Shireman R B, Williams D, Remsen J F
Proc Soc Exp Biol Med. 1986 Mar;181(3):392-8. doi: 10.3181/00379727-181-42270.
The plasma distribution and cellular uptake of [3H]vitamin D3 was studied in vitro using cultured human fibroblasts. Incubation of [3H]vitamin D3 (cholecalciferol) with plasma followed by sequential ultracentrifugal fractionation of the lipoproteins indicated that 2-4% of the radioactivity associated with the very low density lipoprotein (VLDL), 12% with low density lipoprotein (LDL), and approximately 60% with the high density lipoprotein (HDL). The remaining radioactivity, 25%, was associated with the sedimented plasma fractions. By comparison, an average of 86% of the radioactivity from [3H]1,25-dihydroxycholecalciferol associated with the sedimented plasma fractions. The uptake of [3H]vitamin D3 from plasma, LDL, or HDL was studied in cultured human cells; uptake by normal fibroblasts was greatest from LDL and least from plasma. The cellular association of vitamin D3 was time, concentration, and temperature dependent. At a concentration of 50 micrograms LDL/ml of medium, the uptake of [3H]vitamin D3 from LDL at 37 degrees C was rapid and reached a maximum at approximately 4 hr; it was slower from HDL but continued to increase slowly up to 24 hr. The significance of these in vitro findings is uncertain since much of the vitamin D3 absorbed from the intestine reportedly associates with chylomicrons and is rapidly taken up by the liver.
利用培养的人成纤维细胞在体外研究了[3H]维生素D3的血浆分布和细胞摄取情况。将[3H]维生素D3（胆钙化醇）与血浆一起孵育，随后对脂蛋白进行连续超速离心分级分离，结果表明，与极低密度脂蛋白（VLDL）相关的放射性为2 - 4%，与低密度脂蛋白（LDL）相关的为12%，与高密度脂蛋白（HDL）相关的约为60%。其余25%的放射性与沉淀的血浆组分相关。相比之下，[3H]1,25 - 二羟胆钙化醇的放射性平均有86%与沉淀的血浆组分相关。在培养的人细胞中研究了从血浆、LDL或HDL摄取[3H]维生素D3的情况；正常成纤维细胞从LDL的摄取量最大，从血浆的摄取量最小。维生素D3与细胞的结合具有时间、浓度和温度依赖性。在培养基中LDL浓度为50微克/毫升时，37℃下从LDL摄取[3H]维生素D3的速度很快，约4小时达到最大值；从HDL摄取的速度较慢，但在24小时内持续缓慢增加。由于据报道从肠道吸收的大部分维生素D3与乳糜微粒结合并迅速被肝脏摄取，这些体外研究结果的意义尚不确定。
