The template bleeding time tested in the present study was not prolonge in rats given aspirin (single doses ranging from 1 to 200 mg/kg b.w.). In contrast, bleeding after the transection of tails immersed in saline at 37°C was significantly longer in aspirin treated than in control rats. This prolongation was maximal 1 hour after aspirin (200 mg/kg) and was back to normal within 24 hours, when platelet malondialdehyde formation was still completely inhibited. Both template and transection bleeding times were significantly prolonged in thrombocytopenic and thrombocytopathic rats and in normal rats given a pyrimido-pyrimidine compound (SH-869). These data suggest that platelets are important in the haemostatic process of the rat, but that the platelet defect induced by aspirin is not detectable by the bleeding time measurement techniques used. These may be sensitive not only to platelet dysfunction but also to modifications of vascular tone and blood flow and to blood coagulation and fibrinolysis systems. The complex and contrasting effects of aspirin on haemostatic factors other than platelets (for instance on vascular prostacyclin and fibrinolysis) may influence bleeding times measured by different techniques and contribute to the puzzling results obtained so far with this drug.
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine