A ganglionic blocker (or ganglioplegic) is a type of medication that inhibits transmission between preganglionic and postganglionic neurons in the autonomic nervous system, often by acting as a

nicotinic receptor antagonist A nicotinic antagonist is a type of anticholinergic drug that inhibits the action of acetylcholine (ACh) at nicotinic acetylcholine receptors. These compounds are mainly used for peripheral muscle paralysis in surgery, the classical agent of this t ...

. Nicotinic acetylcholine receptors are found on skeletal muscle, but also within the route of transmission for the parasympathetic and sympathetic nervous system (which together comprise the autonomic nervous system). More specifically, nicotinic receptors are found within the ganglia of the autonomic nervous system, allowing outgoing signals to be transmitted from the presynaptic to the postsynaptic cells. Thus, for example, blocking nicotinic acetylcholine receptors blocks both sympathetic (excitatory) and parasympathetic (calming) stimulation of the heart. The nicotinic antagonist hexamethonium, for example, does this by blocking the transmission of outgoing signals across the autonomic ganglia at the postsynaptic nicotinic acetylcholine receptor. Because ganglionic blockers block both the

parasympathetic nervous system The parasympathetic nervous system (PSNS) is one of the three divisions of the autonomic nervous system, the others being the sympathetic nervous system and the enteric nervous system. The enteric nervous system is sometimes considered part ...

and sympathetic nervous system, the effect of these drugs depends upon the dominant tone in the organ system. The opposite of a ganglionic blocker is referred to as a ganglionic stimulant. Some substances can exhibit both stimulating and blocking effects on autonomic ganglia, depending on dosage and/or duration of action. An example for such a "dual" action is nicotine, which does this via depolarization block (see classification below).

Examples

The first ganglion-blocker to be used clinically was tetraethylammonium, although it was soon superseded by better drugs. Nicotinic receptor antagonists: *

hexamethonium Hexamethonium is a non-depolarising ganglionic blocker, a nicotinic (nAChR) receptor antagonist that acts in autonomic ganglia by binding mostly in or on the nAChR receptor, and not the acetylcholine binding site itself. It does not have any e ...

pentolinium Pentolinium is a ganglionic blocking agent which acts as a nicotinic acetylcholine receptor antagonist. Formulated as the pentolinium tartrate salt, it is also known as Ansolysen. It can be used as an antihypertensive drug during surgery or to ...

* mecamylamine * trimetaphan * tubocurarine *

pempidine Pempidine is a ganglion-blocking drug, first reported in 1958 by two research groups working independently, and introduced as an oral treatment for hypertension. Pharmacology Reports on the "classical" pharmacology of pempidine have been publis ...

benzohexonium Hexamethonium is a non-depolarising ganglionic blocker, a nicotinic (nAChR) receptor antagonist that acts in autonomic ganglia by binding mostly in or on the nAChR receptor, and not the acetylcholine binding site itself. It does not have any e ...

chlorisondamine Chlorisondamine is a nicotinic acetylcholine receptor antagonist that produces both neuronal and ganglionic blockade. Chlorisondamine has been shown to form noncovalent complexes with various biomolecules including sphingomyelin Sphingomyeli ...

* pentamine Nicotinic receptor agonists (acting through depolarization block): * nicotine Blocking ACh release in autonomic ganglia (although these have many other actions elsewhere): *

botulinum toxin Botulinum toxin, or botulinum neurotoxin (BoNT), is a neurotoxic protein produced by the bacterium ''Clostridium botulinum'' and related species. It prevents the release of the neurotransmitter acetylcholine from axon endings at the neuromu ...

Uses

Ganglionic blockers are used less frequently now than they were in the past, because antihypertensives with fewer side effects are now available.

Hexamethonium Hexamethonium is a non-depolarising ganglionic blocker, a nicotinic (nAChR) receptor antagonist that acts in autonomic ganglia by binding mostly in or on the nAChR receptor, and not the acetylcholine binding site itself. It does not have any e ...

has been described as the "first effective antihypertensive drug". However, they are still used in some emergency situations, such as aortic dissection or autonomic dysreflexia.

Side effects

* Cardiovascular: Orthostatic hypotension with or without reflex

tachycardia Tachycardia, also called tachyarrhythmia, is a heart rate that exceeds the normal resting rate. In general, a resting heart rate over 100 beats per minute is accepted as tachycardia in adults. Heart rates above the resting rate may be normal ( ...

* ENT/glands: xerostomia, dry eyes, blurred vision, reduced bronchial secretion,

hypohidrosis Hypohidrosis is a disorder in which a person exhibits diminished sweating in response to appropriate stimuli. In contrast with hyp''er''hidrosis, which is a socially troubling yet often benign condition, the consequences of untreated hypohidros ...

* GIT: gastroparesis,

constipation Constipation is a bowel dysfunction that makes bowel movements infrequent or hard to pass. The stool is often hard and dry. Other symptoms may include abdominal pain, bloating, and feeling as if one has not completely passed the bowel moveme ...

, urinary retention * Sexual dysfunction: failure of

erection An erection (clinically: penile erection or penile tumescence) is a physiological phenomenon in which the penis becomes firm, engorged, and enlarged. Penile erection is the result of a complex interaction of psychological, neural, vascular, ...

and

ejaculation Ejaculation is the discharge of semen (the ''ejaculate''; normally containing sperm) from the male reproductory tract as a result of an orgasm. It is the final stage and natural objective of male sexual stimulation, and an essential compone ...

* in overdose risk of peripheral circulatory collapse (shock) and paralytic ileus

References

{{Acetylcholine metabolism and transport modulators Neuropharmacology Nicotinic antagonists

Examples

Uses

Side effects

See also

References