Evidence for involvement of alpha 2-adrenoceptors in the nucleus ambiguous in baroreflex-mediated bradycardia.

Abstract

Microinjection of noradrenaline and clonidine into the nucleus ambiguus elicited dose-dependent bradycardia with insignificant alteration of blood pressure. Phenylephrine failed to elicit any cardiovascular effect. The bradycardic effects of noradrenaline and clonidine were antagonized by piperoxan but not by phenoxybenzamine. Adrenergic neurone blockade with local guanethidine pretreatment also abolished the response to clonidine. No significant cardiovascular effect of clonidine microinjection into the nucleus ambiguus was observed in bilaterally vagotomized animals. The baroreflex bradycardia induced by volume loading as abolished by yohimbine and piperoxan but not by phenoxybenzamine, microinjected bilaterally into the nucleus ambiguus. These results demonstrate the presence of cardioinhibitory, presynaptic alpha 2-adrenoceptors in the nucleus ambiguus and their involvement in baroreflex bradycardia.

• Authors: S Gurtu, D K Sharma, J N Sinha, K P Bhargava
• Journal: Naunyn-Schmiedeberg's archives of pharmacology (Naunyn Schmiedebergs Arch Pharmacol) Vol. 323 Issue 3 Pg. 199-204 (Jul 1983) ISSN: 0028-1298 [Print] Germany
• PMID: 6137774 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Adrenergic alpha-Agonists
• Adrenergic alpha-Antagonists
• Receptors, Adrenergic, alpha
• Clonidine
• Norepinephrine
• Guanethidine

Topics

• Adrenergic alpha-Agonists (pharmacology)
• Adrenergic alpha-Antagonists (pharmacology)
• Animals
• Blood Pressure (drug effects)
• Cats
• Clonidine (pharmacology)
• Female
• Guanethidine (pharmacology)
• Heart Rate (drug effects)
• Male
• Medulla Oblongata (physiology)
• Microinjections
• Norepinephrine (pharmacology)
• Pressoreceptors (drug effects, physiology)
• Receptors, Adrenergic, alpha (physiology)
• Reflex (drug effects)
• Vagotomy