THE EFFECT OF ALTERNATING PERIODS OF LOADING AND UNLOADING ON SATELLITE CELL PROLIFERATION IN ADULT QUAIL MUSCLE

Abstract

This study tested the hypothesis that hypertrophic adaptation following previous loading-unloading periods doesn't require satellite cell activation but results in increased protein accumulation and expression of muscle regulatory factors. The left wing of 18 Japanese quail received a stretch overload corresponding to approximately 10% bodyweight, while the contralateral side served as an intra-animal control. The first group of birds received stretch for 14 days (S14), after which they were sacrificed. The second group underwent a 14-day unloading period after the initial 14-day stretch (U14). The third group of birds was reloaded for 7 days (R7), while the fourth group was reloaded for 14 days (R14) subsequent to the 28 days loading-unloading intervention. Muscle weight increased similarly after 14 days of weighting (142%) and after 7 (143%) or 14 (136%) days of reloading relative to the intra-animal control muscles. Experimental muscles from group U14 had atrophied relative to group S14, but they were still 44% larger than the intra-animal control. Satellite cells were labeled during initial weighting in group S14 or during reweighting in groups R7 and R14 using a constant release BrdU pellet. Nuclei that were immunopostive for BrdU were visualized by immunocytohemistry and the percent of labeling was calculated relative to the total number of nuclei in each muscle cross-section. BrdU positive nuclei (satellite cells) represented 80% of the total myonuclei pool after 14 days of loading and this was similar to the level of satellite cell activation after 7 days of reloading. These data suggest that satellite cells proliferate and are involved in hypertrophic adaptations following unloading. Funded by NIH AG17143