Effect Of Low-concentration Tributyltin,Cadmium And Their Combination On The Hypothalamic-pituitary-thyroid Axis And Antioxidant Index In Cyprinus Carpio

Tributyltin(TBT)and cadium(Cd),which are typical endocrine disruptors of environment,can affect the development and endocrine metabolism of aquatic organisms and result in toxic effects to them.Several studies have reported the toxicity effect of Cd and TBT individually,but it is hard to see the studies about the combined effect of them on fish.Actually,the research for combined effect of TBT and Cd on fish is more meaningful for the toxicological evaluation in real environment.In this study,common carp(Cyprinus carpio),an important economic fish of fresh water,was exposed to low concentration Cd2+,TBT and their mixture for 1 day,2 days,4 days,8 days,16 days,32 days and 48 days.Morphometric indices,antioxidant responses,hematological parameters and the expression of genes about HPT axis were analyzed to determine the toxicity effect of Cd,TBT and their mixture on HPT axis as well as antioxidant responses.The main results of the experiments were as follows:1.Compared with control group,after 48 days exposure,the condition factor(CF)of TBT group was significant reduction while hepatosomatic index(HSI)of TBT group and the co-exposuret group were showed significantly increased.There was no significant effect of Cd on CF and HSI.As far as morphometric indices,the combined toxicity effect on fish is weaker than TBT alone for the long-term exposure.2.In the early stage exposure,the Cd,TBT and their mixture induced/inhibited the antioxidant indicator(SOD,CAT,MDA,GR and GSH)and hematological parameters(glucose and total protein)to a certain degree.While after the long-term exposure,the joint exposure of Cd and TBT,compared with Cd and TBT alone,had a weaker toxicity effect on antioxidant response(SOD,CAT,GR,GSH)and strengthened the toxicity effect on the levels of MDA,glucose and total protein.3.According to observation on thyroid tissue of common carp,serious damage was caused by Cd,TBT and their mixture after long-term exposure.It can lead to epithelial cell hyperplasia,the height of epithelial cell increasing and the size of thyroid follicle changing.And the thyroid colloid was even depleted in Cd or TBT alone exposed group.These results show that the exposure of Cd or TBT alone results more serious damage for thyroid tissue than the joint exposure.4.To research the Cd,TBT and their mixture toxicological effects for endocrine metabolism on common carp,we also measured hormone in plasma.The hormone of T3 and T4 were significantly changeds in all exposure groups.Especially in co-exposure group,the level of T3 and T4 were remarkly decreased at early 2 days exposure,on the whole,the interference effect on hormone levels caused by the joint exposure of Cd and TBT was much stronger than Cd or TBT exposure alone.5.Expression genes of the HPT axis were remarkly affected in all exposure groups to a certain degree.The expressions of genes related to HPT axis were different in different exposure groups as well as different exposure time.These results showed that Cd,TBT and their mixture are able to disturb the HPT axis through affecting the expression of the genes of HPT axis.