Document Detail

Neuronal norepinephrine responses of the rostral ventrolateral medulla and nucleus tractus solitarius neurons distinguish the I1- from the alpha2-receptor-mediated hypotension in conscious SHRs.
MedLine Citation:
PMID:  15965355     Owner:  NLM     Status:  MEDLINE    
We tested the hypothesis that the I1 receptor mediates the reduction in rostral ventrolateral medulla (RVLM) neuronal norepinephrine (NE; index of sympathetic activity) that leads to hypotension independent of other brainstem areas or the alpha2-adrenergic receptor. To this end, we developed a model that permitted measurement of real-time changes in neuronal NE in the RVLM or nucleus tractus solitarius (NTS) along with blood pressure and heart rate in the conscious SHR in response to localized microinjections of selective I1 (rilmenidine) or alpha2-adrenergic (alpha-methylnorepinephrine; alpha-MNE) agonist versus the mixed I1/alpha2 agonist clonidine. To further support the hypothesis, we investigated the effects of localized selective alpha2- (SK&F86466) or I1 (efaroxan) blockade on the reductions in neuronal NE and blood pressure elicited by intra-RVLM rilmenidine. In the latter experiment, changes in RVLM neuronal c-Fos (another marker of sympathetic neural activity) were also investigated. Intra-RVLM rilmenidine (40 nmol) or clonidine (1 nmol) similarly reduced RVLM NE and blood pressure; these responses were approximately 2-fold greater than those elicited by the pure alpha2-adrenergic agonist alpha-MNE (10 nmol). By contrast, intra-NTS rilmenidine or clonidine had no effect on NTS NE or blood pressure versus significant reductions in both parameters by alpha-MNE. Intra-RVLM rilmenidine decreased c-Fos expression, and these responses were abolished by efaroxan but not by SK&F 86466. These findings suggest: (1) in the RVLM, I1-receptor signaling suppresses cardiovascular neuron activity, which leads to lowering of blood pressure; (2) although the alpha2-adrenergic receptor in the RVLM serves a similar role, it does not exert a tonic neuronal inhibitory effect and is not essential, as a downstream signaling entity, for the I1-evoked neurobiological effects in the brainstem. The potential confounding effects of anesthetics on the I1 and/or alpha2 receptor-mediated neuronal and cardiovascular responses were circumvented in the present study.
Guichu Li; Xu Wang; Abdel A Abdel-Rahman
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Publication Detail:
Type:  Comparative Study; Journal Article; Research Support, N.I.H., Extramural; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Journal of cardiovascular pharmacology     Volume:  46     ISSN:  0160-2446     ISO Abbreviation:  J. Cardiovasc. Pharmacol.     Publication Date:  2005 Jul 
Date Detail:
Created Date:  2005-06-20     Completed Date:  2006-05-22     Revised Date:  2007-11-14    
Medline Journal Info:
Nlm Unique ID:  7902492     Medline TA:  J Cardiovasc Pharmacol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  52-62     Citation Subset:  IM    
Department of Pharmacology, Brody School of Medicine, Greenville, North Carolina 27858-4353, USA.
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MeSH Terms
Adrenergic alpha-Agonists / pharmacology
Adrenergic alpha-Antagonists / pharmacology
Area Postrema / drug effects,  metabolism*
Benzazepines / pharmacology
Benzofurans / pharmacology
Blood Pressure / drug effects
Clonidine / pharmacology
Heart Rate / drug effects
Hypotension / physiopathology*
Imidazoles / pharmacology
Interleukin-1 / pharmacology*
Motor Activity / drug effects,  physiology
Neurons / cytology,  metabolism
Nordefrin / pharmacology
Norepinephrine / metabolism*
Oxazoles / pharmacology
Rats, Inbred SHR
Receptors, Adrenergic, alpha-2 / agonists,  antagonists & inhibitors,  physiology*
Solitary Nucleus / drug effects,  metabolism*
Grant Support
Reg. No./Substance:
0/Adrenergic alpha-Agonists; 0/Adrenergic alpha-Antagonists; 0/Benzazepines; 0/Benzofurans; 0/Imidazoles; 0/Interleukin-1; 0/Oxazoles; 0/Receptors, Adrenergic, alpha-2; 4205-90-7/Clonidine; 51-41-2/Norepinephrine; 54187-04-1/rilmenidine; 6539-57-7/Nordefrin; 73943-10-9/benalfocin; 89197-32-0/efaroxan

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