Effect of Thyroxine, Thiouracil and Ambient Temperature on the Utilization of Vitamin a by Vitamin A-deficient Rats

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Abstract
Vitamin A-deficient rats supplemented with vitamin A, exposed to 35°C for 3 weeks and restricted to 10 g of feed daily gained in body weight more efficiently than similarly treated rats at 21°C. The rats at 35° had significantly heavier livers, stored less hepatic vitamin A (µg/g), but total hepatic vitamin A storage was essentially the same at either temperature. Daily treatment with 7.5 µg L-thyroxine sodium resulted in a significantly decreased liver weight, whereas feeding thiouracil at 0.5% of the diet resulted in a significant increase in liver weight. Hepatic vitamin A storage (µg/g) in the thyroxine-treated rats was significantly greater than in the thiouracil-treated rats but total vitamin A storage was unaffected by hormone treatment. Vitamin A supplementation levels above 50 IU were followed by decreases in protein-bound iodine (PBI) with the highest level of supplementation resulting in a decrease in both PBI and thyroid weight. A significant quadratic response of thyroid weight to level of supplemental vitamin A was observed.