The effect of acetylsalicylic acid on fibrin gel lysis by tissue plasminogen activator.

The in vitro effect of acetylsalicylic acid (ASA) on fibrin gel lysis by exogenous t-PA was studied in 13 patients with angina pectoris. Six patients received 75 mg, and seven patients 160 mg of ASA. Plasma clots were formed and lysed in microtiter plate wells and turbidity monitored spectrophotometrically. Mean lysis times in the 75 mg group were 8.7, 11.4 and 11.2 min during ASA treatment, and after 1 and 2 weeks ASA withdrawal respectively. Reduced changes were observed in the 160 mg group. Additionally, a relationship was found between the fibrin fiber mass/length ratio, i.e. fiber thickness in mature clots and lysis times after ASA administration (P = 0.0015). Importantly, fibers are thicker during treatment with ASA. It was subsequently demonstrated that the potential to produce thicker fibers by varying the thrombin concentration has a noticeable effect on turbidimetric profiles in the presence of exogenous t-PA. This effect was similar to the changes observed during and after ASA treatment. Thus, these results suggest that the enhancement of fibrin gel lysis during ASA treatment may be due to alterations in gel structure. In addition, a reduction in the fibrin mass in lower turbidity clots, suggests an added mechanism by which ASA may enhance lysis.