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

Abstract

Retinol absorbed and generated from dietary beta-carotene can be esterified by retinol esterifying enzyme(s) in intestinal absorptive cells. In this study, we observed the developmental changes and villus-crypt distribution of the activities of two retinol esterifying enzymes (lecithin-retinol acyltransferase (LRAT); and acyl-CoA-retinol acyltransferase (ARAT) in chick duodenum) to seek the possibility that these enzymes play distinct roles in retinol absorption and metabolism. Intestinal LRAT activity was barely expressed in embryonic stages until 2-3 d before hatching, when its activity becomes 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 embryogenesis, and was elevated to the maximal level 3-4 d after hatching. An assay of LRAT and ARAT activities along the villus-crypt axis of the duodenum by a cryostat sectioning technique revealed that between the day of hatching and 1 d posthatch, an abrupt induction of LRAT activity occurred only in the villus region of the duodenum, where a coordinated induction of cellular retinol-binding protein, type II (CRBPII), was observed. In contrast, the rise in ARAT activity observed around the hatching period occurred at the broader portions of the villi including the area of villus-crypt junction. These observations in the developmental changes and distribution of LRAT and ARAT activities suggest that LRAT activity but not ARAT activity is closely related to the induction of CRBPII in the duodenum of developing chicks.