 In the sympathetic nervous system the output connections mainly release noradrenaline, although acetylcholine is released at a few points, such as the sudomotor innervation of the sweat glands.Acetylcholine in the serum exerts a direct effect on vascular tone by binding to muscarinic receptors present on vascular endothelium.These cells respond by increasing production of nitric oxide, which signals the surrounding smooth muscle to relax, leading to vasodilation.