Agonist-specific refractory states of bovine platelets-disappearance of synergism in aggregation.

The specificity of refractory state of bovine platelets developed by various agonists was examined. When bovine unwashed platelets were preincubated with 5-hydroxytryptamine (5HT) (or ADP), they became non responding to that agonist (refractory) but they responded quite normally to collagen, thrombin and ADP (or 5HT). When platelets became refractory to 5HT, the synergistic aggregation normally obtained with this agonist plus ADP was lost, but that with ADP plus thrombin was not changed. Platelets made refractory to ADP (or 5HT) after the aggregation and disaggregation cycle by the agonist responded normally to 5HT (or ADP). These results strongly indicate that platelets become refractory to one agonist without impairing the sensitivity to any other agonists.