Drugs acting in the Parasympathetic system Flashcards
What does Rest and Digest (agonist) activation cause?
- Salivation
- Slowed heart rate
-Bronchoconstriction - Stimulation of mucus secretion
- Increased motility
- Stimulation of secretion
- Contraction of detrusor muscle
- Relaxation of sphincter – micturition
What effects do antagonists have on the parasympathetic nervous system?
- Dry mouth
- Increased heart rate
- Bronchodilation
- Inhibition of mucus secretion
- Decreased motility
- Inhibition of secretion
- Relaxation of detrusor muscle, contraction of sphincter = decreased micturiyion
How does neurotransmission occur in the parasympathetic nervous system?
-Muscarinic ach receptors to ACH in vesicles of postganglionic neuron.
- Nicotinic ACH receptors to ACH in vesicles in Preganglionic neuron
- Postganglionic to Preganglionic neuron
What are Nicotinic acetylcholine receptors?
A type of ligand-gated ion channel receptors
- Fast neurotransmission
How does neurotransmission occur in muscarinic ach receptors?
- Acetylcholine-esterase converts ACh into acetyl and choline
- Transporters move choline into the cell
- Converted to acetylcholine in vesicles
- Ion channels
What are properties of muscarinic ach receptors?
- Have 7 transmembrane helices
- agonists/antagonists bind in between the helices
- G proteins are bound on the intracellular face of the receptor
What is the process of intracellular signalling for muscarinic acetylcholine receptors?
- GQ G PROTEIN
- PLC = phospholipase C. Enzyme that converts PIP2 to IP3 and DAG
- IP3 receptors cause Ca 2+ to be released from SR
- Ca 2+ causes contraction through activation of myosin light chain kinase (MLCK)
What agonists drugs act at muscarinic receptors?
- Acetylcholine
- Muscarine
-Pilocarpine
What antagonist drugs act at muscarinic receptors?
- Atropine
-Ipratropium
-Tiotropium
What is the difference in muscarinic antagonists?
- Atropine - crosses membranes easily
- Ipratropium and Tiotropium = charged and don’t cross membranes easily
- Ipratropium : Fast-acting short duration
- Tiotropium = Slow acting Long duration
What are the actions of atropine?
Low to High dose:
- Dry mouth
- Increases HR
- Dilation of pupils, blurring of near vision
- Reduced peristalsis
- Difficulty in micturition
What reduces the side effects of antagonists?
- Through route if administration
What happens when acetylcholinesterase is inhibited?
- Inhibition of achsterase leads to an increased conc. of ACH in the synapse and increased activation of receptors
- ACH inhibitors include neostigmine and poisons
- Poisons are irreversible inhibitors of achsterase
- Pralidoximine - drug that can reverse the binding but only if given soon after the irreversible inhibitors
