TRAINING INCREASES COLLATERAL-DEPENDENT MUSCLE BLOOD-FLOW IN AGED RATS

The potential for physical training to enhance collateral-dependent blood flow (BF) to the hindlimbs of aged male rats (Fischer 344) was evaluated following bilateral femoral artery ligation at 20.5 mo of age. Rats were either Limited to cage activity (sedentary, n = 11) or trained by a mild-intensity treadmill program (trained, n = 14), which involved walking twice a day at 15 m/min (15% grade) to fatigue, 5 days/wk for 8-11 wk. Exercise tolerance of the trained rats increased from similar to 5 to similar to 25 min/bout by week 7, whereas exercise tolerance of the sedentary group changed little (to similar to 8 min/bout) during the training period. At similar to 23 mo age, animals were surgically prepared for hindquarter perfusion (aortic pressure = 100 +/- 1.3 mmHg) and force measurement of the left gastrocnemius-plantaris-soleus (GPS) muscle group during isometric contractions at 4, 8, 15, 30, and 45 tetani/min via sciatic nel-ve stimulation(similar to 6 V, 0.1-ms square waves at 100 Hz for 100 ms). Although initial force development was similar between groups (12.9 N/g), trained rats maintained tension better at 8, 15, 30, and 45 tetani/min (P < 0.01). BF to the entire hindlimb of the trained group, determined with Sr-85 15-mu m microspheres, was 43% greater (P < 0.05) than in the sedentary group. Thus collateral-dependent BF was improved by physical training. The greatest increase in BF was to the distal limb muscles (similar to 78%), the tissues most at risk during intermittent claudication. BF to the GPS muscle group was 67 +/- 10 ml . min(-1). 100 g(-1) in trained vs. 30 +/- 4.9 ml . min(-1). 100 g(-1) in sedentary group. This improved BF could have meaningfully contributed to the improved exercise tolerance observed during treadmill walking. The results demonstrate that even a mild-intensity exercise program of walking can improve collateral-dependent BF to the affected hindlimb of aged rats.