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 uptake. However, significant inhibition of the coupling mechanism (high 125I-labeled monoiodotyrosine plus diiodotyrosine/125T3 plus T4 ratio and low 125T3 and T4 concentrations) did occur with the highest dose of vitexin. These results provide direct evidence in vivo of C-GF antithyroid activity, strongly supporting the concept that C-GF are the goitrogens in millet.
Gaitan
E
E
University of Mississippi School of Medicine, Jackson, USA.
Cooksey
R C
RC
Legan
J
J
Lindsay
R H
RH
D000818:Animals; D047310:Apigenin; D005260:Female; D005419:Flavonoids / Q000032:analysis* / Q000494:pharmacology*; D007453:Iodide Peroxidase / Q000378:metabolism; D008897:Panicum / Q000737:chemistry*; D051381:Rats; D017208:Rats, Wistar; D013961:Thyroid Gland / Q000187:drug effects*
D005419:Flavonoids; D047310:Apigenin; C032731:vitexin; D007453:Iodide Peroxidase