Effects of glucose administration on glucose and lipid metabolism in two strains of gibel carp (Carassius gibelio)

We compared the glucose clearance ability of gibel carp CAS III (A strain) with gibel carp Dongting (DT strain). A previous study suggested that these two strains responded to insulin differently. As insulin plays an important role in glucose utilization, we hypothesized that the ability to eliminate excess glucose after a glucose load would differ between A strain and DT strain. To test this hypothesis, fasted specimens of both strains of gibel carp were injected with glucose. As expected, glucose induced hyperglycemia in both A strain and DT strain. In both strains, mRNA levels of the glycolytic enzyme 6-phosphofructokinase (6PFK) increased in the white skeletal muscle 8 h post-injection, while expression levels of glucose-6-phosphatase (G6Pase), fructose 1,6-bisphosphatase (FBPase), and phosphoenolpyruvate carboxykinase (PEPCK) decreased in the liver 8 h post-injection. In the DT strain, both GLUT4 expression and muscular glycolytic processes increased, as reflected by elevated hexokinase 2 (HK2) and pyruvate kinase (PK) mRNA expression levels. The DT strain also returned to basal glycemia more quickly than the A strain (within 6 h versus more than 12 h). The glycogen concentration in the liver of the DT strain was higher than that of the A strain, indicating that the DT strain was better able to store glucose as glycogen than the A strain. Overall, the DT strain was better able to clear excess blood glucose after the glucose tolerance test than the A strain.