Journal of Lipid Research, Vol 32, 1521-1527, Copyright © 1991 by Lipid Research, Inc.
Ontogeny of two vitamin A-metabolizing enzymes and two retinol-binding proteins present in the small intestine of the rat
DE Ong, PC Lucas, B Kakkad and TC Quick
Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN 37232.
The patterns of expression of cellular retinol-binding protein (CRBP),
cellular retinol-binding protein, type two [CRBP(II)], lecithin: retinol
acyltransferase (LRAT), and microsomal retinal reductase were examined for
rat small intestine during the perinatal period. CRBP was present (15 pmole
per mg soluble protein) at the earliest time examined, the 16th day of
gestation, declining by 70% by birth, maintained to adulthood. In contrast,
CRBP(II) appeared 2-3 days before birth, rising to its highest level (500
pmole per mg soluble protein) by day 3 after birth, then declining by 50%
during the late suckling period to the adult level. Immunohistochemistry
revealed that CRBP(II) initially appeared in the epithelial cell layer in a
patchy manner, resolving by birth into an even staining of all
villus-associated enterocytes. In contrast, CRBP was evenly expressed in
the epithelial cell layer at day 17/18 but was absent by birth. Intestinal
LRAT activity increased rapidly in the 2 days prior to birth, then declined
at weaning to the adult level. Microsomal retinal reductase was measurable
in the intestine at birth, but not detected during the early suckling
period, reappearing at day 21. Considerable increase was then observed
coincident with weaning, when carotenes, from which retinal is derived,
became an important source of vitamin A. The pattern of appearance of these
elements appears to prepare the intestine for the necessary processing of
vitamin A required after birth.