BLUNT INJURY AUGMENTS INTERLEUKIN-6 BUT NOT TUMOR-NECROSIS-FACTOR IN ISOLATED, PERFUSED RAT HINDLIMBS

An isolated, perfused hindlimb model in rats was used to examine the immediate inflammatory response after blunt tissue injury. A femur-fracture degloving model was used in isolated rat hindlimbs perfused with a modified Kreb's buffer (pH 7.4) containing albumin, washed human red blood cells (RBCs), amino acids, and glucose at 37-degrees-C. Arterial and venous perfusate was sampled at 5, 20, and 80 minutes of perfusion. Initial experiments were conducted in perfusate void of white blood cells (WBCs), group 1 (-inj/-WBC, n = 6) and group 2 (+inj/-WBC). Subsequent experiments were conducted in perfusate containing activated WBCs, group 3 (-inj/+WBC, n = 6) and group 4 (+inj/+WBC, n = 7). Hindlimb muscle was analyzed for adenylate energy charge (EC) and lactate-to-pyruvate ratios (LPR) at the end of each perfusion. This preparation appeared metabolically stable in that oxygen consumption and lactate remained stable during the 80-minute perfusion and muscle EC and LPR indicated aerobic metabolism. Tumor necrosis factor (TNF) and thromboxane B2 (TXB2) were measured in all four groups while prostaglandin F (PGF1alpha), IL-6, myeloperoxidase, and 8-isoprostane were measured in groups 3 and 4. Initial perfusions in the -WBC hindlimbs indicated no change in TNF release after injury. The TXB2 level increased during perfusion irrespective of injury. The PGF1alpha was elevated at 80 minutes in both groups 3 and 4, however at 20 minutes PGF1alpha levels were higher in group 4 compared with group 3. Interestingly, the IL-6 level was significantly elevated at 80 minutes in group 4 but not in group 3. Myeloperoxidase activity was not significantly altered during perfusion in either group 3 or 4. 8-Isoprostane was not detected in the venous perfusate. These data indicate that IL-6 is an important early mediator released directly from the endothelium of injured tissue that is well perfused. In the presence of WBCs, blunt injury evokes the early release of this cytokine from the endothelium of the injured tissue.