Histamine H2-receptor mediated positive dromotropic effect in the canine atrioventricular node.
The role of histamine H2-receptors in AV nodal conduction was estimated in the blood-perfused AV node preparation of the dog. Histamine injected into the AV node artery caused an initial, predominant, dose-related prolongation of the AH interval, which was followed by a slight but significant shortening. Diphenhydramine, an H1-antagonist, abolished the initial prolongation, but the shortening was slightly enhanced. Cimetidine, an H2-antagonist, abolished the shortening and potentiated the initial prolongation. Dimaprit, an H2-agonist, caused only a slight, dose-related shortening of the AH interval, which was abolished by cimetidine. The shortening induced by either histamine or dimaprit was slightly suppressed, but was never abolished by atenolol, a beta-blocker, which completely abolished the noradrenaline-induced shortening. These results indicate that a positive dromotropic effect via H2-receptors exists in the canine AV node, although the main effect of histamine on AV nodal conduction is a negative one via H1-receptors.
Motomura
S
S
Department of Pharmacology, Yamanashi Medical College, Japan.
Hashimoto
K
K
D000818:Animals; D001262:Atenolol / Q000494:pharmacology; D001283:Atrioventricular Node / Q000187:drug effects*; D002927:Cimetidine / Q000494:pharmacology; D017259:Dimaprit; D004155:Diphenhydramine / Q000494:pharmacology; D004285:Dogs; D005260:Female; D006329:Heart Conduction System / Q000187:drug effects*; D006632:Histamine / Q000494:pharmacology; D008297:Male; D009638:Norepinephrine / Q000494:pharmacology; D011970:Receptors, Histamine H2 / Q000502:physiology*; D013268:Stimulation, Chemical; D013890:Thiourea / Q000494:pharmacology
D011970:Receptors, Histamine H2; D001262:Atenolol; D002927:Cimetidine; D006632:Histamine; D004155:Diphenhydramine; D013890:Thiourea; D009638:Norepinephrine; D017259:Dimaprit