Nicotinic receptors are blocked by which of the following:

Correct Answer: B

Rationale: The correct answer is B: Trimetaphan. Nicotinic receptors are blocked by non-depolarizing neuromuscular blockers like Trimetaphan. Propranolol (A) is a beta-blocker, Prazosin (C) is an alpha-1 blocker, and Pilocarpine (D) is a muscarinic agonist, none of which block nicotinic receptors. Therefore, Trimetaphan (B) is the only choice that directly blocks nicotinic receptors.

Correct Answer: D

Rationale: The correct answer is D, Edrophonium. Edrophonium is a short-acting cholinesterase inhibitor used in the diagnosis of myasthenia gravis. It does not possess muscarinic blocking activity, as its mechanism of action involves inhibition of acetylcholinesterase leading to increased acetylcholine levels at the neuromuscular junction. The other choices, Amitriptyline (A) is a tricyclic antidepressant with anticholinergic properties, Meperidine (B) has weak antimuscarinic effects, and Ipratropium (C) is an anticholinergic medication used in respiratory conditions. These choices exhibit muscarinic blocking activity, unlike Edrophonium.

Correct Answer: A

Rationale: The correct answer is A: Stimulation of beta adrenergic receptors. Propranolol is a beta-blocker that works by blocking beta adrenergic receptors, not stimulating them. Blocking these receptors leads to decreased heart rate, reduced cardiac contractility, and lowered blood pressure. Choices B, C, and D are incorrect because propranolol actually blocks beta adrenergic receptors, depresses cardiac contractility, and decreases blood pressure, respectively.

Correct Answer: D

Rationale: The correct answer is D because catecholamines are structurally similar to adrenaline and noradrenaline, sharing a catechol nucleus and amine group. This similarity allows them to exert similar pharmacologic effects such as increasing heart rate and blood pressure. Adrenergic receptor blockers (A) inhibit the action of catecholamines, atropine-like drugs (B) block muscarinic receptors, and neostigmine and physostigmine (C) are cholinesterase inhibitors, not catecholamines.

Correct Answer: D

Rationale: The correct answer is D: "Inhibits breakdown of acetylcholine, thereby improving activation of skeletal muscle by acetylcholine." Rationale: 1. Pyridostigmine is an acetylcholinesterase inhibitor, which means it blocks the breakdown of acetylcholine. 2. In myasthenia gravis, there is a decrease in acetylcholine receptor sites, leading to muscle weakness. 3. By inhibiting the breakdown of acetylcholine, pyridostigmine increases the availability of acetylcholine at the neuromuscular junction, improving muscle activation. 4. This mechanism helps alleviate muscle weakness in myasthenia gravis patients. Summary: A: Incorrect. Pyridostigmine does not block muscarinic receptors or change the preference of acetylcholine stimulation. B: Incorrect. Pyridostigmine does not inhibit reuptake of acetylcholine; it acts by inhibiting its breakdown