Influence of suspension hypokinesia on rat soleus muscle

Abstract

Hindlimb hypokinesia was induced in rats by the Morey method to characterize the response of the soleus muscle. Rats suspended for 1-4 wk exhibited continuous and significant declines in soleus mass, function, and contractile duration. Soleus speeding was in part explained by an alteration in fiber type. The normal incidence of 70-90% type I fibers in the soleus muscle was reduced after 4 wk of suspension to 50% or less in 9 of 11 rats. A significant decline in type I myosin isozyme content occurred without a change in that of type II. Other observed histochemical changes were characteristic of denervation. Consistent with soleus atrophy, there was a significant increase in lysosomal (acid) protease activity. One week of recovery after a 2-wk suspension was characterized by a return to values not significantly different from control for muscle wet weights, peak contraction force, one-half relaxation time, and type I myosin. Persistent differences from control were observed in maximal rate of tension development, contraction time, and denervation-like changes.

Ultrastructural and metabolic profiles on single muscle fibers of different types after hindlimb suspension in rats.

“…They also reported that these changes might reflect a transformation of fast-twitch fibers to slow-twitch fibers. On the other hand, TEMPLETON et al (1984) and THOMASON et al (1987) reported an increase of fast-type myosin isozyme composition and fast-twitch fiber number, but no change in the total fiber number in various muscles following suspension hypokinesia. These results suggest that transformation from slow-twitch to fast-twitch type fiber occurred following suspension.…”

Nandrolone Decanoate Reduces Changes Induced by Hindlimb Suspension in Voltage-Dependent Tension of Rat Soleus Muscle

“…[The Japanese Journal of Physiology 53: [77][78][79][80][81][82][83][84][85][86][87]2003] Numerous studies have shown that chronic hindlimb suspension reduces maximal tension, and induces a shortening in twitch development and relaxation of slow-twitch muscles. Furthermore, a shift in isometric twitch kinetic characteristics and potential dependence of activation and inactivation curves (calculated from K ϩ contracture experiments) toward those of fast-twitch muscles has also been reported [6][7][8][9]. Different approaches to reduce the effect of suspension have been tested, like chronic stimulation, removal of synergist muscle, and treatment with androgenic-anabolic steroids (AAS) [10,11].…”

Effects of Hypodynamia-Hypokinesia on the Muscle Spindle Discharges of Rat Soleus Muscle

“…Indeed, Gajdosik (2001) showed that passive stiffness was influenced by lengthening deformation of the connective tissues of the endomysium, perimysium, and epimysium (PEC) of the muscle belly with a large contribution of the perimysium due to its large amount in a muscle. After HH, a decrease in the concentration of myofibrillar proteins and a relative increase in the proportion of noncontractile tissue (Flynn and Max 1985;Herbert et al 1988;Templeton et al 1984) in the rat soleus muscles have been observed. More recently, Brown and Hasser (1996) have also described an increase in connective tissue.…”

“…Moreover, the passive tension of in situ rat soleus muscle increased after 7 and 14 days of whole body suspension (Gillette and Fell 1996). A relative increase in the proportion of noncontractile tissue particularly in the soleus and gastrocnemius muscles has also been described (Flynn and Max 1985;Herbert et al 1988;Templeton et al 1984). Therefore we suggest that the stretch transmission might be affected after an episode of HH and the electrophysiological afferent discharges of endings consequently modified.…”