Antithyroid effects in vivo and in vitro of vitexin: a C-glucosylflavone in millet.

Millet diets rich in C-glycosylflavones (C-GF) are goitrogenic, and its three most abundant C-GF inhibit in vitro thyroid peroxidase, suggesting that these compounds are the goitrogens in millet. However, proof of a cause and effect relationship between C-GF and goitrogenesis requires a demonstration of in vivo antithyroid activity by the purified isolated compounds. Vitexin, one of the three major C-GF in millet, was used to test this hypothesis. Twenty-four female Wistar rats, divided into groups of six rats each and fed Purina iodine-rich diet (12 micrograms I-/day.rat), were administered acutely by gastrointestinal tube goitrogen-free water (controls), methimazole (0.5 mumol), and vitexin (20 and 80 mumol). 125I (1 microCi) was injected ip 1 h later, and the rats were killed 2 h after the injection. The thyroid glands were removed and analyzed for their content of total 125I and 125I-labeled compounds. Rats given vitexin, in contrast to those receiving methimazole, did not show suppressed thyroid 125I...