Vitamin A deficiency reduces uptake of β-carotene by brush border membrane vesicles but does not alter intestinal retinyl ester hydrolase activity in the rat

Vitamin A deficiency has been reported to result in mild structural and functional changes within the small intestine. The objective of this study was to measure the impact of vitamin A deficiency in the rat on several functional aspects of β-carotene uptake and intestinal retinyl ester hydrolysis. These included uptake of ¹⁴C-β-carotene by brush border membrane vesicles (BBMV) and in vitro activity of intrinsic retinyl ester hydrolase (REH). Rats (n = 33) were randomly assigned to receive one of three dietary treatments: vitamin A deficient (-VA), vitamin A sufficient pair-fed (PF), or vitamin A sufficient free access-fed (FA). Liver, serum retinol, and growth data were used to verify clinical vitamin A deficiency. Rats in the -VA group were clinically vitamin A deficient by Day 56 on a vitamin A-free diet and, at that point, all rats were randomly assigned to one of two experimental treatments: BBMV studies or REH activity assays. Uptake of ¹⁴C-β-carotene by BBMV was significantly suppressed (P < 0.05) in -VA rats when compared to both PF and FA control rats during early passive uptake equilibration (10-20 sec). Uptake was also significantly decreased by BBMV isolated from -VA rats compared to PF controls, but not FA controls, after a 10-min incubation (P < 0.05). In vitro activity of REH was not impacted by vitamin A deficiency in rats, although a trend for greater activity from -VA rats was noted. These data suggest that vitamin A deficiency impairs enterocyte membrane uptake of β-carotene without altering the enzymatic activity of intrinsic REH. (C) Elsevier Science Inc. 2000.