Study Of Reproductive Toxicity In Male Rats Exposed To DBP And B[a]P

Along with the development of human society and expanding process scale of industry and agriculture, more and more pollutants were discharged into environment and increased the contamination of organic pollutants, especial persistant organic pollutants (POPs). The POPs are chemical substances that persist in the environment, bioaccumulate through the food web, and pose a risk of causing adverse effects to human health. Because the POPs are mixtured in the environment and affect the human health in a combination pattern, it is very important to study the combination toxicity of the POPs. Our previous studies show that phthalates and polycyclic aromatic hydrocarbon (PAHs) are the most popular pollutants in surface water. Both of them have been showed to possess repeoductive toxicity, which can lead to the atrophy of testis, loss of spermatocyte and decreasing of T concentration. But most of previous studies are carried on by using single compounds at high dosage and the results can't reflect the adverse effect exposure to mixture pollutants at low dosage. In the present study we chose DBP and B[a]P as the model chemicals of organic pollutants in surface water, and test the single or combined reproductive toxicity of them on male rats and the mechanism also be investigated by using molecular biological techniques.The main results of this study are as follows:1. In this study, the growth and general appearance of the animals treated with DBP and B[a]P were normal throughout the experiment. No obvious lesion were observed in major organs, including testis and epididymis. The coefficient of liver were increased slightly. The observation indicated that liver were sensitive for toxic effect.2. The changes of histomorphology in the groups treated with DBP were insignificant, but the atrophy seminiferous tubules and vacuoles degeneration of seminiferous epithelium were observed in the groups treated with B[a]P at both dosages. The testicular ultrastructure observed by electronic microscope showed that both of DBP and B[a]P caused mitochondrion dropsy and endoplasmic reticulum expanding in testicular cells. The adverse effect of combined groups were similar with B[a]P groups. The toxicity in combined groups were not stronger than that of DBP or B[a]P groups alone.3. The result of sperm evaluation showed that the sperm amounts were increased in the early period of the experiment in the two groups treated with DBP and B[a]P. The tendency in combined treatment groups were similar with DBP groups. But in the late period of experiments, the stimulation effect were disappeared and the sperm amounts were decreased significantly in combined treatment groups of low dosage. Comparaed with control grouop, the percentages of abnormal sperm were increased in B[a]P groups at the 3rd month and in combined treatment group of high dosage at the 1st and 3rd months, respectively.4. Both of DBP and B[a]P can stimulate the secretion of Testosterone and this effect in B[a]P groups were stronger than that of DBP groups. The stimulation effect in combined treatment groups were weaker than that of B[a]P group.5. The expression of androgen-binding protein(ABP)and transferring(Tf) were affected by DBP and B[a]P. The ABP mRNA level were inhibited at the 1st month, then increased from the 2nd month to 3rd month in each treatment group. The Tf mRNA level were inhibited at the 1st and 2nd month while increased at the 3rd month in each treatment group. The similar tendency were observed in combined treatment groups.6. The effect of DBP and B[a]P on the antioxidant system in testis were insignificant. The activity of SOD in B[a]P groups were decreased while the activity of CAT in these groups were increased. There were no significant difference in the activity of SOD,CAT and GSH-PX between DBP groups and control group. In combined treatment groups, the activity of SOD and GSH-PX were partly inhibited but the activity of CAT were stimulated. The amount of MDA were not increased significantly between treatment groups and control. This result suggested that the antioxidant systems in testis were in a compensation state and no obviously oxidative damages were showed.7. Cell proliferation were inhibited respectively in low dosage groups of DBP and B[a]P. In high dosage groups of DBP and B[a]P, a transitory increasing of cell proliferation were observed, but these phenomenon disappeared along with prolongation of the treatment time. Compared with control group, cell proliferation were also significantly decreased in combined treatment groups, but the differences were not significantly between the combined treatment groups and DBP or B[a]P groups alone.8. There were no significant differences for the spermatogenic cell apoptosis between control and DBP groups. In B[a]P groups, the spermatogenic cell apoptosis were significantly elevated, which is reflected that the reproductive toxicity of B[a]P is more severe than DBP. Spermatogenic cell apoptosis were also increased in combined treatment groups and showed the similar effect of B[a]P.9. The expression of ERK1/2, phospho-ERK1/2, JNK and phospho-JNK in testis were determined by Western blot. The results showed that the total ERK1/2 protein levels were not affected in all treatment groups at three time points. Phospho-ERK1/2 (p-ERK1/2) levels were markedly decreased after exposure to 50mg/kg.bw DBP and 5mg/kg.bw B[a]P. This inhibited effect were also occurred in combined treatment group of low dosage at the 2nd month and high dosage at the 3rd month, repectively. The data suggested that both DBP and B[a]P induced expression of ERK1/2 phosphorylated protein, but the time point of the inhibited effect is different in the groups of two dosages.10. The expression of both total JNK and phospho-JNK were induced in low dosage of DBP and B[a]P group. Only phosphorylation levels of JNK were enhanced in high dosage of DBP and B[a]P group. In combined treatment groups, no significant changes in total JNK levels occurred but phosphor-JNK levels were markedly elevated at the 3rd month. There were no significant differences between combined treatment groups and DBP or B[a]P groups. These results indicated that DBP and B[a]P can induce both total and phosphorylated JNK levels.Conclusion:Both DBP and B[a]P can cause certain adverse effect on the male reproductive system at the dosages of our experiment and the adverse effect were not appeared only as inhibited effect. Biphasis effect were observed in some results, such as Testerone content, expression of ABP and Tf mRNA. The biphasis effect showed exciting effect at early stage of the treatment and then inhibited along with the increasing of dosage. Because the regulation of spermatogenesis is a complex and non-unidirectional process, any factors which can excite or inhibit the cell functions may affect the spermatogenesis. The results of this study showed that the toxicity of B[a]P is more severe than that of DBP. The toxicity can be reflected from the histopathology observation, ratio of abnormal sperms and spermatogenic cell apoptosis. In present study, most damage effect treated by combination of DBP and B[a]P were similar to that of B[a]P and enhanced effect of the toxicity were not observed. This result suggest that some antagonistic effects were generated after combined DBP with B[a]P. Considering that the combined effect is complicated, the mechanism of this effect should be probed in the further research.