Pulmonary edema and impaired gas exchange function are worrisome early complications of heart-lung transplantation. The present study was designed to determine the effect of a new prostacyclin analog, OP-41483, on these complications with the use of a heart-lung autoperfusion model. Twenty-four mongrel puppies (4 to 6 kg) were evenly divided into four groups according to the oxygen content of inspired air (group 1, 95%; group 2, 60%) and the use of an intravenous drip of OP-41483 (0.1 microgram/kg/min) (group 3, 95% + OP; group 4, 60% + OP). During the course of these experiments, systolic pressure and cardiac output were maintained constant at 100 mm Hg and 40 ml/kg/min, respectively. Pulmonary arterial pressure was almost constant in each group throughout the experiment. Arterial oxygen tension (Pao2) was significantly decreased in groups 1 (410 +/- 49 to 237 +/- 38 mm Hg, p less than 0.01) and 2 (368 +/- 44 to 243 +/- 26 mm Hg, p less than 0.01) over the 5-hour autoperfusion period but was maintained at a high level in groups 3 (488 +/- 70 to 447 +/- 39 mm Hg) and 4 (431 +/- 33 to 430 +/- 35 mm Hg). Pathologic findings (perivascular edema and capillary dilatation) were significant in group 1 but less marked in group 2. However, no abnormal pathologic changes were observed in groups 3 or 4. These data demonstrated that OP-41483 was effective in preventing functional and pathologic pulmonary disturbances at a dosage (0.1 microgram/kg/min) that is reported to induce no undesirable hemodynamic effect.