A Comparative Study On Glucose Tolerance Ability In Different Fish Species

The experiment was conducted to determine the effect of three fish species on biochemical indices in plasma and liver/muscle glycogen content.In the meanwhile,the experiment was conducted to determine the effect of dietary carbohydrate levels(CBH)and starvation on the growth performance,biochemical indices in plasma and liver/muscle glycogen content of the grouper.The sequences of gGLUT1 have been cloned and analyzed.The aim of this article was to perform a glucose tolerance test in different fish species in order to know the cause of the high glucose levels for fish nutrition.The content of studies and results are as followings:1.In this experment,three fish species(Oreochromis niloticus,C_O 201±7 g;Trachinotus ovatus,210±13 g,C_T;Rachycentron canadum,C_R,220±12 g)were allotted to three groups,14 fish in each treatment were selected and injected with 300 mg glucose per l00 g body weight for glucose tolerance test(GTT)after the end of experiment and blood sampling at 0,1,3,6,12,24,48 h.The results showed that plasma glucose levels were significant increased in 1h and then decreased within 12 h in C_O and C_T(P<0.05).Plasma glucose levels in C_R increased in 3h and then returned to the initial values within 6h after being injected.Plasma insulin content in C_O and C_R were increased at 3 h and then decreased,but insulin level of C_T group significant decreased within 1h and then increased(P<0.05).Glycogen content in liver and plasma triglyceride levels were significantly increased at 3 h?6 h after injection in C_O and C_T(P<0.05).Plasma triglyceride levels in C_R decreased in 1h and then increased at 3 h after being injected.The results of this study indicate that the C_O group glucose tolerance ability is the strongest of three fish species;but the C_R group is the lowest.2.The experiment was conducted to determine the effect of dietary carbohydrate levels(CBH)and starvation on the growth performance,biochemical indices in plasma and liver/muscle glycogen content of the grouper.Total 300 fish were randomly distributed into5 treatments which triplicate groups of 20 fish(initial weight:35±0.28g)in each treatment.Three isonitrogenous and isoenergetic diet were formulated containing three carbohydrate levels(35%C_H,21%C_M,7%C_L),combined with starvation group(S)and refeeding group(R,starve 4W+refeeding 4W,21%carbohydrate in the diet).Experiment last 8W.14 fish in each treatment were selected and injected with 300 mg glucose per l00 g body weight for glucose tolerance test(GTT)after the end of experiment and blood sampling at 0,1,3,6,12,24,48 h.The results showed that the weight gain and specific growth rate increased with dietary carbohydrate level increased but no significant difference(P>0.05),and the feed coefficient rate of C_L group was the highest(P<0.05).Plasma glucose levels significant increased in 1-3h and then decreased in C_H,C_M and C_L(P<0.05).Plasma glucose levels in C_M returned to the initial values within 6h after being injected and initial level of plasma glucose content in C_H and C_L were obtained within 12 h.Plasma insulin content in C_H,C_M and C_L were decreased at 1h and then increased,but insulin level of C_L group significant decreased at 3h(P<0.05).Glycogen content in liver and plasma triglyceride levels were significantly increased in C_H,C_M and C_L within 1h after injection(P<0.05).C_M,S and R group present persistent hyperglycemia after injected and C_M restore initial level quickly within 6h.Plasma insulin levels of C_M and R group significant decreased within 1h(P<0.05),but that of R group continued to rise within 12 h.Plasma triglyceride levels of C_M were higher than that of S and R groups within 0 to 6 h(P<0.05).The results of GTT indicate that proper carbohydrate level in diet(21%)and continuous feeding can significantly improve glucose tolerance of the grouper.3.The GLUT1 cDNA was acquired using rapid amplification of the cDNA ends(RACE)and RT-PCR(GenBank Accession No:JQ623903),and named gGLUT1.gGLUT1 c DNA sequence was analysed using bioinformatics,The GLUT1 cDNA is 2126 bp,it contains 223 bp 3?-UTR,437 bp 5?-UTR and 1,476 bp ORF.The ORF contains 491 amino acids.RT-PCR analysis showed that GLUT1 was exrpessed in heart,muscle,liver,intestine and stomache.The mRNA of GLUT1 was most highly expressed in heart.This study also suggested that GLUT1 mRNA level in heart had no significant chang within 6 h(P>0.05).GLUT1 mRNA level in muscle,brain and live were decreased slowly within 6 h;but it started raising from 3 h to a peak value after injection in muscle,which was attained the peak at 12 h after be injeced(P<0.05).The results from this study showed that metabolic adjustments caused by glucose injection can be concerned with the delay action of GLUT1,and the delay of GLUT1 mRNA levels were the important reason on glucose intolerant.