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In the IgE-sensitized Brown Norway rats, the intravenous antigen challenge resulted in systemic anaphylactic shock without thrombocytopenia. In the IgG-sensitized Wistar rats, thrombocytopenia occurred during the anaphylactic shock. It is linked with circulating immun-complexes. Treatment of IgG-sensitized Wistar rats by antiplatelet serum, by promethazine (anti-H1), cyproheptadine (anti-5-HT1) or phenidone, a cyclo-oxygenase and lipoxygenase inhibitor, did not protect against the anaphylactic shock. In the rat, platelets did not play a significant rôle in the pathogenesis of the various forms of the anaphylactic shock.

Brown Norway rats have been actively sensitized against hen ovalbumine mixed with anti Bordella pertussis vaccine. After ten to twelve days, IgE are detected in the blood, but no precipitins. Anaphylactic shock induced by i.v. injection of 1 mg.100 g-1 body weight of ovalbumine is caracterized by a vascular collapse, the animal dying in about 15 minutes. This collapse is identical with the same general anaphylactic reaction as observed in the Wistar rats, which have large amounts of precipitins in the blood.

Pretreatment of actively IgG sensitized Wistar rats with indomethacin, diethylcarbamazine or phenidone respectively, does not modify the evolution of the anaphylactic shock. Neither prostaglandins nor leukotrienes seem to play a significant role in the pathogenesis of this vascular collapse.

1. Rat serum levels in beta-glucuronidase and beta-galactosidase are higher than plasma levels. Rat platelets release these lysosomial enzymes during blood coagulation in vitro. 2. After anaphylactic shock, in the sensitized rat, there is no increase in beta-galactosidase and beta-glucuronidase plasma levels. The tissues of the sensitized rat do not release these enzymes during the antigen-antibody reaction. The blood platelet level is diminished after anaphylactic shock and the serum levels of the lysosomial enzymes are decreased. 3. In thrombopenic rat, anaphylactic shock is identical as in control animals. Rat platelets do not play a significant role in the anaphylactic shock.