Abstract
Summary Single injections of ovalbumin to presensitized rabbits dramatically increased the circulating activities of plasma tissue-type plasminogen activator (t-PA) and plasminogen activator inhibitor (PAI-1) and induced a severe thrombocytopenia. These effects occurred in a time- and dose-dependent manner, the maximum circulating levels of t-PA and PAI-1 being observed 30 min after administration of the antigen. In order to determine the importance of platelet activating factor (PAF) in this phenomenon, SR 27417, a potent and selective PAF receptor antagonist, was administered prior to antigen challenge. The intravenous administration of SR 27417 strongly inhibited the effects of ovalbumin, showing that t-PA and PAI-1 increase resulting from the anaphylaxis reaction depend on PAF release. SR 27417 also strongly inhibited ovalbumin-induced thrombocytopenia. The mechanism of action of PAF leading to t-PA and PAI-1 increase during anaphylaxis is still unclear, but might be considered as a contributing mechanism during the allergic reaction.
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