Parasympathetic Postganglionic Blocking Agents

Organs controlled by the autonomic nervous system usually are innervated by both the sympathetic and the parasympathetic systems. There is a continual state of dynamic balance between the two. systems. Theoretically, one should achieve the same end result by either stimulation of one of the sy.s-tems or blockade of the other. Unfortunately, there is usually a limitation to this type of generalization. There are. however, three predictable and clinically useful results from blcK king the muscarinic effects of ACh. 

Mydriatic effect dilution of the pupil of ihc eye and cydnptegia. u puralysis of the ciliary structure of the eye. resulting in u paralysis of uccommodaiion for near vision 

Antispasmodic effect lowered lone and motility of the GI tract and the genitourinary tract 

Antisecretury effect reduced. salivation Umtisialagogwe). reduced perspiration (unhidrntic), and reduced acid and gastric secretiun 

These three general effects of parasympatholytics can be expected in some degree from any of the known drugs, though occasionally one must administer rather heroic doses to demonstrate the effect. The mydriatic and cyclopicgic 

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Similar considerations would apply at the synapse between the preganglionic fibre and the nerve cell of the postganglionic fibre of the sympathetic and parasympathetic systems and curare is the blocking agent (fig. 7 A). 

Adrenergic neurone blocking agents usually interfere with postganglionic sympathetic nervous transmission but they do not exert any effect on the parasympathetic nervous system. 

These agents inhibit the muscarinic actions of acetylcholine at postganglionic parasympathetic neuroeffector sites including smooth muscle, secretory glands, and CNS sites. Large doses may block nicotinic receptors at the autonomic ganglia and at the neuromuscular junction. 

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