Repeated Exposures To Low-level OPs Chlorpyrifos Induced Reproductive Toxicity And Its Mechanisms In Male Rats

Organophosphorus insecticides (OPs) are the most widely used pesticides in the control of insects around the home and in agriculture practice in the world. Because of their relatively short residual period and low cost, broad-spectrum in controlling insecticide, which are easy to be accepted by farmer. OPs residue is the most outstanding issue in pesticide residue in food agriculture, homes, gardens, and in veterinary practice. The widly use of OPs around the world continues to produce detectable levels of OPs in the environment, thereby posing an ongoing risk for low-level exposure. Chronic exposure to OPs, especially the low-level envireonmental exposure requires more attention. Though, epidemiology study show that those may have disordered reproductive who touch with OPs for a long time. Males'reproductive ability reduce obviously in which region OPs pollution seriously, main representation changes are sperm quality (normal spermatozoa, sperm counts and motile), reduced sperm fertilization ability and infertility. Repeated exposure to low-level OPs can result in abnormalities of sperm chromatin . Compared with normal, 82% workers of those who had the experiences of occupational exposure had higher percent inmature sperms . However, the mechanism of OPs caused male reproductive toxicity is not clearly.Chlorpyrifos (O,O'-dithyl-O-3,5,6-trichloro-2-pyrydyl phosphorothionate, CPF) is one of the most widely used, broad-spectrum, efficiency and low-toxic OPs throughout the world. It is still one of the most widely used insecticides all over the word. Since the elimination of acephatemet, methyl parathion, parathion, monocrotophos and phosphamidon in agriculture in 2007, CPF had been recommend as the low-toxic OPs replacement in agriculture in China. These days, CPF has become one of the major pesticides detected in farm products in China. It is very important to study repeated exposure to low-level CPF caused reproductive function. Chronic exposures to CPF, especially at the dosages without eliciting any systemic toxicity, require greater attention and further study.The subject is divided into two parts; the first part study indicated that repeated exposures to low dose of CPF may induce the male reproductive toxicity, In the present study, male Wistar rats were administrated CPF through intragastric for 16 consecutive weeks to evaluate the reproductive impacts of CPF at the subthreshold doses(1, 5 and 10 mg/kg and equal volumes of olive oil vehicle) daily. Doses that do not elicit any other signs of OPs toxicity, e.g. excessive salivation, urination, defecation, muscle fasiculations and so on. The reproductive changes were studied and the mechanisam of chronic low-level CPF exposure was explored. After exposure 16 consecutive weeks,testicular and epididymal viscera weight and organ coefficients were calculated, testicular histopathologic changes were evaluated by hematoxylin and eosin (HE) staining, the sperm abnormality,total sperm count and the sperm mobility were examined. The activities of alkaline phosphatase(AKP),acid phosphatas(ACP) ,lactate dehydrogenase(LDH) andγ-glutamyltransferase (γ-GT) were measured. The second part though the germ cell apoptosis of testicular were evaluated with TUNEL,immunohistochemistry and immunofluorescence assay, receptor expression of correlation hormone accommodation and the key enzymes in testosterone synthesis. To investigate the effect of Chlorpyrifos on reproductive toxicity in male rats and explore the possible mechanisms.There were no effects on weight changes and food consumption detected during the 16 weeks exposures to CPF, and the daily dosages of 1.0, 5.0 and 10.0 mg/kg CPF for 16 weeks did not produce overt signs of cholinergic toxicity,such as excessive salivation, urination, defecation, muscle fasiculations etc. The histopathological examine showed that CPF can lead to atrophia of the contorted seminiferous tubules, the amount of spermatogenic cells decreased,and it was occure with degeneration, defluxion,dropsy. The amount of spermatogenic cells decreased in seminiferous tubules which have increased ability though BrdU essay. The total sperm counts, the percentage of sperm mobility decreased and the sperm abnormality increased in CPF treated rats ,and lead to injury of testicular follicle. There were significant increase LH,decrease T and decreases in the activities of AKP andγ-GT in the CPF treated rats i ,which had correlations with the decrease of sperm quality..After exposures to low-level CPF, the TUNEL results showed the significant apoptosis of spermatogenic cells.The expression of BAX,Bcl-2,Fas,FasL and Caspase-3 in testis were up-regulated.At last,the antioxygen balance was broken down,which destroyed the normal dynamic equilibrium of apoptosis of spermatogenic cell to sustain normal spermatogenesis process.There was another possible mechanism to cause male reproductive toxicity,with stimulating hypothalamic -pituitary-testicular axis. The level of increasing LH and decreasing T in serum, expression of hormone receptor,cholesterol transmembrane transport regulatory factor and key enzymes in testosterone synthesis decreased in the treated groups compared the control. Hormone receptor impairment and the inhibition of key enzymes in testosterone synthesis.The current study demonstrated adverse effects of chloropyrifos exposure on male rats outcome though hormones changed with reproductive toxicity effects on testis hormone receptor and testosterone synthesis key enzymes may be another mechanism to cause male reproductive toxicity.Based on the above findings,the study indicated that repeated exposures to low dose of CPF may induce the male reproductive toxicity, though the death receptor and mitochondrion path regulated germ cell apoptosis,reduced germ cells,inhibiation the progress of germ production may be one of the mechanism.CPF exposure on male rats outcome with reproductive toxicity effects on testis hormone receptor and testosterone synthesis key enzymes ,with stimulating hypothalamic -pituitary-testicular axis may be another mechanism. It has great significance to study repeated exposure to low-level CPF contribution to reproductive toxicity mechanism, provide scientific data for the health risk assessment of OP pesticides.