Study on the physiological role of intestinal cellular retinol-binding protein, type II

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We investigated the physiological roles of cellular retinol-binding protein, type II (CRBP(II)) and obtained the following results.(1) We purified CRBP(II) from chicken intestine (17 kDa) and rat intestine (16 kDa). Using the antisera prepared against CRBP(II), we developed enzyme-linked immunosorbent assay (ELISA) system for CRBP(II). Chicken CRBP(II) showed the binding specificities to both retinol and retinal.(2) During perinatal development of chicken intestine, CRBP(II) level was elevated by 10 fold from Day 20 of embryogenesis to 1 day after hatching.(3) CRBP(II) was highly expressed in duodenum and jejunum (especially in the mid-villus region) of chicken, but the level was low in the ileum.(4) CRBP(II) was also expressed in the liver around the hatching period of chicken, but the level was very low after 5 days of age. The temporarily appearing hepatic CRBP(II) might play some role in beta-carotene metabolism in the liver, because intestinal luminal beta-carotene content, serum … More beta-carotene concentration, and hepatic retinal reductase activity were all elevated during the perinatal period.(5) Since intestinal CRBP(II) directs absorbed retinol to lecithin:retinol acyltransferase (LRAT), we measured both CRBP(II) and LRAT activity in the small intestine of animals subjected to surgery or dietary manipulations. The rats subjected to jejunum-bypass operation showed elevated level of CRBP(II) in the remaining jejunal segment. Intestinal LRAT activity was enhanced in parallel with the increase in CRBP(II) around the hatching period of chicken, and both CRBP(II) and LRAT activity were reduced by feeding vitamin A-depleted diet. Feeding rats the protein malnourished diets led to reduction in LRAT activity, but not CRBP(II) contents, in jejunum.(6) We prepared CRBP(II)cDNA probe using chicken intestinal mRNA's as a template, and demonstrated that CRBP(II)mRNA was expressed shortly before the appearance of CRBP(II) proteins in duodenum and liver of chicken, suggesting the transcriptional regulation of CRBP(II) in this perinatal period. Less