The effect of collagen mediated platelet release on plasma prekallikrein activation

Collagen mediated platelet aggregation caused -5.6 +/- 6.7% inhibition and +39.1 +/- 15.2% potentiation of prekallikrein activation in plasma from normal healthy volunteers between 20-40 and 50-65 years of age, respectively (n = 15, p less than 0.01). The amounts of platelets factor-four (PF4) released in the two groups were not significantly different. Collagen treatment in the presence of indomethacin caused +11.5 +/- 3.6% and +59.6 +/- 19.5% potentiation in the 20-40 and 50-65 age groups respectively (p less than 0.02). Adrenaline mediated platelet aggregation caused -55.2 +/- 7.1% and -35.2 +/- 8.3% inhibition in the 20-40 and 50-65 age groups, respectively. Collagen treatment of platelet-deficient-plasma and platelet-rich-plasma in EDTA also caused potentiation of prekallikrein activation. The results indicate that the observed degree of prekallikrein activation after platelet aggregation is a net result of the inhibitory effect of PF4 and the potentiatory effect of activated platelets. The potentiatory effect was greater after collagen treatment as compared to adrenaline treatment, and in the 50-65 age group as compared to the 20-40 age group.