牛磺酸对代谢综合征大鼠胸骨舌骨肌结构与功能的影响

Effects of taurine on alterations in structure and function of sternohyoid muscle in metabolic syndrome rats

目的探讨代谢综合征（MS）参与阻塞性睡眠呼吸暂停低通气综合征（OSAHS）的发病及其机制。方法将21只SD大鼠单纯随机分为正常对照组（A组，nt=6）、代谢综合征组（B组，n=8）和牛磺酸干预组（C组，nt=7），A组给予正常饮食，B组和C组给予高脂饲料使其具有MS特征后，B组继续给予高脂饲料12周，C组给予高脂饲料加牛磺酸12周。应用肌球蛋白ATP酶组织化学法对3组大鼠胸骨舌骨肌毛细血管和Ⅰ、Ⅱ型肌纤维染色并进行图像分析，应用电刺激法测定等长收缩胸骨舌骨肌肌条在不同刺激频率下收缩性能的变化。结果（1）B组胸骨舌骨肌丙二醛含量明显高于A组和C组，超氧化物歧化酶（SOD）活性明显低于A组和C组。（2）B组胸骨舌骨肌毛细血管密度、毛细血管／肌纤维比率（C／F）和Ⅰ型肌纤维截面积[（140±5）个／mm^2，0．90±0．11，（6119±165）μm^2]明显低于A组[（278±17）个／mm^2，1．43±0．05，（9371±68）μm^2,均P〈0．01]和C组[（269±10）个／mm^2，1．40±0．07，（9007±136）μm^2，均P〈0．01]。（3）B组胸骨舌骨肌在10、20、30、40、50、60Hz的电刺激频率下肌张力明显低于A组和C组（均P〈0．05）。（4）在诱导疲劳试验中，B组胸骨舌骨肌1、2、3、4、5min张力百分比[（80．5±8．1）％、（64．1±1．2）％、（59．1±1．1）％、（56．4±10．9）％、（53．5±9．1）％]明显低于A组[（87．7±3．5）％、（78．5±1．5）％、（76．0±1．2）％、（72．3±15．0）％、（68．7±17．2）％，均P〈0．05]和C组[（87．4±2．4）％、（77．9±5．5）％、（73．6±1．1）％、（71．3±8．7）％、（68．0±6．7）％，均P〈0．05]。结论MS可经氧化应激反应介导降低大鼠胸骨舌骨肌毛细血管密度、C／F和Ⅰ型肌纤维截面积，从而降低上气道肌肉收缩性能，参与OSAHS的发病。

Objective To investigate the alterations in structure and function of sternohyoid muscle of metabolic syndrome （MS） rats effects and the effects of taurine thereupon contractile properties. Methods Twenty-one healthy male SD rats were randomly assigned to three groups： control group （Group A, n = 6） fed with normal food, MS group （ Group B, n = 8） fed with high-lipid forage for 9 weeks to induce MS and then fed with the same high-lipid forage for 12 weeks in addition, and taurine group（ Group C, n =7）, fed with high-lipid forage for 20 weeks and given gastric perfusion of taurine 50 mg·d^-1 · kg-1 since the tenth week for 12 weeks. Venous blood samples were collected to undergo biochemical examination of plasma total cholesterol （TC）, triglyceride （TG）, high-density lipoprotein （HDL）, low-density lipoprotein （LDL）, and glucose （Glu）. Radioimmunoassay was used to detect the plasma insulin. The sternohyoid muscles were collected. Muscle tissue homogenate was made. The superoxide dismutase （SOD） and malondialdehy （MDA） levels were measured. Myosin-ATPase histochemistry was used to assay the size and capillary density of the isolated sternohyoid muscles. Isometric contractile properties were determined by electrostimulating the strips of isolated sternohyoid muscles at different frequencies （from 10 Hz to 100 Hz） to observe the changes of the sternohyoid contractile properties in different conditions. Results （ 1 ） The levels of TG, LDL, Glu, PGI, and MDA of Group B were significantly higher than those of Groups A and C, while the HDL level of Group B was significantly lower than that of Group A （ P 〈 0. 01 ）. The OD level of Group B was significantly lower than those of Groups A and C. （2） The capillary density, capillary-to-fiber ratio （C/F）, and cross-sectional area of type I fiber in sternohyoid muscles of Group B were（ 140±5）/ mm^2 ,0.90±0. 11, and（6119 ± 165） μm^2 respectively, all significantly higher than those of Group A [ （ 278 ~ 17 ）/mm^2, 1.43 ± 0. 05, and （ 9371 ± 68 ） μm^2 respectively, all P 〈 0. 01 ] and Group C [ （ 269 ± 10）/mm^2, 1.40±0.07, and （9007±136） μm^2 respectively, all P 〈0.01]. （3） The tensions of sternohyoid muscle of Group B at the frequencies from 10 Hz to 60 Hz were （29 ± 6 ）g/cm^2, （34 ± 7 ）g/ cm^2, （41 ± 6 ） g/cm^2, （ 47 ± 6 ） g/cm^2, （ 53 ± 7 ） g/cm^2, and （ 59 ± 20 ） g/cm^2 respectively, all significantly lower than those of Group A group[ （40 ± 3 ） g/cm^2, （ 52 ± 13 ） g/cm^2, （ 60 ± 17 ） g/cm^2, （ 74 ± 32 ） g/cm^2, （80 ±29）g/cm^2, and （96 ±24）g/cm^2 respectively, all P 〈0. 051 and Group C [ （43 ±26）g/cm^2 ,（48 ± 6） g/cm^2, （ 55 ± 9 ） g/cm^2, （ 67 ± 14 ） g/cm^2, （ 75 ± 15 ） g/cm^2, and （ 80 ± 15 ） g/cm^2 respectively, all P 〈 0.05]. （4） In fatigue test, the tension percentages of sternohyoid muscle at the time intervals of 1 min, 2 min, 3 min, 4 min, and5 rain of Group B were（80.5±8.0）%, （64.1±1.2）%, （59.1±1.1）%, （56.4 ±10.9）%, and（53.5 ± 9. 1 ）% respectively, all significantly lower than those of Group A [（87.7±3.5）%, （78.5 ± 1.5）%, （76.0 ± 1.2）%, （72.3 ± 15.0）%, and （68.7 ± 17.2）% respectively, all P 〈 0. 05 ] and Group C group [ （ 87. 4 ± 2. 4 ） %, （ 77. 9 ± 5. 5 ） %, （ 73.6 ± 1.1 ） %, （71.3±8.7）%, and（68.0±6.7） respectively, all P 〈0.05]. Conclusion With the development of MS, the capillary density, C/F, cross-sectional area of type I fiber of upper airway muscles decrease, in part via oxidative stress, which leads to reduction of the contractile function of upper airway muscles, thus contributing to the onset of obstructive sleep apnea-hypopnea syndrome.