Studies in vitamin A. 9. The role of the thyroid in carotene and vitamin A metabolism

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Abstract
Feeding large amts. of thiouracil to rabbits on a high carotene diet does not cause the appearance of either carotene or retinene in the blood plasma. This indicates that thiouracil does not inhibit intestinal "carotenase." Neither thiouracil nor desiccated thyroid has any qualitative or quantitative effect on the stability of colloidal solns. of beta-carotene. Thiouracil inhibits and desiccated thyroid stimulates the absorption of beta-carotene from the intestinal tract of rats. When administered with thiouracil, desiccated thyroid counteracts the inhibition by the drug. Neither thiouracil nor desiccated thyroid has any effect on the plasma-vit. A levels of rabbits. The detn. of plasma-vit. A levels is suggested to be of little or no value in diagnosing thyroid dysfunction.