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Effects of aging and exercise training on the myogenic mechanism of skeletal muscle arterioles.

(1) Solis, Fredy M.; (2)Muller-Delp, Judy; (3)Smith, Barbara; (1) Delp, Michael. (1) Applied Physiology and Kinesiology, University of Florida, Gainesville, FL, United States; (2) Physiology and Functional Genomics, University of Florida, Gainesville, FL, United States; (3) Physical Therapy, University of Florida, Gainesville, FL, United States.

Purpose/Hypothesis: The myogenic response, which is the tendency of small arteries to constrict in response to elevation of intravascular pressure and dilation after a decrease in intravascular pressure, is diminished with advancing age. These age-related changes in which blood vessels' walls become less tolerant of sudden increases in pressure have detrimental effects on the aerobic capacity and cardiovascular performance during exercise. Endurance exercise training protocols have shown to improve the attenuated blood flow response in working muscles during exercise in the aged population. Therefore the purpose of this study was to determine the effect of aging and exercise training on the myogenic response in skeletal muscle resistance arterioles from 2 skeletal muscles composed of different fiber type (soleus and white portion of the gastrocnemius) and whether or not this effect takes place in the vascular smooth muscle. Number of Subjects: 74 Fischer 344 rats. Materials/Methods: Animals were placed in one of 4 experimental groups: young and old sedentary, young and old exercise trained (ET). The training protocol consisted of 10 to 12 weeks of treadmill running. The gastrocnemius-plantaris-soleus muscle group was carefully dissected free from both hindlimbs and placed in cold (4[degrees]C), first-order (1A) arterioles were isolated from the muscles and cannulated with micropipettes and transferred to the stage of an inverted microscope. The myogenic responses were recorded in the presence of 2 mM extracellular [Ca.sub.2.sup.+] from 0 cm[ H.sub.O ] up to 140 cm[ H.sub.O ] by 10 cm[ H.sub.O ] increments. Results: 1A arterioles from soleus and gastrocnemius muscle displayed vascular constriction as pressure was increased within the examined range. Results from this study showed a stronger myogenic reaction in the arterioles from young animals than in those from old rats (p < 0.05), at the same time exercise training induces a stronger myogenic reaction in both young and old ET animals (p = 0.006) in soleus but not in gastrocnemius. Removal of the endothelium abolishes the aging and training effect. Conclusions: This study provides evidence that (I) the myogenic response from isolated resistance arterioles from the soleus and superficial portion of the gastrocnemius muscle were impaired in senescent Fischer 344 rats, (II) endurance exercise training induced development of a stronger and more robust vasoconstriction of skeletal muscle resistance arterioles as intraluminal pressure increased, and (III) the myogenic constriction was diminished in arterioles in which the endothelium had been removed. The findings indicate that this vascular responsiveness in exercise trained animals was mediated primarily by changes in the endothelium. Clinical Relevance: The physiological impact of this reduced myogenic response of the resistance vasculature in the aged population could have a negative effect on the skeletal muscle vasculature to increase resistance during fluctuating physiological challenges, such as orthostatic tolerance.
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Publication:Cardiopulmonary Physical Therapy Journal
Date:Dec 1, 2011
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