Plasma Ca influences vitamin D metabolite levels as rats develop vitamin D deficiency.
The hypocalcemia that accompanies vitamin D deficiency is a major obstacle to proper interpretation of the role(s) of vitamin D metabolites in Ca-sensitive tissues. This paper describes the development and complete characterization of a dietary regimen with which normocalcemia was maintained in rats throughout the development of vitamin D deficiency. Normal weanling rats were fed diets containing 0.8% Ca, 0.5% P, and vitamin D3 (group A), or vitamin D-deficient diets containing 0.8% Ca and 0.5% P (group B); 2.0% Ca and 1.25% P (group C); or 2.0% Ca, 1.25% P, and 20% lactose (group D) for 19 wk. Group D rats were normocalcemic and normophosphatemic with normal parathyroid hormone (PTH) levels throughout the study. In contrast, from 4-19 diet wk, groups B and C were hypocalcemic with elevated PTH. Initially, plasma 25-hydroxyvitamin D3 [25(OH)D3] levels decreased most rapidly, and 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] levels decreased least rapidly in group B rats, such that plasma 25(OH)D3 levels were reduced to 200-300 pg/ml before a decrease in 1,25(OH)2D3 levels was observed. However, vitamin D metabolite levels were similar in groups B, C, and D from 4-19 wk. Duodenal active Ca transport mirrored changes in plasma 1,25(OH)2D3 levels and was abolished after 10 wk. The results also suggested that vitamin D may not be necessary for normal bone mineralization since tibia mineral content and plasma alkaline phosphatase levels were similar in normocalcemic groups A and D throughout the study.
Kollenkirchen
U
U
Department of Physiology, Tulane University School of Medicine, New Orleans, Louisiana 70112.
Walters
M R
MR
Fox
J
J
D000818:Animals; D002112:Calcifediol / Q000097:blood*; D002117:Calcitriol / Q000097:blood*; D002118:Calcium / Q000097:blood / Q000378:metabolism*; D002136:Calcium, Dietary / Q000494:pharmacology*; D002762:Cholecalciferol / Q000494:pharmacology*; D004386:Duodenum / Q000502:physiology / Q000503:physiopathology; D006706:Homeostasis; D007408:Intestinal Absorption; D008297:Male; D010281:Parathyroid Hormone / Q000097:blood; D010710:Phosphates / Q000097:blood; D051381:Rats; D011919:Rats, Inbred Strains; D012016:Reference Values; D014808:Vitamin D Deficiency / Q000097:blood*
D002136:Calcium, Dietary; D010281:Parathyroid Hormone; D010710:Phosphates; D002762:Cholecalciferol; D002117:Calcitriol; D002112:Calcifediol; D002118:Calcium