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Chapter 10: Adrenoceptor Blockers

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?

(A) Cardiac stimulation

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

(C) Mydriasis

(D) Relaxation of bronchial smooth muscle

(E) Relaxation of the uterus

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.

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?

(A) Bronchoconstriction from α-blocking agents

(B) Acute heart failure exacerbation from β blockers

(C) Impaired blood sugar response with α blockers

(D) Increased intraocular pressure with β blockers

(E) Sleep disturbances from α-blocking drugs

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.

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.

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

(A) Acetylcholine

(B) Edrophonium

(C) Isoproterenol

(D) Nicotine

(E) Norepinephrine

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

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