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 vitamins A, E, ascorbic acid and carotenoids in the liver and blood plasma of the neonatal chick were investigated. 2. In the 1st 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. Retinyl acetate in corn oil (1.72; 4.30; 8.60 or 17.2 mg) was intubated directly into the crop daily during the first 5 d after hatch. 3. The intubation of vitamin A increased its accumulation in the liver, with a plateau at about 6,000 microg/g, and was associated with inhibition of vitamin E and carotenoid utilisation from the liver during postnatal development. 4. Moderate amounts of vitamin A intubation increased ascorbic acid concentration 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 (GSH-Px) and superoxide dismutase (SOD) activities in the chicken liver and brain. 6. It is concluded that the effect of vitamin A on development of the antioxidant system in the neonatal chick is dose-dependent and an excess of vitamin A can compromise the antioxidant defence system.