Antithyroid activity of goitrin in chicks

Antithyroid activity of orally administered goitrin was assessed by parallel-line assay in chicks using four indices. The relative potency of goitrin in chicks was estimated to be approximately 0.31 times the potency of PTU in causing enlargement of thyroid gland, 0.06 times in effect on depression in plasma thyroid hormone, and 0.08 times in inhibitory effects on biosynthesis of thyroid hormone in the gland. It might be concluded that thyroid hormone synthesis is not so much suppressed to the degree expected from the enlargement of thyroid gland when goitrin is administered orally to the chick.