TNF-α mRNA expression in diaphragm muscle after endotoxin administration

We studied gene expression and production of TNF-α in the diaphragm tissue and changes of muscle contractile properties after endotoxin injection (Escherichia coli, 20 mg/kg) in 88 rats. We assessed the muscle contractile properties by force-frequency curves and twitch kinetics using dissected diaphragm muscle strips. The peak tensions of force-frequency curves decreased from control values (2.15 ± 0.2 kg/cm²) up to 4 h (0.81 ± 0.17, p < 0.001), and then increased at 6 h (1.36 ± 0.19, p < 0.05) after endotoxin injection. The cytotoxic activity on L929 cells in arterial blood samples maximally increased at 2 h (p < 0.001), then decreased to 6 h (p < 0.05). TNF-α mRNA in diaphragm tissue was detected by Northern blot method at 1 and 1.5 h, and the immunolocalization of TNF-α was evaluated at 2 and 4 h by immunohistochemistry in the muscle tissues. Furthermore, preinjection with anti-m TNf-α antibody prevented the decrement of force-frequency curves after endotoxin injection of 10 μl/kg. From this evidence that TNF-α gene expression and production occurred in the diaphragm tissue, but anti-m TNF- α antibody preinjection prevented the deterioration of diaphragm muscle contractile properties, we suggest that TNF-α may act on muscle cells extracellularly.