Localization in the CNA of adrenoceptors which facilitate a cardioinhibitory reflex.
In dogs (pentobarbitone, 25 mg/kg) the brain was removed rostrally to the pons, leaving the cerebellum intact (decerebrate animals). In other animals the cerebellum was additionally removed (bulbar animals). In all animals beta-adrenoceptors were blocked by toliprolol (5 mg/kg s.c.). Angiotensin (0.025-0.3mug/kg) was repeatedly injected i.v. and the resulting maximal reflex bradycardia was recorded. Intracisternal (i.ci.) injection of clonidine, 0.5 to 1 mug/kg, in decerebrate or i.v. injection of 10 or 30 mug/kg in bulbar animals significantly facilitated the reflex bradycardia. This effect was antagonised by a subsequent injection of piperoxan 50 mug/kg i.ci. in decerebrate or 1 mg/kg i.v. in bulbar animals. It is concluded that the facilitatory action of clonidine is mediated by alpha-adrenoceptors within the medulla oblongata.
D000319:Adrenergic beta-Antagonists; D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002531:Cerebellum; D003000:Clonidine / Q000494:pharmacology; D003655:Decerebrate State; D003864:Depression, Chemical; D004146:Dioxanes / Q000494:pharmacology; D004285:Dogs; D005260:Female; D006321:Heart / Q000187:drug effects*; D006339:Heart Rate / Q000187:drug effects; D008297:Male; D008526:Medulla Oblongata / Q000187:drug effects*; D010880:Piperidines / Q000494:pharmacology; D011412:Propanolamines / Q000494:pharmacology; D011941:Receptors, Adrenergic; D012018:Reflex; D014630:Vagus Nerve / Q000502:physiology*
D000319:Adrenergic beta-Antagonists; D004146:Dioxanes; D010880:Piperidines; D011412:Propanolamines; D011941:Receptors, Adrenergic; D000804:Angiotensin II; D003000:Clonidine