SLEEPER, M. M., C. F. KEARNS, and K. H. McKEEVER. Chronic clenbuterol administration negatively alters cardiac function. Med. Sci. Sports Exerc., Vol. 34, No. 4, pp. 643–650, 2002.
Chronic administration of pharmacological levels of β2-agonists have been shown to have toxic effects on the heart; however, no data exist on cardiac function after chronic clenbuterol administration. The purpose of this study was to examine the effect of therapeutic levels of clenbuterol on cardiac performance.
Twenty unfit Standardbred mares were divided into four experimental groups: clenbuterol (2.4 μg·kg−1 twice daily 5 d·wk−1) plus exercise (20 min at 50% V̇O2max) (CLENEX;N = 6), clenbuterol (CLEN;N = 6), exercise (EX;N = 4), and control (CON;N = 4). M-mode and two-dimensional echocardiography (2.5-MHz sector scanner transducer) were used to measure cardiac size and function before and immediately after an incremental exercise test, before and after 8 wk of drug and/or exercise treatments.
After treatment, CLENEX and CLEN demonstrated significantly higher left ventricular internal dimension (LVD) at end diastole (+23.7 ± 4.8%; +25.6 ± 4.1%), LVD at end systole (+29.2 ± 8.7%; +40.1 ± 7.9%), interventricular septal wall thickness (IVS) at end diastole (+28.9 ± 11.0%; +30.7 ± 7.0%), IVS at end systole (+29.2 ± 8.7%; +40.1 ± 7.9%), and left ventricular posterior wall systolic thickness (+43.1 ± 14.%; +45.8 ± 14.1%). CLENEX and CLEN had significantly increased aortic root dimensions (+29.9 ± 6.1%; +24.0 ± 1.7%), suggesting increased risk of aortic rupture.
Taken together, these data indicate that chronic clenbuterol administration may negatively alter cardiac function.
University of Pennsylvania, School of Veterinary Medicine, Philadelphia, PA; and Department of Animal Sciences, Rutgers-The State University of New Jersey, New Brunswick, NJ
Submitted for publication March 2001.
Accepted for publication September 2001.