The Study Of Reproductive Toxicity In Pregnancy Mouse And Its Offspring Exposure To Methoxychlor

In the past few years, scientists found that the effects of endocrine disrupting chemcals(EDCs) could produce profound harmful to the reproduction and grouth of human being and animals. And this may be one of the reasons related to sterility, miscarriage, malfunction of newborn animals. The sensitive of the reproducing ones to the EDCs is more than the others. The evaluation of the EDCs have became more important to medical studys. Early prenatal stages of embryo development may be one of the sensitive targets to EDCs because estrogen receptors (ER) was found in all blastomeres of the embryos throughout preimplanatation periods of development. Thus,it is possible that in vivo exposure of preimplantation embryos to ecoestrogens may alter developmental processes in mice and other mammals. Long-term toxicity effects of in vivo exposures to proestrogen methoxychlor (MXC) or estradiol (E) were studied during early pregnancy to mouse dams and their offsprings. Our researches were divided into two parts. Part 1: A MXC toxicity model was established, and toxicity effects of MXC to pregnant mouse was evaluated. The pregnant mice were randomly divided into 5 groups. Three exposured groups had been administered by subcutaneous injections once per day for 8th. MXC was dissolved in sesame oil. Sesame oil was used as negative control while estradiol was used as positive control. Pregnant mice were killed when pregnant for 17.5 days and the viscera relative weight was measured. The changed body weights, counts of number corpora luteum and pregnancy outcome of the pregnant mice were observed. The concentrations of estradiol (E2) and progesterone (P) in sera of pregnant mice were determined by radioimmunoassay. The morphological analysis of placenta tissues was examined by light and electron microscopy. Results showed that with the increase of the MXC ,the gained weights of pregnant mice reduced and the nidation quantity decreased. The weights of 166.67 mg/kg BW treated group in GD14.5 and GD17.5 were 43.51±2.03 and 15.59±1.18 respectively; while the gained weights of them were 46.79±2.53 and 18.87±0.55 respectively( P < 0.05). However, the incidence of the adverse pregnancy outcome (fetal death, absorption) went up while at the same time the concentrations of E2 and P in sera went up. Significant differences in these indexes were found between the experiment groups and negative control group (P < 0.05). Significantly lower amount of glycogen was observed in spongiotropho- blasts 1asts especially in those glycogen cells of MXC mice compared with control ones.We found that MXC can disrupt reproductive function ,which resulted in dysgenesis and maldevelopment in mice. The experiment suggests that aspirin might reduce the storage of glycogen in placenta and decrease the liberation of glucose from the placenta,which may lead to insufficiency of the energy necessary to the development of normal embryo.This might be one of the reasons that aspirin interferes with fetal development and produces congenita1 maldevelopmen of mice;especially in the 166.67 mg/kg BW MXC group.Part 2: The study of offsprings development and reproductive toxicity in offspring on early pregnancy exposure MXCWe erected the MXC toxicity model for early pregnant mouse just like the first experiment. Pregnant dams were divided randomly into sesame oil, 166.67mg/kg of MXC, 0.033 mg/kg of E. spontaneous delivery. Litter size, sex ratio at birth, and anogenital distance (AGD) in offspring of both sexes were examined, as well as vaginal opening in female offspring. The concentrations of LH, FSH and testosterone (T) in sera of the pregnant mice were determined using radioimmunoassay. The expression of ERαand ERβmRNA on oil group placenta was investigated by reverse transcription-ploymerase chain reaction (RT-PCR) and the immunhistochemistry (SP-assay). The results show that high mortality rate was recorded in MXC-exposed offspring due to infanticide. Exposures to either E or MXC did not change sex ratio at birth, but the litter size was smaller in the former group; On postnatal Day 21, male pups exposed to either E or MXC at early pregnant stage exhibited shorter AGD than the controls, with the change most pronounced after MXC treatments. AGD in female offspring was unaffected after MXC exposures, but E treatments produced longer AGD in the females than that recorded in the controls; early pregnant exposures to E or MXC also accelerated sexual maturation as significantly more females exhibited precocious vaginal opening at weaning; In males, MXC exposure during early pregnancy decreased serum LH and FSH, but not testosterone levels. The mRNA expression and protein expression of ERαon placenta villi of MXC or E groups were significantly higher than those in sesame oil groups (P<0.05), while those of ERβdidn't obviously changed. We drew the conclusion that exposures to MXC or E at preimplantation stages cause long term alteration of sexual development during weaning in offspring of both sexes; Also, MXC treatments retarded both growth and weight of both sexes of offspring, in comparison to controls. the protein expressions of ERαand ERβon placenta were correlation with the mRNA expressions of ERαand ERβ, and there was no obstruction on expressions of ERαand ERβ. The higher estrogen level in MXC or E group may be correlated to the higher expression of ERα.