Effects of polymyxin B and Salmonella typhimurium antiserum on horses given endotoxin intravenously

Abstract

Summary Polymyxin B and an antiserum against an Re mutant Salmonella typhimurium were evaluated for protective effect in an equine model of endotoxemia. Six 3- to 5-month-old foals were given endotoxin (0.25 μg/kg of body weight) iv after no pretreatment, or pretreatment with polymyxin B (6,000 U/kg, iv ) or S typhimurium antiserum (1.5 ml/kg, iv ). When given without pretreatment, endotoxin caused transient recumbency and increases in rectal temperature, and heart and respiratory rates. In addition, leukopenia and increases in circulating tumor necrosis factor ( tnf ) and interleukin 6 ( il -6) activities were detected. Compared with results obtained when endotoxin was given alone, pretreatment with polymyxin B resulted in significantly ( P < 0.05) lower maximal plasma tnf and il -6 activities, and significantly lower rectal temperature and respiratory rate. In contrast, compared with effects of endotoxin given without pretreatment, use of antiserum was associated with significantly ( P < 0.05) higher respiratory rate, maximal plasma il -6 activity, and total tnf response (as determined by areas under curves of plasma tnf vs time). These results indicate that polymyxin B may have potential as a treatment for equine endotoxemia. Salmonella typhimurium antiserum had no positive effect in this model, and, under certain conditions, may exacerbate the actions of endotoxin.