title: Effects of implants of trenbolone acetate, estradiol, or both, on muscle insulin-like growth factor-I, insulin-like growth factor-I receptor, estrogen receptor-{alpha}, and androgen receptor messenger ribonucleic acid levels in feedlot steers.
abstract: We previously showed that a combined trenbolone acetate (TBA)/estradiol-17beta (E2) implant significantly increases IGF-I mRNA levels in the LM of feedlot steers by 28 d after implantation. Here we compare the effects of E2 (25.7 mg), TBA (120 mg), and combined TBA (120 mg)/E2 (24 mg) implants on IGF-I, IGF-I receptor (IGFR-1), estrogen receptor (ER)-alpha and androgen receptor (AR) mRNA levels in the LM of steers. Twenty yearling crossbred steers with an average initial BW of 421.1 +/- 3.6 kg were stratified by BW and randomly assigned to 1 of 4 treatments: 1) nonimplanted, control; 2) implanted with TBA and E2; 3) implanted with E2; or 4) implanted with TBA. Steers were weighed weekly starting on d 0, and muscle biopsy samples were taken from each steer on d 0 (before implantation), 7, 14, and 28. Ribonucleic acid was prepared from each sample and real-time reverse transcription-PCR was used to determine the levels of IGF-I, IGFR-1, ER-alpha, and AR mRNA. Body weight of implanted steers, adjusted by using d-0 BW as a covariant, tended (P = 0.09) to be greater than that of control steers. On d 7 and 28, IGF-I mRNA levels were greater (58 and 78%, respectively; P < 0.009) in E2-implanted animals than in control steers. Similarly, on d 28 the LM IGF-I mRNA level was 65% greater (P = 0.017) in TBA/E2-implanted steers than in control animals. In contrast, the TBA implant did not increase (P = 0.99) LM IGF-I mRNA levels after 28 d of implantation. Muscle IGFR-1, AR, and ER-alpha mRNA levels were not different (P > 0.47) in any of the treated groups compared with the control group. These data suggest that E2 is responsible for the increased muscle IGF-I mRNA level observed in steers implanted with a combined TBA/E2 implant.
authors.affiliation: Animal Growth and Development Laboratory, Department of Animal Science, University of Minnesota, 348 ABLMS, Eckles Avenue, St. Paul 55108, USA.
authors.forename: M S
authors.initials: MS
authors.lastname: Pampusch
authors.forename: M E
authors.initials: ME
authors.lastname: White
authors.forename: M R
authors.initials: MR
authors.lastname: Hathaway
authors.forename: T J
authors.initials: TJ
authors.lastname: Baxa
authors.forename: K Y
authors.initials: KY
authors.lastname: Chung
authors.forename: S L
authors.initials: SL
authors.lastname: Parr
authors.forename: B J
authors.initials: BJ
authors.lastname: Johnson
authors.forename: W J
authors.initials: WJ
authors.lastname: Weber
authors.forename: W R
authors.initials: WR
authors.lastname: Dayton
mesh_terms: D000818:Animals; D001835:Body Weight / Q000187:drug effects; D002417:Cattle / Q000378:metabolism*; D004343:Drug Implants; D004958:Estradiol / Q000008:administration & dosage / Q000494:pharmacology*; D047628:Estrogen Receptor alpha / Q000235:genetics; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation / Q000187:drug effects*; D007334:Insulin-Like Growth Factor I / Q000235:genetics; D008297:Male; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D011897:Random Allocation; D017526:Receptor, IGF Type 1 / Q000235:genetics; D011944:Receptors, Androgen / Q000235:genetics; D014204:Trenbolone Acetate / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: D004343:Drug Implants; D047628:Estrogen Receptor alpha; D012333:RNA, Messenger; D011944:Receptors, Androgen; D004958:Estradiol; D007334:Insulin-Like Growth Factor I; D017526:Receptor, IGF Type 1; D014204:Trenbolone Acetate