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Modulation of renal production of 24,25- and 1,25-dihydroxyvitamin D3 in young and adult rats by dietary calcium, phosphorus, and 1,25-dihydroxyvitamin D3. 1982

H J Armbrecht, and T V Zenser, and B B Davis

The purpose of this study was to examine the effects of dietary calcium (Ca), phosphorus (P), and vitamin D3 metabolites on the renal metabolism of 25-hydroxyvitamin D3 (25OHD3) to either 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] or 24,25-dihydroxyvitamin D3 [24,25-(OH)2D3] in the rat. The regulation of 25OHD3 metabolism was studied in both young and adult rats, since previous studies have suggested a change in the renal metabolism of 25OHD3 with age. Renal 25OHD3 metabolism was measured in vitro by incubating renal cortical slices with tritiated 25OHD3 and quantifying tritiated metabolites by high pressure liquid chromatography. The apparent Michaelis constant for the conversion of 25OHD3 to 1,25-(OH)2D3 in this system was 1.16 microM. Experiments were conducted in rats fed a vitamin D-deficient diet containing either 0.02% Ca (low Ca) or 1.20% Ca (high Ca) for 4 weeks. Young rats (4 weeks old) fed the low Ca diet demonstrated a 2.8-fold increase in 1,25-(OH)2D3 production, but no change in 24,25-(OH)2D3 production compared to young rats fed the high Ca diet. Adult rats (12 months old) fed the low Ca diet showed no change in 1,25-(OH)2D3 production, but exhibited a decrease in 24,25-(OH)2D3 production compared to adult rats fed the high Ca diet. Repletion of the young rats fed the low Ca diet with 1,25(OH)2D3 resulted in a marked decrease in 1,25-(OH)2D3 production and an increase in 24,25-(OH)2D3 production. Repletion of the adult rat resulted in no change in 1,25-(OH)2D3 production, but a significant increase in 24,25-(OH)2D3 production. When young rats were fed diets containing various levels of Ca and P, it was found that 1,25-(OH)2D3 production was inversely correlated with plasma Ca over the range 4--13 mg/dl. Since the plasma Ca level of the adult rat was 11-12 mg/dl regardless of diet, this high concentration may explain the lack of 1,25-(OH)2D3 production observed in the adult.

UI MeSH Term Description Entries
D007668 Kidney Body organ that filters blood for the secretion of URINE and that regulates ion concentrations. Kidneys
D008297 Male Males
D010758 Phosphorus A non-metal element that has the atomic symbol P, atomic number 15, and atomic weight 31. It is an essential element that takes part in a broad variety of biochemical reactions. Black Phosphorus,Phosphorus-31,Red Phosphorus,White Phosphorus,Yellow Phosphorus,Phosphorus 31,Phosphorus, Black,Phosphorus, Red,Phosphorus, White,Phosphorus, Yellow
D002117 Calcitriol The physiologically active form of vitamin D. It is formed primarily in the kidney by enzymatic hydroxylation of 25-hydroxycholecalciferol (CALCIFEDIOL). Its production is stimulated by low blood calcium levels and parathyroid hormone. Calcitriol increases intestinal absorption of calcium and phosphorus, and in concert with parathyroid hormone increases bone resorption. 1 alpha,25-Dihydroxycholecalciferol,1 alpha,25-Dihydroxyvitamin D3,1, 25-(OH)2D3,1,25(OH)2D3,1,25-Dihydroxycholecalciferol,1,25-Dihydroxyvitamin D3,1 alpha, 25-dihydroxy-20-epi-Vitamin D3,1,25(OH)2-20epi-D3,1,25-dihydroxy-20-epi-Vitamin D3,20-epi-1alpha,25-dihydroxycholecaliferol,Bocatriol,Calcijex,Calcitriol KyraMed,Calcitriol-Nefro,Decostriol,MC-1288,MC1288,Osteotriol,Renatriol,Rocaltrol,Silkis,Sitriol,Soltriol,Tirocal,1 alpha,25 Dihydroxyvitamin D3,1,25 Dihydroxycholecalciferol,1,25 Dihydroxyvitamin D3,1,25 dihydroxy 20 epi Vitamin D3,Calcitriol Nefro,D3, 1 alpha,25-Dihydroxyvitamin,D3, 1,25-Dihydroxyvitamin,D3, 1,25-dihydroxy-20-epi-Vitamin,KyraMed, Calcitriol,MC 1288
D002118 Calcium A basic element found in nearly all tissues. It is a member of the alkaline earth family of metals with the atomic symbol Ca, atomic number 20, and atomic weight 40. Calcium is the most abundant mineral in the body and combines with phosphorus to form calcium phosphate in the bones and teeth. It is essential for the normal functioning of nerves and muscles and plays a role in blood coagulation (as factor IV) and in many enzymatic processes. Coagulation Factor IV,Factor IV,Blood Coagulation Factor IV,Calcium-40,Calcium 40,Factor IV, Coagulation
D002136 Calcium, Dietary Calcium compounds in DIETARY SUPPLEMENTS or in food that supply the body with calcium. Dietary Calcium
D004032 Diet Regular course of eating and drinking adopted by a person or animal. Diets
D004100 Dihydroxycholecalciferols Cholecalciferols substituted with two hydroxy groups in any position. Dihydroxyvitamins D
D006887 Hydroxycholecalciferols Hydroxy analogs of vitamin D 3; (CHOLECALCIFEROL); including CALCIFEDIOL; CALCITRIOL; and 24,25-DIHYDROXYVITAMIN D 3. Hydroxyvitamins D,Hydroxycholecalciferol
D000367 Age Factors Age as a constituent element or influence contributing to the production of a result. It may be applicable to the cause or the effect of a circumstance. It is used with human or animal concepts but should be differentiated from AGING, a physiological process, and TIME FACTORS which refers only to the passage of time. Age Reporting,Age Factor,Factor, Age,Factors, Age

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