Thyroid Function of Chicks after Withdrawal of (—)-5-Vinyl-2-oxazolidinethione, a Goitrogen in Rapeseed

Thyroid function of chicks after withdrawal of goitrin, a goitrogen in rapeseed, from the diet following 21 days feeding was investigated. Increased thyroid weight (about 4 times that of the control) and thyroidal 131 I uptake (about 2.7 times that of the control) induced by 21 days feeding of 0.05% goitrin were decreased gradually after withdrawal of goitrin. Other synthesizing steps of thyroid hormone in the gland, such as iodination of tyrosines and coupling of iodotyrosines and synthesizing of thyroxine, and plasma level of thyroid hormone were completely recovered within 2 days after withdrawal of goitrin. Distinct rebound phenomena were observed in circulating level of thyroid hormone and synthesis of thyroxine in the gland after the withdrawal. These results suggest that depression in metabolism of thyroid hormone induced by administration of goitrin may be restored in a relatively short time after withdrawal of goitrin, despite hypertrophy of thyroid gland which persist for relatively longer time.