Submitted to: Comparative Biochemistry and Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/27/2006
Publication Date: 6/1/2006
Citation: Salem, M., Levesque, A., Moon, T., Rexroad III, C.E., Yao, J. 2006. Anabolic effects of feeding beta-2 adrenergic agonists on rainbow trout muscle proteases and myofibrillar proteins. Comparative Biochemistry and Physiology. 1 44(2) 145-154. Interpretive Summary: Protein turnover is the net effect of two dynamic cellular processes, protein synthesis and degradation. Protein turnover limits animal growth efficiency, as approximately 15 to 25% of the energy consumption of growing animals is used for protein breakdown and re-synthesis. Consequently, reduction of the cost of protein turnover is a strategic goal toward enhancement of animal growth efficiency. Oral administration of beta-2 adrenergic agonists (BAA) has been shown to increase muscle protein and decrease muscle fat in growing poultry, pigs, sheep and cattle. The mechanism of this effect involves altering protein degradation and synthesis rates. Studies of BAA administration have been conducted on several fish species including rohu fish, channel catfish, blue catfish and rainbow trout. These studies demonstrated that BAAs had much less anabolic effects in fish than in mammals. To achieve an effective utilization of BAAs in aquaculture, a better assessment of the precise mechanisms by which they modulate fish muscle accretion and degradation is needed. This study provides perspectives of the anabolic effects of the BAAs in rainbow trout muscle by up-regulation in synthesis of myofibrillar proteins and down regulation of the proteolytic enzyme system.
Technical Abstract: Beta-2 adrenergic agonists (BAAs) act as repartitioning agents in an intermediary metabolic pathway that redistributes nutrients to decrease adipose tissue and increase muscle accretion. This mechanism involves altering the protein degradation and synthetic rates. 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: 1) activities and mRNA accumulation of genes in the major proteolytic pathways including calpains, the multi-catalytic proteasome and cathepsins, and 2) mRNA accumulation of genes encoding the myofibrillar proteins, fast-twitch and slow-twitch myosin heavy chains (f-MHC and s-MHC, respectively) and beta-actin. RACT caused significant increases in mRNA accumulation of the calpain catalytic subunit (Capn1), the regulatory subunit (cpns), and the calpastatin large isoform (CAST-L). However, there was no corresponding net change in calpain enzymatic activity. CLEN caused a significant increase in mRNA accumulation of the proteasome alpha subunit without a corresponding change in 20S enzymatic activity. RACT caused a significant decrease in cathepsin D activity without affecting mRNA accumulation suggesting that the action is at the post-transcriptional level. In addition, CLEN as well as RACT caused highly significant increases in mRNA accumulation of the f-MHC and beta-actin genes suggesting an anabolic role of BAA on myofibrillar proteins. Neither CLEN nor RACT affected the mRNA expression of the s-MHC gene indicating no transformation of muscle fiber-type. This study suggests BAA may induce RBT muscle accretion by altering both protein synthesis and degradation.