Although
aspirin is effective in the prevention and treatment of
cardiovascular diseases, the optimal dose remains uncertain. The purpose of this study was to compare the platelet inhibitory and
prostacyclin-sparing effects of 2 doses (81 and 325 mg) and forms (enteric-coated and regular) of
aspirin. Since platelet reactivity has been reported to increase after strenuous exercise, a known trigger of
myocardial infarction, subjects were studied following maximal treadmill exercise as well as at rest. Forty male healthy subjects were evaluated using a randomized, double-blind, parallel study design. Blood samples were obtained before and after maximal treadmill exercise at baseline and after 7 days on
aspirin therapy. Both enteric and regular
aspirin in 81- and 325-mg dosages markedly inhibited
adenosine diphosphate and
epinephrine-induced aggregation at rest and after exercise.
Aspirin also inhibited the platelet response to
collagen as assessed by a longer lag time to aggregation. The prolongation of lag time was greater for 325 mg than for 81 mg (100 +/- 7 vs 91 +/- 7; p = 0.04, after exercise). There were no significant dose-related differences in plasma 6-keto-prostaglandin F1alpha level; however, enteric-coated
aspirin inhibited the exercise-induced increase in 6-keto-prostaglandin F1alpha to a lesser extent than regular
aspirin. Although both doses (81 and 325 mg) and types (regular and enteric-coated) of
aspirin inhibited
adenosine diphosphate and
epinephrine-induced aggregation equally, the 325-mg dose inhibited
collagen-induced aggregation to a greater extent than 81 mg. The greater platelet inhibition observed with 325 mg may be clinically relevant in
acute coronary syndromes characterized by plaque
rupture with extensive
collagen exposure and platelet activation.