Evidence for a central alpha-sympathomimetic action of clonidine in the rat.
The antihypertensive effects of clonidine (0.15 mg kg-1, i.p.) were studied in conscious DOCA/saline hypertensive rats having chronically implanted arterial cannulae. The response to clonidine was markedly reduced by simultaneously administered desipramine (3 mg kg-1, i.p.), antagonized dose-dependently by piperoxan (2-10 mg kg-1, i.v.) and prevented by pretreatment with phentolamine (0.2 mg, i.c.v.). Pretreatment with 6-hydroxydopamine (3 x 250 mu-g, i.c.v.), haloperidol (1 mg kg-1, i.p.), p-chloro-N-methylamphetamine (3.5 mg kg-1, i.p.) or 5,6-dihydroxytryptamine (50 mu-g and 25 mu-g, i.c.v.) did not significantly modify the antihypertensive response. It is concluded that the antihypertensive response to clonidine is mediated via stimulation of central alpha-adrenoceptors and is independent of central dopaminergic receptors and intact central serotoninergic neurons. The necessity for intact central noradrenergic neurons remains uncertain.
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology; D003000:Clonidine / Q000494:pharmacology* / Q000627:therapeutic use; D004298:Dopamine / Q000502:physiology; D006973:Hypertension / Q000139:chemically induced / Q000188:drug therapy; D007668:Kidney / Q000502:physiology; D008297:Male; D009474:Neurons / Q000502:physiology; D009638:Norepinephrine / Q000502:physiology; D051381:Rats; D012701:Serotonin / Q000502:physiology; D013997:Time Factors
D000316:Adrenergic alpha-Agonists; D000959:Antihypertensive Agents; D012701:Serotonin; D003000:Clonidine; D004298:Dopamine; D009638:Norepinephrine