Regionalized adaptations and muscle fiber proliferation in stretch-induced enlargement.
The relative contribution of increases in fiber area to stretch-induced muscle enlargement was evaluated in the slow tonic fibers of the anterior latissimus dorsi of adult Japanese quails. A weight corresponding to 10% of the bird's body mass was attached to one wing. Thirty days of stretch in 34 birds averaged 171.8 +/- 13.5% increase in muscle mass and 23.5 +/- 0.8% increase in muscle fiber length. The volume density of noncontractile tissue increased in middle and distal regions of stretch-enlarged muscles. Mean fiber cross-sectional area increased 56.7 +/- 12.3% in the midregion of stretched muscles. Further analysis indicated slow beta-fiber hypertrophy occurred in proximal, middle, and distal regions; however, fast alpha-type fiber hypertrophy was limited to middle regions of stretched muscles. Stretched muscles had a significant increase in the frequency of slow beta-fibers that were less than 500 microns 2 in all regions and fast alpha-type fibers in middle and distal regions. Total fiber number was determined after nitric acid digestion of connective tissue in 10 birds. Fiber number increased 51.8 +/- 19.4% in stretched muscle. These results are the first to clearly show that muscle fiber proliferation contributes substantially to adult skeletal muscle stretch-induced enlargement, although we do not know whether the responses of the slow tonic anterior latissimus dorsi might be similar or different from mammalian twitch muscle.
Alway
S E
SE
Department of Cell Biology and Anatomy, University of Texas, Southwestern Medical Center, Dallas 75235.
Winchester
P K
PK
Davis
M E
ME
Gonyea
W J
WJ
D000222:Adaptation, Physiological; D000818:Animals; D003094:Collagen / Q000378:metabolism; D003238:Connective Tissue / Q000473:pathology; D003370:Coturnix; D006984:Hypertrophy; D024510:Muscle Development; D009132:Muscles / Q000473:pathology / Q000502:physiology; D009218:Myosins / Q000378:metabolism; D013314:Stress, Mechanical
D003094:Collagen; D009218:Myosins