Dietary carbohydrates induce changes in glucosensing capacity and food intake of rainbow trout

We hypothesize that variations in dietary carbohydrate levels produce changes in glucosensor parameters in previously characterized glucosensing areas (hypothalamus and hindbrain) related with the regulation of food intake of a carnivorous fish species like rainbow trout. Therefore, we fed trout with standard, carbohydrate-free (CF) or high-carbohydrate (HC) diets for 10 days to assess changes in glucosensing system and food intake. Fish fed CF diet displayed hypoglycemia and increased food intake. Fish fed a HC diet displayed hyperglycemia and decreased food intake. Changes in food intake due to dietary carbohydrates were accompanied in hypothalamus and hindbrain of fish fed with HC diet by changes in parameters involved in glucosensing, such as increased glucose, glucose 6-phosphate, and glycogen levels and increased glucokinase (GK), glycogen synthase, and pyruvate kinase activities as well as increased GK and GLUT2 expression. All those results address for the first time in fish, despite the relative intolerance to glucose of carnivorous species, that dietary carbohydrates are important regulators of the glucosensing system in carnivorous fish, suggesting that the information generated by this system can be associated with the changes observed in food intake.