The role of apelin in regulating glucose metabolism in common carp ( Cyprinus carpio L.)

Apelin plays pivotal roles in fluid homeostasis, food intake and energy metabolism in mammals. However, the regulatory role of apelin in glucose metabolism in teleosts is still unclear. In this study, we investigated the regulatory role of Pyr-apelin-13 in glucose metabolism of common carp (Cyprinus carpio L.). The results showed that apelin mRNA abundance was significantly increased in the foregut and hepatopancreas after glucose injection. Insulin and glucagon also up-regulated apelin mRNA levels in the foregut, hepatopancreas and hepatocytes. In vivo, intraperitoneal injection of Pyr-apelin-13 induced hypoglycaemia through the up-regulation of mRNA expression and activity of hexokinase (HK) coupled with the down-regulation of mRNA expression and activity of glucose-6-phosphatase (G6Pase) in the hepatopancreas. In vitro, upon incubation of the primary hepatocytes with Pyr-apelin-13 (0, 10, 100 and 1000 nM), the mRNA expression of glucokinase (GK) was increased, whereas the mRNA expression of phosphoenolpyruvate carboxykinase (PEPCK) and G6Pase was reduced. For glucose transport, the glucose transporter 2 (GLUT2) mRNA expression increased in the hepatopancreas, intestine, primary enterocytes and hepatocytes after Pyr-apelin-13 treatment. Collectively, our data may provide a basis for further studies on elucidation of the role and mechanism of apelin in glucose metabolism of teleosts.