Bone tissue of hypokinetic rats: effects of 24,25-dihydroxycholecalciferol and varying phosphorous content in the diet.

Severe hypokinesia of rats given the diet with a ratio of Ca:P = 1:0.5-1:3 was accompanied by hypocalcemia, development of osteoporosis, and some intensification of renal calcinosis. The decrease of phosphorus consumption (Ca:P = 1:0.5-1:1) prevented a development of these changes in intact animals and increased bone mineralization in hypokinetic ones. Excessive phosphorus consumption (Ca:P = 1:3) produced hypocalcemia, hyperphosphatemia, and some osteoporotic changes in the bones of intact animals and intensified these changes with hypokinesia. Administration of 24,25-dihydroxycholecalciferol, an active metabolite of vitamin D3, at a dose of 1.25 micrograms/d prevented a development of bone disorders, thus effectively stimulating diaphyses and epiphyses mineralization and correcting hypocalcemia in hypokinetic rats. 24,25(OH)2D3 at the same dose did not intensify nephocalcinosis and produced no toxic symptoms with hypokinetic animals.