Acetylcholine is a cholinergic neurotransmitter with a poor selectivity of action. When acting on blood vessels, it can cause the muscle layer of vascular arteries and veins to relax, and its contraction can be caused by direct action at high doses. When it acts on bronchial smooth muscle, it can make it contract and increase the secretion of bronchial glands. When applied to the smooth muscle of the gastrointestinal tract, it can promote the movement of the stomach and intestines, and cause the sphincter of the stomach and intestines to relax and increase the secretion of the stomach and intestines. Acting on the bladder forceps causes contraction. When applied to the iris sphincter and ciliary muscle of the eye, it can cause contraction, which is used for pupil narrowing and myopia viewing, etc.