| Abstract: | 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. 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. Nordimaprit and the selective H1-receptor agonist 2-pyridyl-ethyl-amine (2-PEA) did not modify the patterns of cardiac anaphylaxis. The positive inotropic and chronotropic responses of the isolated heart to exogenous histamine appear to be partly reduced in the presence of dimaprit. 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. |
