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KMID : 0360419840200020007
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Korean Journal of Pharmacology
1984 Volume.20 No. 2 p.7 ~ p.14
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The Influence of Imipramine on the Effect of Clonidine in Pithed Rats
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Abstract
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In pithed rats, rising in diastolic blood pressure by clonidine, when intravenously injected, is expressed as the postsynaptic action, and inhibitory action on electrical stimulation-induced tachycardia by clonidine is expressed as the presynaptic inhibitory action.
In this study it was aimed to observe the inhibitory effect of imipramine caused by a single and chronic administration on both postsynaptic and presynaptic action of clonidine in pithed rats, and discussed in relation with the mechanism of antidepressant action of imipramine.
1) A rise of diastolic blood pressure by clonidine was not antagonized by prazosin, but by both phentolamine and piperoxan.
2) The inhibition by clonidine of tachycardia which was induced by electrical stimulation was also antagonized by phentolamine and piperoxan, but not by prazosin.
3) The increase in diastolic blood ´pressure in response to clonidine was inhibited by both a single or chronic administration with imipramine (20 mg/kg). It was more pronounced in the latter.
4) The inhibitory action of clonidine on the tachycardia was markedly inhibited by both types of administration with imipramine, between which there showed little difference.
It is concluded that the presynaptic a2-adrenoceptor is rather sensitively affected by a single administration with imipramine, and a long-term imipramine treatment may inhibit both pre- and postsynaptic a27adrenoceptors, simultaneously.
Furthermore, it was seemed unlikely that these results provide the evidence ;to support the fact that the subsensitivity of presynaptic a2-adrenoceptor may be the mechanism of action of tricyclic antidepressant.
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