title: On the regulatory importance of 1,25-dihydroxyvitamin D3 and dietary calcium on serum levels of 25-hydroxyvitamin D3 in rats.
abstract: The serum level of 25-hydroxyvitamin D3 in rats was found to vary with the dietary intake of calcium. An increase in the dietary intake of calcium was found to be associated with an increase in the concentration of 25-hydroxyvitamin D3 and a decrease in the concentration of 1,25-dihydroxyvitamin D in serum. Intraperitoneal administration of 1,25-dihydroxyvitamin D3 was found to depress the serum concentration of 25-hydroxyvitamin D3 in rats on both medium and high calcium diets. These changes in the serum levels of 25-hydroxyvitamin D3 were not associated with statistically significant changes in the activity of mitochondrial vitamin D3 25-hydroxylase in the liver. Possible mechanisms for the regulation of the level of circulating 25-hydroxyvitamin D3 in serum are discussed.
mesh_terms: D000818:Animals; D002112:Calcifediol / Q000097:blood*; D002117:Calcitriol / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D004032:Diet; D008297:Male; D008930:Mitochondria, Liver / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D002117:Calcitriol; D002112:Calcifediol; D002118:Calcium