Effect of 1 alpha, 24(R)-dihydroxyvitamin D3 on calcium metabolism in the rat

It has been suggested that 1 alpha, 24(R)-dihydroxyvitamin D3 (1,24(OH)2D3), a chemically synthesized vitamin D analogue, may have the property to enhance whole-body Ca retention and may thus be of use in osteoporosis. In order to test this hypothesis the main fluxes of Ca metabolism were measured in vitamin D-replete rats injected ip with 1.24(OH)2D3 at daily doses of 25, 50 and 100 pmol for 10 days. As compared with pair fed control animals, rats treated with 1,24(OH)2D3 displayed a significant rise in net intestinal absorption of Ca and in urinary excretion of Ca, and increase in bone resorption but no significant change in bone formation. Whole body Ca retention was not changed at 25 pmol/day and showed a trend to decrease at 50 and 100 pmol/day. In conclusion these results do not suggest that among available vitamin D analogues, 1,24(OH)2D3 would be particularly useful for increasing bone Ca retention in osteoporosis.