Altered regional blood flow responses to submaximal exercise in older rats

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Abstract
Maximal aerobic capacity and the ability to sustain submaximal exercise (Ex) declines with advancing age. Whether altered muscle blood flow (BF) plays a mechanistic role in these effects remains to be resolved. The present investigation determined the effects of aging on the hemodynamic and regional BF response to submaximal Ex in rats. Heart rate (HR), mean arterial pressure (MAP), and BF to different organs (kidneys, splanchnic organs, and 28 hindlimb muscles) were determined at rest and during submaximal treadmill Ex (20 m/min, 5% grade) with radiolabeled microspheres in young (Y; 6-8 mo old, 339 ± 8 g, n = 9) and old (O; 27-29 mo old, 504 ± 18 g, n = 7) Fischer 344 × Brown Norway rats. Results demonstrated that HR, MAP, and BF to the pancreas, small and large intestine, and total hindlimb musculature were similar between Y and O rats at rest. BF to the kidneys, spleen, and stomach were 33, 60, and 43% lower, respectively, in O compared with Y rats. BF to the total hindlimb musculature increased ( P < 0.05) during Ex and was similar for both Y and O rats (Y: 16 ± 3 to 124 ± 7 vs. O: 20 ± 3 to 137 ± 12 ml·min-1·100 g-1). However, in O vs. Y rats, BF was reduced in 6 (highly oxidative) and elevated in 8 (highly glycolytic) of the 28 individual hindquarter muscles or muscle parts examined ( P < 0.05). During Ex, BF to the spleen and stomach decreased ( P < 0.05) from rest in Y rats, whereas BF decreased in the kidneys, pancreas, spleen, stomach, as well as the small and large intestines of O rats. In conclusion, these data demonstrate that, despite similar increases in total hindlimb BF in Y and O rats during submaximal Ex, there is a profound BF redistribution from highly oxidative to highly glycolytic muscles.