VASCULAR ADAPTATIONS IN RAT HINDLIMB SKELETAL-MUSCLE AFTER VOLUNTARY RUNNING-WHEEL EXERCISE

To test the hypothesis that voluntary running-wheel exercise would eli cit vascular adaptations in rat skeletal muscle, male Sprague-Dawley r ats (202 +/- 5 g) were cage confined (C, n = 11) or housed in cages wi th free access to running wheels (R, n = 13) for 12 wk. Vascular trans port capacity was determined in maximally vasodilated (papaverine) hin dquarters of C and R rats with measurements of total and regional (rad iolabeled microspheres) flow capacity and capillary filtration coeffic ient. R rats voluntarily ran 29 +/- 4 km/wk over the 12-wk period; how ever, performance of individual rats varied greatly (range 4-74 km/wk) . Citrate synthase activity was increased in the medial head (81%, P < 0.001) and the red long head (88%, P < 0.001) of the triceps brachii muscle in R rats but not in the white long head (25%, P = 0.06). Capil lary filtration coefficient was 27% greater in R compared with C rats (0.040 +/- 0.003 vs. 0.031 +/- 0.002 ml . min(-1) 100 g(-1) . mmHg(-1) , respectively, P < 0.001) suggesting that there was an increase in mi crovascular surface area available for fluid exchange. Total hindquart ers flow was increased in R rats (P < 0.05) at all perfusion pressures examined, indicative of an increased flow capacity. Regional flows re vealed that skin flow was unchanged in R rats and that the increase in total flow was due to increased skeletal muscle flow capacity. These results indicate that voluntary running-wheel exercise elicits adaptiv e increases in skeletal muscle vascular transport capacity and oxidati ve capacity comparable to those seen in treadmill-trained rats and sup port the use of voluntary running-wheel exercise as a less stressful t raining modality in exercise studies using rats.