CHARACTERIZATION OF THE ACUTE-PHASE RESPONSE OF HEIFERS TO A PROLONGED LOW-DOSE INFUSION OF LIPOPOLYSACCHARIDE

The effect of a prolonged low dose infusion of bacterial lipopolysacch aride (LPS) on acute phase-like reactions was examined in heifers. LPS (2 mu g kg(-1) disserved in 100 ml water), or saline was infused (at 1 ml min(-1)) intravenously for 100 minutes and blood samples were tak en at various times before, during and after the infusion. The serum c oncentrations of tumour necrosis factor-alpha (TNF alpha), interleukin -1beta (IL-1 beta), interleukin-6 (IL-6) and serum amyloid A (SAA) and the rectal temperature increased in response to the LPS infusion. Ser um TNF alpha increased before the increases in IL-1 beta and IL-6 and remained high from 20 minutes after the onset of the infusion until th e end of the sampling period (six hours). The LPS-induced increases in serum IL-1 beta and IL-6 were biphasic. Plasma cortisol and lactate c oncentrations also increased, and plasma glucose and beta-hydroxybutyr ate concentrations decreased in response to the LPS infusion. The simi larity of these reactions to changes observed in response to bacterial infections shows that the prolonged infusion of low doses of LPS is a good model for studying the acute phase response to Gram-negative bac terial infection in heifers.