Which of the following is a direct-acting parasympathomimetic that readily passes the blood-brain barrier and is commonly used in the treatment of glaucoma:

Correct Answer: A

Rationale: The correct answer is A: Pilocarpine. Pilocarpine is a direct-acting parasympathomimetic that readily passes the blood-brain barrier due to its small molecular size. It is commonly used in the treatment of glaucoma by constricting the pupil and increasing the outflow of aqueous humor. Carbachol and Bethanechol are also parasympathomimetics, but they do not readily cross the blood-brain barrier. Methacholine is a muscarinic receptor agonist, not commonly used in the treatment of glaucoma. Therefore, the most suitable choice that meets the criteria provided in the question is pilocarpine.

Correct Answer: A

Rationale: The correct answer is A because dopamine is not effective orally due to its inability to cross the blood-brain barrier. Dopamine is mainly metabolized by MAO and COMT enzymes (B). It is primarily excreted in the urine as homovanillic acid, not vanillylmandelic acid (C). Dopamine stimulates dopamine receptors (D), not α, β1, and D receptors.

Correct Answer: B

Rationale: Dobutamine is a positive inotrope that increases cardiac contractility, making it a suitable choice for treating heart failure by improving cardiac output. It is not typically used for hypertension, glaucoma, or arrhythmias. Hypertension is usually managed with antihypertensive medications like ACE inhibitors or beta-blockers. Glaucoma is treated with medications that reduce intraocular pressure. Arrhythmias are commonly managed with antiarrhythmic drugs or procedures such as ablation. Therefore, choice B, heart failure, is the correct answer for the use of dobutamine.

Correct Answer: D

Rationale: The correct answer is D: Blockade of acetylcholine release from all cholinergic nerves. Botulinum toxin exerts its effects by inhibiting the release of acetylcholine from presynaptic nerve terminals at neuromuscular junctions. This leads to muscle paralysis, which is a characteristic feature of botulism. A: Massive release of adrenaline from the adrenal medulla is incorrect because botulinum toxin does not affect the adrenal medulla or adrenaline release. B: Blockade of alpha and beta adrenergic receptors is incorrect because botulinum toxin does not directly block adrenergic receptors. C: Stimulation of acetylcholinesterase enzyme is incorrect because botulinum toxin inhibits acetylcholine release rather than stimulating acetylcholinesterase. In summary, the correct answer D directly correlates with the mechanism of action of Botulinum toxin, while the other choices are unrelated to how Botulinum toxin exerts

Correct Answer: B

Rationale: The correct answer is B because phenylephrine stimulates α-adrenergic receptors, leading to vasoconstriction and mucous membrane decongestion. This action helps relieve nasal congestion. Choice A is incorrect because phenylephrine does not block muscarinic receptors. Choice C is incorrect because phenylephrine does not block β-adrenergic receptors. Choice D is incorrect because phenylephrine is not typically used for managing hypertension.