Involvement of p38 Mitogen-Activated Protein Kinase in the Induction of Tolerance to Hemorrhagic and Endotoxic Shock

Abstract Background. Exposure to sublethal hemorrhage (SLH) makes rats tolerant to subsequent hemorrhagic or septic shock and is associated with altered NF-κB activity. The purpose of this study was to explore whether changes in p38 mitogen-activated protein (MAP) kinase activity also occur in the induction of tolerance by SLH. Methods. Rats were made tolerant by SLH or sham operation. Twenty-four hours later rats were exposed to lipopolysaccharide (LPS) or had peritoneal macrophages (Mφ) isolated. CNI-1493, a p38 MAP kinase inhibitor, or saline was given prior to SLH. Lungs were harvested 1 h after SLH or LPS and total protein was extracted. Peritoneal Mφ were stimulated with LPS (10 μg/ml) and total protein was isolated 1 h later. Active, dually phosphorylated p38 MAP kinase was determined by Western blot. Tumor necrosis factor (TNF) was measured in Mφ supernatants by enzyme-linked immunosorbent assay (ELISA) 18 h after LPS. Results. SLH activated p38 MAP kinase in the lung and this was inhibited by CNI-1493. Twenty-four hours later, lung p38 MAP kinase activity increased to the same degree in tolerant and sham rats following LPS, but much more prominently in the CNI-1493 treated rats. There was no p38 activity in peritoneal Mφ at baseline, and similar to lung p38, LPS led to increased p38 activity which was most significant in Mφ from rats that received CNI-1493 prior to SLH. TNF production by tolerant Mφ in response to LPS was significantly ( P t test) decreased and p38 inhibition with CNI-1493 at the time of SLH reversed the inhibitory effects of tolerance on TNF production. Conclusions. TNF production by tolerant Mφ following a second insult (LPS) is attenuated despite preservation of normal p38 MAP kinase activity. However, activation of this intracellular second messenger is a necessary step in the “cellular reprogramming” that occurs during the induction of tolerance by SLH.