Effect of vitamin A on the antioxidant system of the chick during early postnatal development

1. The effect of increasing vitamin A doses on the concentrations of vitami ns A, E,, ascorbic acid and carotenoids in the liver and blood plasma of th e neonatal chick were investigated. 2. In the Ist experiment 75 d-old chickens were divided into 3 equal groups and in the 2nd experiment 100 d-old chickens were divided into 5 groups. R etinyl acetate in corn oil(1.72; 4.30; 8.60 or 17.2 mg) was intubated direc tly into the crop daily during the first 5 d after hatch. 3. The intubation of vitamin A increased its accumulation in the Ih er. wit h a plateau at about 6.000 mug/g, and was associated with inhibition of vit amin E and carotenoid utilisation from the liver during postnatal developme nt. 4. Moderate amounts of vitamin A intubation increased ascorbic acid concent ration in the liver; kidney brain and plasma. A further increase in vitamin A intubation had an adverse effect on ascorbic acid concentrations in the plasma and brain. 5. The 2 highest inputs of vitamin A decreased glutathione peroxidase (GSI- I-Px) and superoxide dismutase (SOD) activities in the chicken liver and br ain. 6. It is concluded that the effect of vitamin A on development of the antio xidant system in the neonatal chick is dose-dependent and an excess of vita min A can compromise the antioxidant defence system.