title: Role of alpha 1- and alpha 2-adrenoceptors in the modulation of the baroreflex vagal bradycardia.
abstract: Yohimbine (100 micrograms/kg), an alpha 2-adrenoceptor blocking agent when injected into the vertebral artery of anaesthetized dogs decreased the vagally mediated bradycardia induced by carotid sinus nerve stimulation. Intracisternal administration of phenylephrine (30 micrograms/kg) an alpha 1-adrenoceptor agonist decreased, whereas AR-C 239 (5 micrograms/kg) and prazosin (5 micrograms/kg) two potent alpha 1-adrenoceptor antagonists injected into the vertebral artery, potentiated the bradycardiac response. These results suggest the presence of two types of alpha-adrenoceptors to modulate the baroreceptor pathway: alpha 1-adrenoceptors inhibit and alpha 2-adrenoceptors facilitate the transmission of baroreceptor impulses.
mesh_terms: D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001919:Bradycardia / Q000209:etiology*; D004285:Dogs; D005260:Female; D008297:Male; D010656:Phenylephrine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D011311:Pressoreceptors / Q000502:physiology*; D011941:Receptors, Adrenergic / Q000502:physiology*; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D012018:Reflex; D014630:Vagus Nerve / Q000502:physiology*; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D000317:Adrenergic alpha-Antagonists; D011941:Receptors, Adrenergic; D011942:Receptors, Adrenergic, alpha; D010656:Phenylephrine; D015016:Yohimbine; D011224:Prazosin