Augmented insulin action on rates of protein synthesis following
resistance exercise in rats.
Fluckey, James D., Thomas C. Vary, Leonard S. Jefferson, and Peter A.
Farrell.
Noll Physiological Research Center, University Park, PA 16802 and
Department of Cellular and Molecular Physiology, Pennsylvania State
University College of Medicine, Hershey PA. 17033
APStracts 2:0208E, 1995.
The purpose of this study was to investigate whether or not insulin
has a modulatory effect on rates of protein synthesis in skeletal
muscle following four days of resistance exercise. Twenty-four male
Sprague-Dawley rats were operantly conditioned to engage in a
resistance exercise protocol that facilitated the full extension of
the hindlimb. Following the entrainment period, the animals were
randomly assigned to exercised (ACUTE; n=12) or nonexercised (NONEX;
n=12) groups. Each ACUTE rat completed four resistance exercise
sessions consisting of 50 repetitions each. Resistance was applied to
the backs of the animals via a leather and velcro vest, with
increased resistance each session (70, 120, 120 and 190 g). Each
session was separated by 48 h. NONEX animals engaged in the exercise
sessions without applied resistance. Rates of protein synthesis for
the first portion fo the study (Study 1; ACUTE = 6, NONEX = 6) were
assessed 16 h postexercise by incorporation of [3H]phenylalanine into
muscle protein using the flooding dose protocol. Results from Study 1
demonstrated significantly higher rates of protein synthesis in ACUTE
vs. NONEX soleus (100+9 vs. 72+9 nmol F . g-1 . h-1, respectively;
means+SE; p<0.05) and gastrocnemius (48+7 vs. 25+2 nmol F . g-1 . h
-1, respectively; p<0.05), but not in extensor digitorum longus (EDL;
59+6 vs. 47+9 nmol F . g-1 . h-1, respectively; p>0.05). Assessment
of rates of protein synthesis for the second portion of the study
(Study 2; ACUTE = 6, NONEX = 6) was conducted using a bilateral
hindlimb perfusion with [3H]phenylalanine, where a medium with
insulin (6.25 ng . ml-1) was infused into one iliac artery, and a
medium without insulin into the contralateral artery. Soleus and
gastrocnemius in the ACUTE animals had significantly higher (p<0.05)
rates of protein synthesis with insulin vs. no insulin. Rates of
protein synthesis in ACUTE soleus without insulin were not different
(p>0.05) than NONEX soleus. ACUTE gastrocnemius rates of protein
synthesis without insulin were significantly lower (p<0.05) than
NONEX gastrocnemius. Insulin had no effect on rates of protein
synthesis for any muscles in NONEX rats (p>0.05). No differences were
observed in rates of protein synthesis for the EDL, regardless of
group or insulin status (p>0.05). These results suggest that insulin
is a necessary component for the elevation of rates of protein
synthesis in muscles composed predominately of slow (soleus) or fast
(gastrocnemius) twitch fibers following resistance exercise.
Received 8 June 1995; accepted in final form 7 September 1995.
APS Manuscript Number E263-5.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95