Effect Of Alpha-ketoglutarate On Grass Carp Under The Chronic Ammonia Exposure

In this experiment,grass carp(Ctenopharyngodon idellus)was selected to investigate the effects of dietary supplementation of?-KG on chronic ammonia exposure.270 healthy grass carps(average initial weight,24.79±0.11 g)were randomly assigned to three groups:C,exposed to tap water and fed basic diet;T1,exposed to 18.37 mg/L ammonia water and fed basic diet;T2,exposed to 18.37 mg/L ammona water and fed 0.75%?-KG added diet.Each group had 3 replicates and each replicated 30 fish.The experiment lasted for 42 days and samples were taken on day 1,7 and 42 respectinely.The results are as follows:On day 1,the brain and plasma ammonia content in T1 group was significantly highter than that in control group under ammonia exposure(P<0.05),and the addition of?-KG could effectively relieve this kind of increase of ammonia content in brain and plasma(P<0.05).In addition,the content of glutamine in plasma and brain of T1 group was also significantly highter than that of control group(P<0.05),and this increase was accompanied by a significant decrease in glutamic acid content(P<0.05).This indicates that the mechanism of detoxification of grass carp by synthesizing glutamine under ammonia exposure has been initiated,and the supply of glutamic acid in the brain does not fully satisfy the requirement of glutamine synthesis.However,the content of glutamine in the brain of T2 group was significantly higher than that of T1 group(P<0.05),and there was no significant decrease of glutamate in the brain,indicating that the addition of?-KG can supplement glutamic acid in the brain of grass carp timely and provide sufficient substrate for the synthesis of glutamine.Besides,?-KG can effectively reduce the decrease of aspartate content in brain caused by ammonia exposure(day 1)(P<0.05),and significantly increase histidine in the brain(P<0.05),which is favorable to the maintenance of energy metabolism in brain and protection of the nervous system in grass carp.Under ammonia exposure,plasma albumin(day 1)and proline content(day 42)in T2 group were significantly higher than those in T1 group(P<0.05).In addition,the expression of SOD and GPX mRNA in the intestine was significantly lower in the T1 group than in the control group(P<0.05),and the expression of HSP70 mRNA in the grass carp kidney in the T1 group was not significantly different from that in the control group.However,the addition of?-KG can effectively reduce the decrease of SOD and GPX mRNA expression in the intestine and up-regulate the expression of HSP70 mRNA in grass carp kidney(P<0.05).This indicates that dietary?-KG has positive effect on the antioxidation and free radical scavenging of grass carp under ammonia exposre.On day 1,urea contetn in the liver of grass carp of T1 group was no significantly different grom that of the control group under amonia exposure,and the addition of?-KG increase the content of urea of grass carp.On day 7 and 42,the urea in liver of T1 group was significantly lower than that of the control group(P<0.05),while the addition of?-KG could effectively alleviate the phenomenon(P<0.05).Besides,?-KG can effectively reduce the decrease of AST and ALT activity in grass carp plasma of group T2(day 7),and significantly increase the glycogen content in liver of group T2(day 42)(P<0.05).This shows that?-KG can increase the energy reserves of grass carp under the ammonia exposure and increase the urea synthesis in vivo,which is beneficial to the detoxification of the body.On day 1,the Rhag mRNA expression in the grass carp kidney of T1 group was significantly increased under ammonia exposure(P<0.05),while the Rhag mRNA expression in T2 group was significantly lower than that in T1 group(P<0.05).On day 7,the activities of gill Na~+/K~+-ATPase in grass carp were significantly higher in T1 and T2 group(P<0.05),and the activities of Na~+/K~+-ATPase in T2 grass carp were significantly higher than those in T1 group(P<0.05).In addition,the expression of Rhcg1 mRNA in grass carp kidney of T2 group was significantly lower than that of T1 group(P<0.05).On day 42,the expression of Rhag and Rhcg1mRNA in T1 and T2 groups increased significantly(P<0.05).This results showed that grass carp can relieve ammonia exposure to some extent through the transport of ammonia by Rhag and Rhcg2,and?-KG can increase the activity of Na~+/K~+-ATPase in grass carp under ammonia exposure and promote ammonia transport in the body.