AJP - Regulatory, Integrative and Comparative Physiology, Vol 267, Issue 2 365-R371, Copyright © 1994 by American Physiological Society
Resistance exercise and growth hormone as countermeasures for skeletal muscle atrophy in hindlimb-suspended rats
J. K. Linderman, K. L. Gosselink, F. W. Booth, V. R. Mukku and R. E. Grindeland
National Aeronautics and Space Administration/Ames Research Center, Moffett Field 94035-1000.
Unweighting of rat hindlimb muscles results in skeletal muscle atrophy,
decreased protein synthesis, and reduced growth hormone (GH) secretion.
Resistance exercise (ladder climbing) and GH treatment partially attenuate
skeletal muscle atrophy in hypophysectomized hindlimb-suspended rats. It
was hypothesized that a combination of multiple bouts of daily resistance
exercise and GH (1 mg.kg-1.day-1) would prevent skeletal muscle atrophy in
growing nonhypophysectomized hindlimb-suspended rats. Hindlimb suspension
decreased the absolute (mg/pair) and relative (mg/100 g body wt) weights of
the soleus, a slow-twitch plantar flexor, by 30 and 21%, respectively, and
the absolute and relative weights of the gastrocnemius, a predominantly
fast-twitch plantar flexor, by 20 and 11%, respectively (P < 0.05).
Exercise did not increase soleus mass but attenuated loss of relative wet
weight in the gastrocnemius muscles of hindlimb-suspended rats (P <
0.05). Hindlimb suspension decreased gastrocnemius myofibrillar protein
content and synthesis (mg/day) by 26 and 64%, respectively (P < 0.05).
The combination of exercise and GH attenuated loss of gastrocnemius
myofibrillar protein content and synthesis by 70 and 23%, respectively (P
< 0.05). Results of the present investigation indicate that a
combination of GH and resistance exercise attenuates atrophy of unweighted
fast-twitch skeletal muscles.
