• The Korean Journal of Pharmacology
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• v.22 no.2
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• pp.115-122
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• 1986

To delineate the relationship between subtypes of central alpha-adrenoceptor and central calcium channel, influences of intracerebroventricular (icv) diltiazem and nifedipine on the changes of blood pressure and heart rate by icv methoxamine and clonidine were investigated in urethane-anesthetized rabbits. 1) Methoxamine (1mg, icv) produced pressor and bradycardiac effect and clonidine $(30\;{\mu}g,\;icv)$ produced hypotension and bradycardia. 2) Icv diltiazem and nifedipine elicited dose-dependent deprcssor and bradycardiac responses. The depressor response to nifedipine was more prominent than that to diltiazem but the bradycardiac effect of nifedipine was smaller than that of diltiazem. The depressor responses to icy nifedipine $(35{\mu}g)$ and icv diltiazem $(400{\mu}g)$ were persistent but those to intravenous (iv) nifedipine $(35{\mu}g/kg)$ and diltiazem $(200{\mu}g/kg)$ were transient. 3) The pressor response to methoxamine was little affected by pretreatment with in diltiazem $(400{\mu}g)$ or icv nifedipine $(35,\;350{\mu}g)$ but the bradycardiac response to methoxamine was significantly attenuated by the same pretreatment. 4) The depressor response to clonidine was markedly attenuated by pretreatment with icv diltiazem $(400{\mu}g)$ or icv nifedipine $(35,\;350{\mu}g)$ but not affected by pretreatment with iv diltiazem $(200{\mu}g/kg)$ or iv nifedipine $(20{\mu}g/kg)$. Pretreatment with icv and iv diltiazem or nifedipine reduced the bradycardiac effect of clonidine. 5) Pretreatment with icv clonidine had no effect on the depressor and bradycardiac responses to in diltiazcm or icv nifedipine. These results indicate that diltiazem and nifedipine have no effect on icv methoxamine-induced pressor response elicited by the activation of central alpha-l adrenoceptors whereas the icv clonidine-induccd depressor and bradycardiac effects which result from the activation of central alpha-2 adrenoceptors are inhibited by the calcium antagonists.