Clot retraction facilitates clot lysis.

Platelet facilitation of clot lysis was studied using the dilute clot lysis assay, a standardized assay for fibrinolysis shown to correlate with the development of postoperative deep vein thrombosis. Clots prepared from dilute platelet poor plasma showed prolonged clot lysis when compared with clots prepared in a similar fashion from dilute platelet rich plasma. Since in the presence of platelets clot retraction or contraction occurred, we evaluated a possible direct contribution of retraction to clot lysis. Dilute platelet poor plasma clots were compacted by centrifugation, to a similar extent as that achieved during clot retraction in dilute platelet rich plasma. These clots now lysed at a rate that approached that seen with dilute platelet rich plasma clots. Using an alternate alternate approach, dilute platelet rich plasma clots were treated with cytochalasin B to prevent clot retraction. Such clots now showed prolonged lysis similar to that seen with dilute platelet poor plasma. The prolonged lysis of cytochalasin B treated dilute platelet rich plasma clots was corrected by artificial compaction of the clots. The results suggest that clot retraction markedly facilitates clot lysis, and shows that a major role of platelets to facilitate clot lysis is the effect of these cells to cause clot retraction.