TRANSGENERATIONAL EFFECTS OF THE XENOESTROGEN METHOXYCHLOR (M) IN RATS

Abstract

The current study was conducted to evaluate the utility of using the estrogenic pesticide M as a model chemical to induce epigenetic alterations in male rats. Previously, we demonstrated that exposure to M in utero and during lactation induced the delayed anovulatory syndrome in female offspring and reduced testis weights in male offspring. Recently, it was reported that M exposure during gonadal differentiation induces epigenetic alterations in male rats resulting in effects that include infertility and severe histopathological lesions of the testis that are transmitted from the offspring to subsequent generations. The current experiment was designed to determine if we could replicate either the effects of M that we had seen in male and female rat offspring or the effects on testis histopathology and male fertility. LE rats (5-6/group) were dosed orally with M at 50, 100 and 200 mg/kg/d from day 8 of pregnancy to day 9 of lactation. Vaginal smears were collected from the female offspring for 19 days after weaning and at 124 days of age. Female offspring were necropsied at 13 months and body, liver, adrenal, kidney, pituitary, ovarian and uterine weights were measured and all tissues were examined for histopathological lesions. At 11 months, male offspring were mated with control females to assess fertility, after which they were necropsied. Body, liver, kidney, adrenal, epididymal, seminal vesicle and testis weights were recorded, these tissues were examined for histopathological lesions and cauda epididymal sperm were enumerated. In female offspring, the age at vaginal opening was accelerated by maternal M treatment at 50, 100 and 200 mg/kg/d. Most high dose females displayed a “pin-hole” like vaginal opening by 12–13 days of age. After weaning, the vaginal smears of M-treated females were fully cornified on 50% of days versus 25% in the control group. From 124 to 142 days, the vaginal smears of treated females were cornified 80–90% of the time versus 45-50% in control females. In addition, histopathological lesions were increased in a dose-related manner in the ovary and uterus. The ovaries displayed an increase in luteinized stromal cells and squamous metaplasia of the epithelial lining in the lumen and endometrial glands was present in the uterus. Treated male offspring displayed reduced testis and epididymal weights. However, there were no dose-related histopathological alterations in the testis or any other organ or reductions in male fertility. Taken together, these results indicate that the xenoestrogen M has more robust effects on female than male rat offspring. Among the effects in the males, effects on testis and epididymal weights were robust enough to be detected in this relatively small study. However, M did not cause any dose-related alterations of testis histopathology or male fertility. If M truly induces testis histopathological lesions and male infertility, detection of these effects would require a significantly larger number of animals than we used in this study which examined 45 males (7–16/group). We are evaluating the feasibility of conducting a larger transgenerational, epigenetic study with M but such a study would be problematic since the penetrance of the effects on testis histology and fertility, if any, appear to be so low. This is an abstract of a proposed presentation and does not necessarily reflect EPA policy. (platform)