Advanced age is associated with altered skeletal muscle hemodynamic control during the transition from rest to exercise. This study investigated the effects of aging on the functional role of nitric oxide (NO) in regulating total, inter- and intra-muscular hindlimb hemodynamic control at rest and during submaximal whole-body exercise. We hypothesized that NO synthase inhibition (N(G)-nitro-L-arginine-methyl-ester, L-NAME; 10 mg/kg) would result in attenuated reductions in vascular conductance (VC) primarily in oxidative muscles in old compared to young rats. Total and regional hindlimb muscle VC were determined via radiolabelled microspheres at rest and during treadmill running (20 m/min, 5% grade) in nine young (6-8 mo) and seven old (27-29 mo) male Fisher 344xBrown Norway rats. At rest, L-NAME increased mean arterial pressure (MAP) significantly by ~17% and 21% in young and old rats, respectively. During exercise, L-NAME increased MAP significantly by ~13% and 19% in young and old rats, respectively. Compared to young, L-NAME administration in old rats evoked attenuated reductions in total hindlimb VC during exercise (i.e., down by ~23% in old vs. 43% in young rats; P