Which of the following cholinomimetics activates both muscarinic and nicotinic receptors?

Correct Answer: C

Rationale: Nicotine is the correct answer because it activates both muscarinic and nicotinic receptors. Nicotinic receptors are ligand-gated ion channels found at neuromuscular junctions and autonomic ganglia. Muscarinic receptors are G-protein coupled receptors found in various tissues. Lobeline primarily acts on nicotinic receptors, pilocarpine primarily acts on muscarinic receptors, and bethanechol primarily acts on muscarinic receptors. Therefore, nicotine is the only cholinomimetic that activates both receptor types.

Correct Answer: C

Rationale: The correct answer is C: Uterus. Both alpha and beta1 adrenergic stimulation in the uterus leads to relaxation of the smooth muscle. Alpha adrenergic stimulation causes vasoconstriction in blood vessels (choice A). In the intestine (choice B), alpha adrenergic stimulation leads to decreased motility while beta1 adrenergic stimulation increases heart rate in bronchial muscles (choice D). Thus, the uterus is the only tissue where both alpha and beta1 adrenergic stimulation have the same effect of muscle relaxation.

Correct Answer: D

Rationale: Step-by-step rationale for why Phenoxybenzamine (choice D) is the correct answer: 1. Phenoxybenzamine is an irreversible alpha receptor antagonist, blocking alpha-1 and alpha-2 receptors. 2. It forms covalent bonds with the receptors, leading to long-lasting and irreversible blockade. 3. This irreversible binding distinguishes Phenoxybenzamine from reversible alpha blockers like Prazosin (choice C). 4. Tolazoline (choice A) is a nonselective alpha blocker, and Labetalol (choice B) is a mixed alpha and beta blocker, but neither are irreversible. Summary: Phenoxybenzamine is the correct choice as it irreversibly blocks alpha receptors, unlike the other options which are either nonselective or reversible blockers.

Correct Answer: C

Rationale: The correct answer is C: Zolpidem. Zolpidem is an imidazopyridine derivative commonly used as a hypnotic drug for treating insomnia. This is because zolpidem acts specifically on the GABA-A receptor complex, binding to a distinct site that enhances the inhibitory effects of GABA neurotransmission, leading to sedative and hypnotic effects. A: Pentobarbital is a barbiturate, not an imidazopyridine derivative. B: Temazepam is a benzodiazepine derivative, not an imidazopyridine. D: Chloral hydrate is a sedative-hypnotic drug but not an imidazopyridine derivative. Therefore, the correct choice is C, Zolpidem, due to its unique pharmacological profile as an imidazopyridine derivative with specific GABA-A receptor activity.

Correct Answer: B

Rationale: Phenytoin is primarily used for treating Grand mal epilepsy, also known as tonic-clonic seizures. This is because Phenytoin is effective in controlling the spread of seizure activity in the brain. Petit mal epilepsy is better treated with other medications like Ethosuximide, and myoclonic seizures are typically managed with different drugs like valproic acid. Therefore, the correct answer is B as Phenytoin is specifically indicated for treating Grand mal epilepsy.