Further Studies on Release of Serotonin and Histamine During Anaphylaxis in the Rabbit

1. Reserpine injected intravenously into rabbits in the amount of 0.1 mg/kg causes a marked lowering of platelet serotonin and histamine without reducing serotonin or histamine in the intestinal tract below the normal range. 2. Sensitized rabbits, pretreated with 0.1 mg/kg of reserpine, had an elevated plasma level of histamine but not of serotonin during anaphylaxis. These findings suggest that the major portion of the rise in plasma serotonin during anaphylaxis is secondary to a release from platelets, whereas the histamine found in the plasma is probably released both from platelets and tissues. In rabbits that had been pretreated with 5 mg/kg of reserpine, histamine levels in the plasma during anaphylaxis were still elevated. 3. The significance of levels attained in the plasma as an index of release from tissues during anaphylaxis is discussed.