Tick the second messenger of G-protein-coupled (metabotropi receptor:

Correct Answer: D

Rationale: The correct answer is D: cAMP. G-protein-coupled receptors activate adenylyl cyclase, leading to the production of cAMP, which acts as the second messenger. cAMP then triggers downstream signaling cascades. Choice A (Adenylyl cyclase) is the enzyme activated by G-protein-coupled receptors, not a second messenger itself. Choice B (Sodium ions) is not typically involved in GPCR signaling pathways. Choice C (Phospholipase C) generates inositol trisphosphate and diacylglycerol, which are part of a separate signaling pathway, not the second messenger system for GPCRs.

Correct Answer: A

Rationale: The correct answer is A: Physostigmine, which penetrates the blood-brain barrier. Physostigmine is a reversible cholinesterase inhibitor that can cross the blood-brain barrier, allowing it to exert its effects on cholinesterase enzymes in the central nervous system. This property makes it useful in conditions where increasing cholinergic activity in the brain is desired, such as in the treatment of Alzheimer's disease. Choice B, Edrophonium, is a reversible cholinesterase inhibitor but does not effectively penetrate the blood-brain barrier. Choice D, Neostigmine, is also a reversible cholinesterase inhibitor but is primarily used for its effects on peripheral cholinesterase enzymes and does not cross the blood-brain barrier effectively.

Correct Answer: D

Rationale: The correct answer is D: Atracurium. Atracurium is metabolized to laudanosine, which readily crosses the blood-brain barrier and may cause seizures. Pancuronium (A) does not readily cross the blood-brain barrier. Succinylcholine (B) does not have a breakdown product that crosses the blood-brain barrier. Tubocurarine (C) does not produce a breakdown product that causes seizures.

Correct Answer: B

Rationale: Step 1: Norepinephrine is a neurotransmitter that acts on both alpha and beta receptors. Step 2: Norepinephrine has more potent effects on alpha receptors compared to epinephrine. Step 3: Choice A is correct as norepinephrine has similar effects on beta1 receptors in the heart and similar potency at alpha receptors. Step 4: Choice C is incorrect as tissue necrosis is associated with dopamine, not norepinephrine. Step 5: Choice D is incorrect as norepinephrine increases both diastolic and systolic blood pressure. Step 6: Choice B is correct as norepinephrine does not decrease mean pressure below normal before returning to the control value, making it the exception among the effects listed.

Correct Answer: B

Rationale: The correct answer is B: Phentolamine. Phentolamine is an alpha receptor antagonist that can rapidly reverse the vasoconstriction caused by local infiltration of norepinephrine. It works by blocking alpha receptors, leading to vasodilation and improved blood flow in the affected area. Propranolol (A) is a beta-blocker and not effective in reversing alpha receptor-mediated vasoconstriction. Tamsulosin (C) is an alpha-1 blocker primarily used for benign prostatic hyperplasia, not for acute vasoconstriction reversal. Ergotamine (D) is a vasoconstrictor used in treating migraines, which would exacerbate the problem in this scenario.