Effects of histamine agonists and antagonists on luminol-dependent chemiluminescence of granulocytes

Histamine inhibited luminol-dependent chemiluminescence (CL) of granulocytes in a dose-dependent manner, with an ID50 of about 3 X 10(-5) M. Dimaprit, a selective H2-agonist, produced a histamine-like effect. Furthermore, cimetidine, ranitidine, and TZU 0460, which are selective H2-antagonists, but not mepyramine, a selective H1-antagonist, blocked the inhibitory effect of histamine on CL. Thus it may be concluded that the inhibitory effect of histamine is mediated via histamine H2-receptors. H1- and H2-antagonists per se, except at extremely high concentrations, had no effect on CL of granulocytes.