Factors Influencing Thrombin Induced Platelet Release Reaction

To study the effect of pH and platelet counts on thrombin induced platelet release reaction, washed human platelets labeled with ¹⁴C-serotonin were suspended in phosphate buffered saline of varying pH values for 15 minutes with thrombin concentrations between 1,1 and 0,068 NIH U/ml of suspension. The amount of serotonin released caused by the thrombin added was dependent on the pH of the incubation medium with an optimum in the range of pH 7,4 -7,6. This effect was more marked with higher thrombin concentrations. The serotonin release controles without thrombin were not influenced by the different pH values and were always less than 10%. The amount of platelets in the reaction mixture influenced the release values not significantly at thrombin concentrations of 1,1 and 0,27 NIH U/ml While with 0,068 NIH U/ml a significant dependence of the release on the number of platelets was observed, resulting in higher release values in platelet mixtures with lower platelet counts.

Therefore it can be concluded that the pH is of major influence on the release reaction especially at high thrombin concentrations while the platelet count is of importance only at low thrombin concentrations.