Ganglionic Blockers Flashcards
What do ganglionic blockers act upon?
cholinergic nicotinic receptors in autonomic ganglia, thereby reducing hypertension arising from sympathetic nervous system over-activity.
What are some ganglionic blockers?
- mecamylamine (Inversine)
- Trimethaphan
Are ganglionic blockers used often?
No, they have a lack of specificity and many adverse effects and have been replaced by more specific drugs with less global effects upon the ANS
Where are cholinergic nicotinic (Nn) receptors found?
autonomic ganglia and in the adrenal medulla.
This receptor sub-type is distinct from the nicotinic Nm receptor found on the neuromuscular junction
Describe ACh transmission.
The preganglionic nerve releases ACh onto postganglionic cells. When two molecules of ACh bind a nicotinic AchR, a
conformational change occurs in the receptor, resulting in the formation of an ion
pore. The initial excitatory post-synpatic potential (EPSP) results from the inward Na+ current (and perhaps Ca2+ current) through the nicotinic receptor channel.
What happens if the
EPSP is of sufficient magnitude?
It triggers an action potential spike, which is followed by a slow inhibitory post-synaptic potential (IPSP), a slow EPSP, and a late, slow
EPSP. The slow IPSP and slow EPSP are not seen in all ganglia.
The electrical events subsequent to the initial EPSP are thought to modulate the probability that a
subsequent EPSP will reach the threshold for triggering a spike.
What else can affect the slow potentials of the postganglionic neuron?
Other interneurons,
such as catecholamine-containing, small, intensely fluorescent (SIF) cells, and axon
terminals from sensory, afferent neurons also release transmitters and they may influence the slow potentials of the postganglionic neuron.
A number of cholinergic,
peptidergic, adrenergic, and amino acid receptors are found on the dendrites and
soma of the postganglionic neuron and the interneurons.
The preganglionic fiber releases ACh and peptides; the interneurons store and release catecholamines,
amino acids, and peptides; the sensory afferent nerve terminals release peptides. The
initial EPSP is mediated through nicotinic (Nn) receptors, the slow IPSP and EPSP
through M2 and M1 muscarinic receptors, and the late, slow EPSP through several
types of peptidergic receptors.
What is the predominant tone in the arterioles and veins?
sympathetic (adrenergic) in both
What are the effects of ganglionic blockade of arterioles?
- vasodilation
- increased peripheral blood flows
- hypotension
What are the effects of ganglionic blockade of veins?
- dilations
- peripheral pooling of blood
- decreased venous return
- decreased cardiac output
What is the predominant tone in the heart?
parasympathetic (cholinergic)
By exerting regulatory control over the SA and AV nodes, the parasympathetic system ensures that cardiac activity enjoys constant regulatory control.
What are the effects of ganglionic blockade of the heart?
tachycardia
How does ganglionic blockers work?
They are competitive ganglionic blockers against ACh. If one of the two required molecules of Ach is blocked, then the channel fails to open and the EPSP does
not occur, so neurotransmission is interrupted.
Are ganglionic blockers commonly used for HTN?
No, Ganglionic blockers are not routinely used in
the treatment of chronic hypertension in large part because of their side effects and because there are numerous, more effective, and safer antihypertensive drugs that can be used
