Platelet aggregation induced by anaphylatoxin and its inhibition

Anaphylatoxin (AT), a splitting product of the fifth component of the complement system can be prepared by incubation of rat plasma with low-molecular weight dextran (MW 2000) at 37 degrees C, or by treatment with cobra venom factor. Using the turbidimetric method of Born the effect of AT was studied on platelets from man, dog, rabbit, cat, guinea pig, and rat. AT was found to induce aggregation only in platelet rich plasma from cat and guinea pig. This aggregation could be reduced by several known inhibitors of aggregation and platelet function, such as phentolamine, tosylarginine-methylester (TAMe), p-chloromercuribenzoate (PCMB), and ethylenediamine-tetraacetic acid (EDTA) whereas adenosine, methysergide-bimaleinate, and mepyramine-maleate proved to be ineffective. Experiments with PCMB and TAMe suggest a release reaction induced by AT. Further more, there is evidence that with platelets from guinea pigs AT produces some tachyphylactic state.