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Chapter 10: Adrenoceptor Blockers

A patient presents at the emergency department with threatened anaphylaxis. Respiratory obstruction appears likely if she is not treated immediately. Her past medical history includes hypertension, for which she is receiving an adrenoceptor blocker. The emergency physician plans to use epinephrine to treat her anaphylactic reaction. Which of the following effects of epinephrine would be blocked by prazosin but not by metoprolol?

(A) Cardiac stimulation

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

(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 any β blocker. 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.

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

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