Tumor necrosis factor-alpha (TNF) is believed to play an important role in mediating many of the pathophysiologic changes accompanying bacterial sepsis. In order to characterize the cardiopulmonary responses to TNF in a young animal model and to determine to what extent these changes were secondary to cyclooxygenase byproducts, three groups of mechanically ventilated piglets received an infusion of either TNF, indomethacin followed by TNF (Indo+TNF) or neither (control). Compared to controls at 120 min, TNF resulted in the following changes beginning 30-60 min after the infusion began: mean pulmonary artery pressure (Ppa) increased from 1.7 +/- 0.3 to 4.4 +/- 0.7 kPa (13 +/- 2 to 33 +/- 5 mm Hg) (p < 0.001); cardiac output (CO) fell from 0.28 +/- 0.05 to 0.20 +/- 0.07 liters/kg/min (p < 0.01); mean arterial blood pressure (Psa) decreased from 9.5 +/- 1.2 to 7.9 +/- 1.9 kPa (71 +/- 9 to 59 +/- 14 mm Hg) as did pH from 7.49 +/- 0.04 to 7.13 +/- 0.17 (p < 0.001). Dynamic lung compliance (Cdyn) also decreased; however, pulmonary resistance (RI) remained unchanged. Thromboxane B2 (TxB2) rose in all animals at 60 min coincident with Psa elevation and was significantly blocked by Indo (p < 0.03). In the Indo+TNF group the early TNF-induced rise in Psa was blunted compared to the TNF group [2.9 +/- 1.2 vs. 3.6 +/- 0.8 kPa (22 +/- 3 vs. 27 +/- 6 mm Hg; p < 0.04)] as were the late decreases in pH and Psa (p < 0.04). There were no significant changes in Cdyn secondary to Indo. Although delayed, the hemodynamic changes observed with TNF infusion are similar to those reported for piglets receiving group B streptococci; however, in contrast to the latter the early changes secondary to TNF are only mildly effected by indomethacin. The significant improvement in the late occurring hypotension and acidosis suggests that TNF may act in part via the cyclooxygenase pathway as a mediator of the late hypotension associated with sepsis.