Relaxation of isolated rabbit veins mediated by latent histamine H2-receptors

Isolated rabbit veins preconstricted by either norepinephrine, methoxamine or potassium were relaxed by histamine in the presence of mepyramine, a histamine H1-antagonist. The relaxation was not antagonized by atropine, propranolol and indomethacin but by an H2-antagonist cimetidine. It is likely that histamine relaxes the rabbit veins through H2-receptors.