Cholinergic Agonists
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Questions and Answers

Which of the following statements about carbachol is true?

  • It is primarily used in the treatment of glaucoma.
  • It has a short duration of action.
  • It provides miosis for eye surgery. (correct)
  • It is commonly used due to its receptor selectivity.

Why is pilocarpine considered less potent compared to ACh and its derivatives?

  • It can penetrate the CNS at therapeutic doses. (correct)
  • It is not stable to hydrolysis by AChE.
  • It has a quicker onset of action.
  • It is a quaternary amine.

What effect does pilocarpine have when applied topically to the eye?

  • Increased intraocular pressure
  • Rapid miosis (correct)
  • Relaxation of the ciliary muscle
  • Dilation of the pupil

Why has the use of pilocarpine for stimulating secretions been limited?

<p>Its lack of potency (D)</p> Signup and view all the answers

In which condition is pilocarpine the drug of choice for emergency lowering of intraocular pressure?

<p>Glaucoma (D)</p> Signup and view all the answers

Why is carbachol rarely used despite its high potency?

<p>It is a quaternary amine. (C)</p> Signup and view all the answers

What are the two classes of postsynaptic cholinergic receptors?

<p>Muscarinic and nicotinic (C)</p> Signup and view all the answers

What enzyme is responsible for cleaving acetylcholine in the synaptic cleft?

<p>Acetylcholinesterase (AChE) (B)</p> Signup and view all the answers

What happens when acetylcholine binds to a receptor on a cell?

<p>It initiates a nerve impulse in a postganglionic fiber (D)</p> Signup and view all the answers

What is the main function of cholinergic receptors on effector organs?

<p>To activate specific enzymes (B)</p> Signup and view all the answers

How is choline recycled in the cholinergic neuron?

<p>By being transported back into the neuron with a high-affinity uptake system (A)</p> Signup and view all the answers

Which molecules mediate the activation of specific enzymes in effector cells after binding of ACh to a receptor?

<p>Second messenger molecules (D)</p> Signup and view all the answers

Which enzyme specifically cleaves acetylcholine into acetate and choline?

<p>Acetylcholinesterase (B)</p> Signup and view all the answers

What is the mechanism of action of reversible anticholinesterase agents?

<p>Inhibiting the breakdown of acetylcholine (C)</p> Signup and view all the answers

Which reversible AChE inhibitor has a short duration of action due to rapid renal elimination?

<p>Edrophonium (D)</p> Signup and view all the answers

Where does acetylcholinesterase (AChE) act within the nerve terminal?

<p>Both pre- and postsynaptic membranes (A)</p> Signup and view all the answers

What is the main function of reversible anticholinesterase agents?

<p>Preventing the breakdown of acetylcholine (C)</p> Signup and view all the answers

Which type of receptors can be affected by reversible AChE inhibitors?

<p>Both muscarinic and nicotinic receptors (A)</p> Signup and view all the answers

What is the rate-limiting step in acetylcholine synthesis at cholinergic neurons?

<p>Uptake of choline (B)</p> Signup and view all the answers

Which enzyme catalyzes the reaction of choline with acetyl coenzyme A to form acetylcholine in the cytosol?

<p>Choline acetyltransferase (D)</p> Signup and view all the answers

What is the role of choline in acetylcholine synthesis at cholinergic neurons?

<p>Choline combines with acetyl coenzyme A to form acetylcholine (D)</p> Signup and view all the answers

Which drug can inhibit the carrier system responsible for transporting choline into the cytoplasm of cholinergic neurons?

<p>Hemicholinium (B)</p> Signup and view all the answers

What is the fate of acetylcholine after it binds to the receptor at cholinergic neurons?

<p>Degradation in the synaptic cleft (C)</p> Signup and view all the answers

Apart from sweat glands, where else does the postganglionic sympathetic division of sweat glands use ACh?

<p>Muscles of somatic system (D)</p> Signup and view all the answers

What is the intermediate duration of action for neostigmine?

<p>30 minutes to 2 hours (C)</p> Signup and view all the answers

Which of the following is a therapeutic use of neostigmine?

<p>Managing symptoms of myasthenia gravis (A)</p> Signup and view all the answers

What adverse effect is NOT associated with neostigmine use?

<p>CNS side effects (A)</p> Signup and view all the answers

Why is neostigmine contraindicated when intestinal or urinary bladder obstruction is present?

<p>It stimulates the affected muscles, worsening the obstruction (B)</p> Signup and view all the answers

Which cholinesterase inhibitor has a duration of action longer than neostigmine but still intermediate?

<p>Pyridostigmine (A)</p> Signup and view all the answers

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?

<p>Acetylcholine (ACh) (A)</p> Signup and view all the answers

What is the primary adverse effect associated with reversible anticholinesterase agents such as donepezil, rivastigmine, and galantamine?

<p>GI distress (C)</p> Signup and view all the answers

What is the mechanism of action of irreversible anticholinesterase agents like organophosphates?

<p>Covalent binding to AChE (B)</p> Signup and view all the answers

Which compound is an irreversible anticholinesterase agent that forms a covalent bond at the active site of AChE?

<p>Echothiophate (B)</p> Signup and view all the answers

What is required for the restoration of acetylcholinesterase (AChE) activity after irreversible inhibition by organophosphates?

<p>Synthesis of new enzyme molecules (A)</p> Signup and view all the answers

Which of the following is a true statement about the mechanism of action of echothiophate?

<p>It permanently inactivates AChE via covalent binding (A)</p> Signup and view all the answers

Which organophosphate compound is used as an insecticide and can bind covalently to AChE?

<p>Parathion (C)</p> Signup and view all the answers

What is the major disadvantage of tacrine compared to other anticholinesterases?

<p>Hepatotoxicity (C)</p> Signup and view all the answers

Which anticholinesterase agent permanently inactivates AChE by forming a covalent bond at its active site?

<p>Echothiophate (D)</p> Signup and view all the answers

Why were many irreversible organophosphate anticholinesterases initially developed by the military?

<p>For nerve agent use in warfare (A)</p> Signup and view all the answers

What happens to the AChE enzyme after it is covalently modified by echothiophate?

<p>It slowly releases ethyl groups (D)</p> Signup and view all the answers

What is the primary toxic manifestation of toxicity with irreversible AChE inhibitors like organophosphates?

<p>Nicotinic and muscarinic signs (D)</p> Signup and view all the answers

Why is pralidoxime (2-PAM) ineffective in treating the central nervous system (CNS) effects of organophosphates?

<p>It cannot penetrate the CNS (D)</p> Signup and view all the answers

What effect can pralidoxime have on peripheral effects of organophosphates if administered before aging of the alkylated enzyme occurs?

<p>Reverses both muscarinic and nicotinic peripheral effects (C)</p> Signup and view all the answers

Why is pralidoxime less effective with newer nerve agents that lead to aging of the enzyme complex within seconds?

<p>The enzyme aging process occurs too quickly (B)</p> Signup and view all the answers

In the context of anticholinesterase agents, what does pralidoxime essentially displace on the enzyme?

<p>Phosphate group of organophosphate (D)</p> Signup and view all the answers

What is the limitation of pralidoxime in reversing the effects of organophosphates if aging of the alkylated enzyme has already occurred?

<p>It cannot reverse nicotinic effects fully (D)</p> Signup and view all the answers

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