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. 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.
Contents
Because ganglionic blockers block both the parasympathetic nervous system and sympathetic nervous system, the effect of these drugs depends upon the dominant tone in the organ system.
Examples
The first ganglion-blocker to be used clinically was tetraethylammonium, although it was soon superseded by better drugs.
Nicotinic receptor antagonists:
Nicotinic receptor agonists (acting through depolarization block):
Blocking ACh release in autonomic ganglia (although these have many other actions elsewhere):
Uses
Ganglionic blockers are used less frequently now than they were in the past, because antihypertensives with fewer side effects are now available. Hexamethonium 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.