Expression of the renal 25-hydroxyvitamin d-24-hydroxylase gene:
regulation by dietary phosphate .
Wu, Shixin, Jane Finch, Min Zhong, Eduardo Slatopolsky, Marvin Grieff,
and Alex J. Brown.
Renal Division, Washington University School of Medicine, St.
Louis, MO 63110
APStracts 3:0040F, 1996.
1,25-Dihydroxyvitamin D3 plays a key role in phosphate (Pi)
homeostasis through its phosphatemic actions on intestine and bone.
In turn, dietary Pi restriction increases serum 1,25-(OH)2D3 by
stimulating its production, but its effect on vitamin D catabolism is
less clear. Here, we have examined the effects of dietary Pi on the
expression of the renal vitamin D-24-hydroxylase (24-OHase), the
first enzyme in the catabolic pathway for vitamin D compounds. Rats
fed a low Pi (0.02% P) diet (LPD) showed a 5-fold decrease in renal
24-OHase mRNA compared to rats fed a normal Pi (0.67% P) diet (NPD).
24-OHase mRNA and 24-OHase activity decreased within 24 hours of Pi
restriction, reached a minimum by 48 hours and remained low through
14 days. Decreased 24-OHase mRNA was observed with more moderate Pi
restriction (0.2% P) but higher Pi (1.2% P) did not increase 24-OHase
mRNA over the 0.8% P diet. 24-OHase mRNA correlated well with plasma
Pi (r = 0.862, p < 0.001). In conclusion, renal 24-OHase
expression is regulated by dietary phosphate at the mRNA level.
Received 13 November 1995; accepted in final form 15 February
1996.
APS Manuscript Number F385-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 13 March 96