Resistance exercise and growth hormone as countermeasures for skeletal muscle atrophy in hindlimb-suspended rats

Abstract

Unweighting of rat hindlimb muscles results in skeletal muscle atrophy, decreased protein synthesis, and reduced growth hormone (GH) secretion. Resistance exercise (ladder climbing) and GH treatment partially attenuate skeletal muscle atrophy in hypophysectomized hindlimb-suspended rats. It was hypothesized that a combination of multiple bouts of daily resistance exercise and GH (1 mg.kg-1.day-1) would prevent skeletal muscle atrophy in growing nonhypophysectomized hindlimb-suspended rats. Hindlimb suspension decreased the absolute (mg/pair) and relative (mg/100 g body wt) weights of the soleus, a slow-twitch plantar flexor, by 30 and 21%, respectively, and the absolute and relative weights of the gastrocnemius, a predominantly fast-twitch plantar flexor, by 20 and 11%, respectively (P < 0.05). Exercise did not increase soleus mass but attenuated loss of relative wet weight in the gastrocnemius muscles of hindlimb-suspended rats (P < 0.05). Hindlimb suspension decreased gastrocnemius myofibrillar protein content and synthesis (mg/day) by 26 and 64%, respectively (P < 0.05). The combination of exercise and GH attenuated loss of gastrocnemius myofibrillar protein content and synthesis by 70 and 23%, respectively (P < 0.05). Results of the present investigation indicate that a combination of GH and resistance exercise attenuates atrophy of unweighted fast-twitch skeletal muscles.

Growth hormone and mild exercise in combination increases markedly muscle mass and tetanic tension in old rats

“…Interactive effects of GH administration and exercise have been demonstrated on skeletal muscle mass; while exercise alone had minimal effects in maintaining the mass of unloaded muscles in hypophysectomized rats, there was a strong interaction effect of exercise and GH in combination, increasing muscle mass (7). In agreement with this, the combination of GH injections and exercise on hind limb suspended rats had greater effects on muscle protein synthesis than GH or exercise alone, and the loss of myo®brillar proteins was counteracted (8). Furthermore, GH/IGF-I and brief bouts of muscle loading have shown interactive effects in attenuating the loss of myonuclei induced by hindlimb suspension in rats (19), and ameliorates the apoptosis associated with hind limb unloading (20).…”

“…Furthermore, there seems to be an interaction on muscle mass when GH administration is combined with exercise (7). The decrease in protein synthesis in m. gastrocnemius seen after hindlimb suspension of rats was reduced when GH administration and exercise were combined, but no effect was seen with either GH administration or exercise alone (8). In some human studies, however, GH exercise was no more effective than exercise without GH supplementation at increasing muscle mass and maximal voluntary muscle strength (9±11).…”

Bowman-Birk inhibitor concentrate prevents atrophy, weakness, and oxidative stress in soleus muscle of hindlimb-unloaded mice

“…Mechanical unloading causes muscle weakness due to two parallel processes, overt atrophy and contractile dysfunction. Atrophy reflects a mismatch between synthesis and breakdown of muscle protein; mechanical unloading affects both, slowing protein synthesis (26) and accelerating breakdown (7). Contractile dysfunction has been observed in human studies (1,11) and animal experiments (16,37) but is a more enigmatic process.…”

Age-dependent effects of treadmill exercise during a period of inactivity

“…Although exercise benefits have been noted, the exercises are either too aggressive or not suited to the very old rat that might be susceptible to muscle damage (Herbert et al, 1988;Pierotti et al, 1990;Linderman et al, 1994). One study that investigated isometric exercise in rats, an exercise that does not cause muscle damage, did not prevent the inactivity induced decline in gastrocnemius muscle function (Hurst and Fitts, 2003).…”