Figure 2. Cumulative concentration-response curves for S(+) ketamine (A), R(-) ketamine (B), and racemate (C) on norepinephrine-contracted aortic rings. Endothelium-intact ([circle, open]), endothelium-denuded ([lozenge, open]), and Nomega-nitro-L-arginine-treated endothelium-intact ([square, open]) preparations were studied. The insets show the same data as a function of absolute tension. Data are given as means +/- SEM. Parentheses indicate the number of preparations studied. For maximum tensions and half-maximum effective concentration values, see Table 1.