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

1.在18日龄鸡胚肠CRBP(II)mRNA的表达水平在孵化前后迅速升高。CRBP(II)mRNA的发育规律与CRBP(II)蛋白的发育规律是平行的。维甲酸X受体(RXR)在胚胎和孵化后的雏鸡肠道中持续表达。2.在器官培养中，视黄醇和甲状腺激素对CRBP(II)的诱导存在协同作用。在添加9-顺式维甲酸的培养液中，CRBP(II)的水平显著升高。添加脂肪酸(亚油酸)或合成的花生四烯酸类似物(5，8，3.摄入过量的维生素A，而不是过量的β-胡萝卜素，会导致未酯化的视黄醇在大鼠肠道中的蓄积量超过CRBP(II)的结合量。过量的维生素A使卵磷脂：视黄醇酰基转移酶(LRAT)活性增加。CRBP(II)可能在防止游离视黄醇对小肠的毒性作用中起重要作用。4.老龄大鼠(600日龄)空肠CRBP(II)水平呈下降趋势。5.CRBP(II)mRNA在大鼠空肠绒毛-隐窝轴上的分布与CRBP(II)蛋白有所不同，表明其基因水平在分化绒毛下部较低，在中绒毛下部最高。高脂(玉米油)日粮大鼠空肠CRBP(II)基因及其蛋白水平显著升高，CRBP(II)基因的表达可能受长链不饱和脂肪酸或其代谢产物的调节。

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.