Androgen receptors and testosterone in men--effects of protein ingestion, resistance exercise and fiber type.

Author(s): Hulmi JJ, Ahtiainen JP, Selanne H, Volek JS, Hakkinen K, Kovanen V, Mero AA

Affiliation(s): Department of Biology of Physical Activity, University of Jyvaskyla, Jyvaskyla, Finland. juha.hulmi@sport.jyu.fi

Publication date & source: 2008-05, J Steroid Biochem Mol Biol., 110(1-2):130-7. Epub 2008 Mar 30.

Publication type: Randomized Controlled Trial; Research Support, Non-U.S. Gov't

The purpose of this study was to examine the impact of protein ingestion on circulating testosterone and muscle androgen receptor (AR) as well as on insulin-like growth factor-I (MGF and IGF-IEa) responses to a resistance exercise (RE) bout in (57-72 year) men. Protein (15 g whey) (n=9) or placebo (n=9) was consumed before and after a RE bout (5 sets of 10 repetition maximums), and vastus lateralis muscle biopsies were taken pre, 1 and 48 h post-RE. The protein ingestion blunted the RE-induced increase in serum free and total testosterone while the RE bout significantly increased muscle AR mRNA levels in older men (P<0.05). However, protein ingestion did not significantly affect AR mRNA or protein expression, or MGF and IGF-IEa mRNA expression at 1 and 48 h post-RE. Immunohistochemical staining of muscle cross-sections was done with antibodies specific to AR and MyHC I and II and showed that there seems to be within or near the type-I muscle fibers a greater staining of ARs than within or near the type-II fibres. In conclusion, the protein ingestion hinders RE-induced increase in serum testosterone in older men but may not significantly affect muscle AR, MGF or IGF-IEa gene expression. Furthermore, the present study shows that even older men are able to increase muscle AR mRNA expression in response to a RE bout.