The differential effect of aspirin on human platelet activation in aspirin-sensitive asthmatics and normal subjects.

1. The in vitro effect of aspirin on platelet aggregation and ATP release induced by platelet activating factor (PAF), arachidonic acid (AA) and collagen (COL) was assessed in 10 aspirin-sensitive (ASP+) asthmatic patients and 10 normal subjects. 2. For PAF, but not AA or COL, both the baseline EC50 and minimum concentration required to produce a maximum response for aggregation were significantly increased in ASP+ asthmatics compared with normal subjects (P < 0.05). Maximum ATP released was greater in ASP+ patients for all agonists but the difference was most significant for PAF (P < 0.025). 3. In ASP+ asthmatics COL induced, but not AA induced, aggregation was less sensitive to inhibition by aspirin compared with normals (P < 0.01). Similarly, analysis of the area under the percent inhibition concentration-response curve showed aspirin to be less effective in inhibiting platelet aggregation induced by PAF in ASP+ asthmatics than in normal subjects (normal subjects: 155 +/- 11 mg% ml-1, ASP+ asthmatics: 115 +/- 19 mg% ml-1; P < 0.05). 4. Regression analysis showed a poor correlation (r = 0.25, P < 0.4933) between the degree of aspirin induced inhibition of ATP release and platelet aggregation induced by PAF in ASP+ asthmatics. 5. The significant differences observed in platelet responses to PAF, COL and to aspirin in ASP+ asthma patients further suggests an abnormality in platelet function exists in this syndrome.