Document Detail

Clenbuterol diminishes aerobic performance in horses.
MedLine Citation:
PMID:  12471305     Owner:  NLM     Status:  MEDLINE    
PURPOSE: The purpose of this 8-wk study was to examine the effect of therapeutic levels of clenbuterol on aerobic performance and hemodynamics associated with exercise. METHODS: Twenty-three unfit Standardbred mares were divided into four experimental groups, clenbuterol (2.4 microg x kg(-1) body weight twice daily) plus exercise (20 min at 50% O2max; CLENEX; N = 6), clenbuterol only (CLEN; N = 6), exercise only (EX; N = 5), and control (CON; N = 6). All horses performed an incremental exercise test (GXT) to measure maximal oxygen consumption (O2max), blood lactate concentration, total plasma protein concentration, and hematocrit. Plasma volume, heart rate, right ventricular pressure (RVP), and pulmonary artery pressure (PAP) were measured before and after the treatment/training. Each horse also performed an exercise capacity test (ECT) in which they ran at their pretreatment O2max speed until exhausted. RESULTS: There were no significant changes in blood lactate, total protein, or hematocrit for any group during either the GXT or ECT. CLENEX decreased (P < 0.05) O2max (-6.2%) and velocity to O2max (-10.0%), whereas both CLENEX and CLEN decreased (P < 0.05) in time to exhaustion (-20.5+/-4.7 and -20.9 +/- 5.6%). EX alone increased (P < 0.05) O2max (+6.5%), velocity to O2max (+10.0%), velocity to produces lactate concentration of 4 mmol (+13.5%), and time to exhaustion (+32.3 +/- 15.0%). Plasma volume was altered (P < 0.05) in CLENEX (-10%) and EX (+27%) but not in CLEN. Posttest recovery HR was higher (P < 0.05) at 2 min post-GXT in the CLENEX, CLEN, and CON compared with their pretest values; RVP remained elevated at 2 min of recovery in the CLEN and CON groups; however, in the EX, recovery HR and RVP had returned to pre-GXT levels by 2 min of recovery. CONCLUSIONS: These data suggest that the combined effect of therapeutic levels of clenbuterol and training decrease aerobic performance and that the resultant reduction in plasma volume may affect improvements in cardiovascular function during recovery normally seen with exercise training.
Charles F Kearns; Kenneth H McKeever
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Publication Detail:
Type:  Comparative Study; Evaluation Studies; Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Medicine and science in sports and exercise     Volume:  34     ISSN:  0195-9131     ISO Abbreviation:  Med Sci Sports Exerc     Publication Date:  2002 Dec 
Date Detail:
Created Date:  2002-12-09     Completed Date:  2003-03-28     Revised Date:  2007-11-15    
Medline Journal Info:
Nlm Unique ID:  8005433     Medline TA:  Med Sci Sports Exerc     Country:  United States    
Other Details:
Languages:  eng     Pagination:  1976-85     Citation Subset:  IM; S    
Equine Science Center, Department of Animal Science, Rutgers the State University of New Jersey, New Brunswick, NJ 08901-8525, USA.
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MeSH Terms
Adrenergic beta-Agonists / adverse effects*
Biological Markers / blood
Blood Proteins / drug effects,  metabolism
Clenbuterol / adverse effects*
Exercise Test
Exercise Tolerance / drug effects,  physiology
Hemodynamics / drug effects,  physiology
Horses / physiology*
Lactates / blood
Models, Animal
Oxygen Consumption / drug effects,  physiology
Physical Conditioning, Animal
Plasma Volume / drug effects,  physiology
Psychomotor Performance / drug effects*
Reference Values
Time Factors
Reg. No./Substance:
0/Adrenergic beta-Agonists; 0/Biological Markers; 0/Blood Proteins; 0/Lactates; 37148-27-9/Clenbuterol

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

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