. Aging induces muscle-specific impairment of endothelium-dependent dilation in skeletal muscle feed arteries. J Appl Physiol 93: 1685-1690, 2002; 10.1152/ japplphysiol.00461.2002.-We tested the hypothesis that aging decreases endothelium-dependent vasodilation in feed arteries perfusing rat skeletal muscle. In addition, we tested the hypothesis that attenuated vasodilator responses are associated with decreased endothelial nitric oxide synthase (eNOS) and superoxide dismutase-1 (SOD-1) expression. Soleus feed arteries (SFA) and gastrocnemius feed arteries (GFA) were isolated from young (4 mo) and old (24 mo) male Fischer 344 rats. Feed arteries from the right hindlimb were cannulated with two glass micropipettes for examination of endothelium-dependent [acetylcholine (ACh)] and endothelium-independent [adenosine (Ado) or sodium nitroprusside (SNP)] vasodilator function. Feed arteries from the left hindlimb were frozen and used to assess eNOS and SOD-1 protein and mRNA expression. In SFA, endothelium-dependent dilation to ACh was reduced in old rats (0.9 Ϯ 0.04 vs. 0.8 Ϯ 0.03), whereas dilator responses to Ado and SNP were similar in SFA of young and old rats. In GFA, vasodilator responses to ACh, Ado, and SNP were not altered by age. eNOS and SOD-1 protein expression declined with age in SFA (Ϫ71 and Ϫ54%, respectively) but not in GFA. eNOS and SOD-1 mRNA expression were not altered by age in SFA or GFA. Collectively, these data indicate aging induces muscle-specific impairment of endothelium-dependent vascular function in SFA. endothelial nitric oxide synthase; superoxide dismutase; nitric oxide; acetylcholine; sodium nitroprusside RESULTS FROM SEVERAL STUDIES indicate that endothelial function in conduit arteries declines with age in humans and animals (3,4,7,8,10,11,16,23). The endothelial dysfunction induced by aging is characterized by blunted vasodilator responses of conduit arteries to select endothelium-dependent agonists (3,4,7,8,10,11,16,23). The mechanism(s) for the detrimental effects of age on endothelium-dependent dilation is not fully understood; however, age-associated decrements in the ability of endothelial cells to produce and/or release nitric oxide (NO) may contribute to the dysfunction (3,11,16). This speculation is supported by experimental evidence indicating that vasodilation in response to ACh and bradykinin is impaired in aorta from senescent subjects, whereas dilation to sodium nitroprusside (SNP) is not compromised (3,5,16).An age-associated decline in the expression of endothelial NO synthase (eNOS), decreasing local production of NO, is one mechanism that may contribute to impaired endothelium-mediated dilation in conduit arteries of senescent animals. Indeed, age-related reductions eNOS mRNA expression have been reported in aorta of senescent rats (3, 6). Alternatively, decreased expression of Cu/Zn-dependent superoxide dismutase (SOD-1) may contribute to impaired endothelium-mediated dilation by compromising the ability to scavenge superoxide anion (O 2 Ϫ ⅐), decreasing the bio...