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 it s three most abundant C-GF inhibit in vitro thyroid peroxidase, sugges ting that these compounds are the goitrogens in millet. However, proof of a cause and effect relationship between C-GF and goitrogenesis req uires a demonstration of in vivo antithyroid activity by the purified isolated compounds. Vitexin, one of the three major C-GF in millet, wa s used to test this hypothesis. Twenty-four female Wistar rats, divide d into groups of six rats each and fed Purina iodine-rich diet (12 mu gI(-)/day.rat), were administered acutely by gastrointestinal tube goi trogen-free water (controls), methimazole (0.5 mu mol), and vitexin (2 0 and 80 mu mol). I-125(1 mu Ci) was injected ip 1 h later, and the ra ts were killed 2 h after the injection. The thyroid glands were remove d and analyzed for their content of total I-125 and I-125-labeled comp ounds. Rats given vitexin, in contrast to those receiving methimazole, did not show suppressed thyroid I-125 uptake. However, significant in hibition of the coupling mechanism (high I-125-labeled monoiodotyrosin e plus diiodotyrosine/T-125(3) plus T-4 ratio and low T-125(3) and T-4 concentrations) did occur with the highest dose of vitexin. These res ults provide direct evidence in vivo of C-GF antithyroid activity, str ongly supporting the concept that C-GF are the goitrogens in millet.