Metabolic effects of a fat- and carbohydrate-rich meal in rats

To investigate meal-induced changes in hepatic fat and carbohydrate metabolism in rats, hepatic venous, portal venous, and aortal plasma levels of several metabolites as well as changes in hepatic glycogen and lactate content were measured during and after the first nocturnal meal following a 12-h fast. The rats were fed a diet with about 46%, 41%, and 13% of the total energy (approximate to 16.5 kJ/g) derived from carbohydrates, fats, and protein, respectively. During the later part of the meal and thereafter, plasma triglyceride level increased in all blood vessels. After a transient initial decrease, portal venous and aortal nonesterified fatty acid (NEFA) levels, net hepatic NEFA uptake, and hepatic beta-hydroxybutyrate (BHB) production increased and reached fasting (meal onset) values by 30 min after the meal. Although liver glycogen did not change significantly, the liver released glucose continuously. The liver initially accumulated lactate and maintained a high lactate concentration despite switching from lactate uptake to net release of lactate around 10 min into the meal. Taken together, these data indicate that hepatic glycolysis, gluconeogenesis, and considerable fatty acid oxidation occur concurrently in rat liver during and after a fat- and carbohydrate-rich meal. The findings are relevant to contemporary hypotheses of the metabolic control of eating and, in particular, to hypotheses linking hepatic fatty acid oxidation to postprandial satiety.