Prostanoids such as prostacyclin and thromboxane A2 have recently been suggested to play important roles in cold ischemia/reperfusion injury. The purpose of this study was to investigate the effect of thromboxane A2 synthetase inhibitor (OKY-046) on cold-stored livers of the rat using an ex vivo perfusion system. Addition of OKY-046 to preservation solution and the perfusate of livers stored cold (4 degrees C) in lactated Ringer's solution resulted in significantly lower glutamic pyruvic transaminase release (3.01 +/- 0.86 IU/g liver vs. 1.79 +/- 1.08 IU/g liver at 120 min after perfusion; P < 0.05), reduced perfusate ammonia levels (8.51 +/- 2.51 micrograms/dl/g liver vs. 3.62 +/- 1.71 micrograms/dl/g liver at 60 min; P < 0.05 and thereafter), lower perfusate taurocholate levels (0.63 +/- 0.10 vs. 0.18 +/- 0.05 at 15 min; P < 0.01 and thereafter), perfusate hyaluronic acid clearance (0.934 +/- 0.132 vs. 0.76 +/- 0.127 at 30 min; P < 0.05 and thereafter), and a reduced number of trypan blue-positive sinusoidal lining cells (50.1 +/- 9.9%; vs. 17.4 +/- 7.0%; P < 0.01). Histologically, the liver preserved for 6 hr in simple cold lactated Ringer's solution exhibited interstitial edema, various degrees of hepatocyte swelling, and sinusoidal stenosis, as well as dilatation, while the livers treated with OKY-046 demonstrated much less hepatocyte swelling, and change in sinusoidal width was nearly absent. We conclude that OKY-046 reduces post-preservation reoxygenation injury by protecting sinusoidal endothelial cells and hepatocytes.