Cholinoreceptor Antagonist

Question 1

Describe the consequences of cholinoreceptor blockade on nicotinic receptors.

Answer 1

Nicotinic receptor blockade drugs: hexamethonium (blocks ion channel and is an antihypertensive) and trimetaphan (blocks receptor and is hypotensive drug). They take advantage of the use dependent block which is when drugs are more effecting when the ion channels are open.

After taking a nicotinic receptor blockade at rest, the parasympathetic pathway Is blocked, if take blockade during activity the SNS pathway is blocked.

Unwanted effects: hypotension, decreased renin secretion and therefore water retention, pupil dilation, GI and bladder dysfunction and bronchodilation, decreased exocrine secretion

Question 2

Describe the consequences of cholinoreceptor blockade on muscarinic receptors.

Answer 2

The only target specific parasympathetic organs eg atropine and hyoscine (blocks PNS and SNS sweat glands).

Atropine at low dose has little effect but at high dose: restlessness, agitation, CNS excitation. Hyoscine at low dose causes sedation and amnesia and at toxic dose causes CNS depression or paradoxical excitation (cox lipid soluble goes to brain)

Question 3

Describe the uses of muscarinic receptor antagonist

Answer 3

1. Ophthalmic - examination of the retina eg (tropicamide) stops pupil constriction
2. Anaesthetic premedication - blocks parasympathetic pathway
3. Motion sickness
4. Parkinson’s - blocks M4 and stimulate B1 - more dopamine
5. Asthma - salbutamol
6. IBS - M3

However the side effects: decreased sweating, thermoregulation mismanaged, decreased secretion, cyclopegia (parlayse lens) and CNS disturbance