Biological Activity of 1,24(R)-Dihydroxyvitamin 3 and 1,24(S)-Dihydroxyvitamin D3 in the Rat

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Abstract
The activities of 1,24(R)-dihydroxyvitamin D3 and 1,24(S)-dihydroxyvitamin D3 were compared with that of 1,25-dihydroxyvitamin D3 in the stimulation of intestinal Ca transport, mobilization of bone Ca, elevation of serum inorganic P concentration, and in healing rickets in vitamin D-deficient rats. The 1.alpha.-hydroxyvitamin D3 was also compared with the 1,24-dihydroxyvitamin D3 compounds in antirachitic activity. In all parameters 1,25-dihydroxyvitamin D3 is .apprx. 10 times more active than either 1,24(R)-dihydroxyvitamin D3 and 1,24(S)-dihydroxyvitamin D3. In antirachitic activity 1,25-dihydroxyvitamin D3 is .apprx. 2 times more active than 1.alpha.-dihydroxyvitamin D3, which in turn is 2 times more active than 1,24(R)-dihydroxyvitamin D3. The 1,24(R)-dihydroxyvitamin D3 and 1,24(S)-dihydroxyvitamin D3 compounds are equally active, except in the healing of rickets, where the 1,24(S)-dihydroxyvitamin D3 elicits weak biological activity.