Nervous system drugs cholinergics

Studies of the parasympathetic nervous system and cholinergic agents led to the concept of neurochemical transmission and virere instrumental in the development of early drug receptor hypotheses and our understanding of the stereochemical influence on drug action. An excellent summary of this history is presented by Holmstedt (2). 

Giolinergic drugs mimic the activity of the parasympathetic nervous system (PNS). They also are called parasympathomimetic drugs. An understanding of the PNS is useful in understanding the cholinergic dni. ... 

The symptoms that followed the daily intramuscular administration of D.F.P. for 5 days mimicked most of the muscarine-like and nicotine-like effects (see p. 37) of cholinergic drugs. There were also effects on the central nervous system. 

Cholinesterase inhibitors have less marked effects on vascular smooth muscle and on blood pressure than direct-acting muscarinic agonists. This is because indirect-acting drugs can modify the tone of only those vessels that are innervated by cholinergic nerves and because the net effects on vascular tone may reflect activation of both the parasympathetic and sympathetic nervous systems. The cholinomimetic effect at the smooth muscle effector tissue is minimal since few vascular beds receive cholinergic innervation. Activation of sympathetic ganglia may increase vascular resistance. 

Blood vessels receive no direct innervation from the parasympathetic nervous system. However, parasympathetic nerve stimulation dilates coronary arteries, and sympathetic cholinergic nerves cause vasodilation in the skeletal muscle vascular bed (see Chapter 6 Introduction to Autonomic Pharmacology). Atropine can block this vasodilation. Furthermore, almost all vessels contain endothelial muscarinic receptors that mediate vasodilation (see Chapter 7 Cholinoceptor-Activating Cholinesterase-Inhibiting Drugs). These receptors are readily blocked by antimuscarinic drugs. 

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