Document Detail

Sympathetic restraint of muscle blood flow during hypoxic exercise.
MedLine Citation:
PMID:  19297541     Owner:  NLM     Status:  MEDLINE    
Control of exercising muscle blood flow is a balance between local vasodilatory factors and the increase in global sympathetic vasoconstrictor outflow. Hypoxia has been shown to potentiate the muscle sympathetic nerve response to exercise, potentially limiting the increase in muscle blood flow. Accordingly, we investigated sympathetic restraint to exercising muscle during whole body exercise in hypoxia. Six dogs chronically instrumented with ascending aortic and hindlimb flow probes and a terminal aortic catheter were studied at rest and mild [2.5 miles/h (mph), 5% grade] and moderate (4.0 mph, 10% grade) exercise while breathing room air or hypoxia (Pa(O(2)) approximately 45 mmHg) in the intact control condition and following systemic alpha-adrenergic blockade (phentolamine). Hypoxia caused an increase in cardiac output (CO), hindlimb flow (Flow(L)), and blood pressure (BP), while total (Cond(T)) and hindlimb conductance (Cond(L)) were unchanged at rest and mild exercise but increased with moderate exercise. During both mild and moderate exercise, alpha-blockade in normoxia resulted in significant vasodilation as evidenced by increases in CO (10%), Flow(L) (17%), Cond(T) (33%), Cond(L) (43%), and a decrease in BP (-18%), with the increase in Cond(L) greater than the increase in Cond(T) during mild exercise. Compared with the normoxic response, alpha-blockade in hypoxia during exercise resulted in a significantly greater increase in Cond(T) (59%) and Cond(L) (74%) and a correspondingly greater decrease in BP (-34%) from baseline. These findings indicate that there is considerable hypoxia-induced sympathetic restraint of muscle blood flow during both mild and moderate exercise, which helps to maintain arterial blood pressure in hypoxia.
Michael K Stickland; Curtis A Smith; Benjamin J Soriano; Jerome A Dempsey
Publication Detail:
Type:  Journal Article; Research Support, N.I.H., Extramural; Research Support, Non-U.S. Gov't     Date:  2009-03-18
Journal Detail:
Title:  American journal of physiology. Regulatory, integrative and comparative physiology     Volume:  296     ISSN:  0363-6119     ISO Abbreviation:  Am. J. Physiol. Regul. Integr. Comp. Physiol.     Publication Date:  2009 May 
Date Detail:
Created Date:  2009-04-28     Completed Date:  2009-06-25     Revised Date:  2013-06-02    
Medline Journal Info:
Nlm Unique ID:  100901230     Medline TA:  Am J Physiol Regul Integr Comp Physiol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  R1538-46     Citation Subset:  IM    
John Rankin Laboratory of Pulmonary Medicine, University of Wisconsin-Madison, Madison, Wisconsin, USA.
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MeSH Terms
Adrenergic alpha-Antagonists / pharmacology
Anoxia / physiopathology*
Blood Pressure / drug effects,  physiology
Cardiac Output / drug effects,  physiology
Models, Animal
Muscle, Skeletal / blood supply*
Physical Conditioning, Animal / physiology*
Prazosin / pharmacology
Regional Blood Flow / drug effects,  physiology*
Sympathetic Nervous System / physiology*
Grant Support
Reg. No./Substance:
0/Adrenergic alpha-Antagonists; 19216-56-9/Prazosin

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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