Evaluation of Disuse Atrophy of Rat Skeletal Muscle Based on Muscle Energy Metabolism Assessed by 31P-MRS.

Abstract

The purpose of this study was to evaluate disuse atrophy of skeletal muscle using a hind-limb suspension model, with special reference to energy metabolism. Twenty-four Sprague-Dawley rats were divided into four groups: control group (C), hind-limb suspended for 3 days (HS-3), for 7 days (HS-7) and for 14 days . The gastrocnemius-plantaris-soleus (GPS) muscles in each group were subjected to the following measurements. After a 2-min rest, contraction of the GPS muscles was induced by electrical stimulation of the sciatic nerve at 0.25 Hz for 10 min, then the frequency was increased to 0.5 and 1.0 Hz every 10 min. During the stimulation, twitch forces were recorded by a strain gauge, and 31 P-MRS was performed simultaneously. M a x i m u m t en s i o n wa s m e a s u r e d a t th e m u s cl e contraction induced at 0.25 Hz; the wet weight of the whole and each muscle in the GPS muscles was also measured. From the 31 P-MR spectra during muscle contraction, the oxidative capacity was calculated and compared among the groups. The weights of the whole GPS muscles in C, HS-3, HS-7 and HS-14, were 2.66 ± 0.09, 2.39 ± 0.21, 2.34 ± 0.21 and 2.18 ± 0.14 (g) respectively. Thus, the muscle mass significantly decreased with time (p<0.05). Among the GPS muscles, the decrease in weight of the soleus muscle was especially remarkable; in the HS-14 group its weight decreased to 60% of that in the C group. We evaluated maximum tension and oxidative capacity as the muscle function. The maximum tensions in C, HS-3, HS-7 and HS-14 were 519 ± 43, 446 ± 66, 450 ± 23 and 465 ± 29 (g), respectively. This was significantly greater in the C group than in any other groups, however there were no significant differences among the three HS g r oups . T h e oxi dat i ve c apac i t y d uri n g m usc l e contraction in the C group was higher than in any HS group and it did not further decrease even if the suspension of the limbs was prolonged beyond 3 days. The present study showed that in disuse atrophy, muscle mass and muscle function did not change simultaneously. Thus, it is necessary to develop countermeasures to p r e v e n t m u s c l e a t r o p h y a n d m u s c l e f u n c t i o n deterioration independently.

Alteration of cathepsin-D expression in atrophied muscles and apoptotic myofibers by hindlimb unloading in a low-temperature environment

“…In addition, the percentage of type I myofibers showing an extremely strong immunoreaction for cathepsin-D were decreased in the HULT rats, whereas type II myofibers showing a weak immunoreaction for cathepsin-D were increased in these rats. In disuse muscle atrophy, the turnover of muscle protein metabolism 40 ) and muscle energy metabolism 41 ) is lower, and the decrease in the level of inactive cathepsin-D observed in the present study may be caused by a decrease in the number of type I myofibers, increase in the number of type II myofibers, and decrease in the turnover rate of muscle protein metabolism and muscle energy metabolism. In addition, the fiber-type composition during development is known to transform from a fast type to a slow type, whereas that of muscle atrophy shifts from a slow type to a fast type 42 , 43 , 44 ) .…”

Muscle oxygenation and ATP turnover when blood flow is impaired by vascular disease

“…Using various of these measures, there is, as expected, a good relationship between mitochondrial content and aerobic capacity in comparative studies [86] and between muscles of differing fibre type content [87]. Furthermore PCr recovery is slowed in primary mitochondrial disease [88][89][90] and in some migraine disorders [91,92]; where mitochondrial content or function is reduced, e.g., cardiac failure [93,94], experimental cardiac infarction [37,95] and disuse atrophy [96]. The case of dialysed uraemic patients is controversial as there is evidence of slow PCr recovery [88,[97][98][99], but with a number of possible causes [100].…”

Low‐volume muscle endurance training prevents decrease in muscle oxidative and endurance function during 21‐day forearm immobilization

“…1997) or the immobilization of forearm in humans (Kitahara et al. 2003), and hind limb suspension in animals (Yoshida et al. 2001) – on muscle oxidative metabolism.…”