The effect of heat on cytokine production in rat endotoxemia

Objective: To determine whether heat stress protects the endotoxemic rat by up-regulation of the counterinflammatory cytokine interleukin (IL)-10, the reby attenuating the inflammatory response. Design: A total of 16 rats were assigned to either the heat stress group (n = 8) or the control group (n = 8). The heat stress group was warmed to a t emperature of >42 degrees C (107.6 degrees F) rectally for 10-15 mins; 20 h rs later, all rats were intubated, paralyzed, and ventilated. After jugular venous and arterial catheterization, endotoxin was given intravenously. Ar terial blood was removed at 0, 2, 4, and 5 hrs for blood gases, tumor necro sis factor (TNF)-alpha, nitric oxide metabolites (NO), IL-10, and macrophag e inflammatory protein (MIP)-2, The alveolar macrophages were removed, coun ted, and then incubated for 24 hrs. The supernatant was analyzed for TNF-al pha, NO, IL-10, and MIP-2. Setting: University research laboratory, Subjects: Male Sprague-Dawley rats (n = 16). Interventions: Administration of heat before endotoxin infusion. Measurements and Main Results: Alveolar-arterial oxygen gradient was lower in the heat stress group at 4 and 5 hrs after endotoxemia. Plasma and alveo lar macrophage supernatant concentrations of TNF-alpha, NO, and IL-10 were not affected by heat. Plasma and alveolar macrophage supernatant MIP-2 conc entrations were higher in endotoxemic rats receiving heat pretreatment comp ared with controls. Conclusions: Our study demonstrates that heat leads to pulmonary protection of short duration in severe endotoxemia. This protection was not mediated by plasma TNF-alpha, IL-10, or NO. Contrary to our hypothesis, pretreatment with heat increased rather than decreased the plasma MIP-2 concentration a nd alveolar macrophage production of MIP-2 in endotoxemia. The mechanism of heat-conferred pulmonary protection in endotoxemia remains unclear. Alveol ar macrophages do not produce IL-10 in endotoxemia. The increased MIP-2 pro duction by heated alveolar macrophages was not attributable to alterations in production of either TNF-alpha or IL-10. The significance of increased M IP-2 by endotoxin-exposed alveolar macrophages in heated rats is unknown.