1,25-Dihydroxyvitamin D3 and 24,25-Dihydroxyvitamin D3: Key Components of the Vitamin D Endocrine System

Effects of 6-9 days of vitamin D3 (D3), 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], 24,25-dihydroxyvitamin D3 [24,25(OH)2D3], or 1,24,25-trihydroxyvitamin D3 [1,24,25(OH)3D3] on Mg metabolism were studied in vitamin D-deficient (-D) rats. Mg absorption expressed as percent intake increased with 1,25(OH)2D3 and 1,24,25(OH)3D3. Urinary Mg (UMg) increased with no change in serum Mg (SMg) or Mg balance. 1,25(OH)2D3 was threefold more potent than 1,24,25(OH)3D3 in raising serum Ca and Mg absorption. In a separate experiment in pair-fed rats given D3, 1,25-(OH)2D3, or 1,24,25(OH)3D3, the diet contained either 0.03 or 0.2% Mg; 1,25(OH)2D3 and D3 lowered SMg after 3 days; UMg increased after 24 h to remain elevated. D3 and 1,25(OH)2D3 augmented Mg absorption; feeding 0.2% Mg lowered Mg absorption in -D animals. All sterols augmented Mg absorption in -D rats; both the earlier action of 1,25(OH)2D3 and 1,24,25(OH)3D3 suggests that 1-hydroxylation is necessary. Suppressed Mg absorption with 0.2% Mg in -D rats suggests two transport processes, with one vitamin D dependent. Higher UMg with decreased SMg with 1,25(OH)2D3 suggests reduced tubular reabsorption.

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Effects of 1,25-Dihydroxyvitamin D3 on Voltage-Sensitive Calcium Channels in the Vitamin D Endocrine System

Vitamin D ◽

10.1016/b978-012252687-9/50047-4 ◽

2005 ◽

pp. 751-760 ◽

Cited By ~ 1

Author(s):

MARY C. FARACH-CARSON ◽

JOEL J. BERGH

Keyword(s):

Vitamin D ◽

Calcium Channels ◽

Endocrine System ◽

Dihydroxyvitamin D3 ◽

1,25 Dihydroxyvitamin D3

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Effect of vitamin D3 metabolites on calcium and phosphorus metabolism in chick embryos

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1985.248.3.e281 ◽

1985 ◽

Vol 248 (3) ◽

pp. E281-E285 ◽

Cited By ~ 2

Author(s):

L. E. Hart ◽

H. F. DeLuca

Keyword(s):

Vitamin D ◽

Embryonic Development ◽

Vitamin D3 ◽

Chorioallantoic Membrane ◽

Sole Source ◽

Chick Embryos ◽

Dihydroxyvitamin D3 ◽

Total Body Calcium ◽

1,25 Dihydroxyvitamin D3 ◽

24,25 Dihydroxyvitamin D3

The biochemical nature of the physiological defect found in chick embryos from hens supported on 1,25-dihydroxyvitamin D3 as their sole source of vitamin D is described. Vitamin D-deficient hens (44-wk-old) were divided into six groups of five and dosed daily for 19 wk with either 2.0 micrograms of 25-hydroxyvitamin D3, 2.0 micrograms of 24,24-difluoro-25-hydroxy-vitamin D3, 0.4 micrograms of 1,25-dihydroxyvitamin D3, 2.0 micrograms of 24,25-dihydroxyvitamin D3, 0.4 micrograms of 1,25-dihydroxyvitamin D3 plus 2.0 micrograms of 24,25-dihydroxyvitamin D3, or vehicle only. Normal embryonic development was found in eggs from hens given 25-hydroxyvitamin D3 or 24,24-difluoro-25-hydroxyvitamin D3, whereas embryos from hens given 1,25-dihydroxyvitamin D3, 24,25-dihydroxyvitamin D3, or their combination were abnormal and failed to hatch. Embryos from hens fed 1,25-dihydroxyvitamin D3 and/or 24,25-dihydroxyvitamin D3 had vitamin D deficiency: low bone ash, low plasma calcium, low total body calcium, and extremely high plasma phosphorus. Because the shell is the major source of calcium for the developing embryo, calcium transport from the shell to the embryos across the chorioallantoic membrane apparently fails, giving rise to the observed defects in embryonic development.

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