| Organotin compounds are important organometallic compounds in industry. They have been widely used as stabilizers in polyvinyl chloride (PVC), antifouling paints, pesticides and fungicides. About 70 percent of organotin compounds are as stabilizers in PVC. Since that tributyltin can induce imposex in marine life was found, organotin pollution has aroused great concern. A series of investigations have been made in many countries, and then many legislative restrictions were drawn up to restrict the production and applications of organotin compounds. Dibutyltin dilaurate (DBTD) is a stabilizer which is widely used in PVC transparent products. Though the toxicity of DBTD is a little less than that of TBT, studies have demonstrated that DBTD had adverse effects on immune system and nervous system. Our laboratory had found that after new born Wistar rats were peritoneal injected with DBTD for five days, their testosterone increased on 30th and 90th day and the weight of testis dramatically increased. This suggested that DBTD had affected the reproductive development of male rats. In this study, in order to explore the reproduction toxicity of DBTD and its mechanism of action, we treated pregnant Wistar rats with various dose DBTD and detected the viscera coefficient, the activities of enzymes of testis, sperm count in epididymis and hormone concentrations.ObjectiveIn order to explore the reproduction toxicity of DBTD and its mechanism of action, then to provide experimental and theoretical evidence for control of DBTD pollution, we treated the pregnant Wistar rats with DBTD, and then studied the reproductivesystem of mature male offspring.MethodsVirgin female rats in proestrus were mated overnight with males at the ration of 2:1. Successful mating was indicated by the presence of pessum in the vagina at 8:00-9:00 on the following morning (day 0 of pregnancy). Pregnant rats were randomly divided into four groups (control, 10, 20 and 30 mg/kg DBTD) with 4 animals per dose group. DBTD was administered daily from days 12-20 of gestation. The volume of DBTD solution administered was adjusted to 5ml/kg of body weight. Animals were kept with a constant light cycle (12h of light, 12h of darkness), relative humidity and optimal temperature. They had free access to food and tap water. The offspring rats were weaned on postnatal day (PND) 21, and divided based on sexuality. On PND70, 10 male mature rats randomly selected from each group were killed by decapitation after weighed and trunk blood (about 4-5ml) was collected. Immediately after collection, the blood was centrifuged at 3000g.min-1 for 10 min Aliquots of the supernatant were collected in microcentrifuge tubes and stored at -20℃for measurement of the hormones. Separate testis and epididymis for measurement of the viscera coefficient. Two testes selected randomly from two rats in every group were immersed in neutral formalin for pathological section. Other testes were stored at -80℃for determinations of enzyme activities and testosterone, epididymis at -20℃for sperm count.Results1 The effects of DBTD on the pregnant rats and fetusesThe pregnant rats in every group were normal and no poisonous symptom was observed. There were no significant differences in the body weight gain of pregnant rats from days 12-20 of gestation, litter size and sex ratio of fetuses between the trial and the control group.2 The effect of DBTD on the male offspring rats growthThe male rats in every group were normal and no poisonous symptom was observed. Compared with the control group, every treated group showed no distinct difference in body weight in the male offspring rats. 3 The effect of DBTD on sexual organs and sperm count in the male offspring ratsAppearances of the epididymis and testis were not significantly different. There were no distinct differences in epididymis weight and the viscera coefficient of epididymis between the trial and the control group. The testis weight and viscera coefficient of testis in 30mg/kg group increased significantly compared with the control group (P<0.01, P<0.05) , while sperm counts in 20 and 30mg/kg groups increased significantly (P<0.05, P<0.01) .4 The effect of DBTD on the enzyme activities in testis in the male offspring ratsTendency of first increase then decrease in activities of succinate dehydrogenase (SDH), acid phosphatase (ACP) and lactate dehydrogenase (LDH) can be observed in testis. The activities of ACP in 10 and 20mg/kg groups, the activities of LDH in 10mg/kg group and the concentration of nitric oxide (NO) in 30mg/kg group were all significantly increased compared with the control group (P<0.05) , while the activities of SDH and nitric oxide synthase (NOS) were not.5 The effects of DBTD on levels of the hormone in serum and testis in the male offspring ratsThere were no differences in luteinizing hormone (LH) and follicle stimulating hormone (FSH) between the trial and the control. Serum level of testosterone in 30mg/kg increased significantly (P<0.05 ), while testosterone in testis in every group increased significantly (P<0.05, P<0.05 , P<0.01) .6 The pathological change in testis in male offspring ratsThere was no distinct change between the trail and the control group.ConclusionsExposure to DBTD within the concentration in this experiment from days 12-20 of gestation can affect the synthesis and metabolism of testosterone in the male offspring rats. That the weight of testis and sperm counts increased may be due to the increase of testosterone in serum and testis, which was not regulated by hypothalamic-pituitary-testicular axis. With the increase of sperm counts, the compensation in the enzyme activities in testis appeared, but no pathological change.
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