The Significance and Mechanism of an Increased Serum Phenylalanine-Tyrosine Ratio during Infection.

摘要

Infections or inflammatory states often cause significant increases in serum phenylalanine-tyrosine ratio. To identify responsible mechanisms, rats were given lethal doses of Streptococcus pneumoniae; serum phenylalanine and phenylalanine-tyrosine ratios increased significantly. Hepatic phenylalanine hydroxylase activities were slightly decreased when compared to noninfected controls. Infected and noninfected rats showed comparable oxidation rates for C(14)-phenylalanine given with an oral phenylalanine load, as a pulse-oral dose, or as an intraperitoneal injection. Serum proteins of infected rats contained almost twice as much total radioactivity as that found in controls, while the amount of labeled phenylalanine in skeletal muscle protein was significantly reduced in the infected group. Isolated muscles from infected rats released more phenylalanine and less tyrosine than control muscles. The data were consistent with an increased flux of phenylalanine into serum, most likely as the result of increased skeletal muscle catabolism.