Effects of implants of trenbolone acetate, estradiol, or both, on muscle insulin-like growth factor-I, insulin-like growth factor-I receptor, estrogen receptor-ά, and androgen receptor messenger ribonucleic acid levels in feedlot steers

M. S. Pampusch, Michael E White, Marcia Hathaway, T. J. Baxa, K. Y. Chung, S. L. Parr, B. J. Johnson, Wanda J Weber, William R Dayton

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37 Scopus citations

Abstract

We previously showed that a combined trenbolone acetate (TBA)/estradiol-17ß (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)-α 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-α, 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-α 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.

Original languageEnglish (US)
Pages (from-to)3418-3423
Number of pages6
JournalJournal of animal science
Volume86
Issue number12
DOIs
StatePublished - Dec 2008

Keywords

  • Bovine
  • Estradiol-17ß
  • Insulin-like growth factor-I
  • Muscle
  • Trenbolone acetate

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