Effects of different carbohydrates and different carbohydrate levels on mRNA expression of glucose metabolism related genes in different feeding stages of Songpu mirror carp (Cyprinus carpio)

This experiment was aimed to study the effect of different carbohydrates and different carbohydrate levels on mRNA expression of glycolytic enzyme (glucose kinase, GK; hexokinase, HK), gluconeogenesis enzyme (Glucose -6- phosphatase, G6Pase; phosphoenolpyruvate carboxykinase, PEPCK), glucose metabolism related genes (Insulin-like Growth Factor-Ⅰ, IGF-Ⅰ; Growth Hormone Receptor, GHR) in different feeding stages of Songpu mirror carp (Cyprinus carpio). Four experimental diets were formulated to contain two carbohydrates (starch and glucose) diets with two levels (250 g /kg and 500 g/kg) (Low level starch group: LS; High level starch group: HS; Low level glucose group: LG; High level glucose group: HG) two carbohydrates (glucose and starch) and two carbohydrate levels (25% and 50%) (LS/HS/LG/HG) using 2×2 double factor experimental design, 420 Songpu mirror carp (mean weight=8.30±0.15 g) were randomly divided into 4 dietary treatments with 3 triplicates and 35 fish per triplicate and were reared for 7 weeks. The results showed that in different feeding stages, the mRNA expression levels of HK gene and IGF-Ⅰ gene in different experimental groups were basically in the same trend. The mRNA expression levels of HK gene at feeding 1W was significantly increased and then decreased. The mRNA expression level of IGF-Ⅰ gene was significantly increased at feeding 3W. IGF-Ⅰ gene expression increased significantly at feeding 3W. In different feeding stages, the mRNA expression levels of GK, PEPCK, G6Pase and GHR genes were affected by carbohydrate levels and carbohydrate types. At low carbohydrate level (LS group and LG group), the mRNA expression levels of these genes showed the same trend. The mRNA expression levels of GK and GHR genes were significantly higher at feeding 1W and then began to decline. The mRNA expression level of PEPCK gene was the highest at feeding 3W. The mRNA expression level of G6Pase genes were significantly higher at feeding 1W, then began to decline and showed a rising trend at feeding 7W. At high carbohydrate levels, the mRNA expression level of GK gene in HS group was not significantly different at different feeding stages. But the mRNA expression level of GK gene in HG group was increased significantly at feeding 1W. The mRNA expression level of PEPCK gene in HS group and HG group had no significant difference at different feeding stages. The mRNA expression level of G6Pase gene in HS group had no significant difference at different feeding stages. But the mRNA expression level of G6Pase gene in HG group was increased significantly at feeding 3W. The mRNA expression level of GHR gene in HG group had no significant difference at different feeding stages, while the mRNA expression level of GHR gene in HS group was increased significantly at feeding 3W.In the early feeding stage (1W), the mRNA expression level of HK gene was significantly promoted by high carbohydrate diet. While, the mRNA expression levels of PEPCK, G6Pase and GHR genes were suppressed by high carbohydrate diet. In conclusion, this study investigated the effects of different carbohydrates and carbohydrate levels on the expression trend of enzymes and genes involved in glucose metabolism at different feeding stages. It provides a theoretical basis for the application of carbohydrate in feed.