HEPATIC MITOCHONDRIAL RESPIRATION AND TRANSPORT OF REDUCING EQUIVALENTS IN RATS FED AN ENERGY DENSE DIET

OBJECTIVE: To measure hepatic mitochondrial respiration as well as the ability of hepatic mitochondria to transport reducing equivalents by shuttle systems in rats fed an energy dense diet. DESIGN: Rats were fe d a control (CD) or energy dense (ED) diet for 15 days. MEASUREMENTS: State 3 and State 4 oxygen consumption were measured in isolated mitoc hondria using glutamate+malate or pyruvate+malate as substrate, We als o measured malate-aspartate shuttle activity and mitochondrial alpha-g lycerophosphate dehydrogenase activity. RESULTS: ED rats, in compariso n with CD rats, showed a significantly greater energy intake without a corresponding greater body weight gain and carcass lipid content, Com pared to CD rats, ED rats also showed a significant increase in restin g metabolic rate, which was abolished by propranolol, Hepatic mitochon drial state 3 respiration using glutamate+malate or pyruvate+malate as substrate as well as malate-aspartate shuttle activity significantly decreased, while mitochondrial alpha-glycerophosphate dehydrogenase si gnificantly increased in ED rats compared to CD rats. CONCLUSIONS: Mit ochondrial NADH oxidation is reduced and a greater fraction of cytopla smic NADH can be transported to the mitochondria through the alpha-gly cerophosphate shuttle and oxidized through the respiratory chain from complex II onwards, This mechanism could lead to a decrease in hepatic metabolic efficiency which is in line with the increased energy expen diture occurring in rats fed an energy dense diet.