Regulation Of Plasma Glucose Levels And GLUTs Expression By IGF-1,GH,FGF2 And PDGF-A In Hybrid Grouper(Epinephelus Fuscoguttatus ♀ ×Epinephelus Lanceolatus ♂)

The inability of hybrid grouper(Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂)to tolerate high levels of postprandial plasma glucose is associated with a low rate of glucose utilization by peripheral tissues.Glucose transporters(GLUTs)are one of the rate-limiting factors for glucose uptake in peripheral tissues.In the present study,fish were fed a high-carbohydrate diet(34% corn starch)for 2days and starved diets for 48 h,then four hormones were injected intraperitoneally to determine the regulation of insulin like growth factor 1(IGF-1),growth hormone(GH),fibroblast growth factor 2(FGF2)and platelet-derived growth factor A(PDGF-A)on glucose level and GLUT1,GLUT2 and GLUT4 expression in four important tissues(liver,skeletal muscle,adipose and brain).1.Regulation of plasma glucose levels and GLUT1,2 and 4 expression by IGF-1in hybrid grouperAfter feeding a high-carbohydrate diet for 2 days and starving for 48 hours,experimental fish(body weight: 77.5 ± 5.4 g)were selected and divided into two groups.Fish in the experimental group were injected with 0.5ml IGF-1(0.2 μg/g body weight)in enterocoelia,while the fish of control group were injected with the same dose of PBS buffer(0.01 mol/L).The results showed that 2 h post injection,in contrast with the PBS injected group,the plasma glucose in IGF-1 injected group was obviously decreased(P < 0.05),while the plasma endogenous IGF-1 concentration appeared the opposite tendency(P < 0.01).The m RNA and protein levels of GLUT1 and GLUT2 and protein levels of GLUT4 in liver were significantly increased compared with the control group(P < 0.05).Besides,the protein level of GLUT1 in adipose was significantly increased(P < 0.05).The gene expression levels of insulin-like growth factor 1 receptor a(IGF-1 Ra)and insulin-like growth factor 1receptor b(IGF-1 Rb)were significantly reduced(P < 0.05)in liver and muscle.In adipose,only gene expression level of IGF-1 Rb was decreased significantly(P <0.05).And gene expression level of insulin receptor(IRS)in liver increased significantly(P < 0.01).Overall,IGF-1 had a hypoglycemic effect on hybrid grouper fed a high-carbohydrate diet,and this was through up-regulating the protein levels of hepatic GLUT1,2 and 4 and adipose GLUT1.2.Regulation of plasma glucose levels and GLUT1,2 and 4 expression by GH in hybrid grouperAfter feeding a high-carbohydrate diet for 2 days and starving for 48 hours,experimental fish(body weight: 103.8 ± 5.8 g)were selected and divided into two groups.The experimental group were administrated intraperitoneally with GH at a dose of 0.5 μg/g body weight,and the control group were treated with PBS at a dose of 0.01 mol/L.Results showed that 2 h post injection,plasma glucose level was significantly(P < 0.05)elevated by the GH administration,while plasma endogenous GH concentration did not significantly(P > 0.05)respond to the GH.The m RNA levels of GLUT1,GLUT2 and GLUT4 in liver,muscle,adipose and brain had no significant change.But protein expression level of hepatic GLUT1 was significantly decreased(P < 0.05)and hepatic GLUT2 was apparently elevated in GH administrated group(P < 0.05),the opposite tendency was observed in adipose.Increased gene expression level of hepatic growth hormone receptor 2(GHR2)was obviously observed(P < 0.01).Besides,after GH administration,it was apparent that m RNA level of hepatic IGF-1 was elevated(P < 0.01).In the whole,GH administration can increase the plasma glucose level of hybrid grouper fed a high-carbohydrate diet mainly by down-regulating the protein expression of hepatic GLUT1 and adipose GLUT2.3.Regulation of plasma glucose levels and GLUT1,2 and 4 expression by FGF2 and PDGF-A in hybrid grouperAfter feeding a high-carbohydrate diet for 2 days and starving for 48 hours,experimental fish(body weight: 56.0 ± 2.3 g)were selected and divided into two groups(n=12).The experimental group were administrated intraperitoneally with0.5m L FGF2 at a dose of 0.5 μg/g body weigt and the other group was treated with the Tris buffer(0.5m L).Samples were taken 2 hours later for analysis.In the experiment of PDGF-A,experimental fish(body weight: 46.1 ± 1.9 g)were divided into two groups(n=12).The experimental group was intraperitoneally injected with0.5ml PDGF-A(0.1 μg/g body weight),another group was administrated with sterile water in the equal volume.Samples were also taken for analysis after 2h.Results showed that 2 h post injection,plasma glucose level of the FGF2 group was significantly lower than that of the control group(P < 0.01),and plasma endogenous FGF2 level showed an opposite variation trend.After the FGF2 administration,the m RNA and protein levels of GLUT1 in liver increased significantly(P < 0.05),and the gene expression level of fibroblast growth factor 2 receptor 2(FGFR2)in liver was ascended obviously(P < 0.05)due to the FGF2 administration.No apparent variation in plasma glucose concentration was observed after the PDGF-A administration(P > 0.05).Generally,FGF2 can increase the protein expression of GLUT1 in liver to reduce plasma glucose level of hybrid grouper fed a high-carbohydrate diet.However,PDGF-A had no significant effect on regulating the plasma glucose level of hybrid grouper 2h post the injection.