AJP - Endocrinology and Metabolism, Vol 253, Issue 1 E106-E113, Copyright © 1987 by American Physiological Society
Effect of magnesium depletion on metabolism of 25-hydroxyvitamin D in rats
T. O. Carpenter, D. L. Carnes Jr and C. S. Anast
Resistance to vitamin D in magnesium depletion has been observed in humans
and in animal studies. Variable levels of 1,25-dihydroxyvitamin D
[1,25(OH)2D] have been reported in patients with magnesium depletion, and
studies of vitamin D metabolism in states of magnesium depletion have not
yielded consistent results. We examined effects of magnesium deprivation on
circulating 1,25(OH)2D levels before and after a loading dose of
25-hydroxyvitamin D3 [25(OH)D3], on in vivo conversion of small doses of
radiolabeled 25(OH)D3 to 1,25(OH)2D3 in intact rats, and on in vitro
25-hydroxyvitamin D-1 alpha-hydroxylase (1 alpha-hydroxylase) activity in
rat renal mitochondria. The effects of magnesium-free media on
mitochondrial 1 alpha-hydroxylase activity was examined. Magnesium
depletion did not affect in vivo conversion of 25(OH)D to 1,25(OH)2D. In
vitro 1 alpha-hydroxylase activity was comparable in magnesium-replete and
-deplete animals and was evident in the absence of added magnesium in
incubation media. Our in vivo and in vitro studies are consistent with one
another and demonstrate that in the rat conversion of 25(OH)D to 1,25(OH)2D
is unimpaired in magnesium deficiency. Resistance to vitamin D in magnesium
depletion is likely due to the impaired skeletal responsivity to
1,25(OH)2D, as demonstrated in earlier studies.
