TIME-COURSE OF INCREASED PLASMA CYTOKINES, CORTISOL, AND UREA NITROGEN IN PIGS FOLLOWING INTRAPERITONEAL INJECTION OF LIPOPOLYSACCHARIDE

The emerging view is that reduced feed intake, lean muscle accretion, and growth in immunologically challenged pigs is the result of increas ed cytokine activity, but this has not been directly tested. To begin addressing this issue, 72 crossbred barrows and gilts (11.55 +/- .19 k g BW) were not fed for 12 h and then injected i.p. with 0, .5, or 5 mu g/kg of Escherichia coli lipopolysaccharide (LPS). Blood was collecte d by jugular puncture at 0, 2, 4, 8, 12, and 24 h after injection. Pla sma levels of tumor necrosis factor-alpha (TNF-alpha), interleukin-6 ( IL-6), cortisol, plasma urea nitrogen (PUN), NEFA, and triglycerides w ere determined. Immunological stress was induced by LPS as indicated b y increased secretion of TNF-alpha, IL-6, and cortisol. In pigs receiv ing 5 mu g/kg of LPS, plasma TNF-alpha was increased 10-fold at 2 h af ter injection and was still elevated (P <.01) at 4 h. In these same pi gs, plasma concentration of IL-6 was increased at 2 h and peaked at 4 h with levels exceeding baseline values by 200-fold (P < .01). Cortiso l was elevated at 2, 4, and 8 h after injection (P <.01). The increase d secretion of cytokines and cortisol in pigs injected with 5 mu g/kg of LPS was followed by an increase in protein degradation, as evidence d by PUN values that were increased two- and threefold at 8 and 12 h a fter injection, respectively. However, unlike previous reports in labo ratory animal species, plasma glucose, NEFA, and triglycerides were no t altered by LPS. Nonetheless, as the period of feed deprivation progr essed from 12 to 36 h, plasma NEFA and triglycerides increased (P <.05 ) and plasma glucose tended to decrease. We believe that immunological challenge induces cytokine synthesis and secretion in swine which, in turn, may induce protein catabolism.