Thiouracil and Conversion of Carotene to Vitamin A Measured by Liver Storage in the Rat. ∗

Abstract

In a recent report, Canadell and Valdecasas 1 fed rats, which previously were on a vitamin A-free diet with thiouracil administered in the drinking water, 60 γ of carotene per week. The administered carotene was unable to relieve the ocular symptoms produced by a vitamin A deficiency. However, these symptoms were alleviated if small amounts of thyroid powder were administered with the carotene or vitamin A was fed to the thiouracil-treated animals. Their interpretation of this phenomenon was that it involved an inhibition of carotenase.

If this is true, then the feeding of carotene to vitamin A deficient-animals previously treated with thiouracil should produce little or no vitamin A in the liver. Therefore, this experiment was attempted, and a preliminary report of the results obtained is presented.

Twenty-six rats were placed on a vitamin A-low diet when they were 10 days old. When they reached a body weight of 43 g, they were divided into 2 groups. One group was continued on the same diet for 4 weeks while the second group received a similar diet to which 0.25% of thiouracil had been added. All rats were continued for an additional 2 weeks on identical diets except that they were made vitamin A-free by replacing the commercial casein with vitamin A-free test casein (General Biochemicals, Inc.). Some of the animals in each group received a single oral dose of a solution of β-carotene in cottonseed oil containing 348 ρ while the remaining rats, which served as controls, received cottonseed oil. The animals were sacrificed at 36 hours, 5 days or 7 days. Since the vitamin A levels in the different groups did not show any significant trend with time, the results obtained with animals sacrificed at 36 hours, 5 or 7 days have been averaged together.