Long-term wheel-running prevents reduction of grip strength in type 2 diabetic rats.

Diabetic skeletal muscles show reduced contractile force and increased fatigability. Hands are a target for several diabetes-induced complications. Therefore, reduced handgrip strength often occurs as a consequence of diabetes. The aim of this study was to examine whether long-term exercise can prevent reduction of grip strength in type 2 diabetes mellitus (T2DM) model OLETF rats, and to explore the mechanisms underlying diabetes-induced grip strength reduction. Ten 5-week-old OLETF rats were used as experimental animals, and five non-diabetic LETO rats as controls of OLETF rats. Half OLETF rats performed daily voluntary wheel-running for 17 months (OLETF + EXE), and the rest of OLETF and LETO rats were sedentary. Grip strength was higher in OLETF + EXE and LETO groups than in OLETF group. OLETF group with hyperglycemia showed an increase in HbA1c, serum TNF-α, and muscle SERCA activity, but a decrease in circulating insulin. Each fiber area, total fiber area, and % total fiber area in type IIb fibers of extensor digitorum longus muscles were larger in OLETF + EXE and LETO groups than in OLETF group. There was a positive correlation between grip strength and the above three parameters concerning type IIb fiber area. Therefore, type IIb fiber atrophy may be the major direct cause of grip strength reduction in OLETF group, although there seems multiple etiological mechanisms. Long-term wheel-running may have blocked the diabetes-induced reduction of grip strength by preventing type IIb fiber atrophy. Regular exercise may be a potent modality for preventing not only the progression of diabetes but muscle dysfunction in T2DM patients.

Effects of appropriate-intensity treadmill exercise on skeletal muscle and respiratory functions in a rat model of emphysema.

The number of patients with chronic obstructive pulmonary disease (COPD), a typical respiratory disorder, is rapidly increasing globally. The purpose of this study was to determine the effects of appropriate-intensity treadmill exercise on skeletal muscle and respiratory functions in a rat model of emphysema. Twenty-one Wistar rats were randomly divided into three groups: the sham (SH) group, pulmonary emphysema (PE) group, and emphysema + exercise (EX) group. Cigarette smoke solution and lipopolysaccharide were intratracheally administered for 4 weeks in the PE and EX groups. The rats in the EX group were made to run on treadmills in the latter 2 weeks of the experiment. Lung tissue was stained with anti-macrophage antibodies; the specific force (contractile force per unit cross-sectional area) of the diaphragm and hind-limb muscles was measured, and blood was analyzed for serum cytokine levels. Many macrophages were observed in the lung tissue of the PE group. In the EX group, the population of macrophages was smaller, and the specific force of the diaphragm and extensor digitorum longus muscles was higher than in the PE group. Moreover, the degree of inflammation in the pulmonary tissue was reduced in the EX group. These results suggest that adaptive exercise may improve not only respiratory and muscle functions but also inflammation of the pulmonary tissue associated with emphysema.

The effects of hypoventilation disorder on physiological and biochemical properties of the hindlimb muscles.

The purpose of this study was to determine the physiological and biochemical properties of hindlimb muscles after hypoventilation (HPO) induced by bilateral phrenic nerve denervation. Male Wistar rats (10 weeks-old) underwent HPO by the phrenic nerve denervation at the cervical level or sham surgery. Analyses were performed 4, 8, and 12 weeks after the surgery. The myosin heavy chain (MHC) isoform profile and in vitro isometric contractile properties of the soleus (SOL) and extensor digitrum longus muscles (EDL) were analyzed. From the postoperative period, HPO induced characteristic changes in SpO2 such as hypoventilation disorder. After 12 weeks, significant increases in MHC1 and significant decreases in MHC2a were observed in the MHC isoform composition in SOL. Moreover, significant increases in MHC2a and significant decreases in MHC2b were also observed in the MHC isoform composition in EDL muscles in the HPO compared with sham (SHM) group. In our study, the tidal volume after unilateral phrenic nerve denervation decreased by approximately 12%, and that after bilateral phrenic nerve denervation decreased by approximately 35%. We concluded that the reduction in behavioral activity levels in the HPO group may have resulted in changes of the peripheral skeletal muscles as a result of disuse atrophy.