Developmental induction and villus-crypt distribution of retinol esterifying enzyme activities in chick duodenum

Retinol absorbed and generated from dietary beta-carotene can be esterified by retinol esterifying enzyme(s) in intestinal absorptive cells. In this s tudy, we observed the developmental changes and villus-crypt distribution o f the activities of two retinol esterifying enzymes (lecithin-retinol acylt ransferase (LRAT); and acyl-CoA-retinol acyltransferase (ARAT) in chick duo denum) to seek the possibility that these enzymes play distinct roles in re tinol absorption and metabolism. Intestinal LRAT activity was barely expres sed in embryonic stages until 2-3d before hatching, when its activity becom es detectable; thereafter it abruptly increased to the maximal level at the third day of the posthatch period. In contrast, ARAT activity was present in the duodenum at the earliest stage examined, the 15th day of embryogenes is, and was elevated to the maximal level 3-4d after hatching. An assay of LRAT and ARAT activities along the villus-crypt axis of the duodenum by a c ryostat sectioning technique revealed that between the day of hatching and 1d posthatch, an abrupt induction of LRAT activity occurred only in the vil lus region of the duodenum, where a coordinated induction of cellular retin ol-binding protein, type II (CRBPII), was observed. In contrast, the rise i n ARAT activity observed around the hatching period occurred at the broader portions of the villi including the area of villus-crypt junction. These o bservations in the developmental changes and distribution of LRAT and ARAT activities suggest that LRAT activity but not ARAT activity is closely rela ted to the induction of CRBPII in the duodenum of developing chicks.