Effects of aging and exercise training on skeletal muscle blood flow and resistance artery morphology

Abstract

With old age, blood flow to the high-oxidative red skeletal muscle is reduced and blood flow to the low-oxidative white muscle is elevated during exercise. Changes in the number of feed arteries perforating the muscle are thought to contribute to this altered hyperemic response during exercise. We tested the hypothesis that exercise training would ameliorate age-related differences in blood flow during exercise and feed artery structure in skeletal muscle. Young (6-7 mo old, n = 36) and old (24 mo old, n = 25) male Fischer 344 rats were divided into young sedentary (Sed), old Sed, young exercise-trained (ET), and old ET groups, where training consisted of 10-12 wk of treadmill exercise. In Sed and ET rats, blood flow to the red and white portions of the gastrocnemius muscle (Gast(Red) and Gast(White)) and the number and luminal cross-sectional area (CSA) of all feed arteries perforating the muscle were measured at rest and during exercise. In the old ET group, blood flow was greater to Gast(Red) (264 ± 13 and 195 ± 9 ml · min(-1) · 100 g(-1) in old ET and old Sed, respectively) and lower to Gast(White) (78 ± 5 and 120 ± 6 ml · min(-1) · 100 g(-1) in old ET and old Sed, respectively) than in the old Sed group. There was no difference in the number of feed arteries between the old ET and old Sed group, although the CSA of feed arteries from old ET rats was larger. In young ET rats, there was an increase in the number of feed arteries perforating the muscle. Exercise training mitigated old age-associated differences in blood flow during exercise within gastrocnemius muscle. However, training-induced adaptations in resistance artery morphology differed between young (increase in feed artery number) and old (increase in artery CSA) animals. The altered blood flow pattern induced by exercise training with old age would improve the local matching of O(2) delivery to consumption within the skeletal muscle.

Fig. 1.

Resting blood flow in red gastrocnemius (Gast_Red, A), mixed gastrocnemius (Gast_Mixed, B), and white gastrocnemius (Gast_White, C) of young and old sedentary (Sed) and exercise-trained (ET) rats.

Fig. 2.

Blood flow measured during steady state of exercise in Gast_Red (A), Gast_Mixed (B), and Gast_White (C) of young and old Sed and ET rats. *P < 0.05 vs. Sed of corresponding age group. †P < 0.05 vs. young group in the same condition. #P = 0.055 vs. young Sed.

Fig. 3.

Vascular conductance calculated during steady state of exercise in Gast_Red (A), Gast_Mixed (B), and Gast_White (C) of young and old Sed and ET rats. *P < 0.05 vs. Sed of corresponding age group. †P < 0.05 vs. young group in the same condition. #P = 0.055 vs. young Sed.

Fig. 4.

Percent differences in exercising muscle blood flow between Sed and ET young and old groups. Percent difference was calculated as follows: [(blood flow ET − blood flow Sed)/blood flow Sed] × 100.

Fig. 5.

Average number of feed arteries and average cross-sectional area (CSA) of feed arteries perforating gastrocnemius muscle from young and old Sed and ET (Ex-trained) animals. *P < 0.05 vs. Sed of corresponding age group. †P < 0.05 vs. young group in the same condition.

Fig. 6.

Average number of feed arteries and average CSA of feed arteries perforating Gast_Red (A), Gast_Mixed (B), and Gast_White (C) from young and old Sed and ET animals. *P < 0.05 vs. Sed of corresponding age group. †P < 0.05 vs. young group in the same condition. #P = 0.08 vs. young Sed.