Platelet activation: a new biological activity of guinea-pig C3a anaphylatoxin.

3H-serotonin-release from labelled gp-platelets is established as a sensitive method for testing a new biological activity of gp-C3a anaphylatoxin in an autologous situation. Time-, dose- and temperature-dependent release reactions as well as specific inhibition by carboxypeptidase B and anti-C3a antibodies show that C3a is a potent and specific inducer of platelet activation. Inactive C3a does not induce 3H-serotonin-release but specifically inhibits the action of C3a on platelets.