HYPERTROPHY AND PROLIFERATION OF SKELETAL-MUSCLE FIBERS FROM AGED QUAIL

The purpose of this study was to determine whether fibers in the anter ior latissimus dorsi (ALD) muscle from aged Japanese quail have decrea sed hypertrophic or proliferative responses to 30 days of stretch over load compared with fibers from adult birds. Two groups of quail were s tudied, 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 correspo nding to 10% of the bird's body weight, and the right wing served as t he intra-animal control. Quails were killed after 30 days of stretch o verload. Total fiber number was quantified by counting all the fibers in a transverse section from the midbelly of the ALD muscle. ALD muscl es 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 muscles in aged quail had a significantly lower increase in muscle mass (33%) and mass corrected f or nonmuscle tissue (36%) compared with the ALD from young adult birds . Age had no effect on fiber type distribution shifts with stretch. Th ese results suggest that although muscles in old birds have a substant ial ability to adapt to enlarge, stretch-induced hypertrophy is attenu ated in muscles from old quail.