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Immunochemical studies on the localization and on the concentration of cellular retinol-binding protein in rat liver
Abstract:
Studies were conducted to characterize the localization and the concentration of cellular retinol-binding protein (CRBP) in rat liver during perinatal development. The studies employed both a specific immunohistochemical staining procedure and a sensitive and specific radioimmunoassay for CRBP. Dramatic changes were seen in both the levels and localization of CRBP. Marked increases in hepatic CRBP levels were seen during the last week of gestation and the first postnatal week, resulting in a quadrupling of CRBP levels in this 2-week interval. During the second postnatal week CRBP levels remained very high (approximately 110 to 120 micrograms/gm of wet weight, with peak values at about day 11 of age). During the third postnatal week, CRBP levels declined, followed by a further decline to adult levels (40 to 50 micrograms/ml) postweaning. A changing pattern of immunohistochemical localization of CRBP was seen that correlated with the changes in CRBP levels. In fetal livers at days 11 to 13 of gestation, CRBP was selectively localized in perisinusoidal cells that resembled stellate (fat-storing) cells in their location and shape but that lacked the lipid droplets usually seen in these cells in adult liver. During the final week of fetal development and the first postnatal week, a progressive increase in CRBP in parenchymal cells was seen. By the second postnatal week, very strong staining for CRBP was seen in all parenchymal cells. The staining of parenchymal cells for CRBP then declined, and by weaning (day 21) the pattern of localization of CRBP in liver resembled that seen in the adult, with low to medium staining seen in parenchymal cells and strongly intense staining in perisinusoidal stellate cells. Thus, the rise and then decline in intensity of CRBP staining in parenchymal cells paralleled the pattern of changes seen in CRBP levels during the perinatal period. In the placenta, CRBP was selectively localized in the trophoblast layer of the chorioallantoic placenta and in the entodermal layer of the yolk sac placenta. These findings suggest that either retinol is metabolized or plays a functional role at these placental sites.