Inhibition of 25-hydroxyvitamin D3 production by 1, 25-dihydroxyvitamin D3 in rats

Archives of Biochemistry and Biophysics
G G Reinholz, H F DeLuca

Abstract

The regulation of the hepatic vitamin D3 25-hydroxylase enzyme system by 1,25-dihydroxyvitamin D3 was examined using male rats. Circulating 25-hydroxyvitamin D3 levels decreased in response to increasing doses of 1,25-dihydroxyvitamin D3 as determined by HPLC and serum protein binding assay. A maximum reduction in serum 25-hydroxyvitamin D3 of 57.7% was achieved by the administration of 1,25-dihydroxyvitamin D3 and higher doses produced no further reduction. The in vitro rate of vitamin D 25-hydroxylation by liver homogenates from rats given 1,25-dihydroxyvitamin D3 was also reduced by 60.4%. Whole rat extracts from animals given [3H]vitamin D3 contained 50.4% less 25-[3H]hydroxyvitamin D3 in treated rats given 1,25-dihydroxyvitamin D3 than in those given only the vehicle. Further, 1,25-dihydroxyvitamin D3 treatment had no effect on in vivo disappearance of 25-[3H]hydroxyvitamin D3. Taken together, these results demonstrate that the decrease in 25-hydroxyvitamin D3 levels observed in 1,25-dihydroxyvitamin D3-treated rats results from a decrease in production and not an increase in the metabolic clearance of 25-[3H]hydroxyvitamin D3.

Citations

Apr 6, 2000·The Biochemical Journal·P Honkakoski, M Negishi
Mar 12, 2009·Menopause : the Journal of the North American Menopause Society·George MoschonisYannis Manios
Sep 11, 2002·The Journal of Nutrition·M A TryfonidouH A W Hazewinkel
Jul 1, 2004·The Journal of Steroid Biochemistry and Molecular Biology·M A Tryfonidou, H A W Hazewinkel
Sep 21, 2021·The Journal of Clinical Endocrinology and Metabolism·Cora M BestAndrew N Hoofnagle

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