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.
Purpose: 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.
Methods: 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.
Results: 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.
Conclusion: Taken together, these data indicate that chronic clenbuterol administration may negatively alter cardiac function.