Activation state of muscle satellite cells isolated from steers implanted with a combined trenbolone acetate and estradiol implant

Muscle satellite cells were isolated from seven yearling steers implanted f or 31 d with a combined implant that contained 120 mg of trenbolone acetate (TBA) and 24 mg of estradiol (E-2) and from seven nonimplanted, control st eers. Implanted steers had a 28% greater ADG and a 23% greater feed efficie ncy than did nonimplanted steers. Implanted steers had increased (P <.001) circulating IGF-I concentrations on d 6, 14, and 31 after implantation, and circulating IGF-I concentrations in control steers remained constant or de creased (P <.05) at these times. Maximum fusion percentage was greater (P < .005) in satellite cell cultures isolated from implanted steers (ISC cultur es) than in satellite cell cultures isolated from control steers (NSC cultu res) (72.8% vs 54.8%, respectively). Satellite cell cultures isolated from implanted steers (ISC cultures) also contained a greater (P <.001) number o f myotube nuclei than did NSC cultures (7,998 nuclei/cm(2) vs 5,150 nuclei/ cm(2), respectively). After 72 h in culture, the number of cells (corrected for plating density) was 43% greater (P <.05) in ISC cultures than in NSC cultures. [H-3]Thymidine incorporation rates per 10(5) cells at 24 and 34 h after plating were greater (P <.05) in ISC cultures than in NSC cultures; however, incorporation rates did not differ at 72 h. These data indicate th at TEA + E-2 implantation may result in an in vivo activation of muscle sat ellite cell proliferation that can be detected in cell culture. This activa tion may play an important role in TEA + E-2-enhanced muscle growth.