AJP - Cell Physiology, Vol 259, Issue 1 C92-102, Copyright © 1990 by American Physiological Society
Muscle fiber formation and fiber hypertrophy during the onset of stretch-overload
S. E. Alway, W. J. Gonyea and M. E. Davis
Department of Anatomy, Cell Biology, and Neuroscience, Oral Roberts University School of Medicine, Tulsa, Oklahoma 74171.
The contributions of fiber hypertrophy and new fiber formation to the onset
of stretch-induced muscle enlargement were evaluated in the anterior
latissimus dorsi (ALD) of adult Japanese quails, because it was not known
whether the mechanisms which initiate new fiber formation were dependent on
first achieving significant fiber hypertrophy. A weight corresponding to
10% of the bird's body mass was attached to one wing, and eight birds were
killed after each day during the first week of stretch. Muscle mass was
significantly increased after 48 h of stretch; however, the elevation in
nonmuscle tissue accounted for this increase. Muscle mass corrected for
non-muscle tissue was significantly greater than the intra-animal control
by the fourth day of stretch. Mean fiber cross-sectional area did not
change during days 0-6, but cross-sectional area was 30.0 +/- 17.2% greater
than the intra-animal control areas at day 7. Fiber number determined after
nitric acid digestion of connective tissue was 27.1 +/- 5.8% greater than
the intra-animal control at days 5-7 of stretch, but the number of fibers
in the control muscles at days 5 and 6 were lower than at day 0. Thus new
fiber formation was not preceded by significant fiber hypertrophy. These
results fail to support a mechanism for new fiber formation which involves
fiber splitting from hypertrophied myofibers during the first week of
stretch.
