THROMBIN ACTIVITY ON DISSECTED AND ANASTOMOSED HUMAN ARTERIES

The mechanism of anastomotic thrombosis in microvascular surgery remai ns poorly understood. We hypothesized that thrombin activity at anasto moses plays a major role in this process. To study this, a surgically relevant human artery anastomosis model was used to (i) measure surfac e thrombin activity on anastomoses and on intact vessel, (ii) determin e the inhibitability of surface thrombin by heparin and recombinant hi rudin (r-hirudin), and (iii) determine the anastomotic and intact vess el binding capacity for additional thrombin. Human placental artery se gments were placed in chambers in which 0.2 cm(2) of luminal surface w as exposed to citrated platelet-poor plasma for 10 min at 37 degrees C . The fibrinopeptide A (FPA) concentration (indicating the action of t hrombin on fibrinogen) in the supernatant was then measured using an E LISA assay. Intact vessels and anastomoses expressed equivalent thromb in activity that could not be inhibited by heparin at a concentration (0.3 U/ml) that is sufficient to prolong the activated partial thrombo plastin time two-fold. Conversely, the concentration of heparin routin ely used in intraoperative vessel irrigation solutions (50 U/ml) was a ble to completely block thrombin activity at both sites. r-Hirudin (0. 3 heparin equivalent anti-IIa U/ml) was able to inhibit nearly all of the thrombin activity on each site. Each site was able to bind and exp ress the activity of additional thrombin, indicating the potential for increased vessel thrombogenicity after local clot has formed and has been removed. These data indicate the presence of thrombin on dissecte d human vessels and its presence in equal amounts on intact and anasto mosed vessels when measurement is made before blood flow resumes. Furt hermore, vessel-associated thrombin is resistant to a standard systemi c concentration of heparin but is susceptible to the much higher hepar in concentration that can be delivered locally by the surgeon during v essel irrigation. (C) 1996 Academic Press, Inc.