Inhibition of passive cutaneous anaphylaxis by several histamine (H1) and serotonin antagonists in the rat

Drugs of the pizotifen type (pizotifen, cyproheptadine), possessing high H1-antihistamine and high antiserotonin activities in animal experiments, exert potent inhibitory actions on the passive cutaneous anaphylaxis (PCA) reaction in the rat. The drug pipethiadene, a 4,9-dihydrothieno(2,3-c)-2-benzothiepin derivative also belongs to this group. Selective histamine H1-antagonists alone are unable to cause pronounced reduction of the intensity of the PCA reaction in the rat, but in local reactions induced in rats by compound 48/80, histamine H1-receptors seem to play major role.