Study On The Effects Of Hyperglucidic Stimulus At First Feeding On Gluconeogenesis Pathway In Siberian Sturgeon(Acipenser Baerii) Under Different Nutritional Status

Based on the concept of nutritional programming in higher vertebrates, we studied the effects of high-glucose stimulus at first feeding on gluconeogenesis regulation in Siberian sturgeon (Acipenser baerii) under different nutritional status. The objective of the study was to explore the possibility of improving the carnivorous fish glucose metabolism regulation and their ability of dietary carbohydrates utilization by artificially induced at first feeding, and to reveal the difference on ability of dietary carbohydrates utilization and regulatory mechanism of gluconeogenesis pathway in Siberian sturgeon comparing to mammals and carnivorous teleosts, and to study the effects of high-glucose stimulus at first feeding and dietary carbohydrate content on the fillet quality of juvenile sturgeon.First of all, we cloned the full-length cDNAs of the key enzymes of gluconeogenesis pathway, including phosphoenolpyruvate carboxykinase (PEPCK-C and PEPCK-M), fructose-1, 6-bisphosphatase (FBPase) and glucose-6-phosphatase (G6Pase) from Siberian sturgeon liver for latter gene expression analysis using degenerate perimers RT-PCR and RACE methods.Then we conducted a continuous feeding experiment from the larval to juvenile stage. From first feeding to yolk absorption (8-12 days post-hatching, dph), the sturgeon larvae were fed with a high-glucose diet (S,57% glucose) as hyperglucidic stimulus and fed with a carbohydrate-free diet (F) as control. At 13 dph, each group of fish was assigned to two treatments. One treatment was fed with a high-carbohydrate diet (H,35% dextrin), and the other treatment was fed with a carbohydrate-free diet until 20th wk, named as SH, SF, FH and FF respectively. At the end of the 20th wk, each group was starved for 21 days, and then refed for 21 days. We explained the effects of hyperglucidic stimulus at first feeding on regulatory mechanism of gluconeogenesis in Siberian sturgeon through detecting the growth performance, activities and mRNA expressiones of the key gluconeogenic enzymes, plasma glucose and hormones and glycogen at each sampling point, and evaluated the quality of the meat through the analysis of the nutrient composition, physical properties and flavor compounds of the muscles after 20 weeks feeding.Results showed that the hyperglucidic stimulus at first feeding had negative effects on growth at 13, 30 dph and 20th wk, and significantly inhibited the mRNA expression of gluconeogenic enzymes at 13 dph and FBPase mRNA expression when the fish fed with F diet at 30 dph. At the end of 20th wk, the hyperglucidic stimulus at first feeding was increased the postprandial glycemic peak at postprandial 6 h when the fish fed with H diet, and increased the mRNA expression of PEPCK-C and G6Pase at postprandial 24 h whereas inhibited the secretion of glucagon at postprandial 3 and 12 h and the activities of G6Pase at postprandial 6 h when the fish fed with F diet. The concentrations of plasma glucose and total free amino acids in H groups increased progressively over time reaching a peak at postprandial 6 h and 12 h respectively, while F groups maintained stable after meal. The plasma insulin and glucagon concentrations were showed the same trends after feeding, which were significantly lower in F groups than in H groups at postprandial 12 and 24 h. The high carbohydrate intake inhibited the mRNA expression and activity of gluconeogenic enzymes at 30 dph and 20th wk.At starvation 21 days, the mRNA expression of gluconeogenic enzymes in F groups were significantly lower than pre-starvation, while in H groups were no significant difference with the pre-starvation level. The plasma glucose concentrations and liver glycogen contents of F groups were maintained stable, while the liver glycogen contents of H groups were decreased with starvation, and plasma glucose concentrations and muscle glycogen contents in H groups were maintained stable. At refeeding 21 days, the mRNA expression of gluconeogenic enzymes in each group was returned to pre-starvatin levels, and the plasma glucose concentrations and muscle glycogen contents were significantly higher than pre-starvation when the fish fed with H diet. G6Pase activities in FF and FH groups were significantly lower than pre-starvation levels. The hyperglucidic stimulus at first feeding was significantly depressed the plasma insulin and glucagcon concentrations in H group at refeeding 7 days, and was significantly inhibited FBPase activity when the fish fed with F diet. The hyperglucidic stimulus at first feeding significantly decreased the ash and crude protein contents of fillet composition, but increased the adhesiveness and springiness of cooked fillet in F groups. High dietary carbohydrate content significantly reduced the ash and crude protein content of fillet composition and drop loss of muscle, and significantly reduced precursor free amino acid content of biogenic amines, such as tyrosine, lysine, ornithine and arginine.In conclusion, in contrast to carnivorous teleosts, the Siberian sturgeon could inhibit their gluconeogenesis pathway response to a high carbohydrate intake at both transcriptional and post-translational levels, which coincides with the findings in omnivorous fish and mammals. The hyperglucidic stimulus at first feeding was produced a long-term regulatory interference, which was inhibited the growth, and increased the postprandial glycemic peak when the fish fed with high carbohydrate diet, and reduced the response sensitivity of the key gluconeogenic enzymes gene expression and activity and glucagon to nutrition status. However, the Siberian sturgeon might have a capacity to adapt to later nutritional conditions by reversing the changes in the gluconeogenesis pathway which induced by early high glucose stimulus at the transcriptional level during the 20 weeks feeding. The nutritional history has significant impacts on metabolic strategies of Siberian sturgeon to face a short starvation period and subsequent refeeding. The fish, which fed with high carbohydrate diet, can increase the key gluconeogenic enzymes gene expression and breakdown glycogen to maintain the plasma glucose concentrations during starvation. An overcompensation phenomenon of plasma glucose concentrations and liver glycogen contents were also observed in these fish during the period of refeeding. Whereas, the fish which fed with carbohydrate-free diet seemed to use the protein or lipid as a major metabolic fuel to maintain the plasma glucose concentrations and glycogen contents. The dietary carbohydrate content has significant effects on fillet quality of Siberian sturgeon.