Carotene dioxygenase (EC1. 13. 11. 21) activity in rat intestine: effects of vitamin A deficiency and of pregnancy

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Abstract
1. 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 μg 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 (EC1. 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.