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Treatment of healthy rats and mice with a single intravenous injection of recombinant human tumor necrosis factor-alpha (rHuTNF-a) caused a dose-dependent gastrointestinal inflammation. Within 30 min gastric emptying was blocked and tissue edema occurred in the small and large intestine. In the cecum hemorrhage occurred after 4 h at doses 2 250 ag/kg. The cecum exhibited an acute inflammatory response following rHuTNF-a treatment similar to that seen in tumor necrosis at the same dose. The vascular endothelium became swollen, increased numbers of neutrophils and other leukocytes attached to and penetrated the endothelium, and finally hemorrhage occurred. Treatment of rats with daily injections of rHuTNF-a (250 tig/kg per d) for 3 wk failed to produce cachexia. Within 2448 h rats became resistant to the hemorrhagic effect of rHuTNF-a, however, the cytokine still caused a transitory block of gastric emptying after 10 d of treatment. Treatment at 5-or 10-d intervals produced results similar to the initial injection. These results suggest that maximum hemorrhagic response will occur when rHuTNF-a is administered at intervals of 5-10 d rather than daily.

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