Effect of incubation (40 min) with N^ω-nitro-l-arginine methyl ester hydrochloride (l-NAME; 100 μM; N = 11), l-arginine (1 mM; N = 4), (S)-(2-boronethyl)-l-cysteine hydrochloride (BEC;100 μM; N = 9) or N^G-hydroxy-l-arginine (l-NOHA; 100 μM; N = 5), given alone or in combination (N = 15), on contractions to cumulatively increasing concentrations (10 nM to 10 μM) of dexmedetomidine in quiescent rat aortic rings with or without endothelium. Data expressed as concentration-response curves and analyzed by two-way ANOVA followed by the Bonferroni post hoc test (left), and as areas under the curve and analyzed by one-way ANOVA followed by the Newman-Keuls Multiple Comparison post hoc test (right), and shown as mean ± SD. *P < 0.05 compared with l-NAME.