The necessity for calcium for increased renal vitamin D receptor in response to 1,25-dihydroxyvitamin D.
To further investigate the regulation of the vitamin D receptor in the kidney of the rat, we analyzed the response of the receptor to 1,25-dihydroxyvitamin D-3 under conditions of calcium supplementation and calcium restriction. Vitamin D-deficient, male weanling rats, fed a calcium-restricted or calcium-supplemented, vitamin D-deficient diet, were treated for 4 weeks with vitamin D (orally) or 1,25-dihydroxyvitamin D-3 (60 pmol/d by mini-osmotic pump). We also extended the treatment to 8 weeks for one group of animals fed the calcium-supplemented diet. Vitamin D compounds decreased the level of renal receptor in rats fed the low calcium diet. However, in animals given a 1.2% calcium diet, both vitamin D and 1,25-dihydroxyvitamin D-3 increased receptor levels by 130%. After 8 weeks, 1,25-dihydroxyvitamin D-3 had increased the receptor level by 260% while vitamin D had no further effect. Thus, dietary calcium is required for vitamin D to up-regulate the renal vitamin D receptor level. Further, 1,25-dihydroxyvitamin D-3 itself appears to have a marked ability to increase vitamin D receptor levels. These results suggest a complex mechanism of homologous regulation of the vitamin D receptor in the kidney.
Department of Biochemistry, University of Wisconsin-Madison 534706.
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Uhland-Smith
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DeLuca
D000818:Animals; D002117:Calcitriol / Q000008:administration & dosage / Q000172:deficiency / Q000494:pharmacology*; D002118:Calcium / Q000097:blood; D002136:Calcium, Dietary / Q000008:administration & dosage*; D006996:Hypocalcemia / Q000378:metabolism*; D007668:Kidney / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D010758:Phosphorus / Q000097:blood; D051381:Rats; D018167:Receptors, Calcitriol; D011987:Receptors, Steroid / Q000378:metabolism*; D015854:Up-Regulation
D002136:Calcium, Dietary; D018167:Receptors, Calcitriol; D011987:Receptors, Steroid; D010758:Phosphorus; D002117:Calcitriol; D002118:Calcium