The Effect of Cycloheximide on the Interaction between Mitochondrial Respiration and Gluconeogenesis in Guinea Pig and Rat Liver

Cycloheximide (3 to 5mm) caused a decrease in the rate of gluconeogenesis from pyruvate, lactate, or glycerol in the perfused rat and guinea pig liver. In these experiments, oxygen consumption was reduced by 30% with pyruvate but was unaltered with lactate or glycerol as substrates. The inhibition of gluconeogenesis caused by cycloheximide was rapid in onset (100% of maximal inhibition in 1 to 2 min) and immediately reversible upon cessation of cycloheximide infusion. Perfused livers were freeze-clamped in situ before and during cycloheximide infusion and the mitochondrial NAD:NADH ratio was calculated by a measurement of intermediates of the β-hydroxybutyrate dehydrogenase couplet. There was a marked shift toward reduction of the intramitochondrial pool of nicotinamide coenzymes after cycloheximide infusion. Under these conditions, the hepatic levels of ATP, ADP, and AMP were not significantly altered by cycloheximide in livers of rats perfused with lactate. With pyruvate as substrate, the ratio of ATP:ADP was decreased although no change in AMP levels was observed. Our findings indicate that the metabolic effects of cycloheximide are rapidly reversed, with the inhibitory effect on gluconeogenesis not evident after 10 min of recycling of the perfusate through the liver. Previous studies with cycloheximide have shown this compound to block mitochondrial energy transfer at Site I of the respiratory chain. It is suggested that cycloheximide decreases the rate of hepatic gluconeogenesis by an inhibition of mitochondrial energy transfer at Site I.