Effect of incubation (40 min) with, l-arginine (1 mM; N = 15), urea (100 μM; N = 8) or ornithine (100 μM; N = 8) on contractions to cumulatively increasing concentrations (10 nM to 10 μM) of dexmedetomidine in quiescent rat aortic rings with endothelium. All preparations were incubated with N^ω-nitro-l-arginine methyl ester hydrochloride (l-NAME; 100 μM). Data expressed as areas under the curve and analyzed by one-way ANOVA followed by the Newman-Keuls Multiple Comparison post hoc test, and shown as mean ± SD. *P < 0.05 compared with l-NAME.