TNF-ALPHA MESSENGER-RNA EXPRESSION IN DIAPHRAGM MUSCLE AFTER ENDOTOXIN ADMINISTRATION

We studied gene expression and production of TNF-alpha in the diaphrag m tissue and changes of muscle contractile properties after endotoxin injection (Escherichia coli, 20 mg/kg) in 88 rats. We assessed the mus cle contractile properties by force-frequency curves and twitch kineti cs using dissected diaphragm muscle strips. The peak tensions of force -frequency curves decreased from control values (2.15 +/- 0.2 kg/cm(2) ) up to 4 h (0.81 +/- 0.17, p < 0.001), and then increased at 6 h (1.3 6 +/- 0.19, p < 0.05) after endotoxin injection. The cytotoxic activit y on L929 cells in arterial blood samples maximally increased at 2 h ( p < 0.001), then decreased to 6 h (p < 0.05). TNF-alpha mRNA in diaphr agm tissue was detected by Northern blot method at 1 and 1.5 h, and th e immunolocalization of TNF-alpha was evaluated at 2 and 4 h by immuno histochemistry in the muscle tissues. Furthermore, preinjection with a nti-m TNf-alpha antibody prevented the decrement of force-frequency cu rves after endotoxin injection of 10 mu l/kg. From this evidence that TNF-alpha gene expression and production occurred in the diaphragm tis sue, but anti-m TNF-alpha antibody preinjection prevented the deterior ation of diaphragm muscle contractile properties, we suggest that TNF- alpha may act on muscle cells extracellularly.