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

1. The synthesis of l-ascorbic acid from either d-glucuronolactone or l-gulonolactone by liver microsomes of rats is decreased under conditions of hypervitaminosis A; under hypervitaminosis D the synthesis from d-glucuronolactone is increased and that from l-gulonolactone is not affected. 2. The microsomal conversion of l-gulonolactone into l-ascorbic acid is impaired in liver tissues of rats made deficient with respect to either vitamin A or vitamin D when compared with the controls maintained on stock diet.