Vitamin A turnover in rats as influenced by vitamin A status.

Vitamin A turnover was studied in rats fed vitamin A-sufficient (+A) or vitamin A-deficient (--A) diets for 24--25 days. Hepatic vitamin A stores of the +A group (543 microgram) were significantly larger than those of the --A group (11 microgram) and similarly, the plasma vitamin A concentration of the +A group (56 microgram/dl) was significantly higher than that of the --A group (26 microgram/dl). Rats were injected intravenously with plasma containing tritium-labeled retinol (3H-ROH) obtained from vitamin A-deficient donor rats previously fed 3H-ROH. Plasma samples from injected recipients were collected over a 48-hour period. Kinetic analysis of plasma tracer concentration versus time curves indicated that the data fit a three-pool model. The plasma vitamin A turnover rate of the +A group was significantly more rapid than that of the --A group (5.19 versus 1.98 microgram/hour). Plasma fractional turnover rates for the +A group (1.31 hour--1) were not significantly different from those of the --A group (0.90 hour--1). The data suggest that for both dietary groups, the metabolism of retinol associated with the prealbumin and retinol-binding protein complex involved extensive recycling among the liver, plasma, interstitial fluid and peripheral tissues.