Effect of L-NAME and the combination of apamin/charybdotoxin on vasodilation response to Ach. Experiments were performed on aortic rings isolated from control rats (A, D), AIA rats (B, E) and nor-NOHA AIA rats (C, F) 21 days after the onset of arthritis. Cumulative concentration-responses curves with Ach were obtained after a 60-minute incubation period with L-NAME at 10-4 moles/liter (A, B, C) or with apamin-charybdotoxin at 10-7 moles/liter each (D, E, F). Values are the mean ± SEM from 8 to 12 rings. * = P < 0.05, *** = P < 0.001.