McCully K K, Fielding R A, Evans W J, Leigh J S, Posner J D
Department of Medicine, Medical College of Pennsylvania, Philadelphia 19129.
J Appl Physiol (1985). 1993 Aug;75(2):813-9. doi: 10.1152/jappl.1993.75.2.813.
This study compared in vivo measurements of muscle metabolism in humans with magnetic resonance spectroscopy (MRS) and in vitro analysis of biopsies. Healthy subjects [4 young males, 28.2 +/- 6.8 (SD) yr, and 6 older subjects (5 males, 1 female), 66 +/- 6.0 yr] performed a maximal cycle ergometer test, and MRS measurements of the calf muscles and needle biopsies of the lateral gastrocnemius were performed. Biopsies were analyzed for fiber type and citrate synthase (CS) activity. MRS measurements of inorganic phosphate (Pi), phosphocreatine (PCr), ATP, and pH were made using a 1.8-T 78-cm clear-bore magnet-and-spectrometer system. Two or three 5-min bouts of plantar flexion were performed against variable resistance to deplete PCr levels to 50% of resting values (mean end pH 6.99). PCr values during recovery were fit to an exponential curve, and the rate constant (PCrrate) was calculated. PCrrate was used as an index of oxidative metabolism. Older subjects had lower peak O2 uptake (VO2 peak) values (19.2 +/- 5.6 vs. 49.5 +/- 8.1 ml O2.min-1 x kg-1), CS activities (16 +/- 2.8 vs. 25 +/- 2.6 mmol.kg wet wt-1 x min-1), and PCrrate values (25.3 +/- 8. vs. 37.5 +/- 5.3 mmol PCr.kg wet wt-1.min-1) than young subjects. PCrrate correlated with CS activity, and both PCrrate and CS activity correlated with VO2 peak (P < 0.05). No correlations were found between percent fiber type and PCrrate, CS activity, and VO2 peak. These results support studies that showed decreases in muscle metabolism with age in healthy humans and show a good correlation between in vivo and in vitro measurements of oxidative metabolism.
本研究比较了利用磁共振波谱法（MRS）对人体肌肉代谢进行的体内测量与活检组织的体外分析。健康受试者[4名年轻男性，年龄28.2±6.8（标准差）岁，以及6名老年受试者（5名男性，1名女性），年龄66±6.0岁]进行了最大运动强度的蹬车测试，并对小腿肌肉进行了MRS测量以及对腓肠外侧肌进行了针刺活检。对活检组织进行了纤维类型和柠檬酸合酶（CS）活性分析。使用1.8-T、78-cm内径的开放式磁体-光谱仪系统对无机磷酸盐（Pi）、磷酸肌酸（PCr）、三磷酸腺苷（ATP）和pH进行MRS测量。进行两到三次5分钟的跖屈运动，对抗可变阻力以使PCr水平消耗至静息值的50%（平均终末pH值6.99）。恢复过程中的PCr值拟合为指数曲线，并计算速率常数（PCrrate）。PCrrate用作氧化代谢的指标。老年受试者的峰值摄氧量（VO2峰值）较低（19.2±5.6对49.5±8.1 ml O2·min-1·kg-1），CS活性较低（16±2.8对25±2.6 mmol·kg湿重-1·min-1），PCrrate值较低（25.3±8对37.5±5.3 mmol PCr·kg湿重-1·min-1），均低于年轻受试者。PCrrate与CS活性相关，且PCrrate和CS活性均与VO2峰值相关（P<0.05）。未发现纤维类型百分比与PCrrate、CS活性和VO2峰值之间存在相关性。这些结果支持了关于健康人体肌肉代谢随年龄下降的研究，并表明氧化代谢的体内和体外测量之间具有良好的相关性。
