The effect of aspirin on platelet adhesion to chronically damaged pulmonary arteries
was studied in 18 dogs. Chronic injury was produced in all dogs by infection with
the canine heartwonn Dirofilaria immitis(DI). Ten dogs were subjected to 4 days of chronic injury. Eight dogs were subjected
to 30 days of chronic injury. Five of the 4 day injury and 4 of the 30 day injury
dogs received aspirin daily (325 mg/day orally). Aspirin was started 3 days prior
to infection with DI. Pulmonary arteries were perfusion fixed in situ at physiologic pressure. The damaged pulmonary arteries were located by Evan’s blue
staining (2ml/kg of 1% dye glven one hr prior to perfusion) and prepared for scanning
electron microscopy. Both groups of dogs with 4 day DI infection had monolayers of
platelets adhered to exposed subendothelium. Aspirin treated dogs had enhanced platelet
adhesion to damaged arteries. Aspirin treatment for 33 days reduced platelet adhesion.
The damaged arteries of treated dogs infected with DI for 30 days had very few platelets
adhering to the damaged surface. However, non-treated dogs subjected to 30 days of
infection had platelet adhesion equivalent to the 4 day non-treated infection group.
These results suggest that although aspirin is ineffective in preventing platelet
adhesion in short term therapy it is effective when given for longer time periods.
This inhibitory effect may occur due to platelet membrane changes rather than because
of aspirin inhibition of cyclooxygenase.
Keywords
Platelet - Adhesion - Vascular damage - Aspirin
