Transcriptional regulation of the AMP-activated protein kinase and glycolipid metabolism-related genes by insulin and glucagon in blunt snout bream (Megalobrama amblycephala): A comparative study

Abstract

In this study, the effects of insulin and glucagon administration on the glycolipid metabolism of blunt snout bream (Megalobrama amblycephala) were investigated. Fish (average weight 49.5 ± 0.8 g) were intraperitoneally injected with a 0.9% saline solution, a bovine insulin (0.052 mg/kg body weight) and a bovine glucagon (0.075 mg/kg body weight), respectively. Then, samples were taken at 0, 1, 2, 4, 8 and 12 h post injection. The results showed that insulin load induced a significant decrease of plasma glucose level with the minimum observed at 1 h, while the opposite was true after glucagon injection (the highest value was attained at 4 h). After that, plasma glucose levels gradually returned to the normal value. Plasma triglycerides (TG) levels significantly declined during the first 2 h after insulin injection. Then, it increased significantly from 2 to 4 h, and gradually returned to the normal value. The glucagon administration significantly decreased plasma TG levels with the minimum value found at 8 h post-injection. Then, it significantly increased and returned to the basal value with further increasing times. Insulin injection resulted in a significantly increased liver glycogen and lipid contents, which peaked at 2 and 1 h, respectively. However, glucagon injection induced a significant decrease of both parameters. Subsequently, they gradually returned to the normal values. Besides, insulin load significantly decreased the transcriptional levels of AMPKα1, AMPKα2, PEPCK, FBPase, G6pase, PPARα, CPT Ⅰ and ACO during the first 4 h. However, those of GLUT2, GK, PK, SREBP1, FAS and ACCα all increased significantly during the 2–4 h. After the glucagon injection, the transcriptional values of AMPKα1, AMPKα2, PEPCK, FBPase, G6pase, PPARα, CPT I and ACO all increased significantly during the first 8 h, whereas the opposite was true for the remaining indicators during the first 4 h. Overall, exogenous insulin and glucagon significantly affected the glycolipid metabolism of Megalobrama amblycephala. Insulin injection significantly decreased plasma glucose level, but activated AMPK, thus promoting glucose transportation, glycogenesis, glycogenesis and lipogenesis coupled with the depression of gluconeogenesis and fatty acid oxidation, whereas the opposite was true after the glucagon load.