Immune system stimulation (ISS) induced by E. coli lipopolysaccharide (LPS) alters amino acid metabolism in growing pigs

Abstract Text: We previously observed that PRRSV infection increased plasma Met and Thr flux, but decreased Lys flux in growing pigs. These changes reflect modification of AA utilization during ISS. This study evaluated the effects of ISS induced by LPS on whole body protein deposition (PD) and plasma free amino acid (AA) flux and pool size. Ten gilts (BW 9.4 ± 1.1 kg) were surgically fitted with venous catheters, individually housed in metabolism crates, and feed restricted (550 g/d) on a corn-SBM based diet (ME 14.3 MJ/kg, SID Lys 11.5 g/kg). ISS was induced by two intramuscular injections of increasing amounts of LPS (30 and 36 µg/kg BW) given 48 h apart. Blood samples were collected at 0 and 72 h after initiation of ISS, and assayed for hematology and blood chemistry. Body temperature (BT) was monitored on a daily basis. N-balances were determined during a 3-d pre-ISS and a 3-d ISS period. At the end of each N-balance period a single dose of [U-¹³C, U-¹⁵N] AA mixture (Lys, Met, Thr, Trp, Ile, Leu, Val, Phe, Gln) was infused intravenously, and serial blood samples were taken at 0, 2.5, 5, 7.5, 10, 15, 20, 30, and 45 min after tracer administration to determine isotopic enrichment. A double exponential model was fitted to the plasma enrichment for each pig and AA, and equation parameters were used to estimate plasma AA flux and pool size. Blood chemistry, hematology, and BT results indicated that LPS induced effective ISS in pigs (P<0.05). ISS had no effect on PD (59.4 vs. 55.7 g/d; P=0.31), but it decreased plasma flux (µmol/kg BW/h) for Ile (112 vs. 76; P<0.05) and Phe (126 vs. 79; P<0.05). In agreement with PRRSV challenged pigs, LPS tended to reduce the plasma Lys flux (from 394 to 325, P=0.08). Plasma flux of other AA was not affected by ISS. ISS increased and tended to increase the pool size (µmol/kg BW) for free Leu (22 vs. 34, P<0.05) and Gln (16 vs. 25, P=0.11), respectively, but reduced the pool size for free Ile (13 vs. 9.0, P<0.05). Collectively, these results suggest that ISS induced by LPS alters AA flux and pool size in growing pigs. The decrease in Lys, Phe, and Ile flux in LPS induced ISS pigs may be attributed to a reduction in whole body protein synthesis or decreased catabolism of these AA. NPB project #13-082 

Keywords: plasma amino acid flux, immune system stimulation, growing pig