Please use this identifier to cite or link to this item: http://hdl.handle.net/10397/15053
Title: Age-related alteration of vitamin D metabolism in response to low-phosphate diet in rats
Authors: Chau, TS
Lai, WP
Cheung, PY
Favus, MJ
Wong, MS 
Keywords: 25-Hydroxyvitamin D3 1-α hydroxylase
25-Hydroxyvitamin D3 24 hydroxylase
Adult rats
Low-phosphate diet
Vitamin D receptor
Issue Date: 2005
Publisher: Cambridge University Press
Source: British journal of nutrition, 2005, v. 93, no. 3, p. 299-307 How to cite?
Journal: British journal of nutrition 
Abstract: The responses of renal vitamin D metabolism to its major stimuli alter with age. Previous studies showed that the increase in circulating 1,25-dihydroxyvitamin D (1,25(OH)2D3) as well as renal 25-hydroxyvitamin D3 1-α hydroxylase (1-OHase) activity in response to dietary Ca or P restriction reduced with age in rats. We hypothesized that the mechanism involved in increasing circulating 1,25(OH) 2D3 in response to mineral deficiency alters with age. In the present study, we tested the hypothesis by studying the expression of genes involved in renal vitamin D metabolism (renal 1-OHase, 25-hydroxyvitamin D 24-hydroxylase (24-OHase) and vitamin D receptor (VDR)) in young (1-month-old) and adult (6-month-old) rats in response to low-phosphate diet (LPD). As expected, serum 1,25(OH)2D3 increased in both young and adult rats upon LPD treatment and the increase was much higher in younger rats. In young rats, LPD treatment decreased renal 24-OHase (days 1-7, P<0.01) and increased renal 1-OHase mRNA expression (days 1-5, P<0.01). LPD treatment failed to increase renal 1-OHase but did suppress 24-OHase mRNA expression (P<0.01) within 7d of LPD treatment in adult rats. Renal expression of VDR mRNA decreased with age (P<0.001) and was suppressed by LPD treatment in both age groups (P<0.05). Feeding of adult rats with 10 d of LPD increased 1-OHase (P<0.05) and suppressed 24-OHase (P<0.001) as well as VDR (P<0.05) mRNA expression. These results indicate that the increase in serum 1,25(OH)2D3 level in adult rats during short-term LPD treatment is likely to be mediated by a decrease in metabolic clearance via the down-regulation of both renal 24-OHase and VDR expression. The induction of renal 1-OHase mRNA expression in adult rats requires longer duration of LPD treatment than in younger rats.
URI: http://hdl.handle.net/10397/15053
ISSN: 0007-1145
EISSN: 1475-2662
DOI: 10.1079/BJN20041325
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