Development of a Microvascular Thrombosis Model and the Participation of Oxygen Radicals on the Thrombotic Process

We developed a new thrombosis model using a microvasculature of hamster cheek pouch for the kinetic evaluation of thrombotic process in relation to endothelial damage. The thrombus was produced in the venule with excellent reproducibility by the irradiation of the filtered light with the intravascular administration of fluorescein sodium. The thrombotic process, assessed by two parameters such as Ti (initiation time of thrombus formation) and Ts (stopping time of blood flow by thrombus), was dependent on the light intensity and the dye concentration. In the initial stage of thrombus formation, cytoplasmic organella swelling, vacuole formation, luminal membrane rupture and swelling of the nuclear envelope were observed in endothelium. With progress of thrombus formation, these changes became more obvious and focal endothelial denudation was observed at the advanced stage. The thrombus was developed only on the irradiated vascular endothelium without exposure of basement membrane, which suggested that primary endotherial damage could lead to the thrombus formation. Superoxide dismutase (SOD), scavenger of oxygen radicals, was intravenously applied to evaluate the cytotoxic effects of oxygen radicals on endothelium. Continuous infusion of SOD of 5, 000 and 10, 000U/kg/min dose dependently prolonged Ti from 66.8±9.6 to 121.0±46.1 and 186.2±40.0sec, and Ts from 405.9±32.5 to 792.0±190.5 and 921.8±197.2sec (mean±SD, n=10), respectively. Furthermore, morphological changes of endothelium and platelet were markedly reduced by administration of SOD. From these data, oxygen radicals were suggested to cause the injury of endothelium and lead to thrombus formation.