| Objective To study the toxic effects of the exposed automobile exhaust on pregnant rats'placental structure and function and their offspring's gene and growth; in order to provide animal experimental evidence for the experiments about the toxic impact on reproductivity; raise people's awareness of the importance of toxicity of automobile exhaust; and enhance social consciousness about environmental protection.Methods Select 120-day-old Wistar rats, males and females were mated at the ratio of 2:1. Check the vaginal plug of females every morning; and the day that vaginal plug was checked was counted as the day 0 of pregnancy. 70 pregnant rats were randomly divided into 7 groups according to their weights, 3 groups were exposed to gasoline exhaust, 3 groups were exposed to diesel exhaust and set a normal control group as well. Automobile exhaust was mixed with fresh air by the proportion of 1:30, 1:20, 1:10. The pregnant rats were made to inhale the mixed air continually from 3rd to 19th days during pregnancy and 2hours per day. The ones inhaling the fresh air were made the control group. After 24h of the last exposure, made the pregnant rats completely anesthetized, and took out of the fetus by caesarean section, immediately weighed and counted the number of live birth, stillbirth, fetal absorption and the number of placental abruption. Fixed the taken placenta, stained HE and then observed the pathological changes of placenta under the microscope. Tested the level of placental alkaline phosphatase by immunohistochemical method. Made the fetal rats dead by decapitation, and took the liver to observe the frequencies of micronucleus of polychromatic erythrocyte by micronucleus testResults (1) The pregnant rats in control group and low-density group were not abnormal. The water and food consumption of pregnant rats in middle density group did not change significantly. There were some pregnant rats with vaginal bleeding. The coat color of pregnant rats was dull,and the pregnant rats were restless. In high density group, the food intake of pregnant rats reduced significantly. Their coat color was dull. The pregnant rats were lethargic. Their activities reduced and they were not sensitive to the outside world with vaginal bleeding badly. (2)The litter weight in control group was (69.96±6.71) g. The litter weight in gasoline exhaust low, middle and high-density groups were (66.03±8.69) g, (58.68±11.52) g, (50.34±9.45) g, respectively. The litter weight in middle-density group were significantly lower than control group (P <0.05). The litter weight in high-density group was significantly lower, which has statistical significance, compared with the other three groups. The litter weight in diesel exhaust low, middle and high density groups were (65.39±7.46) g, (55.87±10.03) g, (51.08±8.34) g, respectively. The litter weight in middle-density group was lower than control group. The litter weight in high-density group were significantly lower than control group and low-density group, these discrepancies are of statistical significance (P <0.05). Compared with other three groups, the number of placental abruption in high-density group increased, however, these differences are of no statistical significance (P> 0.05). The bad pregnancy outcomes (stillbirth, fetal absorption) increased and live births reduced in high-density group. (3)The difference in offspring's body weight(3.96±0.45)g and length(3.76±0.43)cm between control group, low-density group and middle-density group was not statistically significant (P> 0.05). The offspring's body weight and length in high-density gasoline exhausts group were significantly lower than the control group and low-density group, and the differences have no statistical significance(P <0.05). The offspring's body weight in high-density diesel exhaust group was significantly lower than the other three groups and the offspring's length was significantly shorter than the control group and low-density group. The differences were statistically significant (P <0.05).(4) The placental diameter (1.43±0.08) cm in high-density gasoline exhausts group was significantly longer than the other three groups (P <0.05).The differences of placental weight among these groups are of no statistical significance. But the placental weight in high-density group was higher than the other three groups. Placental factor of weight comparison had no significant difference among groups. The placental weight in high-density diesel exhaust group was significantly higher than the control group and low-density group (P <0.05). The differences of placental weight among these groups have statistical significance (P <0.05). Placental factor in high-density diesel exhaust group was significantly higher than control group, and the differences had statistical significance (P <0.05). (5) The pathological changes of placenta in gasoline exhaust and diesel exhaust groups were much the same. General observation: the color of placenta in control group was dark red. The fetal surface was covered by a transparent amnion, and the surface of that was smooth. The placenta in experimental groups had amaranth and dull appearance. Microscope observation: In control group, the villi were not swelled and the trophoblast cells which were in order had no significant proliferation. There were no significant changes of placental structure in low-density group. In middle-density group, placenta spongiosa trophoblast cells enlarged and the normal cells decreased and cell vacuolation increased. The labyrinth was full of blood. In the high-density group, placenta spongiosa trophoblast giant cells and cell vacuolation increased and the labyrinth trophoblast degenerated. The villi swelled and enlarged,with the intercellular gaps got narrow and the fibrous proteins around villi increased and accumulated. The structure was disordered and the shape of nuclei was irregular. The staining became deeper and the nucleolus disappeared.(6) Compared with the control group, the level of placental alkaline phosphatase in low and middle-density group did not change significantly (P> 0.05). Compared with the control group, the level of placental alkaline phosphatase in high concentration decreased significantly (P<0.05). (7) Compared with the control group, the frequencies of micronucleus in low-density group did not change significantly(P> 0.05). The frequencies of micronucleus in middle and high-density group increased significantly compared with the control group (P <0.01) and this discrepancy has statistical significance.Conclusion (1) Automobile exhaust has toxic effects onembryo. It can reduce the number of live births, and increase the number of stillbirth and fetal absorption. It can also increase the rate of placental abruption. (2) Automobile exhaust has a direct toxic effect on the placenta. It can cause the changes in structure and function of the placenta, and reduce the level of placental alkaline phosphatase. It is prejudicial to the exchange of nutrients and oxygen between maternal and fetal resulting in poor growth and development of offspring. (3) Automobile exhaust has genetic toxicity. It can get across the placental barrier and interfere with cell division. It can also trigger the chromosomal aberration and breakage and cause the damage of DNA .
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