Stress-dependent changes in fibrinolysis, serotonin and platelet aggregation in rats.

The effects of different kinds of acute stress on collagen-induced whole blood platelet aggregation and fibrinolysis in relation to blood serotonergic measures were studied. In rats water-immersion restraint stress resulted in a shortening of euglobulin clot lysis time (ECLT), an increase in tissue plasminogen activator (tPA) activity with a concurrent fall in its inhibitor activity. Footshock caused rather a suppression in fibrinolysis with a prolongation of ECLT and a decline in tPA activity as well as a reduction in whole blood platelet aggregation induced by collagen. Serotonin (5-HT) level, a marker of a severity of stress, increased after footshock application with a concomitant rise in its major metabolite-5-hydroxyindoleacetic acid (5-HIAA). This indicates an enhanced 5-HT metabolism. Following water-immersion restraint stress 5-HT and 5-HIAA levels did not differ from controls. In both groups of stressed animals an inverse correlation between tPA activity and blood serotonin was observed. Our data indicate that these types of stress may influence either fibrinolysis or peripheral serotonergic mechanism in different ways. Acute and severe stress such as footshock by causing an impairment in fibrinolysis and a rise in 5-HT may contribute to the pathogenesis of thrombosis and henceforth to the development of atherosclerosis.