Transfer of Vitamin A from Intestine to Plasma in Lambs Fed Low and High Intakes of Vitamin A

Abstract

Three groups of lambs were fed a low carotene diet supplemented with vitamin A proprionate equivalent to 0, 100 or 12,000 µg retinol per kilogram per day via rumen cannulae. These groups were mildly deficient, normal (control) and intoxicated, respectively. After 17 weeks, abomasal cannulae were implanted, [15-3H]retinol was injected into the abomasum, and jugular blood was sampled for 48 hours. After 7 days, the tracer was injected into a jugular vein, and blood was sampled for 48 hours. Rates of retinol and retinyl ester transport and retinol clearance from plasma reflected intake (P < 0.05); clearance of retinyl esters was unaffected. Mean efficiencies of total vitamin A (retinol and retinyl ester) transfer from digestive tract to plasma were 86, 60 and 60%, whereas those of retinol were 91, 58 and 14% (P < 0.05) for mildly deficient, control and intoxicated lambs, respectively. Thus lower transfer efficiencies were associated with higher transport rates of plasma retinol and retinyl ester and with increased clearance of retinol but not retinyl ester from plasma. These results suggest that vitamin A transfer from intestine to plasma is sensitive to vitamin A intake, and that retinol is the primary form of vitamin A affected.