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KMID : 0043319880110010065
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Archives of Pharmacal Research
1988 Volume.11 No. 1 p.65 ~ p.73
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Effects of Clonidine on the Negative Chronotropic Response Induced by Vagal Stimulation in the Rat
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Hong SC
Huh KH/Chung JK/Park MS
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Abstract
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The effects of clonidine on the negative chronotropic response induced by stimulation of vagus nerve were studied in the presence of propranolol in reserpinized and anesthetized rats. When the heart rate was decreased by stimulation of the vagus nerve, clonidine significantly inhibited vagally induced heart rate decrease (negative chronotropic response) in dose dependent manner. This inhibitory effect of clonidine was virtually abolished by phentolamine, alpha1- and alpha2-adrenoceptor antagonist, and partially antagonized by prazosin, alpha1-adrenoceptor antagonist. On the other hand, when the heart rate was decreased by the infusion of bethanechol, a muscarinic parasympathetic stimulant, clonidine had no effect on the bethanechol-induced heart rate decrease. These results suggest that clonidine inhibits vagally induced negative chronotropic response by activation of presynaptic alpha-adrenoceptors located on the parasympathetic cholinergic nerve terminal in the heart and this effect of clonidine is more related to alpha2-adrenoceptors than alpha1-adrenoceptors.
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