Hepple Russell T, Hagen Jason L, Krause Daniel J, Jackson Cory C
Faculty of Kinesiology and Faculty of Medicine, University of Calgary, Alberta, Canada T2N 1N4.
J Appl Physiol (1985). 2003 Feb;94(2):744-51. doi: 10.1152/japplphysiol.00737.2002. Epub 2002 Oct 4.
Although it is well established that maximal O(2) uptake (Vo(2 max)) declines from adulthood to old age, the role played by alterations in skeletal muscle is unclear. Specifically, because during whole body exercise reductions in convective O(2) delivery to the working muscles from adulthood to old age compromise aerobic performance, this obscures the influence of alterations within the skeletal muscles. We sought to overcome this limitation by using an in situ pump-perfused hindlimb preparation to permit matching of muscle convective O(2) delivery in young adult (8 mo; muscle convective O(2) delivery = 569 +/- 42 micromol O(2) x min(-1) x 100 g(-1)) and late middle-aged (28-30 mo; 539 +/- 62 micromol O(2) x min(-1) x 100 g(-1)) Fischer 344 x Brown Norway F1 hybrid rats. The distal hindlimb muscles were electrically stimulated for 4 min (60 tetani/min), and Vo(2 max) was determined. Vo(2 max) normalized to the contracting muscle mass was 22% lower in the 28- to 30-mo-old (344 +/- 17 micromol O(2). min(-1) x 100 g(-1)) than the 8-mo-old (441 +/- 20 micromol O(2) x min(-1) x 100 g(-1); P < 0.05) rats. The flux through the electron transport chain complexes I-III was 45% lower in homogenates prepared from the plantaris muscles of the older animals. Coincident with these alterations, the tension at Vo(2 max) and lactate efflux were reduced in the 28- to 30-mo-old animals, whereas the percent decline in tension was greater in the 28- to 30-mo-old vs. 8-mo-old animals. Collectively, these results demonstrate that alterations within the skeletal muscles, such as a reduced mitochondrial oxidative capacity, contribute to the reduction in Vo(2 max) with aging.
虽然从成年到老年最大摄氧量（Vo₂max）下降这一现象已得到充分证实，但骨骼肌变化所起的作用尚不清楚。具体而言，由于在全身运动过程中，从成年到老年输送到工作肌肉的对流性氧输送减少会损害有氧能力，这就掩盖了骨骼肌内变化的影响。我们试图通过使用原位泵灌注后肢制备方法来克服这一限制，以使年轻成年（8个月；肌肉对流性氧输送 = 569 ± 42微摩尔氧×分钟⁻¹×100克⁻¹）和中老年晚期（28 - 30个月；539 ± 62微摩尔氧×分钟⁻¹×100克⁻¹）的Fischer 344×Brown Norway F1杂交大鼠的肌肉对流性氧输送相匹配。对后肢远端肌肉进行4分钟（60次强直收缩/分钟）的电刺激，并测定Vo₂max。以收缩肌肉质量归一化后的Vo₂max在28至30月龄（344 ± 17微摩尔氧·分钟⁻¹×100克⁻¹）的大鼠中比8月龄（441 ± 20微摩尔氧×分钟⁻¹×100克⁻¹；P < 0.05）的大鼠低22%。老年动物比目鱼肌匀浆中通过电子传递链复合体I - III的通量低45%。与这些变化一致，28至30月龄动物在Vo₂max时的张力和乳酸流出量降低，而28至30月龄动物的张力下降百分比比8月龄动物更大。总体而言，这些结果表明骨骼肌内的变化，如线粒体氧化能力降低，会导致随着年龄增长Vo₂max下降。
