The effect of hyperthermic preconditioning on the immune system in rat peritonitis

Abstract

Objective: To assess whether hyperthermic (HT) preconditioning prevents the lethal effects of peritonitis by acting on the immune system.¶Design: Prospective, controlled, experimental study.¶Setting: Laboratory and animal facility of the university.¶Materials: Adult male Sprague-Dawley rats.¶Interventions: In the HT groups animals were subjected to hyperthermia (42 °C, 15 min) and 8 h later peritonitis (P) (n = 14) was induced. In the normothermic (NT) groups, animals were subjected to normothermia (38 °C, 15 min) and 8 h later peritonitis (n = 14) was induced. Each group had a corresponding sham laparotomy group (n = 14). Six rats from each group were allowed to live 7 days for survival. In the control group (n = 4), rats were not anesthetized or heat treated.¶Measurements and results: Sixteen hours after peritonitis and laparotomy, rats were killed. Blood was taken to measure the percentage of CD₄ ⁺, CD₈ ⁺, CD₄ ⁺CD₅₆ ⁺, CD₈ ⁺ CD_{11 b} ⁺, NK⁺, B cells and the level of tumor necrosis factor. Grading of peritonitis and the measurement of free oxygen radicals in the peritoneal fluid were undertaken. All rats in the HT + P and sham laparotomy groups survived for 7 days, while in the NT + P group two rats died in 7 days. HT decreased the severity of peritonitis and increased the free oxygen radicals in the peritoneal fluid; however, the difference did not reach statistical significance. HT prevented the decrease in CD₄ ⁺ and B cells and the increase in CD_{11 b} ⁺.¶Conclusions: HT may have a protective role in sepsis by reducing the severity of peritonitis. A causal relation between hyperthermia and an improved immune system seems possible.