Guéant J L, Champigneulle B, Gaucher P, Nicolas J P
Unité INSERM U 308, Medical Faculty, University of Nancy, Vandoeuvre-Nancy, France.
Pancreas. 1990 Sep;5(5):559-67. doi: 10.1097/00006676-199009000-00011.
Vitamin B12 can bind two carrier proteins in the digestive tract, haptocorrin (R binder) and intrinsic factor, but only its binding to intrinsic factor allows its absorption. A malabsorption of vitamin B12 is observed in about 30% of adult patients with exocrine pancreatic insufficiency, using the Schilling test. None of the hypotheses that have tried to explain this malabsorption are entirely satisfactory. A failure to degrade haptocorrin can prevent the binding of vitamin B12 to intrinsic factor. It has also been suggested that pancreatic secretion could modify the structure of intrinsic factor, enabling the uptake of the vitamin B12-intrinsic factor complex by the ileum. Other factors can also affect the binding of vitamin B12 to intrinsic factor, such as the gastric pH and bile. The Schilling test is abnormal in nearly all cases of cystic fibrosis. One explanation could be the gastric hyperacidity observed in this disease. Despite the frequency of abnormal Schilling tests, vitamin B12 deficiency is very rare in cases of exocrine pancreatic dysfunction, in adults as well as in children with cystic fibrosis. The assimilation of this vitamin with a tracer included in food instead of the crystalline labeled cobalamin used in the Schilling test remains to be investigated.
维生素B12在消化道中可与两种载体蛋白结合，即钴胺素结合蛋白（R蛋白）和内因子，但只有与内因子结合才能被吸收。使用希林试验观察到，约30%的外分泌性胰腺功能不全成年患者存在维生素B12吸收不良的情况。试图解释这种吸收不良的假说都不尽人意。钴胺素结合蛋白降解失败会阻止维生素B12与内因子结合。也有人提出，胰腺分泌可能会改变内因子的结构，从而使回肠能够摄取维生素B12 - 内因子复合物。其他因素也会影响维生素B12与内因子的结合，如胃内pH值和胆汁。几乎所有囊性纤维化病例的希林试验结果都异常。一种解释可能是该病中观察到的胃酸过多。尽管希林试验异常的情况很常见，但在成人以及患有囊性纤维化的儿童中，外分泌性胰腺功能障碍病例中维生素B12缺乏却非常罕见。用食物中所含的示踪剂而非希林试验中使用的结晶标记钴胺素来吸收这种维生素的情况仍有待研究。
