What term is used to describe a more gradual decrease in responsiveness to a drug, taking days or weeks to develop?

Correct Answer: C

Rationale: The correct term for a gradual decrease in responsiveness to a drug over days or weeks is "tolerance." Tolerance occurs due to the body adjusting to the drug's effects, requiring higher doses for the same response. Refractoriness refers to a lack of response, not a reduced response. Cumulative effect refers to increased drug effects with repeated doses. Tachyphylaxis is a rapid decrease in responsiveness, not a gradual one. Therefore, "tolerance" is the best fit for the described scenario.

Correct Answer: C

Rationale: The correct answer is C - On effector cell membranes of glandular and smooth muscle cells. The M3 receptor subtype is a muscarinic acetylcholine receptor, which is primarily located on the effector cell membranes of glandular and smooth muscle cells. This receptor subtype plays a key role in mediating parasympathetic responses in these cells. A: In the myocardium - This is incorrect as the M2 receptor subtype is predominantly located in the myocardium, not the M3 subtype. B: In sympathetic postganglionic neurons - This is incorrect as muscarinic receptors are not typically found in sympathetic neurons. D: On the motor end plates - This is incorrect as nicotinic acetylcholine receptors, not muscarinic receptors, are located on motor end plates.

Correct Answer: B

Rationale: The correct answer is B: Tubocurarine. Tubocurarine has the potential to cause the greatest release of histamine among the choices. This is because tubocurarine is a non-depolarizing neuromuscular blocking agent that can directly stimulate histamine release from mast cells, leading to histamine-related adverse effects like hypotension and bronchospasm. Succinylcholine (A) mainly activates nicotinic acetylcholine receptors, while Pancuronium (C) and Rocuronium (D) are less likely to cause significant histamine release compared to Tubocurarine.

Correct Answer: B

Rationale: The correct answer is B: It is used to treat bronchospasm. Dobutamine is a beta1-selective synthetic catecholamine used for its positive inotropic effects in conditions like heart failure. Choice A is correct as dobutamine is beta1-selective. Choice C is incorrect as dobutamine can increase atrioventricular conduction. Choice D is incorrect as dobutamine can cause changes in heart rate and systolic pressure. Therefore, the correct answer is B because dobutamine is not used to treat bronchospasm.

Correct Answer: D

Rationale: Propranolol is a non-selective beta-blocker, used in cardiovascular diseases, hyperthyroidism, and migraine headache. However, it is contraindicated in bronchial asthma due to its potential to induce bronchoconstriction. Propranolol can worsen asthma symptoms by blocking beta-2 receptors in the lungs, leading to bronchoconstriction and exacerbation of asthma. Therefore, the correct answer is D. Choices A, B, and C are incorrect as propranolol is commonly used for these conditions due to its beneficial effects on heart rate, blood pressure, and migraine prevention.