ENDOTOXIN PRETREATMENT INHIBITS NEUTROPHIL PROLIFERATION AND FUNCTION

Gut ischemia/reperfusion (I/R) induces lung injury by a mechanism that involves neutrophils (PMNs). We have previously shown that endotoxin (LPS), when administered after gut I/R, amplifies this lung injury, wh ile treatment with LPS prior to gut I/R prevents lung injury. The purp ose of this study was to determine whether LPS pretreatment (Pre Rx) a lters the PMN inflammatory component of the gut I/R injury. Specifical ly, we focused on whether LPS Pre Rx effected (i) PMN stern cell proli feration, (ii) gut I/R-induced PMN priming, and (iii) gut I/R-induced PMN lung sequestration. Bone marrow was harvested from normal and LPS- pretreated (0.5 mg/kg, ip, 3 days prior) rats, and colony forming unit s-granulocyte/macrophage (CFU-GM) were quantitated using a soft agar c ulture technique. In another experiment, normal and LPS-pretreated rat s were subjected to gut I/R (45 min superior mesenteric artery occlusi on/6 hr reperfusion), and blood and lungs were then harvested. The in vivo priming of PMN was assessed by measuring the difference in supero xide production (O-2(-)) with and without the activating stimulus, N-f ormylmethionyl-leveyl-phenylalanine (fMLP). The quantity of myeloperox idase (MPO) was used as an index of the number of PMN sequestered in l ung tissue. In conclusion, our data indicate that LPS pretreatment inh ibits (i) PMN stem cell proliferation (normal control = 20 +/- 2 vs LP S Pre Rx = 7 +/- 1 CFU-GM/1 x 10(5) cells), (ii) gut I/R-induced PMN p riming (O-2(-) response to fMLP in gut I/R = 46.8 +/- 7.1 vs 4,3-/10(6 ) cells/min in LPS Pre Rx gut I/R animals), and (iii) gut I/R-induced lung PMN sequestration (gut I/R lung MPO = 13.9 +/- 1.0 vs 9.3 +/- 0.2 unit/g in LPS Pre Rx gut I/R animals). (C) 1994 Academic Press, Inc.