[Presynaptic histamine H3-receptors exist on cardiac sympathetic terminals of guinea pig].
This is the first time to report the existence of new presynaptic inhibitory autoreceptors--histamine H3-receptors in guinea pig myocardium. We found that (R)-alpha-methylhistamine (alpha-MeHA), a selective histamine H3-receptor agonist, attenuates the sympathetic inotropic response of isolated guinea pig atria elicited by electrical field stimulation. This inhibition was associated with a marked reduction in endogenous norepinephrine release. The above phenomenon was antagonised by selective histamine H3-receptor antagonists, and inhibited by pretreatment with N ethylmeleimide. The cardiac sympathetic response could be attenuated or facilitated by increase or decrease of endogenous histamine. Our findings indicate that the endogenous histamine might be involved in the modulation of cardiac sympathetic neurotransmission by interacting with histamine H3-receptors and the receptors are probably coupled to a G(o)/Gi protein.
Luo
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Department of Pharmacology, Fourth Military Medical University, Xi'an.
D000818:Animals; D006168:Guinea Pigs; D006321:Heart / Q000294:innervation*; D006632:Histamine / Q000502:physiology; D017442:Histamine Agonists / Q000494:pharmacology; D008761:Methylhistamines / Q000502:physiology; D009200:Myocardial Contraction / Q000187:drug effects; D009638:Norepinephrine / Q000378:metabolism; D017729:Presynaptic Terminals / Q000502:physiology; D018100:Receptors, Histamine H3 / Q000187:drug effects / Q000502:physiology*; D013268:Stimulation, Chemical; D013564:Sympathetic Nervous System / Q000502:physiology*
D017442:Histamine Agonists; D008761:Methylhistamines; D018100:Receptors, Histamine H3; C069357:alpha-methylhistamine; D006632:Histamine; D009638:Norepinephrine