The time course of myonuclear accretion during hypertrophy in young adult and older rat plantaris muscle.
To investigate whether accretion of myonuclei precedes or follows the increase in fibre cross-sectional area and whether this time course is affected by age, left plantaris muscle of 5- and 25-month-old male Wistar rats was overloaded by denervation of its synergists for 1, 2 or 4 weeks. Contralateral plantaris muscle served as control. Myonuclei were counted in haematoxylin-stained cross-sections. While hypertrophy (33% in young adult) became significant after 2 weeks overload (p<0.01), the myonuclear number was increased only at 4 weeks of overload (p<0.001). The time course and magnitude of hypertrophy were similar in young adult and older rats. Older muscles contained 26% more myonuclei per mm fibre length (p=0.001) and had a 10-fold larger proportion of central myonuclei (p<0.001) than young adult muscles. In conclusion, our data indicate that muscle fibre hypertrophy precedes the acquisition of new myonuclei and that the ability to develop hypertrophy is not attenuated or delayed in 25-month-old rat muscle.
van der Meer
Sander F T
SF
Institute for Biomedical Research into Human Movement and Health, Manchester Metropolitan University, Oxford Road, Manchester, M1 5GD, United Kingdom.
Jaspers
Richard T
RT
Jones
David A
DA
Degens
Hans
H
D000375:Aging / Q000473:pathology*; D000818:Animals; D002467:Cell Nucleus / Q000473:pathology*; D006614:Hindlimb / Q000473:pathology; D008297:Male; D018482:Muscle, Skeletal / Q000473:pathology*; D020966:Muscular Disorders, Atrophic / Q000473:pathology*; D051381:Rats; D017208:Rats, Wistar