1. We investigated arteriovenous exchanges of tyrosine and 3-methylhistidine across leg tissue in the postabsorptive state as specific indices of net protein balance and myofibrillar protein breakdown, respectively, in eight patients with cirrhosis and in 11 healthy control subjects. Whole-body protein turnover was also measured using l-[1-13C]leucine.
2. Leg efflux of tyrosine was 45% greater in cirrhotic patients than in normal control subjects [−6.5(1.4 to −19.1) vs −4.2 (−2.2 to −7.7) μmol min−1 100 mg−1 of leg, median (range), P <0.025]. 3-Methylhistidine efflux was not significantly altered.
3. In cirrhosis, whole-body leucine flux was normal but whole-body leucine oxidation was elevated so that whole-body protein synthesis was depressed by 17%.
4. The results indicate the predominant mechanism of muscle wasting in cirrhosis to be a fall in muscle protein synthesis, which is accompanied by an overall fall in whole-body protein turnover.