A, vasodilator effect of ACh and SNP, as indicated by relative vascular conductance (RVC). Symbols denote mean ± s.e.m. of the maximal increase in RVC induced by a 10 min topical application of ACh or SNP in the hamster cheek pouch. The number of experiments is shown in parentheses. With each agonist, the maximal RVC increase changed significantly with concentration (P < 0.05, ANOVA). B, inhibition of vasodilatation as a function of the concentration of NOS inhibitor. Symbols denote the mean ± s.e.m. of maximal RVC increase induced by a 10 min application of 100 μm ACh or 10 μm SNP as a function of the concentration of NG -nitro-l-arginine (l-NNA). ACh was tested after 60 min superfusion with the NOS inhibitor. SNP was tested after 120 min of continuous application of the NOS inhibitor. The number of experiments is shown in parentheses. * Significant differences relative to agonist alone (P < 0.05, unpaired t test, with Dunnett's tables for multiple comparisons with a control).