ADAPTATIONS OF MYONUCLEI TO HYPERTROPHY IN PATAGIALIS MUSCLE-FIBERS FROM AGED QUAIL

Hypertrophic responses to stretch are attenuated in slow-tonic muscles from old quail, relative to young birds. It is not known if the age-a ssociated differences would be similar in fast-twitch muscles after st retch. This study compared the effect of 30 days of stretch overload o n slow beta fibers and fast-alpha fibers in patagialis (PAT) muscles f rom young adult (YA) quail aged 12 weeks, old adult (OA) quail aged 52 weeks and the oldest (OO) quail, aged 90 weeks. The PAT muscle was st retched for 7, 14, 21, or 30 days by a sleeve that was attached to one wing. Birds received a subcutaneously implanted 5'-bromo-2'-deoxyurid ine (BrdU) pellet that provided a constant release of 0.22mg BrdU/g bo dy wt/day to label nuclei that had undergone DNA synthesis during stre tch. Fiber cross-sectional area (CSA) was determined by planimetry fro m slow beta and fast-alpha fibers after identification by myosin ATPas e. Harris hematoxylin was used to identify muscle nuclei. Muscle mass increased by 44.1 +/- 3.1, 32.6 +/- 3.9 and 25.7 +/- 4.3% in YA, OA an d OO birds, respectively. Slow-beta fiber hypertrophy was observed at day 7 of stretch in all birds; however, YA birds had greater hypertrop hy than the older birds. Fast-alpha fibers were unaffected by stretch. No significant difference was observed between PAT muscles From OA an d OO birds. Total fiber number was not significantly elevated in the P AT muscle from any age group after 30 days of stretch. Activated satel lite cells were not detected in stretched muscles of either young or o ld birds. This suggests that the increase in mean slow-beta fiber CSA was potentiated by existing myonuclei rather than by recruiting additi onal nuclei.