The morphology of regeneration of skeletal muscles in the rat

Muscle regeneration was studied by light and electron microscopy in soleus muscles of rat. After segmental crushing the number of fibres increased in some muscles within 30 days, indicating that numerical hyperplasia can take place. Locally applied Ringer solution of 60-70 degrees C caused necrosis of myofibres but left satellite cells and blood supply largely intact. Following phagocytosis, four mechanisms of regeneration were seen. (1) Lost fibres were replaced by clusters of myotubes formed by satellite cells within persisting basal lamina tubes. These clusters displaced the surrounding endomysium and looked like longitudinally 'split' fibres. (2) Viable fibre fragments fused with satellite cells. (3) Satellite cells of surviving fibres proliferated and fused to myotubes localized beneath the basal lamina. (4) Thin new fibres occurred in the interstitium. Their origin remained unknown. After 6 months the mean size of the new myofibres was normal, but the scatter of diameters was increased, central nuclei, fibre 'spliting' and branching, and fibrosis were prominent. Staining for acetylcholinesterase revealed that many fibres were short and not innervated. The similarity with dystrophic muscles in man suggested, that the most prominent histological changes in myopathic muscles may be due to attempts of regeneration.     

Expression of myosin isoforms during notexin-induced regeneration of rat soleus muscles

Myosin isozymes and their fiber distribution were studied during regeneration of the soleus muscle of young adult (4-6 week old) rats. Muscle degeneration and regeneration were induced by a single subcutaneous injection of a snake toxin, notexin. If reinnervation of the regenerating muscle was allowed to occur (functional innervation nearly complete by 7 days), then fiber diameters continued to increase and by 28 days after toxin treatment they attained the same values as fibers in the contralateral soleus. If the muscles were denervated at the time of toxin injection, the early phases of regeneration still took place but the fibers failed to continue to increase in size. Electrophoresis of native myosin showed multiple bands between 3 and 21 days of regeneration which could be interpreted as indicating the presence of embryonic, neonatal, fast and slow myosins in the innervated muscles. Adult slow myosin became the exclusive from in innervated regenerates. In contrast, adult fast myosin became the predominant form in denervated regenerating muscles. Immunocytochemical localization of myosin isozymes demonstrated that in innervated muscles the slow form began to appear in a heterogeneous fashion at about 7 days, and became the major form in all fibers by 21-28 days. Thus, the regenerated muscle was almost entirely composed of slow fibers, in clear contrast to the contralateral muscle which was still substantially mixed. In denervated regenerating muscles, slow myosin was not detected biochemically or immunocytochemically whereas fast myosin was detected in all denervated fibers by 21-28 days. The regenerating soleus muscle therefore is clearly different from the developing soleus muscle in that the former is composed of a uniform fiber population with respect to myosin transitions. Moreover the satellite cells which account for the regeneration process in the soleus muscle do not appear to be predetermined with respect to myosin heavy chain expression, since the fibers they form can express either slow or fast isoforms. The induction of the slow myosin phenotype is entirely dependent on a positive, extrinsic influence of the nerve.     

Characteristics of alpha-aminoisobutyric acid transport in rat skeletal muscles.

alpha-Aminoisobutyric acid (AIB) transport into the intracellular compartment of extensor digitorum longus and soleus muscles was measured (in vitro) after allowance for the equilibration of the amino acid in the extracellular space. The latter was determined with three markers, [14C]inulin, 60Co-EDTA and [3H]mannitol. Net transport of AIB was subsequently divided into its two components, i.e. influx and efflux. Rates of influx were measured as the intracellular accumulation of [14C]AIB after a short incubation (5 min), and efflux was measured as the release of AIB with time (up to maximum of 50 min) from muscles that had previously been preloaded with AIB. This intracellular efflux was resolved into two phases, which probably represent two separate components of exit. The influence of extracellular Na+ on the transport of this neutral amino acid (representing the A system) was investigated. Na+ depletion resulted in lower accumulations of AIB, the effects becoming more pronounced with progressive depletions of external Na+. These changes arose from an inhibition of AIB influx, concomitant with an enhancement of its efflux. In contrast, all components of tyrosine transport (representing the L system) were unaffected by lowering external Na+ concentrations. The net accumulation of AIB was also suppressed by cortisol. This inhibitory effect was, however, Na+-dependent and resulted solely from the steroid's enhancement of AIB efflux, the hormone being without effect on AIB influx.     

Myosin isoform transitions in regeneration of fast and slow muscles during postnatal development of the rat

Regeneration of rat fast (gastrocnemius medialis) and slow (soleus) muscles was examined after degeneration of myofibers had been achieved by injection of cardiotoxin into the hindleg during the first week after birth. Myogenesis in the regenerating muscles was compared to postnatal myogenesis in the contralateral and in control muscles. Synthesis of embryonic and neonatal myosin isoforms was initiated 3 days after injury. These forms were gradually replaced by the intermediate and fast adult isoforms (type II fiber myosins), whose synthesis followed the same curve in regenerating, contralateral, and control muscles. In contrast, synthesis of the slow myosin isoform (type I fiber myosin) was greatly delayed in injured muscles, but eventually became equal to its synthesis in contralateral and control muscles. It therefore appears that synthesis of type II fiber myosins is similarly regulated, probably by thyroid hormone, in developing regenerating and normal muscles, while synthesis of type I fiber myosin depends on other factor(s).     

