Which of the following cholinomimetics is a plant derivative with lower potency than nicotine but with a similar spectrum of action?

Correct Answer: A

Rationale: Rationale: A is correct because lobeline is a plant derivative found in Lobelia plants, acting as a cholinomimetic with lower potency than nicotine but similar action spectrum. Nicotine is a potent cholinomimetic derived from tobacco. Pilocarpine is a cholinomimetic derived from the Pilocarpus shrub with different actions. Carbachol is a synthetic cholinomimetic with different properties. Acetylcholine is a neurotransmitter, not a plant-derived cholinomimetic.

Correct Answer: D

Rationale: Beta2 receptor stimulation primarily leads to vasodilation, bronchodilation, and relaxation of smooth muscles in non-cardiac tissues. It does not cause tachycardia, which is primarily mediated by Beta1 receptor stimulation. Therefore, option D is the correct answer. Option A is incorrect because Beta2 stimulation does not stimulate renin secretion. Option B is incorrect as Beta2 stimulation increases potassium concentration in plasma. Option C is incorrect as Beta2 stimulation causes relaxation of bladder and uterus muscles.

Correct Answer: B

Rationale: The correct answer is B: Stimulation of responses to serotonin. Phentolamine is an alpha-adrenergic blocker, causing vasodilation and reducing peripheral resistance (A). It can lead to tachycardia (C) due to its vasodilatory effects. Phentolamine does not stimulate muscarinic H1 and H2 histamine receptors (D). Serotonin receptors are not affected by phentolamine, making choice B the correct answer.

Correct Answer: D

Rationale: The correct answer is D: All of the above. Barbiturates are known to increase the metabolism of various drugs, including anticoagulants, digitalis compounds, and glucocorticoids. This is because barbiturates induce liver enzymes responsible for drug metabolism, leading to faster clearance of these medications from the body. Therefore, the correct answer is D as barbiturates can affect the metabolism of all the mentioned drug classes. Choices A, B, and C are incorrect as barbiturates do not selectively increase the metabolism of only one of these drug classes, but rather have a broad impact on drug metabolism.

Correct Answer: C

Rationale: Step-by-step rationale: 1. Phenobarbital binds to an allosteric regulatory site on the GABA-BZ receptor. 2. It enhances the affinity of GABA to its receptor, increasing Cl- channel opening duration. 3. This leads to hyperpolarization and inhibits neuronal excitability, preventing seizures. 4. Diazepam (A) and Valproate (B) act on different receptors. 5. Topiramate (D) modulates ion channels but not through the GABA-BZ receptor. Summary: Phenobarbital is the correct answer as it directly targets the GABA-BZ receptor, increasing Cl- channel opening duration. Diazepam, Valproate, and Topiramate act through different mechanisms, making them incorrect choices.