The influence of activity on muscle size and protein turnover.

Abstract

1. The effects of the loss of normal activity can be studied in muscles held in a shortened position by immobilizing the ankle in a plaster cast. Since the innervation remains intact with this procedure, removal of the restraining case allows normal activity to be restored. The soleus and plantaris muscles grew as a function of time after the return of normal activity and these changes in tissue size are explained by changes in the average rates of protein synthesis and protein break‐down as measured by sensitive in vitro techniques. Activity stimulates protein synthesis and inhibits protein break‐down of the soleus muscle, thus enabling the tissue to accumulate protein. Blockage of de novo synthesis of RNA, but not DNA, severely restricted the normal, rapid enhancement of protein synthesis after thr return of activity. 2. The return of isotonic activity to the extensor digitorum longus muscle after immobilization in a lengthened position failed to fully compensate for the loss of the growth‐promoting influence of stretch and the tissue gradually returned to the size of the control muscle. During the recovery process the higher rate of protein turnover and RNA concentrations of the immobilized muscle returned to the lower values of the control.

Efeitos do ultrassom terapêutico associados ao alongamento estático sobre parâmetros histomorfométricos longitudinais de sóleos imobilizados de ratos

“…Immobilization at shortening position induces to atrophy and tissue protein loss 29,30 . Moreover, growth promoting factors do not act in the immobilized muscle at shortening position, and hence, loses sarcomeres and suffers atrophy 21 .…”

“…The functional length of a muscle is important to influence on its contractile properties [18][19][20] and to determine if the muscle adds or loses sarcomeres 20,21 . In the present study, only the immobilized and stretched group with previous therapeutic ultrasound with 0.5W/cm 2 dose did not present statistically significant difference concerning the quantity of sarcomeres in series and muscular length, when compared with the immobilized and non-immobilized muscles were compared; that is to say, this dose associated with stretching presented positive effects concerning recovery of the deleterious effects caused by immobilization.…”

Fiber-type differences in masseter muscle associated with different facial morphologies

“…Fiber transitions from one type to another are common occurrences in development, altered function demands, disease, and aging. 18 In limb muscles, these transitions might be in the direction of slow type or fast type fibers in the sequence of I ↔ I/IIA ↔ IIA ↔ IIA/IIX ↔ IIX. 19 In this study, the transition has been simplified to I ↔ I/II ↔ II because we did not subclassify the type II fiber groups.…”

The influence of immobilization and stretch on protein turnover of rat skeletal muscle.

“…Further supporting this interpretation was the finding that an intraperitoneal injection of actinomycin D, at a dose (1 5 mg/kg body wt.) known to block RNA synthesis (Goldspink 1977), did not prevent or diminish the growth or increased rate of protein synthesis of the EDL after 24 hr of immobilization in the lengthened position. That is, de novo synthesis of RNA is not essential for the rapid induced growth of the EDL, suggesting that the increased protein synthesis (Fig.…”