Pick out the answer which is the most appropriate to the term “receptor”

Correct Answer: C

Rationale: The correct answer is C because a receptor is a specific active macromolecular component of a cell or organism that a drug molecule must bind to in order to elicit a specific effect. This definition aligns with the concept of receptors in pharmacology. A is incorrect because ion channels are not necessarily receptors. B is incorrect because enzymes involved in oxidizing-reducing reactions are not typically considered receptors. D is incorrect because carriers are not the same as receptors in pharmacology. In summary, answer C is the most appropriate as it accurately defines the role of a receptor in pharmacology, while the other choices do not align with the definition of a receptor.

Correct Answer: C

Rationale: Physostigmine is the correct answer as it is a reversible cholinesterase inhibitor. This means it binds to the enzyme temporarily and can be easily displaced, allowing the enzyme to function normally after a while. Physostigmine is commonly used in the treatment of glaucoma and myasthenia gravis. A: Isoflurophate is an irreversible cholinesterase inhibitor, meaning it forms a permanent bond with the enzyme. B: Carbochol is a direct-acting cholinergic agonist, not a cholinesterase inhibitor. D: Parathion is an organophosphate insecticide that irreversibly inhibits cholinesterase enzymes.

Correct Answer: B

Rationale: The correct answer is B: Trimethaphane. Trimethaphane is a short-acting ganglion blocker because it acts quickly to block ganglionic transmission, leading to a rapid onset of action. Homatropine is a muscarinic antagonist used for its anticholinergic effects, not as a ganglion blocker. Hexamethonium is a ganglion blocker, but it is long-acting, not short-acting. Pancuronium is a neuromuscular blocker used for skeletal muscle paralysis, not for ganglionic blockade. Therefore, the correct choice is Trimethaphane due to its fast-acting nature in blocking ganglionic transmission.

Correct Answer: A

Rationale: The correct answer is A: Norepinephrine. Norepinephrine is a direct-acting alpha-1 and beta-1 receptor agonist. It stimulates both alpha and beta receptors directly, leading to vasoconstriction (via alpha-1) and increased heart rate and contractility (via beta-1). Methoxamine (B) is a selective alpha-1 agonist, Isoproterenol (C) is a non-selective beta agonist, and Ephedrine (D) is a mixed-acting sympathomimetic drug with indirect effects. Therefore, norepinephrine is the only choice that directly acts on both alpha and beta receptors.

Correct Answer: B

Rationale: The correct answer is B because alpha-receptor antagonists block alpha2 receptors on vascular smooth muscle, preventing vasoconstriction caused by epinephrine and reducing blood pressure in patients with pheochromocytoma. This helps manage symptoms of hypertension and tachycardia associated with excessive catecholamine release. Incorrect choices: A: Alpha-receptor antagonists do not inhibit the release of epinephrine from the adrenal medulla. C: Alpha-receptor antagonists do not interact with or inhibit beta2 adrenoreceptors. D: Alpha-receptor antagonists do not antagonize the release of renin.