The L-name-resistant component of acetylcholine-induced relaxation of the rat superior mesenteric arterial bed is innervation-dependent.

Using L-NAME and the potassium channel blocker apamin we have investigated the component of acetylcholine-induced vascular relaxation lost when the mesenteric arterial bed is denervated. We have confirmed that vascular denervation produces a reduction of up to 35% in the ability of ACh to cause relaxation in the presence of the alpha agonists methoxamine and cirazoline. A single 30 minute exposure to L-NAME reduced the relaxation to ACh by up to 44% in control vascular preparations and by 85% in denervated preparations. In control preparations, prolonged exposure to L-NAME reduced the relaxation to ACh by up to 66% and by 77% in the presence of apamin. In denervated preparations prolonged exposure to L-NAME reduced the relaxation to ACh by 96%. The almost complete loss of acetylcholine-induced relaxation following prolonged exposure to L-NAME (96.6% in methoxamine and 93.9% in cirazoline) in denervated preparations suggests that innervation is involved in the expression of the L-NAME-resistant relaxation to acetylcholine in the superior mesenteric arterial bed of the rat.