Effects of vitamins A and D on the biosynthesis of L-ascorbic acid by rat-liver microsomes

Effect of supplementing the hen's diet with vitamin A on the accumulation of vitamins A and E, ascorbic acid and carotenoids in the egg yolk and in the embryonic liver

1. The effect of a range of supplementations of vitamin A to the laying hen on the concentration of vitamins A, E, ascorbic acid and carotenoids in the maternal liver, the egg yolk and the embryonic liver were investigated. 2. Four groups of 25 Rhode Island Red hens were fed on standard layer-breeder diets with concentrations of supplemented vitamin A ranging from 0 to 120 micrograms/g retinol equivalents from 28 weeks of age. After 3 months, the concentration of vitamin A in the maternal liver was found to be greatly enhanced in proportion to the increasing rates of supplementation with the vitamin. However, the concentration of vitamin E in the maternal liver was markedly reduced by high dietary contents of vitamin A. 3. The concentration of vitamin A in the yolk of the hens' eggs was markedly increased by the dietary supplementation. However, the concentration of both vitamin E and carotenoids in the yolks were significantly reduced by high dietary contents of vitamin A. 4. The concentration of vitamin A in the liver of the embryo and the day old chick was greatly increased by the high concentrations of maternal vitamin A provision. However, the concentration of vitamin E, carotenoids and ascorbic acid in the embryonic/neonatal liver were significantly reduced by high contents of vitamin A in the maternal diet. 5. The susceptibility of the embryonic/neonatal liver to lipid peroxidation was significantly increased as a result of high provisions of maternal vitamin A. 6. It is concluded that excessive provision of vitamin A to the laying hen results in an adverse effect on vitamin E, carotenoids and ascorbic acid in the embryonic/neonatal liver and can compromise the antioxidant status of the progeny.

Modulations in the biotransformation of tobacco extract and N'-nitrosonornicotine under differential dietary protein status

The modulation of the phase I and phase II biotransformation enzymes upon treatment with tobacco extract (TE) and N'-nitrosonornicotine (NNN) was investigated using male Sprague-Dawley rats fed differential protein diets. It was observed that the animals fed a low protein diet showed an overall decrease in the basal levels of hepatic and pulmonary phase I and II enzymes. TE and NNN significantly decreased the detoxifying system in the low-protein-fed animals. Animals fed 20% protein, however, showed significant increases in glutathione and glutathione S-transferase upon treatment. Furthermore, TE and NNN treatment brought about a significant depletion in the hepatic pool of vitamin A with a concomitant increase in the vitamin C levels.

Vitamin A: not required for adrenal steroidogenesis in rats

Previous work supporting the vitamin A dependency of adrenal function in rats neglected to take into account a secondary effect of the deficiency, a decrease in hepatic ascorbic acid biosynthesis. Vitamin A-depleted rats maintained on a diet free of ascorbate had a decrease in the activity of adrenal 3 beta-hydroxysteroid dehydrogenase, and extensive adrenocortical degeneration. The use of an ascorbate supplement prevented the symptoms. The results suggest that previous evidence for direct involvement of vitamin A in steroidogenesis may have been due to the production of a secondary deficiency, a chronic scorbutic condition.