Exchange of amino acids by muscle and liver in sepsis

The amino acid "central fractional clearance rate" (CFCR), the ratio of the rate of amino acid entry into the extracellular pool to the size of the pool, is a measure of amino acid uptake and clearance by liver and other visceral tissues. In nine normal postabsorptive persons, the mean CFCR was 5%, compared with 21% in 31 seriously infected patients. For comparative purposes, biopsy specimens of liver and muscle were obtained for incubation. In infected patients, the rate of hepatic incorporation of tyrosine into protein was three times that in noninfected patients and correlated well with the CFCR. There was no significant difference in hepatic tyrosine oxidation. In muscle from infected patients, net protein degradation was six times that in noninfected patients. Incubated tissues from rats behaved similarly. Thus, accelerated transfer of amino acid from muscle to viscera for protein synthesis occurs in humans with sepsis, as it does in animals. The CFCR demonstrated the importance to survival of visceral amino acid uptake; it was 35% in surviving patients, and only 19% in those who died.