The antithrombotic effect of human activated protein C on He-Ne laser-induced thrombosis in rat mesenteric microvessels.

The effect of activated protein C (APC) on He-Ne laser-induced thrombosis in rat mesenteric microvessels was studied. APC inhibited platelet-rich thrombus formation in a dose-dependent manner more significantly in venules but also in arterioles. Inhibition of thrombus formation was maximal immediately after intravenous administration and persisted for 40 minutes in venules and 20 minutes in arterioles. The maximum effective blood concentration of APC was 1.04 micrograms/ml. A small but statistically significant prolongation of the activated partial thromboplastin time (APTT) was observed at this blood concentration, demonstrating the anticoagulant effect of APC. Our findings show that APC has a significant inhibitory effect on platelet thrombus formation and suggest that APC is a potent natural antithrombotic agent.