Low dietary calcium reduces 25-hydroxycholecalciferol in plasma of rats.
We investigated whether dietary factors that are known to increase 1,25-(OH)2-cholecalciferol production can deplete plasma 25-OH-cholecalciferol. Plasma concentration of 25-OH-cholecalciferol, its metabolism in vivo and activities of renal mitochondrial 25-OH-cholecalciferol 1-hydroxylase (1-OHase) and 25-OH-cholecalciferol 24-hydroxylase (24-OHase) were measured in rats fed various amounts of calcium (Ca) and phosphorus (P). All diets contained 5 micrograms (200 IU) cholecalciferol per 100 g. For rats fed the "normal" diet (0.7% Ca and 1.2% P) the mean plasma 25-OH-cholecalciferol level was 11.0 +/- 0.8 nmol/L, and the mean 1-OHase activity was 30 +/- 5 fmol/(mg X min). All rats fed the low Ca (0.014%) diet had 1-OHase activities above 200 fmol/(mg X min) and undetectable plasma 25-OH-cholecalciferol levels (less than 2.5 nmol/L). The chi-square test interrelating plasma 25-OH-cholecalciferol and dietary Ca showed statistical significance (P less than 0.001). The high activity of 1-OHase that resulted from dietary Ca restriction increased utilization of 25-OH-cholecalciferol to the point of causing depletion of this metabolite in the circulation.
D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase / Q000378:metabolism*; D000818:Animals; D002112:Calcifediol / Q000097:blood*; D002136:Calcium, Dietary / Q000008:administration & dosage / Q000378:metabolism*; D008297:Male; D009751:Nutritional Requirements; D051381:Rats; D011919:Rats, Inbred Strains; D013250:Steroid Hydroxylases / Q000378:metabolism*; D014807:Vitamin D / Q000096:biosynthesis / Q000097:blood / Q000378:metabolism*
D002136:Calcium, Dietary; D014807:Vitamin D; D013250:Steroid Hydroxylases; D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase; D002112:Calcifediol