We investigated the role that endothelial nitric oxide synthase plays in post-exercise hypotension in spontaneously hypertensive rats. To accomplish this, rats were subjected to a single bout of dynamic exercise on a treadmill at 15 m/min for 20 min. L-nitroarginine methyl ester (L-NAME, 40 mg/kg, i.p.) significantly inhibited post-exercise hypotension (25 +/- 11 and 5 +/- 3 mm, Hg, respectively; P < 0.05). In addition, the superoxide anion generation was decreased, while the plasma nitrite production and serine phosphorylation of endothelial nitric oxide synthase were significantly elevated in spontaneously hypertensive rats at 30 min after the termination of exercise. Taken together, these data demonstrated that the increased phosphorylation of endothelial nitric oxide synthase plays a crucial role in the reduction of arterial pressure following a single bout of dynamic exercise in spontaneously hypertensive rats. (C) 2009 Elsevier Inc. All rights reserved.