SKELETAL MUSCLEAS A ETIOLOGY OF OBESITY AND INSULIN RESISTANCE : INVESTIGATION BY USING FAST-TWITCH FIBER DOMINANT MODEL RATS (FFDR)

最近的研究报告骨骼肌特性与腹部肥胖、胰岛素抵抗和高血压有关。有证据表明，人体肌肉中快缩纤维（%FT）的百分比与胰岛素抵抗呈负相关，也与体脂积累呈正相关。然而，尚待阐明Suwa等人（Am.生理学杂志，271：R432 - R436，1996）的胰岛素敏感性水平低于对照大鼠。FT%纤维在M.腓肠肌和比目鱼肌的肌电活动均显著高于对照组（CR）。本研究的主要目的是调查胰岛素敏感性水平，一些肌肉特征，包括纤维成分和毛细血管密度，以及自由轮跑FFDR和CR之间的距离。FFDR（n=6）和CR（n=8）年龄为8至9周， 关于我们 在这项研究中使用。胰岛素敏感性通过正葡萄糖高胰岛素钳夹法评估90分钟，并计算为60至90分钟的平均葡萄糖输注速率（GIR ; mg/ kg/ min）。在此期间，两组的平均血浆胰岛素浓度无显著差异。FFDR组的体重、脂肪含量和个体肌肉重量与CR组无显著差异，但M组的体重高于CR组。FFDR中的比目鱼肌。M深部的慢缩纤维百分比（%ST）显著降低。腓肠肌和比目鱼肌深层纤维密度较高。腓肠肌和%FTa纤维。与CR相比，在FFDR中观察到比目鱼肌。另一方面，在毛细血管密度、毛细血管与纤维比率和肌纤维周围毛细血管的平均数量方面，FFDR和CR之间没有观察到显著差异。FFDR组GIR（4.9mg/kg/min）与CR组（4.6mg/kg/min）相比无显著性差异。8 ~ 9周龄FFDR组的轮跑距离也显著长于CR组。从这些结果中，肌纤维组成，因此建议不是在年轻的雄性大鼠全身葡萄糖摄取的单一决定因素。本研究的第二个目的是研究高脂饮食对腹部脂肪积累的影响，以及低脂和高脂饮食后FFDR和CR之间的组织化学和生化肌肉特征。本研究采用低脂饮食FFDR（FL ; n=8）、高脂饮食FFDR（FH ; n=9）、低脂饮食CR（CL ; n=7）和高脂饮食CR（CH ; n=7）。每种饮食在8周龄时开始，并维持6周。CH组体重增长和腹脂蓄积显著高于FL和FH组。4组间能量摄入量无显著性差异。虽然M.腓肠肌重量CH组高于FL组和FH组，M组无显著性差异。soleus和M.跖肌群4组。M. FFDR中腓肠肌的%显著低于CR，但FFDR中的% 2DX型纤维显著高于FFDR。在M.腓肠肌2A型和2DX型肌纤维琥珀酸脱氢酶（SDH）活性均显著高于1型肌纤维。从这些结果可以看出，CR和FFDR之间高脂饮食后脂肪积累的差异取决于每种纤维类型氧化能力的差异，而不是肌肉体积的差异。少

Recent studies reported skeletal muscle characteristics to be related to abdominal obesity, insulin resistance, and hyper tension. There is some evidences that the percentage of fast-twitch (%FT) fibers in human muscle is inversely associated with insulin resistance and is also positively related with body fat accumulation. However, it has yet to be elucidated as to whether rats with genetically higher levels of %FT fibers developed by Suwa et al (Am. J. Physiol., 271 : R432 - R436, 1996) had lower levels of insulin sensitivity than control rats. The FT% fiber in both the M. gastrocnemius and soleus in FT fiber dominant model rat (FFDR) were demonstrated to be significantly higher than in control rats (CR). The main purposes of present study was to investigate the levels of insulin sensitivity, some muscle characteristics including fiber composition and capillary density, and the distance for voluntary wheel running between FFDR and CR. FFDR (n=6) and CR(n=8) aged from 8 to 9 weeks wer … More e used in this study. Insulin sensitivity was evaluated by the euglycemic hyper insulinemic clamp for 90min and was calculated as the mean glucose infusion rate (GIR ; mg/ kg/ min) from 60 to 90 min. The mean plasma insulin concentration in both groups during this period showed no significant differences. Neither the body weight, fat contents, and individual muscle weight of FFDR were observed to be significantly different from CR, except for higher the weight of M. soleus in FFDR. A significantly lower levels of percentage of slow-twitch (%ST) fibers in the deep portion of the M. gastrocnemius and soleus, and higher levels of %FTb fibers in the deep portion of M. gastrocnemius and %FTa fibers in M. soleus were observed in FFDR when compared with CR. On the other hand, no significant differences between FFDR and CR were observed regarding the capillary density, capillary to fiber ratio, and the mean number of capillaries around the muscle fiber. The GIR in FFDR (4.9mg/kg/min) was not significantly lower than that in CR (4.6mg/kg/min). Distance covered by wheel running in FFDR at aged from 8 to 9 weeks was also significantly longer than that in CR. From these results, the muscle fiber composition is thus suggested to not be the single determinant of the whole-body glucose uptake in young male rats. The second purpose of present study was to investigate the effect of high-fat diet on abdominal fat accumulation, and histochemical and biochemical muscle characteristics between FFDR and CR after low- and high-fat diet. The FFDR with low-fat diet (FL ; n=8), FFDR with high-fat diet (FH ; n=9), CR with low-fat diet (CL ; n=7) and CR with high-fat diet (CH ; n=7) were used in this study. Each diet were started at age of 8 weeks and were maintained for 6 weeks. Increasing in body weight and abdominal fat accumulation in CH were significantly higher than in FL and FH. No significant Difference was observed in energy intake among 4 groups. Although weight of M. gastrocnemius in CH was higher than in FL and FH, no significant difference were observed in the weight of M. soleus and M. plantaris among 4 groups. The %type1 fibers in M. gastrocnemius in FFDR was significantly lower than in CR, but %type 2DX fibers in FFDR was significantly higher than that in FFDR. In the deep portion of M. gastrocnemius, succinate dehydrogenase (SDH) activity in type 2A and type 2DX fibers is significantly higher than that in type1 fibers in each group. From these results, it is suggested that the difference in fat accumulation after high-fat diet between CR and FFDR is dependent on difference in oxidative capacity of each fiber type but not in the muscles volume. Less