Non-selective β-blockers are contraindicated in:

Correct Answer: C

Rationale: The correct answer is C: Peripheral vascular disease. Non-selective β-blockers can cause vasoconstriction and exacerbate peripheral vascular disease by reducing blood flow to the extremities. This can lead to worsening symptoms and potential tissue damage. Choices A, B, and D are incorrect because non-selective β-blockers are commonly used in angina of effort, systemic hypertension, and thyrotoxicosis, respectively, to decrease heart rate and blood pressure.

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: D

Rationale: The correct answer is D: They increase renin activity. Beta blockers block beta-adrenergic receptors, leading to decreased renin secretion and ultimately decreased renin activity. This results in reduced renin-angiotensin-aldosterone system activation, leading to decreased blood pressure. Choices A, B, and C are incorrect because beta blockers are known to decrease blood pressure, propranolol is extensively metabolized in the liver, and atenolol is eliminated mainly unchanged in urine.

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.