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CARDIOVASCULAR |
1 Division of Exercise Physiology, Department of Physiology and Pharmacology, and the Center for Interdisciplinary Research in Cardiovascular Sciences, West Virginia University School of Medicine, Morgantown, WV 26506, USA
2 Department of Medicine, University of California-San Diego, La Jolla, CA 92093-0673, USA
3 Department of Integrative Physiology, University of Colorado, Boulder, CO 80309-0354, USA
4 Department of Biology, Texas A&M University, College Station, TX 77843-3258, USA
Key structural and functional properties of the skeletal muscle vasculature that underlie diminished vascular conductance with ageing remain obscure. The purpose of this investigation was to test the hypotheses that (1) reduced levels of spontaneous physical activity in old rats are associated with skeletal muscle vascular remodelling (e.g. arterial rarefaction), and (2) consequent to a vascular remodelling, calculated shear stress is maintained in feed arteries of aged muscle at levels commensurate with that in young. Activity during daily light and dark cycles (12–12 h) was measured at 30-s intervals for 2 weeks in young (6 months; n
= 9) and old (24 months; n
= 9) Fisher 344 rats via telemetry. Subsequently, the gastrocnemius complex and soleus muscles were excised and all feed arteries were counted, isolated, cannulated and maximally dilated for measurement of luminal diameter. Resting blood flow was also measured to estimate vessel wall shear-stress in the feed arteries perforating the soleus and gastrocnemius muscles. Overall, young rats were 
1.6 times more active during dark periods and 4 times more active during light periods than old rats. In addition, young rats had approximately one additional feed artery perforating both the soleus (young, 3.3 ± 0.2; old, 2.6 ± 0.2 vessels; P < 0.05) and gastrocnemius (young, 8.8 ± 0.1; old, 7.5 ± 0.2 vessels, P < 0.05) muscles compared with old rats. However, average vessel wall shear stress at rest was similar between young and old rats (soleus: Y, 65 ± 5; O, 64 ± 5 dynes cm–2; gastrocnemius: Y, 329 ± 22; O, 327 ± 27 dynes cm–2) resulting from a larger vessel diameter in arteries from old rats. In conclusion, lower activity levels of old rats likely contribute to resistance artery rarefaction and, consequently, this provides a plausible mechanism for the altered blood flow patterns observed during exercise in aged skeletal muscle.
(Received 25 February 2006;
accepted after revision 22 April 2006;
first published online 27 April 2006)
Corresponding author M. D. Delp: Division of Exercise Physiology, Department of Physiology and Pharmacology, and the Center for Interdisciplinary Research in Cardiovascular Sciences, West Virginia University School of Medicine, Morgantown, WV 26506, USA. Email: mdelp{at}hsc.wvu.edu
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