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This Article Full Text Full Text (PDF) All Versions of this Article: 287/6/E1070    most recent 00329.2004v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (7) Citing Articles via Google Scholar Google Scholar Articles by Fluckey, J. D. Articles by Peterson, C. A. Search for Related Content PubMed PubMed Citation Articles by Fluckey, J. D. Articles by Peterson, C. A.

Insulin facilitation of muscle protein synthesis following resistance exercise in hindlimb-suspended rats is independent of a rapamycin-sensitive pathway

Departments of ¹Geriatrics and ²Physiology and Biophysics, University of Arkansas for Medical Sciences, and the ⁴Central Arkansas Veterans Health Care System, Little Rock, Arkansas 72205; and ³Karolinska Institute, S-171 77 Stockholm, Sweden

Submitted 26 July 2004 ; accepted in final form 6 August 2004

Hindlimb suspension (HS) results in rapid losses of muscle mass, which may in part be explained by attenuated rates of protein synthesis. Mammalian target of rapamycin (mTOR) regulates protein synthesis and has been implicated as a potential mediator of the muscle mass decrement with HS. This study examined the effect of resistance exercise, a muscle hypertrophy stimulant, on rates of protein synthesis after 4 days of HS in mature male Sprague-Dawley rats. Flywheel resistance exercise (2 sets x 25 repetitions) was conducted on days 2 and 4 of HS (HSRE). Sixteen hours after the last exercise bout, soleus muscles were assessed for in vitro rates of protein synthesis, with and without insulin (signaling agonist) and/or rapamycin (mTOR inhibitor). Results demonstrated that soleus mass was reduced (P < 0.05) with HS, but this loss of mass was not observed (P > 0.05) with HSRE. Muscle protein synthesis was diminished (P < 0.05) with HS, with or without insulin. HSRE also had reduced rates of synthesis without insulin; however, insulin administration yielded higher (P < 0.05) rates in HSRE compared with HS or control. Rapamycin diminished protein synthesis in all groups (P < 0.05), but insulin rescued synthesis rates in HS and HSRE to levels similar to insulin alone for each group, suggesting that alternate signaling pathways develop to increase protein synthesis with HS. These results demonstrate that the capacity for an augmented anabolic response to resistance exercise is maintained after 4 days of HS and is independent of a rapamycin-sensitive pathway.

muscle atrophy; flywheel technology; phenylalanine; mammalian target of rapamycin; microgravity

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