Abstract
Vitamin A deficiency in the intact rat evokes an increase in liver ubiquinone and the incorporation of mevalonate into ubiquinone and squalene. This aberration is caused by a metabolic block between squalene and cholesterol. The addition of vitamin A in vitro to vitamin A deficient liver homogenates does not influence the metabolic defect. The vitamin A deficient guinea pig does not exhibit an increase in liver ubiquinone or incorporation of mevalonate into ubiquinone or squalene, but the incorporation into sterols is enhanced.