Female weanling rats were fed on a purified diet containing either no vitamin A, apart from traces present in casein (deficient groups), or the same diet containing 1.55 mg retinol as retinyl acetate/kg (control groups). In one experiment the deficient groups were given 1 microgram retinol/d after 10 weeks, to permit successful reproduction under conditions of marginal vitamin A status. A proportion were mated at 11 weeks after weaning, and fetal development was permitted for 7 d or for 20 d before killing. 2. Carotene dioxygenase (EC 1.13.11.21) activity was measured in a supernatant fraction from intestinal mucosal scrapings. For each group, activity was 20-30% greater in the vitamin-A-deficient animals than in the controls, and the difference reached statistical significance for the virgin and 7 d pregnant animals in the first experiment (severe deficiency) and for the 20 d pregnant animals in the second experiment (less-severe deficiency). 3. It is suggested that low tissue vitamin A levels may feedback to increase carotene dioxygenase activity, by mechanisms at present unknown, presumably to ensure a more efficient use of precursor dietary carotenoids.
