Studies on physiological role of cellular retinolbinding protein, type II in small intestine

1.在鸡胚18 d时，肠道CRBP（II）mRNA表达量开始增加，在出壳前后迅速增加，其表达模式与CRBP（II）蛋白表达模式基本一致，在胚胎期和出壳后的鸡胚中，RXR mRNA持续表达。在鸡胚十二指肠器官培养中，16日龄的鸡胚十二指肠出现了诱导，在添加9-顺式维甲酸的培养基中，（亚油酸酯）或合成花生四烯酸类似物（5，8，11，14-二十碳四烯酸）也增加CRBP（II）及其mRNA。3.喂食过量的维生素A，但不过量的β-胡萝卜素，导致未酯化的视黄醇在大鼠肠道中积累，超过了CRBP（II）的结合能力。大鼠喂食过量的维生素A，其量是NRC推荐需求量的1000倍，显示卵磷脂的增加：视黄醇酰基转移酶（LRAT）活性。CRBP（II）可能在防止未结合的视黄醇在小肠中的毒性作用中起重要作用，但在过量10倍以上的视黄醇时，CRBP（II）结合视黄醇的能力似乎受到限制。4.老年大鼠空肠CRBP（II）水平CRBP（II）mRNA在大鼠空肠沿着绒毛-隐窝轴的分布与CRBP（II）蛋白的分布有一定的差异，空肠LRAT活性的绒毛-隐窝梯度与CRBP（II）蛋白相似，高脂饮食组大鼠空肠CRBP（II）mRNA及其蛋白表达水平显著高于对照组，空肠CRBP（II）mRNA及其蛋白表达水平显著高于对照组，空肠CRBP（II）mRNA及其蛋白表达水平显著高于对照组CRBP（II）基因的表达被认为是由长链不饱和脂肪酸或其代谢产物调节的。

1.The expression of intestinal CRBP (II) mRNA was detected in Day 18 chick embryo and its mRNA level rapidly increased around hatching.The developmental pattern of the CRBP (II) mRNA was in parallel with the pattern of CRBP (II) protein.Retinoid x receptor (RXR) mRNA was constantly expressed in embryonic and post-hatched chick intestines.2.Synergistic effect of retinol and thyroid hormone on CRBP (II) induction occurred in organ culture of Day 16 chick embryonic duodenum.Its level remarkably increased in the medium added 9-cis retinoic acid.The addition of fatty acid (linoleate) or synthetic arachidonic acid analog (5,8,11,14-eicosatetraunoic acid) also increased CRBP (II) and its mRNA.3.Feeding excess vitamin A,but not excess beta-carotene, caused accumulation of unesterified retinol which exceeded binding capacity of CRBP (II) in rat intestine.Rats fed excess vitamin A which was 1000 times the amount of the NRC's recommended requirement, showed the increase in lecithin : retinol acyltransferase (LRAT) activity.The CRBP (II) may play an important role in preventing toxic effect of unbound retinol in the small intestine, but there appears to be a limitation in retinol-binding capacity of CRBP (II) for over 10 times excessive retinol.4.The jejunal CRBP (II) level in the aged rats (600 days-old) tended to be lower.5.Distribution of CRBP (II) mRNA along villus-crypt axis of rat jejunum was somewhat different from that of CRBP (II) protein, showing that its gene level was low in differentiating lower villus and maximum in lower part of mid-villus.The villus-crypt gradient of jejunal LRAT activity was comparable to that of CRBP (II) protein, which showed a maximal level in the mid-villus and low levels in the apical villus and crypt.The CRBP (II) mRNA and its protein levels in jejunum significantly elevated in rats fed a high fat (corn oil) diet.The expression of CRBP (II) gene is proposed to be modulated by long-chain unsaturated fatty acids or their metabolites.