Document Detail

The effect of adrenergic suppression induced by guanabenz administration on exercising thoroughbred horses.
MedLine Citation:
PMID:  17402429     Owner:  NLM     Status:  MEDLINE    
REASONS FOR PERFORMING STUDY: Adrenergic activity accompanies intense exercise and mediates physiological and metabolic responses to exercise. Guanabenz, an antihypertensive drug marketed for human usage, depresses brain vasomotor and cardioaccelerator centres, blocks peripherally adrenergic neurons and is reportedly used as a calming agent in horses but little is known of its effects in the species. OBJECTIVES: To determine if guanabenz induces measurable signs of adrenergic suppression on fit Thoroughbred horses undergoing intense exercise. METHODS: In a random crossover design, 12 exercise conditioned Thoroughbred horses each received guanabenz (0.08 mg/kg bwt i.v.) and placebo at 3-week intervals. An incremental exercise test to exhaustion on a treadmill followed treatment by 1 h. Heart rate, oxygen consumption, carbon dioxide production, plasma lactate, catecholamines, adrenocorticotropic hormone (ACTH) and cortisol, and time to fatigue were monitored. Statistical analysis was performed using mixed-effects linear modelling. RESULTS: Mean heart rate during the exercise period was lower in guanabenz-treated horses (P = 0.04). Mean concentrations of plasma cortisol (P = 0.02) and adrenaline (P = 0.03) were lower for guanabenz-treated horses during the exercise period. Mean run time was slightly but not significantly longer for guanabenz-treated horses, (P = 0.053). No significant effects of guanabenz administration were found for oxygen consumption, carbon dioxide production nor for plasma lactate, noradrenaline and ACTH concentrations. CONCLUSION: Guanabenz administration induced signs of adrenergic suppression including plasma cortisol and adrenaline concentrations and heart rate and may enhance endurance, but did not eliminate increases in hormone concentrations induced by exercise. Clear determination of a positive performance effect of adrenaline, but not noradrenaline, suppression is needed before clinical significance can be determined.
P T Colahan; K A Savage; I R Tebbett; B L Rice; C A Jackson; L Freshwater
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Publication Detail:
Type:  Journal Article; Randomized Controlled Trial    
Journal Detail:
Title:  Equine veterinary journal. Supplement     Volume:  -     ISSN:  -     ISO Abbreviation:  Equine Vet J Suppl     Publication Date:  2006 Aug 
Date Detail:
Created Date:  2007-04-03     Completed Date:  2007-05-02     Revised Date:  2007-05-18    
Medline Journal Info:
Nlm Unique ID:  9614088     Medline TA:  Equine Vet J Suppl     Country:  England    
Other Details:
Languages:  eng     Pagination:  262-6     Citation Subset:  IM    
Department of Large Animal Clinical Sciences and Physiological Sciences, College of Veterinary Medicine, University of Florida, USA.
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MeSH Terms
Adrenergic alpha-Agonists / pharmacology*
Adrenocorticotropic Hormone / blood
Carbon Dioxide / blood
Cross-Over Studies
Epinephrine / blood
Exercise Test / veterinary
Guanabenz / pharmacology*
Heart Rate / physiology*
Horses / blood,  physiology*
Hydrocortisone / blood
Norepinephrine / blood
Oxygen Consumption
Physical Conditioning, Animal / physiology*
Time Factors
Reg. No./Substance:
0/Adrenergic alpha-Agonists; 124-38-9/Carbon Dioxide; 50-23-7/Hydrocortisone; 5051-62-7/Guanabenz; 51-41-2/Norepinephrine; 51-43-4/Epinephrine; 9002-60-2/Adrenocorticotropic Hormone

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

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