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Neonatal exposure to sumithrin shows estrogen-like effect in prepubertal rat development.
Sumithrin, a pyrethroid has been developed as insecticide, and are in use to control in and out door pests, providing potential for human exposure. Hormonal and developmental effects of this chemical, however, has been little characterized. In our previous uterotrophic assay using 18-day old SD female rats, subcutaneous sumithrin treatment (5 to 100 mg/kg/day) for 3 days increased the uterine wet weights in a dose dependent manner, and thus suggested the estrogenic effect of sumithrin in rat development. This study investigated the effect of neonatal exposure to sumithrin on the prepubertal rat development with diethylstilbestrol as a positive control. Sumithrin exposure at 1-5 days after birth caused acceleration in vaginal opening of female rat, delay in preputial separation of male like diethylstilbestrol, an estrogen. In addition, sumithrin-exposed male rats in this period showed significant reduction in anogenital distance, a external sign related to feminization of male in prepuberty (PND 18). Furthermore, neonatal treatment with sumithrin brought significant increases in ovarian and uterine weights while it significantly reduced serum E2 concentration and uterine ER mRNA expression on PND 18 in female rat. In conclusion, our results indicate that neonatal exposure to sumithrin in rat shows estrogen-like effect on various developmental parameters, and may affect the prepubertal rat development through its estrogenic activity.
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