Study objectives: The impairment of cardiac contractility during endotoxemia involves induction of nitric oxide formation through a cascade of events initiated by overexpression of proinflammatory cytokines. We previously showed that hypothermia attenuates endotoxin-induced overexpression of nitric oxide in rat lungs. In the present study, we tested the hypothesis that hypothermia protects against endotoxin-induced myocardial inflammation by changing the balance of pro- and anti-inflammatory cytokines, inhibiting myeloperoxidase, an indicator of neutrophil activity, and inhibiting nitric oxide-mediated protein damage.
Design: Rats were randomized to treatment with either hypothermia (n = 6; 18 to 24°C) or normothermia (n = 6; 36 to 38°C). Endotoxin (15 mg/kg) was administered intravascularly to anesthetized animals, and heart tissue was harvested 150 min later.
Measurements and results: Using enzyme-linked immunosorbent assays (ELISAs), we found that hypothermia induced myocardial expression of the anti-inflammatory cytokines interleukin (IL)-4 and IL-10, while decreasing concentrations of the pro-inflammatory cytokines IL-1β and growth-related oncogene/cytokine-induced neutrophil chemoattractant (rat homolog of IL-8). Electromobility shift assay revealed that hypothermia inhibited the nuclear translocation of nuclear factor-κB. Reverse transcriptase-polymerase chain reaction and Western blot assays revealed that hypothermia attenuated the endotoxin-induced overexpression of both inducible nitric oxide synthase (iNOS) messenger RNA and iNOS protein, respectively. Hypothermia also attenuated nitric oxide-mediated myocardial protein damage, as determined by a nitrotyrosine ELISA. Myocardial myeloperoxidase content, an indicator of neutrophil accumulation and oxidative activity, was also inhibited by hypothermia in endotoxemic rats.
Conclusion: These data demonstrate that hypothermia induces an anti-inflammatory cytokine profile, inhibits neutrophil aggregation, and inhibits the formation of nitric oxide during endotoxemia in the rat.