Facilitation of the Bezold-Jarisch reflex by central stimulation of alpha 2 adrenoceptors in dogs.
The Bezold-Jarisch reflex characterized by hypotension and bradycardia was elicited in anaesthetized artificially respired dogs (pretreated with a beta-adrenoceptor antagonist ) using capsaicin 10 micrograms/kg (i.v.). Intracisternal administration of the highly selective "clonidine-like" alpha 2 adrenoceptor agonists B-HT 920 (10 micrograms/kg) or B-HT 933 (30 micrograms/kg) significantly facilitated this reflex bradycardia. The involvement of central alpha 2-adrenoceptors is suggested as intracisternal administration of the alpha 2 adrenoceptor blocking drugs yohimbine (50 micrograms/kg) and piperoxan (50 micrograms/kg) antagonized this facilitation. B-HT 920 also facilitated the vagally mediated baroreceptor reflex to the hypertensive effect of intravenous noradrenaline (3 micrograms/kg). Although the Bezold-Jarisch reflex and the baroreceptor reflex have different afferent pathways, both reflexes may either converge into a common pathway or have separate neuronal chains within the medulla; however, this study indicates that both have a similar central modulatory system stimulated by alpha 2 adrenoceptors.
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000818:Animals; D001381:Azepines / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects; D002211:Capsaicin / Q000494:pharmacology*; D004285:Dogs; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D008297:Male; D010883:Piperoxan / Q000494:pharmacology; D011311:Pressoreceptors / Q000502:physiology*; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects*; D012018:Reflex / Q000502:physiology*; D012121:Respiration, Artificial; D014630:Vagus Nerve / Q000502:physiology; D015016:Yohimbine / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D001381:Azepines; D011942:Receptors, Adrenergic, alpha; D015016:Yohimbine; C024763:talipexole; D010883:Piperoxan; C015603:azepexole; D002211:Capsaicin