[Role of protein C in endotoxin-induced release of plasminogen activator inhibitor from endothelial cell].

To elucidate the role of protein C (PC) in the release of plasminogen activator inhibitor (PAI) from endothelial cells, the effect of PC and activated protein C (APC) on plasma levels of PAI in endotoxin (ET)-treated rats was examined. When activated by snake venom, human PC significantly prolonged the activated partial thromboplastin time (APTT) of both human and rat plasma samples. Addition of APC also prolonged the APTT of both human and rat plasma samples. PAI activity in plasma from septicemic patients and ET-treated rats was neutralized by APC. A small dose of ET (0.1 microgram/kg) gradually increased plasma PAI activity, which became maximum 3h after ET-treatment. APC administered prior to ET-treatment, PC decreased PAI activity, however, no such inhibition was seen when administered after ET-treatment. A significant negative correlation between PC concentrations and PAI activities was observed in plasma from septicemic patients. These findings indicated that activation of PC on endothelial surface plays a regulatory role in releasing PAI and that endotoxin might inhibit the surface activation of PC.