Gelation of fibrinogen in plasma. A kinetic study by turbidity measurement

Studies of the turbidity profiles of diluted (1/55, v/v) normal plasma, thrombin activity free serum plus commercial fibrinogen, and 0.15 M NaCl, pH 7.4, plus commercial fibrinogen, activated by thrombin or reptilase and measured at 350 nm, have shown that the latency time (LT) hardly varies for the fibrinogen concentration within limits of 0.03-0.15 mg/ml; however, it does vary for the thrombin concentration. The rate of gelation (RG) varies linearly with the fibrinogen (FG) concentration, conforming to the equation RG = 0.027 (FG)1.8; it hardly varies for thrombin concentrations greater than 0.50 NIH U/ml. On the other hand, RG values obtained for 0.46 NIH U/ml of thrombin or 0.92 BU/ml of reptilase show no significant differences. The variation in LT for the thrombin or reptilase concentration allows the rate of activation to be estimated, giving values of 5.9 X 10(-12) and 3.2 X 10(-12) mol/U/s, respectively, for a fibrinogen concentration in plasma of 1.1 X 10(-10) mol/ml. The mean value estimated for the ratio LT/FG in normal plasma is 35.76 +/- 18.3 and 85.62 +/- 18.3 s mg-1 ml for activation by thrombin and reptilase, respectively. We have studied in normal plasma the parameters that define the gelation of fibrin as measured by turbidity curves and their variation according to the fibrinogen concentration. This permits us to establish the kinetics of fibrin gel formation and normal range values.