The antianaphylactic action of histamine H2‐receptor agonists in the guinea‐pig isolated heart

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Abstract
1 The effects of histamine and of H1-and H2-receptor agonists on the response to specific antigen were studied in isolated hearts taken from actively sensitized guinea-pigs. 2 Histamine and H2-receptor agonists (dimaprit, impromidine) dose-dependently decrease the positive chronotropic and inotropic effects, and the severity of arrhythmias evoked by the challenge of sensitized hearts with specific antigen. 3 Nordimaprit and the selective H1-receptor agonist 2-pyridyl-ethyl-amine (2-PEA) did not modify the patterns of cardiac anaphylaxis. 4 The positive inotropic and chronotropic responses of the isolated heart to exogenous histamine appear to be partly reduced in the presence of dimaprit. 5 The H2-receptor agonists decrease the amount of histamine released during cardiac anaphylaxis which is increased by cimetidine, while nordimaprit and PEA were ineffective, indicating an inhibitory function afforded by H2-receptors in cardiac anaphylaxis.