The Effect of the Thyroid on the Conversion of Intravenously Administered Aqueous Dispersions of Carotene to Vitamin a in the Rat

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Abstract
The effect of the thyroid on the conversion of carotene to vitamin A has been studied in the rat, carotene being administered intravenously as an aqueous dispersion in Tween 40 (polyoxyethylene sorbitan monopalmitate). Twenty-four hours after the injection of carotene into normal, hyperthyroid, hypothyroid, and thyroidectomised animals partially deficient in vitamin A, liver levels of vitamin A increased from 1.1 µg to 11.0, 10.6, 12.8 and 10.2µg/liver, respectively, while blood levels of vitamin A increased from 11 µg to 19, 17, 21 and 18 µg/100 ml plasma, respectively. Within 11 days of injection into completely deficient animals, ocular symptoms had disappeared from all 4 treated groups. The rate at which symptoms disappeared was approximately the same in all groups while weight increases, with the exception of the hypothyroid group which was lower, were the same also. From these results it is concluded that the thyroid is without effect on the conversion of carotene to vitamin A.