| Rainbow trout(Oncorhynchus mykiss)is a cold-water species of salmonid,which is cultivated as the main variety in China;the high temperature is an important threat to its aquaculture in summer.In this study,the experimental fish belonged to full-sibling inbreeding individuals.In order to understand its heat stress response(HSR)degree and mechanism,the study took slow heat-up method which was considered to simulate natural heat-up process in cage culture water,and then selected 10 fish to sample at 18?,21?,23?,24?,25? and 26°C,respectively,to investigate the changes of some main biochemical parameters as well as GRP78 mRNA expression in different tissues(liver,mid-kidney,heart,spleen and brain).The results showed:1.During heat stress,rainbow trout spleen respiratory burst(RB)activity increased significantly at 21°C(P<0.05);total superoxide dismutase(T-SOD)activity at 18°C was significantly higher than that at other temperature points(P<0.05);malondialdehyde(MDA)content increased significantly at 23°C(P<0.05),after 23°C,decreased gradually;alkaline phosphatase(AKP)activity maintained the highest level at 18°C,significantly decreased at 21°C(P<0.05);lactate dehydrogenase(LDH)activity at 21? was significantly higher than that at other temperature points(P<0.05);alanine transaminase(ALT)and aspartase aminotransferase(AST)activity at 25? and 26°C was significantly higher than that at other temperature points(P<0.05),respectively;the difference of total bilirubin(T-Bill)content was not significant in the heat-up process of 18~23°C(P>0.05),increased significantly at 24°C(P<0.05),the content of it at 25? and 26°C was 9.6 fold and 21.2 fold as much as that at 18°C(P<0.05),respectively;the difference of creatine kinase(CK)activity was not significant in the heat-up process of 21~25°C(P>0.05),increased significantly at 26°C(P<0.05);lysozyme(LZM)activity peaked at 24°C,at 25? and 26°C was significantly lower than that at other temperature points(P<0.05),respectively;complement 3(C3)content increased gradually;the differences of serum proteins content which include total protein(TP),albumin(ALB),globulin(GLO)were all not significant(P>0.05);the concentrations of calcium(Ca),magnesium(Mg)and phosphate(P)decreased with water temperature rising,and decreased significantly at 21°C(P<0.05),respectively;the glucose(GLU)concentration decreased first and then increased,maintained the highest level at 18°C,significantly decreased at 21°C(P<0.05),the concentration at 25°C and 26°C was significantly higher than that at 24°C(P<0.05),but significantly lower than that at 18°C(P<0.05).The above results indicated that heat stress response occurred and the body changes from normal state into adaptive regulation state at 21°C;24°C was a “key hightemperature point”,the point was a critical point that the body changes from adaptive regulation state to “injury”,the tissues of organism at 25°C and 26°C were damaged severely;the point of 26°C maybe was upper limit of thermal tolerance to temperatures.2.During heat stress,spleen GRP78 mRNA had the lowest expression level and heart had relatively high basal expression level.In liver and mid-kidney,GRP78 mRNA expression continuously increased.In mid-kidney,the expression level at 23? was significantly up-regulated(P<0.05);in liver,the expression level at 25? significantly up-regulated(P<0.05),and liver had largest significant increases across all the tissues;in heart,the expression kept at an even level in the heat-up process of 18~23?(P>0.05),up-regulated significantly at 25°C and 26?(P<0.05);brain had relatively low expression level in the heat-up process of 18~23?,the expression upregulated significantly at 25°C(P<0.05),and then showed a decrease trend at 26°C.It suggested that the mid-kidney is the most sensitive tissue to heat stress;the liver may play a greater role in the protection of heat stress and the body's tolerance to heat is mainly related to the liver damage;the heat tolerance of heart is stronger than that of other tissues;The above results indicated that the significant decrease of Ca,Mg,P and GLU content at 21?,with heat stress commonly induced tissues GRP78 mRNA transcription,and further synthetic GRP78 to protect tissues and cell from heat stress damage(except spleen).After 24?,with the Ca,Mg,P content decreasing and heat stress stronger and stronger,tissues were damaged more and more severely,body needed too much GRP78 to maintain homeostasis and repair heat stress damage.Thus,it led to the GRP78 mRNA expression significantly increased. |
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