Supernatant of traumatized muscle induces inflammation and pain, but not microcirculatory perfusion failure and apoptotic cell death

Soft tissue trauma induces an inflammatory response locally and in remote organs. Although remote organ failure is attributed to the systemic action of locally released mediators, it is so far unclear to what extent a direct cell injury and the consequences of ischemia or a secondary injury due to locally released mediators contribute to the manifestation of tissue damage at the primary site of trauma. Soft tissue trauma was induced by means of a controlled impact injury technique in the hind limb of pentobarbital-anesthetized rats. Additional animals received a femoral arterial infusion of supernatant of traumatized muscle tissue, of nontraumatized muscle, or 0.9% NaCl. Tissue injury was assessed by determining microcirculatory perfusion failure, inflammatory response, apoptotic cell death, and nociceptive pain behavior. Muscle tissue of traumatized animals revealed perfusion failure, tissue hypoxia, and inflammation. Nociceptive testing showed a decrease in mechanical pain thresholds of the affected hind paw. Infusion of supernatant of traumatized tissue induced local inflammation and pain comparable with that of directly traumatized tissue; however, it failed to cause nutritive perfusion failure. Supernatant of nontraumatized muscle did not affect muscle microcirculation and integrity. Only animals that underwent direct trauma presented with apoptotic cell death, as given by in vivo fluorescence microscopy, caspase 3 protein cleavage, and transferase-mediated dUTP nick-end labeling histology. Trauma-associated humoral factors cause post-traumatic hyperalgesia and inflammation, but not microvascular perfusion failure and apoptotic cell death. This finding may prompt future efforts in the therapy of closed soft tissue trauma to focus not only on antimediator strategies, but to add regimens targeting perfusion failure and tissue apoptosis.