PERIPHERAL ADAPTATIONS IN TRAINED AGED RATS WITH FEMORAL-ARTERY STENOSIS

The development and functional significance of exercise-induced periph eral adaptations were evaluated in aged animals with peripheral arteri al insufficiency. Fisher 344 male rats (21 months old) were subjected to bilateral stenosis of the femoral arteries sufficient to limit acti ve hyperemia but not to impair resting blood flow. Beginning the third day after stenosis, animals were (1) exercised by walking (n=12) on a treadmill at 20 m/min at 15% inclination, twice a day, 5 days per wee k, or (2) limited to cage activity (n=10). Exercise tolerance improved from approximate to 5 to approximate to 35 minutes (P<.001) over the 8 weeks of the training program but increased only marginally to appro ximate to 8 minutes for the sedentary group. An isolated hind limb pre paration perfused at equivalent blood flows (approximate to 1 ml . min (-1) . g(-1) with an arterial blood oxygen content of approximate to 2 0 vol%) was used to assess the functional and metabolic impact of musc le-specific adaptations during sequential contraction periods at 4, 8, 15, 30, 45, 60, 75, and 90 tetani per minute. An initially similar fo rce development of approximate to 10 N/g was better maintained (P<.001 ) by the trained group. The peak oxygen consumption attained by the tr ained group of 5.68+/-0.34 mu mol . min(-1) . g(-1) was greater (P<.01 ) than that of the sedentary group (4.34+/-0.29 mu mol min(-1) . g(-1) ). This was due to a greater oxygen extraction, since oxygen delivery was the same (approximate to 10 mu mol . min(-1) . g(-1)) to muscles o f both groups. The improved muscle performance and greater oxygen extr action of trained muscle is attributed to an enriched capillary networ k (5.70+/-0.10 versus 4.68+/-0.11 capillary contacts per fiber, P<.001 ) and a 25% to 100% greater mitochondrial capacity (citrate synthase a ctivity, P<.001) of the fibers. Thus, aged animals with peripheral art erial insufficiency are capable of developing training-induced adaptat ions that serve to improve muscle performance, even if blood flow is n ot improved. Similar activity-related adaptations in elderly patients with intermittent claudication could contribute to an improved exercis e tolerance.