46 Questions
Which of the following statements about carbachol is true?
It provides miosis for eye surgery.
Why is pilocarpine considered less potent compared to ACh and its derivatives?
It can penetrate the CNS at therapeutic doses.
What effect does pilocarpine have when applied topically to the eye?
Rapid miosis
Why has the use of pilocarpine for stimulating secretions been limited?
Its lack of potency
In which condition is pilocarpine the drug of choice for emergency lowering of intraocular pressure?
Glaucoma
Why is carbachol rarely used despite its high potency?
It is a quaternary amine.
What are the two classes of postsynaptic cholinergic receptors?
Muscarinic and nicotinic
What enzyme is responsible for cleaving acetylcholine in the synaptic cleft?
Acetylcholinesterase (AChE)
What happens when acetylcholine binds to a receptor on a cell?
It initiates a nerve impulse in a postganglionic fiber
What is the main function of cholinergic receptors on effector organs?
To activate specific enzymes
How is choline recycled in the cholinergic neuron?
By being transported back into the neuron with a high-affinity uptake system
Which molecules mediate the activation of specific enzymes in effector cells after binding of ACh to a receptor?
Second messenger molecules
Which enzyme specifically cleaves acetylcholine into acetate and choline?
Acetylcholinesterase
What is the mechanism of action of reversible anticholinesterase agents?
Inhibiting the breakdown of acetylcholine
Which reversible AChE inhibitor has a short duration of action due to rapid renal elimination?
Edrophonium
Where does acetylcholinesterase (AChE) act within the nerve terminal?
Both pre- and postsynaptic membranes
What is the main function of reversible anticholinesterase agents?
Preventing the breakdown of acetylcholine
Which type of receptors can be affected by reversible AChE inhibitors?
Both muscarinic and nicotinic receptors
What is the rate-limiting step in acetylcholine synthesis at cholinergic neurons?
Uptake of choline
Which enzyme catalyzes the reaction of choline with acetyl coenzyme A to form acetylcholine in the cytosol?
Choline acetyltransferase
What is the role of choline in acetylcholine synthesis at cholinergic neurons?
Choline combines with acetyl coenzyme A to form acetylcholine
Which drug can inhibit the carrier system responsible for transporting choline into the cytoplasm of cholinergic neurons?
Hemicholinium
What is the fate of acetylcholine after it binds to the receptor at cholinergic neurons?
Degradation in the synaptic cleft
Apart from sweat glands, where else does the postganglionic sympathetic division of sweat glands use ACh?
Muscles of somatic system
What is the intermediate duration of action for neostigmine?
30 minutes to 2 hours
Which of the following is a therapeutic use of neostigmine?
Managing symptoms of myasthenia gravis
What adverse effect is NOT associated with neostigmine use?
CNS side effects
Why is neostigmine contraindicated when intestinal or urinary bladder obstruction is present?
It stimulates the affected muscles, worsening the obstruction
Which cholinesterase inhibitor has a duration of action longer than neostigmine but still intermediate?
Pyridostigmine
What is the main deficiency in patients with Alzheimer's disease that leads to the use of cholinesterase inhibitors like tacrine, donepezil, rivastigmine, and galantamine?
Acetylcholine (ACh)
What is the primary adverse effect associated with reversible anticholinesterase agents such as donepezil, rivastigmine, and galantamine?
GI distress
What is the mechanism of action of irreversible anticholinesterase agents like organophosphates?
Covalent binding to AChE
Which compound is an irreversible anticholinesterase agent that forms a covalent bond at the active site of AChE?
Echothiophate
What is required for the restoration of acetylcholinesterase (AChE) activity after irreversible inhibition by organophosphates?
Synthesis of new enzyme molecules
Which of the following is a true statement about the mechanism of action of echothiophate?
It permanently inactivates AChE via covalent binding
Which organophosphate compound is used as an insecticide and can bind covalently to AChE?
Parathion
What is the major disadvantage of tacrine compared to other anticholinesterases?
Hepatotoxicity
Which anticholinesterase agent permanently inactivates AChE by forming a covalent bond at its active site?
Echothiophate
Why were many irreversible organophosphate anticholinesterases initially developed by the military?
For nerve agent use in warfare
What happens to the AChE enzyme after it is covalently modified by echothiophate?
It slowly releases ethyl groups
What is the primary toxic manifestation of toxicity with irreversible AChE inhibitors like organophosphates?
Nicotinic and muscarinic signs
Why is pralidoxime (2-PAM) ineffective in treating the central nervous system (CNS) effects of organophosphates?
It cannot penetrate the CNS
What effect can pralidoxime have on peripheral effects of organophosphates if administered before aging of the alkylated enzyme occurs?
Reverses both muscarinic and nicotinic peripheral effects
Why is pralidoxime less effective with newer nerve agents that lead to aging of the enzyme complex within seconds?
The enzyme aging process occurs too quickly
In the context of anticholinesterase agents, what does pralidoxime essentially displace on the enzyme?
Phosphate group of organophosphate
What is the limitation of pralidoxime in reversing the effects of organophosphates if aging of the alkylated enzyme has already occurred?
It cannot reverse nicotinic effects fully
Test your knowledge on cholinergic agonists, focusing on the therapeutic uses and adverse effects of carbachol and pilocarpine. Learn about their applications in ophthalmology for miosis and glaucoma treatment.
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