A postsynaptic inhibitory histamine H2-receptor in the mouse isolated vas deferens |
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Authors: | M M Vohra |
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Institution: | (1) Department of Pharmacology, Dalhousie University, B3H 4H7 Halifax, Nova Scotia, Canada |
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Abstract: | The effect of histamine on adrenergic neurotransmission in the mouse isolated vas deferens preparation was investigated. Concentrations of histamine ranging from 0.2 to 650 M depressed, in a dose-related manner, not only the contractile response elicited by field stimulation but also the response caused by the addition of exogenous noradrenaline and acetylcholine. However, the release of 3H]-NA evoked by field stimulation or by high K+ remained unchanged in the presence of these concentrations of histamine. The inhibitory effect of histamine on the contractile responses caused by various stimuli was reduced or completely antagonized by cimetidine, a histamine H2-receptor antagonist but not by mepyramine, a conventional antihistamine. The inhibitory effect of histamine was found to be inversely proportional to both the Ca2+ concentration in the bathing medium and to the frequency of field stimulation. Further, the inhibitory effect of histamine was markedly reduced when Mg2+ was omitted from the bathing medium. It is concluded that the mouse vas deferens preparation contains a post-junctional inhibitory H2-receptor. The stimulation of H2-receptors by histamine inhibits the contractile response of the vas deferens, possibly by decreasing the availability of Ca2+ required for contraction by depressing the influx of Ca2+. |
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