β-agonist Regulate Skeletal Actin Gene Expression
Previously reported studies have provided evidence that ractopamine regulates the expression of skeletal α- actin, but the molecular mechanisms underlying these effects are poorly understood. This was the first study to look specifically at the effects of ractopamine on the transcriptional regulation of a contractile protein in myotube cultures. Our model was sufficient to evaluate the anabolic effects of ractopamine in porcine skeletal muscle. However, we were unable to identify a cis-acting DNA element within the cloned porcine skeletal α-actin promoter that conferred transcriptional responsiveness to ractopamine in porcine skeletal muscle. Thus, it appears that ractopamine promotes the accumulation of skeletal α- actin mRNA in porcine skeletal muscle via a posttranscriptional mechanism. Elucidation of the mechanism whereby ractopamine increase skeletal muscle growth will aid in the development of new strategies, both genetic and pharmacological, to improve lean tissue deposition in livestock species.