe

*Corresponding author for this work

Research output: Contribution to journalArticle

12 Scopus citations

Abstract

We measured in vitro 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) production by kidney proximal tubules prepared by Percoll density centrifugation from male and female rats. 1,25(OH)2D3 in tubule extracts was determined by a sensitive and specific radioreceptor assay. Ingestion of diets adequate in vitamin D3 and containing either normal calcium (1.2% Ca, NC), reduced calcium (0.6% Ca, RCD) or low calcium (0.002% Ca, LCD) increased 1,25(OH)2D3 net synthesis (for male rats, NC vs. RCD vs. LCD 1.8 ± 0.1 SEM vs. 9 ± 2 vs. 17 ± 2 pmol/mg protein/ 20 min; P < 0.05 for all comparisons). At either level of reduced calcium intake, tubules from male rats produced more 1,25(OH)2D3 than tubules from females. Serum 1,25(OH)2D3 and tubule cyclic adenosine monophosphate (cAMP) content rose in parallel with progressive dietary calcium restriction, and males had higher circulating 1,25(OH)2D3 and tubule cAMP content than females at each level of reduced calcium intake. l-Epinephrine (10-4 mol/L), in vitro, increased tubule accumulation of 1,25(OH)2D3 and cAMP. Yohimbine, an α2-receptor antagonist, blocked this response, whereas prazosin was without effect. Increased 1,25(OH)2D3 net synthesis by tubules from male vs. female rats partly explains the higher serum levels and enhanced mineral conservation demonstrated previously in male rats. Preparation of proximal tubules from vitamin D-replete rats permits studies in vitro of 1,25(OH)2D3 production and regulation under more physiologic conditions in which parathyroid hormone, inorganic phosphorus, and calcium may be varied independently.

Original languageEnglish (US)
Pages (from-to)286-292
Number of pages7
JournalThe Journal of laboratory and clinical medicine
Volume106
Issue number3
StatePublished - Sep 1985

ASJC Scopus subject areas

  • Pathology and Forensic Medicine

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