Effects of zinc and vitamin A deficient diets on the hepatic mobilization and urinary excretion of vitamin A in rats

Abstract

Weanling rats were fed diets deficient in zinc (ZD), vitamin A (AD), or both (ZAD) for 3 weeks. Each then received 20 μg of 11,12 3H retinyl acetate. Plasma retinol was monitored for radioactivity for 5 hours and urine for 6 days. Rats were killed and measurements made of plasma and liver vitamin A and plasma and liver vitamin A and plasma zinc. Plasma vitamin A was depressed but growth was not affected in AD rats compared to pair fed controls. Radioactivity appeared most rapidly in the plasma retinol fractions of the two vitamin A depleted groups (AD and ZAD) and was excreted most rapidly in the urine of these same groups. Zinc deficient diets (ZD and ZAD) caused depressed plasma levels of zinc and vitamin A and growth retardation greater than in pair fed controls. However, zinc deficiency had no effect on mobilization of newly ingested vitamin A or urinary excretion of labeled metabolites. Liver stores of vitamin A were lower for ZD rats than for controls. The data indicate that zinc deficiency is not a limiting factor in hepatic vitamin A release except as it influences growth and body demand for the vitamin. The data also suggest that newly absorbed vitamin A is mobilized and utilized in preference to that previously stored in the liver.