Meat science and muscle biology symposium-Role of satellite cells in anabolic steroid-induced muscle growth in feedlot steers

Both androgenic and estrogenic steroids are widely used as growth promoters in feedlot steers because they significantly enhance feed efficiency, rate of gain, and muscle growth. However, despite their widespread use relatively little is known about the biological mechanism by which androgenic and estrogenic steroids enhance rate and efficiency of muscle growth in cattle. Treatment of feedlot steers with a combined estradiol (E2) and trenbolone acetate (TBA) implant results in an increased number of muscle satellite cells, increased expression of IGF-1 mRNA in muscle tissue, and increased levels of circulating IGF-1. Similarly, treatment of bovine satellite cell (BSC) cultures with either TBA or E2 results in increased expression of IGF-1 mRNA, increased rates of proliferation and protein synthesis, and decreased rates of protein degradation. Effects of E2 on BSC are mediated at least in part through the classical E2 receptor, estrogen receptor-α (ESR1), the IGF-1 receptor (IGFR1), and the G protein-coupled estrogen receptor-1 (GPER-1), formerly known as G proteincoupled receptor-30 (GPR30). The effects of TBA appear to be primarily mediated through the androgen receptor. Based on current research results, it is becoming clear that anabolic steroid-enhanced bovine muscle growth involves a complex interaction of numerous pathways and receptors. Consequently, additional in vivo and in vitro studies are necessary to understand the mechanisms involved in this complex process. The fundamental information generated by this research will help in developing future, safe, and effective strategies to increase rate and efficiency of muscle growth in beef cattle.