HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article 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 IGF-I, IGF-I receptor, estrogen receptor- and androgen receptor mRNA levels in feedlot steers

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^*

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

wdayton{at}umn.edu

Abstract

We have previously shown that a combined trenbolone acetate (TBA)/ estradiol-17β (E2) implant significantly increases IGF-I mRNA levels in 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 implanted for 28 d. Five yearling steers per group were implanted with each implant and 5 control steers received no implant. Steers were weighed weekly starting on d 0 and muscle biopsy samples were taken from each steer on d 0 (before implantation), d 7, d 14 and d 28. RNA was prepared from each sample and real-time RT-PCR was used to determine the levels of IGF-I, IGFR-1, ER- and AR mRNA. Body weight of implanted steers, adjusted 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 level 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 • IGF-I • muscle • trenbolone acetate