The independent effect of propofol anesthesia on whole body protein metabolism in humans

Background: The purpose of this study was to examine the effect of general anesthesia with propofol in thr absence of surgical stimulation on whole bo dy protein metabolism. Methods: Six unpremedicated patients were studied. General anesthesia inclu ded propofol (120 mu g . kg(-1) . min(-1)), vecuronium bromide, and oxygen- enriched air. Changes in protein breakdown, protein oxidation, and synthesi s were measured by an isotope dilution technique using a constant infusion of the stable Isotope tracer L-[1-C-13]leucine (0.008 mg . kg(-1) . min(-1) ) before and during 100 min of propofol anesthesia. The plasma concentratio ns of glucose, lactate, non-esterified fatty acids, and cortisol were measu red before and during anesthesia. Results: An isotopic steady state of plasma [1-C-13]alpha-ketoisocaproate ( taken to represent the intracellular leucine precursor pool enrichment for protein synthesis) and expired C-13-carbon dioxide were obtained before and during propofol infusion, Whole body protein breakdown decreased during pr opofol anesthesia by 6% (P < 0.05), whereas protein synthesis and oxidation did not change significantly. Plasma concentration of cortisol decreased a fter 90 min of propofol anesthesia (P < 0.05). No significant changes of pl asma concentrations of glucose, lactate, and non-esterified fatty acids occ urred during propofol administration. Conclusions: Propofol anesthesia did not significantly affect whole body pr otein synthesis and oxidation but caused a small, although significant, dec rease in whole body protein breakdown, possibly mediated through the suppre ssion of plasma cortisol concentration.