Effect of a combined trenbolone acetate and estradiol implant on steady-state IGF-I mRNA concentrations in the liver of wethers and the longissimus muscle of steers.
Treatment of lambs (initial BW 28 kg) for 24 d with a combined implant containing 40 mg of trenbolone acetate (TBA) and 8 mg of estradiol (E2) increased ADG 25% (P < .05, n = 8) and feed efficiency 23% (P < .05, n = 2) compared with unimplanted lambs. By d 3 following implantation, sera from wethers implanted with TBA + E2 showed 32% (307 vs 233 ng/mL) increases (P < .001, n = 8) in IGF-I concentration compared with sera from unimplanted wethers. This increase was maintained throughout the entire 24-d study. Steady-state hepatic IGF-I mRNA levels were increased approximately 150% in implanted lambs compared with unimplanted lambs (P < .05, n = 4). These data suggest that liver may be the source of at least part of the increased circulating IGF-I in TBA + E2-implanted sheep. In steers implanted with Revalor-S (120 mg of TBA and 24 mg of E2) for 40 d, the steady-state concentration of IGF-I mRNA in the longissimus muscle was 68% greater than in the longissimus muscle of unimplanted steers (P = .013, n = 4). Consequently, increased local production of IGF-I by muscle tissue may play a role in increasing circulating IGF-I concentrations as well as an autocrine or paracrine role in stimulating muscle growth in steers implanted with Revalor-S.
Johnson
B J
BJ
Animal Growth and Development Laboratory, Department of Animal Science, University of Minnesota, St. Paul 55108, USA.
White
M E
ME
Hathaway
M R
MR
Christians
C J
CJ
Dayton
W R
WR
D045930:Anabolic Agents / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D002417:Cattle; D017931:DNA Primers; D004343:Drug Implants; D004347:Drug Interactions; D004958:Estradiol / Q000008:administration & dosage / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000096:biosynthesis* / Q000378:metabolism; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism*; D009919:Orchiectomy; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000096:biosynthesis; D012016:Reference Values; D012756:Sheep; D013997:Time Factors; D014158:Transcription, Genetic / Q000187:drug effects*; D014204:Trenbolone Acetate / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology
D045930:Anabolic Agents; D017931:DNA Primers; D004343:Drug Implants; D012333:RNA, Messenger; D004958:Estradiol; D007334:Insulin-Like Growth Factor I; D014204:Trenbolone Acetate