Collagen/endogenous thrombin-induced platelet aggregation in whole blood samples

combined effects of collagen (3.5 mu g/ml) and endogenously generated thrombin (due to addition of 0.35 pmol/l tissue factor) on platelet aggregation in the physiological environment of whole blood by means of the impedance method. Lag times were significantly shorter when a combination of collagen and endogenous thrombin was used to provoke platelet aggregation (41.9 +/- 16.3 s) compared with collagen (173.8 +/- 52.1 s, P< 0.0001) or endogenous thrombin (94.3 +/- 43.6 s, P<0.001). Amplitudes and slopes were the lowest in collagen-induced experiments (2.83 +/- 1.59 Omega and 1.79 +/- 0.45 Omega/min, respectively), whereas they were approximately the same in endogenous thrombin-induced experiments whether Collagen was present or not (13.7 +/- 3.1 versus 11.2 +/- 4.0 Omega and 6.3 +/- 2.8 versus 5.6 +/- 2.3 Omega/min, respectively). No synergistic effect of Collagen and endogenous thrombin on the clot formation process was observed by means of thrombelastometry. Moreover, thrombin potentials in tissue factor-activated plasma samples were approximately the same whether Collagen was present or not (834 +/- 67 versus 809 +/- 63 nmol/l.min). In conclusion, enclogenously generated thrombin is a potent platelet agonist in whole blood, and a combination of Collagen and endogenous thrombin synergistically shortens the lag time until the onset of platelet aggregation.