Exercise training is known to improve vasodilating mechanisms mediated by endothelium-dependent relaxing factors in the cardiac and skeletal muscle vascular beds. However, the effects of exercise training on visceral vascular reactivity, including the renal circulation, are still unclear. We used the experimental model of the isolated perfused rabbit kidney, which involves both the renal macro and microcirculation, to test the hypothesis that exercise training improves vasodilator mechanisms in the entire renal circulation. New Zealand albino rabbits were pen confined (SED; n=24) or treadmill trained (0% grade) for 5 days/wk at a speed of 18 m/min during 60 min over a 12-week period (ExT; n=24). Kidneys isolated from SED and ExT rabbits were continuously perfused in a non-recirculating system under conditions of constant flow and pre-contracted with norepinephrine (NE). The effects of exercise training on renal vascular reactivity were assessed using endothelial-dependent (acetylcholine, ACh; bradykinin, BK) and -independent (sodium nitroprusside, SNP) vasodilators. ACh induced marked and dose-related vasodilator responses in kidneys from SED rabbits, the reduction in perfusion pressure reaching 41 ± 8% (n=6; P<0.05). In the kidneys from ExT rabbits, vasodilation induced by ACh was significantly enhanced to 54 ± 6% (n=6; P<0.05). In contrast, BK-induced renal vasodilation was not enhanced by training [19 ± 8% and 13 ± 4% reduction in perfusion pressure for SED and ExT rabbits, respectively (n=6; P>0.05)]. Continuous perfusion of isolated kidneys from ExT animals with L-NAME (300 µM), an inhibitor of nitric oxide (NO) biosynthesis, completely blunted the additional vasodilation elicited by ACh [reduction in perfusion pressure of 54 ± 6% and 38 ± 5% for ExT and L-NAME + ExT, respectively (n=6; P<0.05)]. On the other hand, L-NAME infusion did not affect ACh-induced vasodilation in SED animals. Exercise training also increased renal vasodilation induced by SNP [36 ± 7% and 45 ± 10% reduction in perfusion pressure for SED and ExT rabbits, respectively (n=6; P<0.05)]. It is concluded that exercise training alters the rabbit kidney vascular reactivity, enhancing endothelium-dependent and independent renal vasodilation. This effect seems to be related not only to an increased bioavailability of NO but also to the enhanced responsiveness of the renal vascular smooth muscle to NO.