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This Article Full Text Full Text (PDF) All Versions of this Article: jas.2008-1085v1 86/12/3418    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Pampusch, M. S. Articles by Dayton, W. R. Search for Related Content PubMed PubMed Citation Articles by Pampusch, M. S. Articles by Dayton, W. R.

Effects of implants of trenbolone acetate, estradiol, or both, on muscle insulin-like growth factor-I, insulin-like growth factor-I receptor, estrogen receptor-, and androgen receptor messenger ribonucleic acid levels in feedlot steers¹

M. S. Pampusch^*, M. E. White^*, M. R. Hathaway^*, T. J. Baxa, K. Y. Chung, S. L. Parr, B. J. Johnson, W. J. Weber^* and W. R. Dayton^*,2

^* Animal Growth and Development Laboratory, Department of Animal Science, University of Minnesota, 348 ABLMS, Eckles Avenue, St. Paul 55108; and and Department of Animal Sciences and Industry, Kansas State University, Manhattan, KS 66506

² Corresponding author: wdayton{at}umn.edu

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

Key Words: bovine • estradiol-17β • insulin-like growth factor-I • muscle • trenbolone acetate