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1 Departments of Kinesiology, Anatomy & Physiology, Kansas State University, Manhattan, KS, USA
* To whom correspondence should be addressed. E-mail: musch{at}vet.ksu.edu.
Maximal aerobic capacity and the ability to sustain submaximal (submax) 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 submax 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 (R) and during submax treadmill EX (20 m/min, 5% grade) with radiolabeled microspheres in young (Y; 6-8 month old, 339±8 g, n=9) and old (O; 27-29 month old, 504±18 g, n=7) Fischer 344 x 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 in O compared to 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/100g, respectively). However, in O vs. Y rats BF was reduced in 6 (highly oxidative) and elevated in 8 (highly glycolytic) of the 28 individual muscles examined (P<0.05). During EX, BF to the spleen and stomach decreased (P<0.05) from R 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 blood flow in Y and O rats during submaximal exercise, there is a profound blood flow redistribution from highly oxidative to highly glycolytic muscles.
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