The effects of tumor necrosis factor on intestinal structure and metabolism. Tumor necrosis factor (TNF), a polypeptide produced predominantly by activated macrophages, is an important mediator of sepsis. We analyzed the specific metabolic changes that occur in the gut following TNF administration. Following general anesthesia, hemodynamic and metabolic indices were measured serially in control dogs (n = 7) and animals receiving a continuous sublethal intravenous infusion of TNF (0.57.10(5) IU/kg/6 hours, n = 7). During TNF infusion mean arterial pressure gradually decreased despite fluid administration, which maintained wedge pressure and cardiac index, which were similar to control animals. While TNF significantly reduced intestinal blood flow to 12 +/- 3 mL/min/kg compared to 28 +/- 3 mL/min/kg (p less than 0.01) in controls, intestinal oxygen consumption was maintained due to an increased extraction rate. Despite hypoperfusion the intestinal exchange of metabolic substrate (glucose, lactate, pyruvate, alanine, glutamine, glutamate, and ammonia) was comparable between the control and TNF-infused animals. However, when substrate carbon balance across the intestinal tract was calculated, it appeared that there was a limitation in fuel availability in the TNF animals. This may be due to competition for fuel between the gut and other major organs. Fuel limitation may jeopardize rapid cell proliferation and mucosal repair and with regional hypoperfusion these processes may account for the mucosal ulcerations observed at the termination of the study. 