[Comparative evaluation of biological activity of 1 alpha,25-dihydroxycholecalciferol and 24,25-dihydroxycholecalciferol in rats].

Deficiency of vitamin D in rats led to impairment of Ca2+ absorption in intestine, hypocalcemia, decrease in specific weight of femur diaphyses, decrease in content of Ca2+ and in the ratio Ca2+/hydroxyproline in diaphyses and epiphyses. These patterns were normalized after daily administration of cholecalciferol (vitamin D3) at a dose of 500 ng (20 IU) into rats within 5 days. I alpha, 25-dihydroxycalciferol at a daily dose of 30 ng stimulated absorption of Ca2+ in intestine, increased the specific weight of diaphyses and content of Ca2+ in diaphysis, but content of Ca2+ in blood and epiphyses was not normalized. Increase in 1,25 (OH)2D3 dose up to 300 ng caused a decrease in the rate of mineralization of diaphyses and epiphyses with simultaneous elevation of the Ca2+ content in blood. 24, 25-dihydroxycalciferol at a dose of 250 ng stimulated effectively both diaphyses and epiphyses mineralization, at the same time the effect was also maintained after 10-fold increase of the dose.