Hypertrophy and proliferation of skeletal muscle fibers from aged quail

The purpose of this study was to determined whether fibers in the anterior latissimus dorsi (ALD) muscle from aged Japanese quail have decreased hypertrophic or proliferative responses to 30 days of stretch overload compared with fibers from adult birds. Two groups of quail were studied, 12-wk-old quail (adult; n = 16) and 90-wk-old quail (aged; n = 16). The left wing of each bird was overloaded with a weight corresponding to 10% of the bird's body weight, and the right wing served as the intra-animal control. Quails were killed after 30 days of stretch overload. Total fiber number was quantified by counting all the fibers in a transverse section from the midbelly of the ALD muscle. ALD muscles in aged quails retained the capacity to increase their muscle mass (145%), total fiber number (49%), and fiber cross-sectional area (54%) in response to stretch overload. The ALD muscle in aged quail had a significantly lower increase in muscle mass (33%) and mass corrected for nonmuscle tissue (36%) compared with the ALD from young adult birds. Age had no effect on fiber type distribution shifts with stretch. These results suggest that although muscles in old birds have a substantial ability to adapt to enlarge, stretch-induced hypertrophy is attenuated in muscles from old quail.