Anabolic effects of feeding beta(2)-adrenergic agonists on rainbow trout muscle proteases and proteins
COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY A-MOLECULAR & INTEGRATIVE PHYSIOLOGY
Authors: Salem, Mohamed; Levesque, Haude; Moon, Thomas W.; Rexroad, Caird E.; Yao, Jianbo
2-Adrenergic agonists (BAAs) act as repartitioning agents in domestic animals by redistributing nutrients away from adipose tissue and towards muscle accretion. The mechanism involves altering the rates of protein degradation and synthesis. The aim of this study was to test the effects of chronic feeding of the BAAs clenbuterol (CLEN) and ractopamine (RACT) on rainbow trout (RBT) muscle. Specifically, we examined the activities and mRNA levels of genes in the major proteolytic pathways including calpains, the multi-catalytic proteasome and cathepsins, and the mRNA levels of genes encoding the myofibrillar proteins, fast-twitch and slow-twitch myosin heavy chains (f-MHC and s-MHC, respectively), and the cytoskeletal protein, p-actin. RACT feeding significantly increased mRNA transcripts of the calpain catalytic subunit (Capn1), the regulatory subunit (cpns), and the calpastatin large isoform (CAST-L), without affecting the calpain enzyme activity. CLEN feeding significantly increased mRNA levels of the proteasome alpha subunit without a corresponding change in 20S enzyme activity. RACT significantly decreased cathepsin D activity without affecting mRNA levels suggesting that the action of RACT may be at the post-transcriptional level. In addition, both CLEN and RACT significantly increased mRNA transcripts of f-MHC and beta-actin genes suggesting an anabolic role of BAAs on myofibrillar and cytoskeletal proteins. Neither CLEN nor RACT altered mRNA expression of the s-MHC gene indicating no transformation of muscle fiber-types. This study supports a role for BAAs in inducing RBT muscle accretion by altering both protein synthesis and degradation. (c) 2006 Elsevier Inc. All rights reserved.
Chronic clenbuterol administration negatively alters cardiac function
MEDICINE AND SCIENCE IN SPORTS AND EXERCISE
Authors: Sleeper, MM; Kearns, CF; McKeever, KH
Purpose: Chronic administration of pharmacological levels of beta2-agonists have been shown to have toxic effects on the hearth 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 mug.kg(-1) twice daily 5 d.wk(-1)) plus exercise (20 min at 50% VO2max) (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.