Comparison of the effects of vitamin D metabolites on collagen synthesis and resportion of fetal rat bone in organ culture

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Abstract
We compared the effects of four vitamin D metabolites, 1α,25 dihydroxy vitamin D3 (1α,25(OH)2D3), 1α hydroxy vitamin D3 (1αOH D3), 25 hydroxy vitamin D3 (25 OH D3), and 24R,25 dihydroxy vitamin D (24R,25(OH)2D3) on resorption and collagen synthesis in fetal rat bone maintained in organ culture. Resorption was quantitated by measuring the release of previously incorporated45Ca from long bone shafts of 19-day fetal rats, and collagen synthesis was assessed by measuring the incorporation of3H-proline into collagenase digestible protein (CDP) in calvaria from 21-day fetal rats. All four compounds stimulated bone resorption and inhibited collagen synthesis, but 1α,25(OH)2D3 was approximately 1000 times more potent in both organ culture systems. Although the differences were small among the other three compounds, the order of potency was 1αOH D3>25 OH D3≧24R,25(OH)2D3. These results suggest that the receptor for 1α25(OH)2D3 in both bone resorbing and bone forming cells has similar affinities for several vitamin D metabolites.