Effects Of Nonylphenol On Pancreatic Function In SD Rats

Objective:Nonylphenol(NP),a typical environmental endocrine disruptor which has estrogen effect,can disturb hormonal functions and inhibit stimulation of the endocrine system.NP has received increasing international attention due to its widespread existence.Nonylphenol is an important chemical raw material and intermediate,which is widely applied in surface active agents,antioxidants,lubricating oil additives,emulsifiers,printing and dyeing auxiliaries,and resin modifying agents.NP has been included in the list of 13 priority hazardous substances regulated by the European Union.NP production increases dramatically these years,which results that NP could be detected in most of the environmental water matrices,including drinking water.In addition,it was also reported that NP had relatively high adsorption coefficients for sediments and soils.For its lipophilic properties and long half-life,NP is ubiquitous and bioaccumulated in the food chain.NP could induce endocrine changes even at low concentrations,causing great disadvantage to human beings and other living creatures.Currently series of researches about reproductive toxicity and immune toxicity of nonylphenol were carried out.But the studies on pancreatic tissue injury induced by NP is still unclarified.So researches on the toxic effects of nonylphenol on pancreas and the mechanism of pancreatic injury caused by nonylphenol exposure are still needed to further determine.This paper aimed to investigate the toxic effect of pancreas with SD rats prepubertal subchronically exposure of NP.By combining with the changes of the related parameters of glucose,the effects on islet beta cells with NP exposure in vivo,the possible mechanisms of pancreatic injury induced by NP were discussed.Methods:32 healthy male SD rats were randomly divided into 4 groups(8 in each group)and gavaged with NP(0,20,60 and 180 mg/kg body weight)in corn oil for 90 consecutive days.The general condition and the body weight of each rat was daily recorded.The fasting glucose was detected regularly.After anesthesia,the abdominal aorta blood was collected to detect the levels of total protein,albumin,globulin,triglyceride,high-density and low-density lipoprotein,blood glucose respectively.The main organs were separated on the ice,weighing and calculating the corresponding organ coefficients,respectively.Oral glucose tolerance test was carried out ten days before the end of the experiment.The contents of insulin in serum and pancreatic tissue were determined by radioimmunoassay.The contents of hexokinase and hepatic glycogen were measured by ELISA.The fluorescence intensities were detected by the living cell work station to evaluate the levels of reactive oxygen species(ROS),intracellular free calcium concentration([Ca2+]i)and mitochondrial membrane potential(MMP)in islet cells.Results:(1)There was a significant difference in body weight between the NP exposed groups and control group.The weight gain of the rats in the 180mg/kg group was significantly lower than that of other three groups in the late period of exposure.During the exposure period,there was no significant difference in daily food intake between the exposed groups and the control group.The daily water intake was increased with the prolonged exposure time,and daily water intake of the 180mg/kg group increased significantly after 5-6 weeks exposed to NP.(2)The comparisons of organ coefficients showed that the pancreas,liver,spleen,kidney,adrenal gland,testis and brain tissue of 180mg/kg group:increased significantly.Compared with the control group,the pancreatic coefficient of the NP-treated groups significantly increased,while the abdominal fat coefficient decreased.(3)NP had no influences on total protein,albumin,glucose and low density in serum.With the increase of exposure dose,the serum triglyceride content increased first and then decreased,and the 180mg/kg group decreased significantly.The levels of high density lipoprotein decreased first and then increased,and the 60mg/kg exposed group significantly decreased.a downward trend in glucose was found,and the difference of glucose was statistically significant between the treated groups and the control group.(4)During the exposure period,no significant differences among the fasting blood glucose levels of the exposed groups and the control group was observed.(5)The results of oral glucose tolerance test showed that there was significant difference of the blood glucose level between 180mg/kg exposure group and control group at 30min.(6)With the increasing dose of NP,insulin levels in serum and pancreatic tissue increased first and then decreased,and the serum insulin levels in 180mg/kg NP treated group decreased significantly,while insulin levels in pancreas in 60mg/kg treated group increased significantly.(7)With the increase of exposure dose,the hepatic glycogen and serum hexokinase levels increased first and then decreased.In comparison with the control group,the hexokinase levels in 180mg/kg group significantly decreased and the hepatic glycogen level in 60mg/kg group significantly decreased.The content of insulin receptor in liver tissue decreased first and then increased,which in 20,60mg/kg exposed group significantly decreased.(8)Compared with the control group,the insulin resistance index(IR)significantly decreased in NP exposed groups,while the insulin sensitivity index(ISI)increased significantly.The insulin secretion index(HOMA-β)in 20,60mg/kg exposed groups significantly increased first,and then decreased to the level of the control group.(9)Compared with the control group,the levels of ROS in 60,180mg/kg group increased.Exposure of NP increased the[Ca2+]i levels and decreased the MMP levels significantly.Conclusion:(1)Subchronically exposed to nonylphenol slowed down the rats’weight gain and increased the daily water intake significantly,suggesting that nonylphenol could affect normal growth and development of rats.(2)Nonylphenol exposure caused organ coefficients of pancreatic,liver,spleen,kidney,adrenal gland,testis and brain increased significantly,suggesting that NP could affect the growth of the major organs of rats.The sensitivity of the pancreas was the highest,which indicates that pancreas is most susceptible to nonylphenol.(3)Only blood glucose,triglyceride,high density lipoprotein levels in blood biochemical indexes changed,suggesting that nonylphenol may not affect the ability of protein synthesis of liver.But NP affected the levels of lipid and glucose in serum,causing blood glucose and lipid level decreased.(4)With the increase of the dose of nonylphenol,the content of hexokinase and hepatic glycogen increased first and then decreased,suggesting that nonylphenol can affect the glycolysis of rat.(5)With the dose increase,the levels of insulin in serum and pancreatic tissue increased first and then decreased,indicating that low dose of nonylphenol can stimulate insulin synthesis and secretion and high dose of nonylphenol play restraining role.The trends of ISI,HOMA-β,and insulin receptor suggested that the injury of lower doses of nonylphenol on pancreatic function could still be recovered via self compensation to increase insulin secretion.However,high dose of nonylphenol could seriously damage pancreatic function to reduce the insulin synthesis and secretion.Only by increasing insulin sensitivity and insulin receptor content can the use of insulin increased and blood glucose levels can be regulated.(6)The levels of ROS,[Ca2+]i and MMP in islet cell were changed after NP exposure,demonstrating that NP could lead to the alteration of the structure of islet cells and apoptosis of islet cells via affecting oxidative stress,[Ca2+]i levels and MMP levels,which induces the damage effects of nonylphenol on pancreatic function.