Adaptations of hepatic lipid and glucose metabolism in response to high‐macronutrient diets in juvenile grass carp

Abstract

It was previously shown that the influence of high-energy diets on growth and flesh quality of grass carp was closely related to energy resource. The mechanisms were explored in this study by investigating the hepatic lipid and glucose metabolism of grass carp. Juvenile grass carp (Ctenopharyngodon idella) with initial body weight (55.0 ± 2.5) g were fed with four purified diets for 11 weeks, with four replicates per diet and 20 fish per replicate. Three high-energy diets with high level of carbohydrate, fat and protein were prepared, and their gross energy was 11% higher than that of control diet. Results showed that the highest contents of hepatic crude fat, total saturated fatty acids, n-6 unsaturated fatty acids and glycogen, as well as the highest grade of hepatocyte steatosis were observed in grass carp fed the high-carbohydrate diet. Data on hepatic mRNA expression indicated that the high-carbohydrate diet increased the genes expression including pk, gck, g6pd, fas and acc-1, while the high-fat diet significantly increased the genes expression including pk, gck, fbp, pck, lpl and hsl. The high-fat and high-carbohydrate diets activated hepatic AMPK/ACC pathway, whereas inhibited TOR/SREBP-1 pathway. In conclusion, the high-carbohydrate diet had a stronger effect on the hepatic lipid accumulation than the high-fat diet in grass carp. The acceleration of lipolysis, glycolysis and gluconeogenesis in liver improved the utilization of the high-fat diet in grass carp. Besides, the high-carbohydrate diet can promote hepatic glycolysis and pentose phosphate shunt and inhibit gluconeogenesis in grass carp.