AGING ALTERS THE REGIONAL BLOOD FLOW RESPONSE TO SUBMAXIMAL EXERCISE IN RATS

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. PURPOSE To determine the effects of aging on the hemodynamic and regional BF response to submaximal EX in rats. METHODS 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 submaximal 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 × Brown Norway rats. RESULTS HR, MAP, and BF to the pancreas, small and large intestine, and hindlimb muscle were similar between Y and O rats at rest. In contrast, BF to the kidneys, spleen, and stomach were 33%, 60%, and 43% lower in O compared to Y rats. During EX, MAP increased from R levels and was similar between Y and O rats. HR increased during EX, but the response was blunted in the O when compared to the Y (O: 457±6 vs Y: 496±13 bpm, P< 0.05). BF to the spleen and stomach decreased (P < 0.05) from R in Y rats during EX. In contrast, BF decreased in the kidneys, pancreas, spleen, stomach, small and large intestines of O rats during EX. BF to hindlimb muscle increased (P < 0.05) during EX and the increase 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 elevated in 8 (highly glycolytic) and reduced in 6 (highly oxidative) of the 28 individual muscles examined (P < 0.05). CONCLUSION O rats respond to submaximal EX with a greater reduction in BF to the kidneys and organs of the splanchnic region when compared to Y rats. Although, during submaximal EX BF to the hindlimb muscle as a whole increases to a similar degree in the Y and O rats, this response is accompanied by a disparity of BF found within and among the different individual muscles in a fiber type dependent manner. Supported by NIH AG19228 & HL50306