The mechanism of action of indirect-acting cholinomimetic agents is:

Correct Answer: B

Rationale: The correct answer is B: Inhibition of the hydrolysis of endogenous acetylcholine. Indirect-acting cholinomimetic agents work by blocking the enzyme acetylcholinesterase, which breaks down acetylcholine. By inhibiting this enzyme, these agents increase the levels of acetylcholine at the receptor sites, leading to prolonged activation of cholinergic receptors. This mechanism results in enhanced cholinergic effects in the body. Choice A is incorrect because indirect-acting cholinomimetic agents do not directly bind to or activate muscarinic or nicotinic receptors. Choice C is incorrect as these agents do not stimulate the action of acetylcholinesterase; rather, they inhibit its activity. Choice D is incorrect because indirect-acting cholinomimetic agents do not release acetylcholine from storage sites; instead, they prevent its breakdown.

Correct Answer: A

Rationale: The correct answer is A: Lipolysis. Beta3-receptors are mainly found in adipose tissue and their stimulation leads to the breakdown of triglycerides into free fatty acids, promoting lipolysis. This effect is beneficial in increasing energy expenditure and weight loss. Explanation for why the other choices are incorrect: B: Decrease in platelet aggregation - This effect is associated with beta2-receptor stimulation, not beta3. C: Bronchodilation - This effect is primarily mediated by beta2-receptor stimulation in the lungs. D: Tachycardia - Stimulation of beta1-receptors, not beta3, is responsible for increasing heart rate.

Correct Answer: C

Rationale: 1. Nonselective alpha-receptor antagonists like phenoxybenzamine are used in treating Pheochromocytoma. 2. Pheochromocytoma is a tumor that causes excess release of catecholamines leading to severe hypertension. 3. Alpha-blockers help control blood pressure by blocking the vasoconstrictive effects of catecholamines. 4. Choice A is incorrect as alpha-blockers can worsen asthma due to bronchoconstriction. 5. Choice B is incorrect as alpha-blockers may worsen arrhythmias by reducing cardiac contractility. 6. Choice D is incorrect as alpha-blockers are not typically first-line for chronic hypertension.

Correct Answer: D

Rationale: The correct answer is D because alterations in hepatic function due to disease can affect drug metabolism, old age can alter drug clearance rates, and drug-induced changes in microsomal enzyme activities can impact drug metabolism. Each factor directly influences the biodisposition of hypnotic agents by affecting their metabolism and elimination. Therefore, all of the factors mentioned in choices A, B, and C can influence the biodisposition of hypnotic agents.

Correct Answer: B

Rationale: The correct answer is B: Primidone. Primidone is a prodrug that is metabolized in the liver to phenobarbital, which is the active antiseizure component. This process allows for a more controlled and sustained release of phenobarbital in the body. Phenytoin (A) works by blocking sodium channels, Felbamate (C) works by multiple mechanisms, and Vigabatrin (D) works by increasing GABA levels. These mechanisms are different from Primidone's pathway of being converted into phenobarbital.