Decreased arteriolar sensitivity to shear stress in adult rats is reversed by chronic exercise activity

Objective: We tested the hypothesis that the decline in endothelium-dependent arteriolar dilation in adult rats is reversed by chronic exercise activity. Methods: Rats were divided into voting (8-10 weeks)-sedentary (SEDY), adult (29-32 weeks)-sedentary (SEDA). and adult-exercised (EXA, treadmill exercise for 18-20 weeks) groups. Responses of isolated arterioles (similar to50 mum at 80 min. Hg) of gracilis muscle were assessed to increases in perfusate flow and vasoactive agents. Results: With no differences in basal tone. maximal flow-induced dilations were not different between arterioles of SEDY and SEDA rat's (71 +/- 2 and 72 +/- 2% of passive diameter. respectively), yet the sensitivity of arterioles to Shear stress (WSS50) was significantly less in SEDA than in SEDY rats (35 +/- 4 vs. 23 +/- 3 dyne/cm(2), respectively). In vessels of EXA rats, maximal flow-induced dilation was significantly augmented (88 2% of passive diameter) and WSS50 (15 +/- 1 dyn/cm(2)) was significantly reduced. Dilation to acetylcholine was enhanced in arterioles of EXA, whereas dilation to sodium nitroprusside was not different in vessels of the three groups. Conclusion: Chronic exercise activity reverses age related reduction in sensitivity of arterioles to increases in wall shear stress.