The activity of alkaline phosphatase in the process of regeneration of rat liver.

Using GOMORI'S technique, the present authors investigated the dynamics of the alkaline phosphatase activity in the process of liver regeneration after partial hepatectomy. In all 80 rats of the Wistar strain were subjected to experiment, 60 to 75% of the liver parenchyma being removed from each of them. In the course of regeneration a gradual increase in the enzyme activity was observed within the first 48 hours following the operation. This was succeeded by a slow decline of the activity, and after the 25th day after the operation the reaction intensity resembled that recorded for the control animals. It was also ascertained that the fatty degeneration of the liver noted in the initial period of regeneration does not inhibit the activity of alkaline phosphatase.     

Effect of parenteral steroids on edema in replanted rat legs

The experiments described demonstrate that parenteral steroid therapy will decrease the amount of postoperative edema in the replanted leg of a rat.     

Neural impacts on the regeneration of skeletal muscles

The regeneration of skeletal muscles is a suitable model to study the development and differentiation of contractile tissues. Neural effects are one of the key factors in the regulation of this process. In the present work, effects of different reinnervation protocols (suture or grafting) were studied upon the regenerative capacity of rat soleus muscles treated with the venom of the Australian tiger snake, notexin, which is known to induce complete necrosis and subsequent regeneration of muscles. Morphological and motor endplate analysis indicated that the regenerative capacity of denervated, and thereafter surgically reinnervated muscles remains impaired compared to that of normally innervated muscles, showing differences in the muscle size, fiber type pattern and motor endplate structure, even 35 days after the notexin injection. A lack or deficiency of secreted neural factors, deterioration of satellite cells and/or incomplete recovery of the sutured or grafted nerves may be the cause of these discrepancies in the regeneration process.     

Time course of changes in lipoprotein lipase activity in rat skeletal muscles during denervation-reinnervation.

The effects of denervation-reinnervation after sciatic nerve crush on the activity of extracellular and intracellular lipoprotein lipase (LPL) were examined in the soleus and red portion of gastrocnemius muscles. The activity of both LPL fractions was decreased in the two muscles within 24 h after the nerve crush and remained reduced for up to 2 wk. During the reinnervation period, LPL activity was still reduced in the soleus and started to increase only on the 40th day. In the red gastrocnemius, LPL activity increased progressively with reinnervation, exceeding control values on the 30th day post-crush. The LPL activity in the soleus from the contralateral to denervated hindlimb was also affected, being increased on the postoperation day and then gradually decreased during the following days. In conclusion, the time course of changes in muscle LPL activity after nerve crush confirmed the predominant role of nerve conduction in controlling muscle potential to take up free fatty acids derived from the plasma triacylglycerols. However, other factors, such as muscle fiber composition and the fiber transformation, should also be considered in this aspect of the denervation-reinnervation process. Moreover, it was found that denervation of muscles from one hindlimb may influence LPL activity in muscles from the contralateral leg.     

Characteristics of palmitic acid transport in muscle membranes: rat skeletal muscles

1-14C Palmitate uptake by isolated rat plantaris muscle was determined over a 5-min. period following preincubation at 37 degrees C in the presence either of increasing concentrations of palmitate or of other fatty acids, carbohydrates and 2-4 DNP or under anaerobic conditions. Palmitate uptake shows a saturation kinetics and is reduced when the incubation medium contains other fatty acids, carbohydrates, 2-4 DNP on under anaerobic conditions. It is suggested that palmitate uptake could depend on presence of glucose and metabolic energy.     

Morphometric characteristics of the muscles of the lower extremities during movement in the human

Systemic investigation of the mechanisms that control locomotions in the man provides elaboration of some problems concerning properties and construction of the locomotory apparatus, especially morphometric characteristics of the muscles--length and shoulder of the thrust force. Various methods for determining length and shoulder of the thrust force are considered. The first method is based on substituting the muscles for mathematical or mechanical model. The second method makes it possible to define the degree of the muscle elongation by means of measuring the distance between the ends of the sectioned tendon; it includes regression equations, connecting a relative elongation of the muscles with the angle change in the joints. As a result of perfection of the previously known methods, mathematical models are made, owing to them it is possible to calculate morphometric characteristics of 8 muscles in the lower extremities using computer facilities. As an example, results of calculations, by means of various methods, morphometric characteristics of the gastrocnemius muscle are presented. They are obtained at registration of the kinematics of the run with a maximal speed. Satisfactive coincidence of the results is obtained.