Summary
A study of platelet aggregation induced by progressive concentrations of collagen
was performed in 40 normal persons, equally grouped by sex, immediately before, and
90 min after, the ingestion of 0.500 g aspirin. Simultaneously, serum ASA-esterase
activity and plasmatic salicylic acid levels were investigated in the pre- and post-ASA
samples respectively. Wide individual variations in platelet responsiveness to collagen
were found when the minimal amount of the aggregating agent necessary to provoke significant
aggregation was located. The percentage of aggregation and the slope were the most
sensible indicators of both the individual variances and the ASA-induced inhibition.
Correlation was found in both groups between the minimal amounts of collagen required
for initiating aggregation pre- and post-ASA. Also a positive correlation was found
between the minimal collagen concentration required to initiate aggregation pre-ASA
and the aspirin-induced inhibition in the aggregation produced by a higher collagen
concentration. Important individual and sexual differences were detected in the serum
content of ASA-esterase activity. A negative significant correlation was demonstrated
between the ASA-esterase activity and the differences in collagen concentrations necessary
to start aggregation pre- and post-aspirin in the men group. Failure to consider individual
variances in platelet reactivity may lead to false conclusions about the ASA affective-ness
as an antithrombotic agent.
