Mahgoub A
Calcif Tissue Int. 1981;33(6):663-6. doi: 10.1007/BF02409505.
Interaction among vitamin D3 metabolites on bone receptor sites is not known. Therefore, interaction between the most potent vitamin D3 metabolite, 1,25(OH)2D3, and the most abundant dihydroxymetabolite, 24R,25(OH)2D3, was studied on isolated rat fetal bone by measuring 45Ca release from prelabeled bones. 24R,25(OH)2D3 at concentrations of 10-50 ng/ml caused marked inhibition of the bone-resorbing activity of 1,25(OH)2D3 at concentrations of 10-50 pg/ml. 24S,25(OH)2 (unnatural enantiometer), on the other hand, at a concentration of 100 ng/ml did not inhibit the bone-resorbing effect of 10 pg/ml 1,25(OH)2D3. 24R,25(OH)2D3 at a concentration of 20 ng/ml did not inhibit the 45Ca-releasing effect of a submaximal concentration of PTH (500 ng/ml). Therefore, the inhibitory effect of 24R,25(OH)2D3 on the bone response to 1,25(OH)2D3 appeared to be specific and probably due to a competitive inhibitory effect. In addition, the inhibitory effect of 24R,25(OH)2D3 was weak, since it could be partially overcome by increasing the concentration of 1,25(OH)2D3.
维生素D3代谢产物在骨受体位点上的相互作用尚不清楚。因此，通过测量预先标记的骨骼中45Ca的释放，在分离的大鼠胎儿骨骼上研究了最有效的维生素D3代谢产物1,25(OH)2D3与最丰富的二羟基代谢产物24R,25(OH)2D3之间的相互作用。浓度为10 - 50 ng/ml的24R,25(OH)2D3显著抑制了浓度为10 - 50 pg/ml的1,25(OH)2D3的骨吸收活性。另一方面，浓度为100 ng/ml的24S,25(OH)2（非天然对映体）并未抑制10 pg/ml 1,25(OH)2D3的骨吸收作用。浓度为20 ng/ml的24R,25(OH)2D3并未抑制次最大浓度的甲状旁腺激素（500 ng/ml）的45Ca释放作用。因此，24R,25(OH)2D3对骨骼对1,25(OH)2D3反应的抑制作用似乎具有特异性，且可能归因于竞争性抑制作用。此外,24R,25(OH)2D3的抑制作用较弱，因为增加1,25(OH)2D3的浓度可部分克服这种抑制作用。
