METABOLIC EFFECTS OF A FAT-RICH AND CARBOHYDRATE-RICH MEAL IN RATS

To investigate meal-induced changes in hepatic fat and carbohydrate me tabolism in rats, hepatic venous, portal venous, and aortal plasma lev els of several metabolites as well as changes in hepatic glycogen and lactate content were measured during and after the first nocturnal mea l 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 c arbohydrates, fats, and protein, respectively. During the later part o f the meal and thereafter, plasma triglyceride level increased in all blood vessels. After a transient initial decrease, portal venous and a ortal nonesterified fatty acid (NEFA) levels, net hepatic NEFA uptake, and hepatic beta-hydroxybutyrate (BHB) production increased and reach ed fasting (meal onset) values by 30 min after the meal. Although live r glycogen did not change significantly, the liver released glucose co ntinuously. The liver initially accumulated lactate and maintained a h igh 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 considera ble fatty acid oxidation occur concurrently in rat liver during and af ter a fat- and carbohydrate-rich meal. The findings are relevant to co ntemporary hypotheses of the metabolic control of eating and, in parti cular, to hypotheses linking hepatic fatty acid oxidation to postprand ial satiety.