Fig. 4. Tension recordings showing the effect of acetylcholine (ACh) on the lateral aorta with (A) or without (B) the presence of the NOS inhibitor N-nitro-L-arginine (L-NNA). The preparations were pre-treated with L-NNA (10^-4 mol l^-1) for approximately 10 min before being constricted with endothelin-1 (ET-1; 10^-8 mol l^-1). At the peak of vasoconstriction, acetylcholine (Ach; 10^-5 mol l^-1) was administered, which only caused a marked vasodilation in the preparation without L-NNA (B) (N=5).