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Chapter 10: Adrenoceptor Blockers

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A patient is to receive epinephrine. She has previously received an adrenoceptor-blocking agent. Which of the following effects of epinephrine would be blocked by phentolamine but not by metoprolol?

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(A) Cardiac stimulation

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(B) Increase of cAMP (cyclic adenosine monophosphate) in fat

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(C) Mydriasis

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(D) Relaxation of bronchial smooth muscle

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(E) Relaxation of the uterus

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Mydriasis caused by contraction of the pupillary dilator radial smooth muscle is mediated by α receptors. All the other effects listed are mediated by β receptors. The answer is C.

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Clinical studies have shown that adrenoceptor blockers have many useful effects in patients. However, a number of drug toxicities have been documented. Adverse effects that limit the use of adrenoceptor blockers include which one of the following?

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(A) Bronchoconstriction from α-blocking agents

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(B) Acute heart failure exacerbation from β blockers

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(C) Impaired blood sugar response with α blockers

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(D) Increased intraocular pressure with β blockers

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(E) Sleep disturbances from α-blocking drugs

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Although chronic heart failure is often treated with certain β blockers, acute heart failure can be precipitated by these drugs. Choices A, C, and E reverse the correct pairing of receptor subtype (α versus β) with effect. Choice D reverses the direction of change of intraocular pressure. The answer is B.

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Four new synthetic drugs (designated W, X, Y, and Z) are to be studied for their cardiovascular effects. They are given to 4 anesthetized animals while the heart rate is recorded. The first animal has received no pretreatment (control); the second has received an effective dose of hexamethonium; the third has received an effective dose of atropine; and the fourth has received an effective dose of phenoxybenzamine. The net changes induced by W, X, Y, and Z in the animals are described in the following questions.

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Drug W increased heart rate in the control animal, the atropine-pretreated animal, and the phenoxybenzamine-pretreated animal. However, drug W had no effect on heart rate in the hexamethonium-pretreated animal. Drug W is probably a drug similar to

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(A) Acetylcholine

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(B) Edrophonium

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(C) Isoproterenol

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(D) Nicotine

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(E) Norepinephrine

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In developing a strategy for this type of question, ...

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