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Figure 5 Effect of NG-monomethyl-L-arginine monoacetate (L-NMMA) treatment or endothelium removal on SR 58611A-induced vasodilation in human internal mammary artery rings constricted with 1 µm phenylephrine (PE). Concentration-response curves to SR 58611A were performed in the absence or in the presence of 100 µmol/l L-NMMA, an inhibitor of nitric oxide synthases, or after endothelium removal. The mean curves resulting from subtraction of the spontaneous relaxation of control vessels are shown. Results are expressed as percentage of relaxation from the contraction level induced by PE. Each point is the mean value of six experiments, and error bars represent SEM. **p < 0.01 indicates significant differences from response to SR 58611A alone.