Summary
Adenosine 5’diphosphate activates platelet factor 3 of intact platelets in citrated, heparinized or native plasma. PF-3 activation is dependent on the dose of ADP, and is achieved with sufficient speed to suggest that it can play a physiological role in blood coagulation. ADP-induced platelet aggregation is inhibited by AMP (but not ATP), 2-chloro adenosine, phosphoenol pyruvate and phosphoenol pyruvate kinase, and diguanidinodiphenyl sulfone. Other agents which aggregate platelets induce PF-3 activation; the effects of norepinephrine, serotonin, low doses of trypsin and thrombin, and endotoxin in the human can be inhibited by AMP but the action of latex or celite particles cannot be fully inhibited by AMP. PF-3 activation requires higher ADP concentrations than does ADP-induced platelet aggregation. Guanidinosuccinic acid blocks the action of ADP on PF-3 activation without affecting its action on aggregation. ADP-induced PF-3 activation is unrelated to activation of factors XII and XI. Though PF-3 activation usually occurs in parallel with platelet aggregation the two actions of ADP of platelets may occur independently.
