INFLUENCE OF ENDURANCE EXERCISE TRAINING ON DISTRIBUTION OF VASCULAR ADAPTATIONS IN RAT SKELETAL-MUSCLE

We hypothesized that an exercise training program consisting of treadm ill running at 32 m/min up a 15% incline, 90 min/day, 5 days/wk for 12 -14 wk, would elicit vascular adaptation in skeletal muscle of all fib er types in rats. This hypothesis was based on previous reports that t his intensity and duration of training caused increases in oxidative c apacity in rat skeletal muscle of all fiber types. Skeletal muscle vas cular transport capacity was examined with measurements of total and r egional (radiolabeled microspheres) flow capacity, capillary filtratio n coefficient (CFC), and permeability-surface area product (PS) for Cr -51-EDTA in maximally vasodilated (papaverine) hindquarters of control (C; n = 25) and exercise-trained (ET; n = 26) rats. CFC was increased in ET (0.038 +/- 0.001 vs. 0.030 +/- 0.001 ml.min(-1).mmHg(-1).100 g( -1); P less than or equal to 0.001). PS was greater in ET than C (7.80 +/- 0.33 vs. 6.39 +/- 0.37 ml.min(-1).100 g(-1); P less than or equal to 0.01). Citrate synthase activity was increased in the soleus (25%; P less than or equal to 0.05), the medial head (35%; P less than or e qual to 0.05), and the red portion of the long head (45%; P less than or equal to 0.005) but not in the white portion of the long head of tr iceps brachii (P = 0.14) of ET rats. Pressure-flow relationships indic ate that total flow was greater (P less than or equal to 0.05) in ET h indquarters at all perfusion pressures. Regional flow data revealed th at increases in flow capacity were not evident in muscles composed of all fiber types as predicted. Training-induced increases in muscle flo w capacity were positively correlated (n = 13; P less than or equal to 0.05) with the percentage of fast-twitch oxidative-glycolytic (FOG) f ibers in individual muscles. No correlation was found between training -induced increases in flow capacity and the percentage of slow-twitch oxidative (SO) or fast-twitch glycolytic fibers. Flow capacity of sole us muscle (predominantly SO) was unchanged after training despite incr eased citrate synthase activity. Thus, in contrast to our hypothesis, vascular flow adaptations elicited by this exercise training regimen w ere not observed in hindlimb muscles of all fiber types but were speci fic for FOG fibers.