Pubertal exposure to saisentong: effects on thyroid and hepatic enzyme activity in juvenile female rats

Saisentong, as a thiadiazole fungicide, is widely used in China. The structure of saisentong shows a closer relationship to N, N-methylene-bis (2-amino-1, 3, 4-thiadiazole) (Bis-A-TDA), which is a teratogen. A few studies have shown that some of the thiadiazole fungicides act as endocrine disruptors via disturbance in thyroid hormone homeostasis. Little is known about the effect of pubertal exposure to saisentong on the development in pubertal female rats. Based on the protocol of the 20-Day Pubertal Female Assay, we attempt to estimate the possible effect of exposure to saisentong on thyroid hormone and hepatic enzyme activity in female rats. Postnatal days (PND) 22 old SD rats were administered with saisentong daily by oral gavage at doses of 0, 5, 10 or 15mg/kg/day for 20 days. After treatment, the rats were sacrificed for blood collection; the reproductive organs, liver, pituitary, adrenal and thyroid gland were harvested. The results indicated that saisentong administration increased thyroid weight and thyroid stimulating hormone (TSH) concentrations, and induced hepatic uridine diphosphate glucuronyl transferase (UDPGT) activities in the highest-dose group, although not statistically significant. The high dose caused a decrease in weight at vaginal opening (VO), but the age at VO was unaffected by saisentong in all treatment groups. No histological changes were observed in uterus and ovaries. These data and changes demonstrate that saisentong is a potential thyroid disrupter in female rat following exposure during development, but does not affect the development of pubertal female rats.