Vieth R
Department of Clinical Biochemistry, University of Toronto, Ontario, Canada.
J Bone Miner Res. 1990 Nov;5(11):1177-82. doi: 10.1002/jbmr.5650051113.
The metabolism of 25-hydroxyvitamin D3 (25-OHD3) was compared following its intracardial or gastric administration. The rats were deprived of calcium and vitamin D. A mixture of radiolabeled (0.3 microCi) and stable (2 micrograms) 25-OHD3 was given as a single dose. After 24 h the rats given the dose by gastric tube had significantly lower serum concentrations of 25-OHD3 and 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] than those injected intracardially. In contrast, serum 24,25-dihydroxyvitamin D3 [24,25-(OH)2D3] was much higher in the rats given the 25-OHD3 dose by gastric tube (6.2 nmol/liter +/- 1.3 SD, n = 7) compared to the intracardial group (0.9 nmol/liter +/- 0.5, p less than 0.001). The preceding results were based on specific radioactivity of metabolites. The same findings were obtained by reanalyzing the samples using conventional competitive binding assays for 25-OHD3, 1,25-(OH)2D3, and 24,25-(OH)2D3. The results show that orally administered 25-OHD3 is partly metabolized to 24,25-(OH)2D3 presystemically.
在经心内或胃给予25-羟基维生素D3（25-OHD3）后，对其代谢情况进行了比较。大鼠被剥夺钙和维生素D。将放射性标记（0.3微居里）和稳定形式（2微克）的25-OHD3混合物作为单剂量给予。24小时后，经胃管给药的大鼠血清中25-OHD3和1,25-二羟基维生素D3[1,25-(OH)2D3]的浓度显著低于心内注射的大鼠。相反，经胃管给予25-OHD3剂量的大鼠血清24,25-二羟基维生素D3[24,25-(OH)2D3]（6.2纳摩尔/升±1.3标准差，n = 7）比心内注射组（0.9纳摩尔/升±0.5，p<0.001）高得多。上述结果基于代谢物的比放射性。通过使用针对25-OHD3、1,25-(OH)2D3和24,25-(OH)2D3的传统竞争性结合测定法重新分析样品，获得了相同的结果。结果表明，口服给予的25-OHD3在进入全身循环之前部分代谢为24,25-(OH)2D3。
