Document Detail

Baroreflex mechanisms buffering alpha-adrenergic agonists in conscious dogs.
MedLine Citation:
PMID:  2889369     Owner:  NLM     Status:  MEDLINE    
To determine the relative importance of the mechanisms utilized by the arterial baroreflex in buffering the pressor and vasoconstrictor responses to alpha-adrenergic receptor agonists, we studied responses to norepinephrine and phenylephrine in conscious dogs. The dogs were studied 2-8 wk after instrumentation with aortic catheters and aortic electromagnetic flow probes to measure arterial pressure and cardiac output. Total peripheral resistance was calculated on-line by a digital computer. The dogs were studied after beta-adrenergic receptor blockade (propranolol 1.0 mg/kg) to eliminate the complicating inotropic effects of the agonists studied. Norepinephrine (0.2 microgram/kg bolus) increased mean arterial pressure by 30 +/- 3 mmHg, total peripheral resistance by 51 +/- 4 mmHg . l-1 . min-1, and decreased heart rate by 26 +/- 3 beats/min. After arterial baroreceptor denervation, norepinephrine increased mean arterial pressure by 69 +/- 8 mmHg, total peripheral resistance by 48 +/- 6 mmHg . l-1 . min-1, and heart rate did not change. After ganglionic blockade (hexamethonium 40 mg/kg), norepinephrine increased mean arterial pressure by 76 +/- 3 mmHg, total peripheral resistance by 47 +/- 4 mmHg X l-1 X min-1, and heart rate did not change. Only after elimination of the buffering by heart rate by use of cholinergic receptor blockade (atropine 0.1 mg/kg) or ventricular pacing could buffering of the vasoconstrictor responses to alpha-adrenergic receptor agonists be demonstrated. Thus in conscious dogs the primary mechanism for buffering increases in arterial pressure induced by alpha-adrenergic receptor agonists is compensatory changes in heart rate and cardiac output with little buffering of total peripheral resistance.
A M Fujii; S F Vatner
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  The American journal of physiology     Volume:  253     ISSN:  0002-9513     ISO Abbreviation:  Am. J. Physiol.     Publication Date:  1987 Oct 
Date Detail:
Created Date:  1987-11-19     Completed Date:  1987-11-19     Revised Date:  2007-11-14    
Medline Journal Info:
Nlm Unique ID:  0370511     Medline TA:  Am J Physiol     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  H728-36     Citation Subset:  IM; S    
Department of Medicine, Harvard Medical School, Boston, Massachusetts.
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MeSH Terms
Adrenergic alpha-Agonists / pharmacology*
Automatic Data Processing
Blood Pressure
Cardiac Output
Heart Rate / drug effects
Hexamethonium Compounds / pharmacology
Norepinephrine / pharmacology
Phenylephrine / pharmacology
Pressoreceptors / physiology*
Propranolol / pharmacology
Reference Values
Reflex / physiology*
Vascular Resistance
Vasoconstriction / drug effects
Grant Support
Reg. No./Substance:
0/Adrenergic alpha-Agonists; 0/Hexamethonium Compounds; 51-41-2/Norepinephrine; 525-66-6/Propranolol; 59-42-7/Phenylephrine; 60-26-4/Hexamethonium

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