The variation of serum glucose, hepatic glycogen content and expression of glucose metabolism-related genes in hybrid grouper (female Epinephelus fuscoguttatus × male Epinephelus lanceolatus) in response to intraperitoneal insulin infusion

The present study was conducted to investigate the effects of insulin on serum glucose, hepatic glycogen content and expression of glucose metabolism-related genes in hybrid grouper. Triplicate groups of five fish were sampled at the 0, 1, 3, 6, 12, 24 or 48-h time point post-bovine insulin (5 μg 100/g fish body mass) injection. A significant decrease of serum glucose content was observed along with the depletion of hepatic glycogen content at the 12-h time point following insulin injection. Hepatic gene expression analysis revealed that the infusion of insulin significantly increased the expression of glucose transporters (GLUTs), GLUT1b and GLUT2. The transcription of gluconeogenesis-related genes, fructose-1,6-bisphosphatase 1a and glucose-6-phosphatase a catalytic subunit tandem duplicate 2, was significantly decreased at the 12-h time point, while the expression of glycolysis-related genes, phosphofructokinase liver b and pyruvate kinase L/R, was significantly up-regulated at the 24-h time point post-insulin injection. Meanwhile, the expression of glucokinase significantly increased immediately following insulin administration. The expression of glycogen synthase liver type significantly decreased at the 12-h time point, while the expression of glycogen phosphorylase liver type was significantly elevated at the 24-h time point following insulin injection. These results suggested that insulin could affect glucose metabolism through regulating gluconeogenesis, glycolysis and glycogen metabolism at the transcriptional level.