[Time course of the disruption of rat's thyroid function by pesticide N'N-methylene-bis].

To study the effect of pesticide N'N-methylene-bis on thyroid function in rats, and the time-effect relationship. N'N-methylene-bis dimethylsulfoxide solution was administered to rats by gavage at a dose of 50 mg/kg body weight for 1, 3, and 5 days respectively. The rats in the control group were given solvent dimethylsulfoxide by oral gavage at the same volume. All animals were sacrificed 1 day after the last dosage, and the levels of FT4 and TSH in serum were measured by radioimmunoassay. The histological changes of thyroid gland were observed, and the expression of PCNA in thyroid was detected by immunohistochemistry. Compared with the solvent control group, the serum FT4 level in rats given N'N-methylene-bis for 3 days significantly decreased, while the TSH level significantly increased in the 3 d and 5 d groups (P<0.05). Hyperplasia of thyroid follicular epithelium was observed in the 3 d and 5 d groups. PCNA positive cells in thyroid of the 3 d and 5 d groups were significantly higher than that of control (P<0.05). The effect of N'N-methylene-bis on the level of serum FT4 and TSH in rats appeared on the 2nd or 3rd day of the experiment. Histopathologic examination showed thyroid gland proliferation of follicular epithelium within 3 days. The combined use of serologic test and histopathologic examination for screening thyroid hormone disruptors may be an effective method.