Abstract
The aim of this study was to investigate effects of dietary metformin supplementation on growth performance, liver function, and glucose metabolism of rice field eel (Monopterus albus) fed high carbohydrate diets (HCDs). Four isonitrogenous and isolipid diets were formulated, different in 15% α-starch (LC), 35% α-starch (HC), and 35% α-starch supplemented with 0.25% (HCM0.25) and 0.5% metformin (HCM0.5), respectively. After 8 weeks, the results showed that HCDs did not affect growth performance, but reduced the activities of amylase and trypsin, and damaged liver function together with the increase of hepatic glycogen content. HCM0.25 did not affect whereas HCM0.5 damaged the growth performance. Activities of amylase in HCM0.25 group and trypsin in both HCM0.25 and HCM0.50 groups were increased. While HCM0.25 lowered serum AST and ALT activities, HCM0.5 showed an increase. HCM0.25 caused a reduction in vacuoles size and a increase in nuclei number, whereas HCM0.5 failed to induce similar effects. The liver glycogen content was reduced by both HCM0.25 and HCM0.5 whereas the muscle glycogen content remained stable. Both HCM0.25 and HCM0.5 enhanced glycolysis–related enzymatic activities (PFK, PK) in liver, while reducing gluconeogenesis (FBPase). Similarly, both treatments upregulated gene expression of pk in liver, while downregulated g6pase, fbpase and pepck. Moreover, HCM0.25 and HCM0.5 increased PFK, G6Pase, FBPase and PEPCK activity in muscle, with HCM0.25 further upregulating gene expressions of hk, pfk, g6pase and pepck. Both treatments downregulated the gene expression of g6pd in muscle, whereas only HCM0.25 upregulated ampkα1, tbc1d1 and glut4. In summary, dietary 0.25% metformin improved liver function, reduced liver glycogen content, and regulated glucose metabolism and AMPKα-TBC1D1-GLUT4 pathway. However, 0.50% metformin did not demonstrate positive effects and even had adverse effects on growth performance.