PROTAMINE INHIBITS COLLAGEN-INDUCED THROMBUS FORMATION IN WHOLE BLOOD

Abstract

Introduction: While an anticoagulant effect of excess protamine has been documented [1], its potential for anti-platelet activity when given in excess is unclear. We used the Clot Signature Analyzer (CSA[registered sign]) to assess the platelet-inhibiting effects of protamine. The CSA tests whole blood shear-induced platelet adhesion, or the platelet-induced hemostasis time, and collagen-induced thrombus formation. Both are tested under arterial shear conditions, allowing assessment of platelet function in a setting mimicking physiologic blood flow. [2] Methods: After HIC approval, paired whole blood samples from 9 volunteers were drawn into syringes containing 120[micro sign]l saline (CTL) or 120[micro sign]l protamine (PROT) at a final concentration of.004 mg/ml. Samples were incubated for 90 seconds, then assayed in the CSA. Statistical analysis was performed using the Wilcoxon signed rank test with significance taken at a P value <or=to 0.05. All values are expressed as the mean +/- SEM. Results: The platelet-induced hemostasis time did not increase significantly with protamine incubation, with a mean of 315 +/- 36 seconds following saline incubation and 433 +/- 65 seconds after protamine incubation (Figure 1, p=0.16). By contrast, collagen-induced thrombus formation was significantly prolonged by protamine from a control time of 433 +/- 99 seconds to 640 +/- 73 seconds after protamine incubation (Figure 1, p<0.01).Figure 1Discussion: The significant prolongation of collagen-induced thrombus formation indicates that protamine in excess inhibits integrin-mediated, collagen-induced platelet aggregation in flowing whole blood. The lack of change in the platelet-induced hemostasis time implies that arterial shear-induced platelet adhesion mediated by platelet GPIb may be less sensitive to the inhibiting effects of protamine.