The central sympatho-inhibitory effect of 5,6-dihydroxy-2-dimethylaminotetralin (M7) is mediated by alpha 2-adrenoceptors.
M7 (5,6-dihydroxy-2-dimethylaminotetralin) produces in anesthetized rats a hypotensive response previously attributed to peripheral dopaminergic mechanisms. We re-examined the effects of this drug on arterial blood pressure, heart rate and sympathetic nerve activity in anesthetized rats and dogs. M7 (1-100 micrograms/kg i.v.) produced in the rats transient dose-dependent pressor effects, with bradycardia and sympatho-inhibition, followed by long-lasting dose-dependent hypotension, bradycardia and sympatho-inhibition. The sympatho-inhibitory and hypotensive effects were comparable in baroreceptor-denervated rats and were reversed by idazoxan (0.1 mg/kg i.v.). The sympatho-inhibitory response induced by M7 (1-100 micrograms/kg) was prevented by treatment with the specific alpha 2-adrenoceptor antagonist, 2-methoxy-idazoxan (0.03 mg/kg i.v.). This central effect of M7 was not altered by treatment with the alpha 1-adrenoceptor antagonist, prazosin (0.1 mg/kg i.v.), and was reduced by treatment with the alpha 2-adrenoceptor antagonists, yohimbine (1 mg/kg i.v.) or idazoxan (0.3 mg/kg i.v.), and the dopaminergic antagonists, haloperidol (0.5 mg/kg i.v.) or sulpiride (3 mg/kg i.v.). Bilateral microinjections of M7 (0.3-3 nmol) into the rostroventral medulla in the rat produced dose-dependent hypotension, bradycardia and sympathetic nerve inhibition which were reversed and prevented by bilateral microinjection of 2-methoxy-idazoxan (1 nmol) into the same sites. Microinjections of 2-methoxy-idazoxan into the rostroventral medulla also inhibited the central effects of M7 at 0.03 mg/kg i.v. In anesthetized dogs, M7 administered into the cisterna magna (1-10 micrograms/kg) reduced arterial blood pressure, heart rate and sympathetic nerve activity; these effects were reversed by administration of 2-methoxy-idazoxan (0.03 mg/kg i.v.). In conclusion, M7, a rigid catecholamine, produces a potent central sympatho-inhibitory and hypotensive effect by activation of alpha 2-adrenoceptors.
Vayssettes-Courchay
C
C
Division of Angiology, Servier Research Institute, Suresnes, France.
Bouysset
F
F
Laubie
M
M
Verbeuren
T J
TJ
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000758:Anesthesia; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002490:Central Nervous System / Q000187:drug effects* / Q000502:physiology; D002946:Cisterna Magna / Q000187:drug effects; D004285:Dogs; D018492:Dopamine Antagonists / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004639:Emetics / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D019329:Idazoxan / Q000031:analogs & derivatives / Q000494:pharmacology; D008297:Male; D008845:Microinjections; D009284:Naphthols / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D011311:Pressoreceptors / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D018341:Receptors, Adrenergic, alpha-2 / Q000187:drug effects / Q000502:physiology*; D013153:Splanchnic Nerves / Q000187:drug effects / Q000502:physiology; D013564:Sympathetic Nervous System / Q000187:drug effects* / Q000502:physiology; D014628:Vagotomy
D000317:Adrenergic alpha-Antagonists; D018492:Dopamine Antagonists; D004639:Emetics; D009284:Naphthols; D018341:Receptors, Adrenergic, alpha-2; C009957:5,6-dihydroxy-2-dimethylaminotetralin; C058525:2-methoxyidazoxan; D019329:Idazoxan