Pharmacological properties of PAF-acether in the guinea-pig: platelet-dependent and independent reactions

The in vivo effects of PAF-acether in the guniea-pig are reviewed, particularly with respect to bronchoconstriction and to platelets, the former being suppressed when the latter are depleted. Bronchoconstriction by PAF-acether is not inhibited by aspirin, and when the latter was associated to mepyramine and to methysergide, bronchoconstriction was blocked, whereas thrombocytopenia persisted. Our results indicated that platelets collected from aspirin--mepyramine--methysergide-treated animals are less reactive for PAF-acether than control platelets, with respect to secretion of ATP, but aggregated fully. Secretion and aggregation are thus dissociable, the former being involved with bronchoconstriction. Results obtained with sulphinpyrazone and with reserpine are also discussed, and lead to the concept that platelet may release a presently unknown mediator when stimulated with PAF-acether.