The objective of this study was to determine if hypertrophy-stimulated increases in MRFs occur in mature myofibers or in proliferating satellite cells. Prior to applying a hypertrophy stimulus, 12 adult quail were exposed to 2500 Rads of gamma irradiation (9 quail served as non-irradiated controls). Muscles of the left wing were then stretch-overloaded using a weight corresponding to 12% of body weight. Three days later RNA was extracted from stretch-overloaded and contralateral control anterior latissimus dorsi muscles and used in ribonuclease protection assays to determine MRF mRNA levels. The elimination of proliferating cells in irradiated muscles was verified histologically by bromodeoxyuridine incorporation. MRF4 and MyoD mRNAs were elevated similarly in non-irradiated and irradiated stretch-overloaded muscles (MRF4; 422±162% and 441±135% above contralateral control muscles, respectively; p=093) (MyoD; 52±30% and 62±18%, respectively; p=0.76). Myogenin mRNA elevation was lower in irradiated muscles (263±78%) than in non-irradiated muscles (1215±176%) (p<0.01). In summary, MRF increases occurred in mature myofibers because the elimination of proliferating satellite cells did not eradicate the hypertrophy-stimulated increases. Proliferating satellite cells contributed only to hypertrophy-stimulated increases in myogenin mRNA.
|Original language||English (US)|
|State||Published - Mar 20 1998|