A Comparative Study On Two Kinds Of Animal Models Of Disuse Muscle Atrophy And Several Classification Methods Of Muscle Fibres

Background: Previous studies indicate that inactivation, immobilization or muscle unloading all can lead to obvious disuse atrophy in skeletal muscles. The muscle atrophy has serious effects on myodynamia, stamina, and daily activities of clinical sufferer or astronaut. Therefore, one of the most important and urgent issues to be solved in clinical medicine, sports medicine, rehabilitation medicine and space medicine is to illuminate the mechanism of muscle atrophy. Establishing a credible model is very important for the study of disuse muscle atrophy. Researchers usually use hindlimb unloading and immobilization animal models in study of disuse atrophy. However, the comparative study of these models has not been reported so far. On the other hand, the histochemistry of myosin adenosine triphosphatease(mATPase), succinic dehydrogenase(SDH) and the immunohistochemistry of myosin heavy chain(MHC) all are used to measure the activities of metabolic enzymes of skeleton muscle and identification of muscle fibre types, but comparative study on these three methods has rarely been reported in recent years.Objective: To compare the effects on health and muscle by these two models of tail suspension and hindlimb immobilization in rat, and to provide researchers with scientific standards for selecting better animal model. To compare advantages and disadvantages of these three methods, this can classify muscle fibres types, anddetermine their scopes of application.Methods: Three groups (namely.7d, 14d and 21d) were established for each model respectively.(l)The changes in body weight, viscera exponent and SOL weight /body weight(W/BW) of experimental animals were observed.(2) The changes of CSA were observed by histochemistry and color picture analysis system.(3) The changes of the activities of mATPase and SDH were observed by histochemistry, moreover, the expression level of MHC by imrnunohistochemistry. Results:(1) Changes in body weight and viscera exponent during different periods under the condition of tail suspension or hindlimb immobilization1) Body weight revealed remarkably increases compared 14d group and 21 d group with 7d group of control (P<0.001),whereas no significantly variation in the two model groups((P>0.05). The result showed that the rise of body weight be restrained in some degree after tail suspension or hindlimb immobilization.2) Except thymus indexes significantly decreased in 14d group compared with 7d group of hindlimb immobilization. (PO.05), the other viscera exponent didn't appear significantly changes (P>0.05).(2) Changes in W/BW and CSA after different period of tail suspension and hindlimbimmobilizationBoth W/BW and CSA of the two model groups decreased significantly and more remarkably with the elongation of time. CSA of type I fibres atrophy more obviously than that of type II. W/BW and CSA of type I fibres revealed significantly decreases at 14d group of tail suspension, as well as 7d group of hindlimb immobilization. The result showed the two models lead SOL disuse atrophy remarkably and more obviously with the elongation of time. The group of hind limb immobilization appears obvious atrophy earlier than that of tail suspension.(3) Changes in activities of maltase and SDH and the expression level of MHC after different period of tail suspension and hind limb immobilization1) By mATPase staining, the ratios of type I muscle fibres in the two model groups both showed remarkable decreases (PO.001). In group of tail suspension, theratios of type I muscle fibres revealed remarkable decreases in 14d group compared with that of in 7d group (P<0.001), and no visible changes compared with that of in 21d group (P>0.05). In group of hindlimb immobilization, the ratios of type I muscle fibres didn't revealed significantly variation in 14d group compared with that of in 7d group (P>0.05),and in 21 d group revealed remarkably decreases compared with 14d group (P<0.001). These results suggest that the aerobic respiration would be weakened and the anaerobic respiration strengthened as a result of tail suspension or hindlimb immobilization, therefore muscle fibres of type I transform to type II rapidly and intensely. This transformation appeared most remarkably at 7d group of hindlimb immobilization and at 14d group of tail suspension.2) By SDH staining , the ratios of type I and type II x revealed remarkable decreasesin the two model groups. But with the elongation of time, there was no remarkable variation ,only 21d group compared with 7d group of tail suspension, the ratios of type I and type II x showed Significant decrease. The results suggest that the transformation of muscle fibres be not obvious and the activity of SDH can not reflect the level of aerobic respiration of muscle fibres.3) By MHC staining, the ratios of type I muscle fibres in the two model groups bothshowed remarkable decreases (PO.001). In group of tail suspension, the ratios of type I muscle fibres revealed remarkable decreases in 14d group compared with that of in 7d group (P<0.001), and no visible changes compared with that of in 21d group (P>0.05). In group of hindlimb immobilization, the ratios of type I muscle fibres didn't revealed significantly variation in 14d group compared with that of in 7d group (P>0.05),and in 21 d group revealed remarkably decreases compared with 14d group (PO.001). The results showed that the types of MHC shift as a result of tail suspension and hindlimb immobilization, that MHC I transform to MHC II rapidly and intensely. This transformation appeared most remarkably at 7d in the groups of hindlimb immobilization and 14d in the groups of tail suspension.Conclusions:(l)Both models (tail suspension and hindimb immobilization) lead rat SOL to obvious atrophy. They are the ideal animal models for research in disuse atrophy. The effects of disuse are the most significant at tail suspension for 14d and hindlimb immobilization for 7d.(2)The mATPase and MHC staining are the ideal classification methods of muscle fibres types, since they can distinguish muscle fibres types easily. Using SDH staining to classify muscle fibres types and estimate the transformation of muscle fibres types is difficult after muscle disuse.