Katz M, O'Brien R
J Lab Clin Med. 1979 Dec;94(6):817-25.
The study of vitamin B12 release from the ileal enterocyte has been hampered by the fact that B12 does not cross the serosa of traditional everted ileal sacs. We studied this release by perfusing the superior mesenteric arteries of starved, heparinized, etherized rats and collecting perfusate from the superior mesenteric vein. The rats were fed 57CoB12 well before study. The standard perfusion medium was Krebs-Henseleit-NaHCO3 buffer containing glucose, dextran, albumin, propranolol, and dexamethasone. The preparation utilized glucose and O2, produced lactate, and was relatively impermeable to [14C]inulin, to D-xylose, and to 57CoB12 bound to an inert human IF. Glucose placed in the gut lumen was transported much more rapidly than D-xylose. Vitamin B12 emerged in the perfusate bound to a protein with a molecular size similar to that of TC II. IF could not be identified in the perfusate. Rat serum, independently of its unsaturated TC II content, increased the rate of transfer of B12 into the perfusate.
由于维生素B12无法穿过传统外翻回肠囊的浆膜，回肠肠细胞中维生素B12释放的研究受到了阻碍。我们通过灌注饥饿、肝素化、乙醚麻醉大鼠的肠系膜上动脉并从肠系膜上静脉收集灌注液来研究这种释放。在研究前很久，就给大鼠喂食了57CoB12。标准灌注培养基是含有葡萄糖、右旋糖酐、白蛋白、普萘洛尔和地塞米松的Krebs-Henseleit-NaHCO3缓冲液。该制剂利用葡萄糖和氧气，产生乳酸，并且对[14C]菊粉、D-木糖以及与惰性人内因子结合的57CoB12相对不渗透。置于肠腔内的葡萄糖比D-木糖转运得快得多。维生素B12以与转钴胺素II分子大小相似的蛋白质结合形式出现在灌注液中。在灌注液中未检测到内因子。大鼠血清，无论其不饱和转钴胺素II含量如何，都会增加维生素B12向灌注液中的转移速率。
