The metabolic bases for "paradoxical" and normal feeding.
Hexoses infused slowly into the duodenum or hepatic-portal vein reduce feeding. However, hexoses can increase food intake following rapid infusion via either of these two routes. Insulin responses and resultant glycemic changes differ following fast and slow duodenal glucose infusion. This is unlikely to be the primary explanation, because fructose affects feeding but is not a secretagogue of insulin under our testing conditions. In follow-up studies, we infused glucose or fructose into the hepatic-portal vein at the fast or the slow rate, and measured 14C incorporation into liver mitochondria and glycogen, and tritiated water uptake into hepatic lipids. Fast infusion of glucose or fructose increased lipid formation, reducing mitochondrial uptake and glycogen formation, and was associated with hunger enhancement. Slow hexose infusion was associated with substrate uptake into mitochondria and glycogen, with reduced uptake into hepatic fat. These findings all are consistent with the previously observed positive correlation seen between mitochondrial oxidation and satiety (28).