EFFECT OF THIOURACIL AND THIOUREA ON THE THYROID GLAND OF THE CHICK11

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Abstract
Approximately 0.1% thiouracil and thiourea in the diet for 14 days was the optimal dosage for the production of maximal enlargement of the thyroid in one to 2-day-old White Plymouth Rock chicks. Maximum thyroid enlargement expressed as thyroid wt. in mg./100 g. of body weight was secured in about 12 days, when White Plymouth Rock chicks were fed 0.1% thiouracil in the diet. Female White Plymouth Rock chicks exhibited a greater thyroid response than did the [male][male] when fed 0.1% thiouracil or 0.1% thiourea in the feed for 14 days. Increasing dosages of thyroxine progressively decreased the thyroid enlargement produced in White Plymouth Rock chicks by 0.1% thiouracil in the diet. There was a sex difference in this regard, the [female][female] requiring greater amts. of thyroxine to depress the thyroid wts. to any given wt. level or to the normal level for their sex. Nine different breeds of chickens were given 0.1% thiouracil in drinking water and the thyroid responses noted. The thyroids of the lighter breeds of chickens gave a greater response as compared to the thyroids of the heavier breeds. The application of these expts. in the formulation of a biological assay for materials having thyroxine-like activity was discussed.