Effects of Crude Rapeseed Glucosinolates and Genistein on Thyroid in Male Wistar Rat

Abstract

Glucosinolates (GLSs) and isoflavone, both indicated as goitrogenic, are important dietary factors in Asian diets. In this study, crude rapeseed GLSs and genistein were administered orally to male rats for 30 days, individually and simultaneously. To determine the effect on the thyroid, both the thyroid hormone (T3, T4 and TSH) levels in serum and the expression levels of genes related to the thyroid function (thyroglobulin (Tg), thyroid peroxidase (TPO) and thyrotropin receptor (TSHr)) were analyzed in thyroid tissue on days 3, 10, 20 and 30. Goitrin, the main breakdown product of the GLSs in rapeseed extract, was measured in the serum of treated groups for day 30. No treatment-related changes were observed in body and organ weights. Goitrin was not detected in the serum. For thyroid hormone analysis, no statistically significant changes were observed except for a decrease in T4 in the genistein group from day 3. Some slight fluctuations of thyroid hormones were found. Significant changes in mRNA expression levels were only observed on day 10, showing decreased Tg, TPO and TSHr expression levels compared to the control group. The present study has shown that both GLSs and genistein have a weak effect on the thyroid when treated with a dose that is similar to the intake of high consumers in humans. The fluctuations caused in thyroid hormone levels and gene expression levels are assumed to be a function of the pituitary-thyroid axis. Thus, it is difficult to observe the antithyroid effect where the individual intake levels of GLSs and isoflavone are relatively safe.