Toverud S U, Dostal L A
J Pediatr Gastroenterol Nutr. 1986 Sep-Oct;5(5):688-95.
During the period of natural weaning in the rat (beginning during the third week) the mechanisms of calcium absorption from the duodenum change from an efficient nonsaturable process, which is insensitive to vitamin D, to a combination of a less efficient nonsaturable process and a saturable vitamin D-dependent component. The stimulatory effect of vitamin D on active calcium transport requires the development of mucosal receptors for 1,25-(OH)2D3 and increasing circulating levels of 1,25-(OH)2D3. Concurrent increases in the concentration of the cytosolic calcium-binding protein (CaBP) support the suggestion that the CaBP mediates, in part, the effect of 1,25-(OH)2D3 on active calcium transport. The decline in the efficiency of nonsaturable calcium absorption during the third week coincides with, but is probably not due to, the loss of pinocytotic capacity of the small intestine. The time of appearance of the receptors for 1,25-(OH)2D3 and the decline in nonsaturable calcium absorption are under glucocorticoid control as are several other maturational events in the intestine at this time.
在大鼠自然断奶期间（从第三周开始），十二指肠钙吸收机制从一种高效的非饱和过程转变为一种效率较低的非饱和过程与一种饱和的维生素D依赖成分的组合，前者对维生素D不敏感。维生素D对钙主动转运的刺激作用需要1,25-(OH)₂D₃黏膜受体的发育以及循环中1,25-(OH)₂D₃水平的升高。胞质钙结合蛋白（CaBP）浓度的同时增加支持了这样的观点，即CaBP部分介导了1,25-(OH)₂D₃对钙主动转运的作用。第三周非饱和钙吸收效率的下降与小肠胞饮能力的丧失同时发生，但可能并非由其所致。1,25-(OH)₂D₃受体出现的时间以及非饱和钙吸收的下降受糖皮质激素控制，此时肠道中的其他几个成熟事件也是如此。
