- 1 The administration of E. coli endotoxin (2 mg/kg i.v.) to anaesthetized cats results in a characteristic acute pulmonary response. This consists of increases in pulmonary artery pressure and airways resistance and a reduction in lung compliance. 2 Plasma concentrations of prostaglandin E2 (PGE2), PGF2 alpha, thromboxane B2 and 6-keto PGF1 alpha were measured by radioimmunoassay in aortic and pulmonary arterial blood samples before, during and after the acute pulmonary response to endotoxin. 3 Endotoxin administration resulted in the rapid release of PGF2 alpha and thromboxane B2 from the lungs. The time course of this release was parallel to that of the pulmonary hypertensive and airways responses to endotoxin. PGE2 and 6-keto PGF1 alpha were released more gradually and with greater variations between individual animals. 4 During the delayed shock phase (2 h after endotoxin) the concentrations of PGE2, PGF2 alpha and 6-keto PGF1 alpha were once again elevated in both the aorta and pulmonary artery. Thromboxane B2 concentrations were not increased at this time. 5 These results suggest that PGF2 alpha and thromboxane A2 may be mediators of the acute pulmonary responses to endotoxin.