A comparison of the effects of denervation on the mechanical properties of rat and guinea‐pig skeletal muscle.

Abstract

SUMMARY1. A fast (extensor digitorum longus) and slow (soleus) twitch muscle were denervated in rats and guinea-pigs and isometric and isotonic contractions were followed for periods of up to 6 months after.2. The decay of tetanic tension with time could be described as exponential. The rate of decay of tension was greatest in rat soleus and least in guinea-pig soleus by a factor of more than three. The fast muscles atrophied at intermediate rates.3. The contraction and relaxation times of soleus and extensor digitorum longus of rat, initially prolonged by denervation, became shorter after 3 weeks. There was no such reversal in either guinea-pig muscle, indeed extensor digitorum longus twitch became even more prolonged. Guinea-pig muscles often showed signs of repetitive response to a single stimulus, resulting in distortion of relaxation of the twitch.4. There was a slowing of isotonic shortening velocity in the late stage of denervation of guinea-pig extensor digitorum longus, accompanied by a fall in the rate of development of isometric tetanic tension. There was a just-significant (P < 0-1) increase in the shortening velocity of rat soleus. None of the other muscles showed any change in either rate characteristic.5. In guinea-pig extensor digitorum longus the type I fibres atrophied less than type II fibres; in all other muscles the atrophy was more uniform, possibly faster in type II. Guinea-pig soleus remained pure type I contrasting with an increase in the numbers of type II fibres in rat soleus. There was a possible increase in the number of type I fibres in guinea-pig fast muscle and no change in the rat.

Effects of chronic electrical stimulation on contractile properties of long‐term denervated rat skeletal muscle.

“…1 ( x ). The regressions of tension on time determined by Al-Amood & Lewis (1989b) are also plotted in the figure, and it is clear that the present data deviate from the extrapolation of the regression in both muscles. Indeed analysis of the present data alone showed that there was no evidence of any loss of tension in either muscle after 125 days denervation (see legend to Fig.…”

“…The first is certainly true: EDL loses tension more slowly than soleus in the first 4 months of denervation when atrophy will be quantitatively more important than necrosis or regeneration. Al-Amood & Lewis (1989b) found that the initial tension loss in EDL was at a rate 1 6 times lower than in soleus, but this is at best only one-third of the difference required to account for the higher equilibrium tension in EDL. It may, therefore, be concluded that soleus and EDL may also differ in their rates of regeneration or necrosis.…”

“…The methods were similar to those described in detail by Al-Amood, Finol & Lewis (1986) and Al-Amood & Lewis (1989b). Briefly, this involved fixing the proximal tendon in a haemostat and the distal tendon was tied to a small loop of stiff surgical thread (braided silk of a thickness appropriate to the predicted tension) for attachment to an unbonded wire strain-gauge dynamometer (compliance less than 01 mm/N, unloaded resonant frequencv 760 Hz).…”

“…We then went on to investigate the effects of electrical stimulation during the last 3-8 weeks of similar denervation. For comparison, we also made observations on the fast twitch extensor digitorum longus muscle (EDL) in which atrophy is slower (Al-Amood & Lewis, 1989b).…”

“…We thought that rat soleus would be a suitable muscle to study because it atrophies faster than other muscles of small laboratory rodents (Al-Amood & Lewis, 1989b) and might degenerate faster. Preliminary histological work confirmed this: at 4 months denervation, rat solei had suffered little fibre loss, whereas at 6 months necrosis was extensive -in one muscle only five fibres were seen in the light microscope.…”