O.49 Whole-body protein synthesis is depressed by anaesthesia

Abstract

We have investigated the effects of anaesthesia for major surgery on plasma leucine flux as an index of whole-body protein turnover. ]] patients undergoing abdominal surgery and ]0 patients undergoing cardiac surgery were infused with ]-[1~C]leucine (0.25-].0 mg/ kg/hr) for at least 6 hr before induction of anaesthesia and for ]-3 hr afterwards. Enrichment of plasma leucine was measured by selective ion monitoring gas chromatography mass spectrometry. In 6 patients estimates of the labelling of blood with 13C02 were made by isotope ratio-mass spectrometry. Whole-body CO2 production was estimated from samples of expired air collected before and after induction of halothane anaesthesia without N20 which interfered with 13CO2 quantitation. As a result of induction of anaesthesia plasma leucine labelling, which had achieved a plateau, showed an acute and significant rise (25-]]0%) within 2 hr, indicating a proportionate fall in leucine turnover. Despite the rise in plasma leucine labelling, enrichment of blood C02 did not rise although there was a slight fall in whole-body CO2 evolution. Thus there was no significant decrease in leucine oxidation. This suggests that the exit of leucine into protein synthesis, the only other process removing leucine from the free pool, was significantly decreased. These resuits suggest that anaesthesia causes marked depression of whole-body leucine flux and protein synthesis. This inhibition of amino acid turnover is likely to place the body in a disadvantageous position with respect to recovery and reBair of tissue injured during surgery.