MUSCLE ADAPTATIONS IN TRAINED RATS WITH PERIPHERAL ARTERIAL INSUFFICIENCY

The influence of training adaptations, induced within the active muscles of rats with peripheral arterial insufficiency, was assessed with an isolated hindlimb preparation. Femoral artery-stenosed rats, showing symptoms of intermittent claudication, were trained for 14-20 wk by running at 20-35 m/min up a 15% grade for up to approximately 1 h/day, 5 days/wk. Similar total hindlimb blood flows (12.6 ml/min) at a similar arterial O2 content (20.7 vol/100 ml) yielded similar blood flows (95-117 ml.min-1.100 g-1) and O2 deliveries (9-11-mu-mol. min-1 .g-1) to the contracting muscle of sedentary (n = 10) and trained (n = 10) rats. Ten-minute periods of tetanic contractions (100 ms at 100 Hz each) at 4, 8, 13, 45, 60, and 90 tetani/min min were used. Muscle force development was better maintained (P < 0.001) by the trained group. Higher peak O2 consumption (P < 0.01) of the trained (5.69 +/- 0.53-mu-mol. min-1 .g-1) compared with the sedentary group (3.66 +/- 0.26 mu-mol.min-1.g-1) involved a greater O2 extraction, since delivery of O2 was not different between groups. Thus adaptations occurred within trained muscle to enhance performance and peak O2 consumption. Muscle citrate synthase activity, an index of mitochondrial content, was greater (P < 0.005) in the trained group, with the low-oxidative white muscle section exhibiting the greatest change (approximately threefold sedentary). Adaptations in this section were probably realized functionally, since improvements in muscle performance were evident early in the contraction sequence. Our results imply that the improved exercise tolerance of the trained rats during treadmill running was due, in part, to local adaptations within the muscle not requiring an increase in muscle blood flow. Similar adaptations could be operative in patients with peripheral arterial insufficiency.