The acute phase response alters cationic amino acid transporter expression in growing chickens (Gallus gallus domesticus)

The effect of an acute phase response (APR) on cationic amino acid transporter (CAT1-3) mRNA expression in liver, muscle, bursa and thymus was determined in broiler strain chickens. The APR was initiated by injecting Salmonella typhimurium lipopolysaccharide subcutaneously (LPS; 1 mg/kg bw). In Experiment 1, CAT1-3 mRNA expression was determined at multiple time points following LPS administration. LPS increased bursa and liver total and high affinity CAT mRNA expression (P < 0.05) and transiently increased pectoralis total CAT mRNA expression (P < 0.05). Total CAT mRNA expression in the thymus decreased 7.7-fold from 0 to 8 h after LPS injection (P < 0.05). In Experiment 2, fasted chicks were uninjected or LPS-injected. LPS increased total and high affinity CAT mRNA 2-fold in both the bursa and liver (P < 0.05) and did not change thymus total and high affinity CAT mRNA expression (P > 0.05). LPS increased liver weight only (P < 0.05) and did not alter the plasma lysine and arginine concentration (P > 0.05). In Experiments 3 and 4, thymocyte proliferation and total protein content were dependent upon the media lysine concentration (P < 0.001). The inability of the thymus to compete for lysine and arginine during the APR may limit the ability of thymocytes to develop during infections.