ACETYLCHOLINE

Acetylcholine 3.1 is a neurotransmitter, which is found in both the central and peripheral nervous system. It is biosynthesized from choline and acetyl co-enzyme A by an enzyme choline acetyl transferase. It is stored in the nerve endings and released as required. Acetylcholine is metabolized and deactivated by acetylcholine esterase and the choline may undergo re-uptake for re-synthesis. Neighbouring group participation by the trimethylammonium ion can favour the hydrolysis of the acetate of acetylcholine.

3.1

Two classes of receptors have been distinguished by selective agonists. These are the nicotinic receptors, which are stimulated by nicotine 3.10 and are typically peripheral receptors associated with neuromuscular function. The others are the muscarinic receptors, which are stimulated by muscarine 3.11. These receptors are found not only in the peripheral system but they also affect heart rate, eye muscle, the respiratory rate and the gastrointestinal tract. There are also important muscarinic receptors in the brain. Examination of the structures of these agonists shows a formal relationship to acetylcholine. In this context it should be borne in mind that the nitrogen atom of the pyrrolidine ring of nicotine readily forms a salt.

3.11                                              3.10