Which of the following statements is true of the parasympathetic nervous system?

Ladislav Volicer, M.D.,Ph.D
Professor of Pharmacology
Boston University School of Medicine

Questions or comments should be mailed to Carol Walsh

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This set of questions should help you to familiarize yourself with drugs acting on the autonomic nervous system, their effects and mechanisms of action. The package is composed of two parts which are independent; each of them consists of ten items.

PART A

The dose-effect curves labeled A, B, C, D, and E below represent curves for drugs administered alone or in combination. Use these curves to help you choose the most appropriate answer for the following items.

I. Before we can consider specific agents, you have to know the basic principles governing receptor-drug interactions. Which of the following statements is true?

a. Drug A is more potent than drug C in producing effect Y.

b. Drug B is more potent than drug A in producing effect Y.

c. Drug B has a higher intrinsic activity than Drug A.

d. Two of the above statements are true

e. None of the above statements is true

II. Many drugs act by affecting the activity of endogenous substances, such as neurotransmitters, autacoids, and hormones. Some of them potentiate an effect, some of them inhibit or antagonize it. There are three types of antagonists: chemical, physiological and pharmacological. Which of the following statements about an agent and its antagonist is true?

a. Atropine is a physiological antagonist of acetylcholine

b. Phenoxybenzamine is a chemical antagonist of norephinephrine

c. Norepinephrine is a pharmacological antagonist of acetylcholine

d. Ipratropium is a pharmacological antagonist of acetylcholine

e. Phentolamine is a physiological antagonist of norephinephrine

III. There are two types of pharmacological antagonists: competitive and non-competitive. A competitive antagonist interacts with the ligand-binding site on a receptor and produces a reversible or irreversible antagonism depending on the kinetics of its binding and dissociation. A non-competitive antagonist interacts with a site on the receptor other than the ligand-binding site or within the receptor signal transduction mechanism.

If you assume that some of the dose-effect curves shown above were obtained with a combination of an agonist and an antagonist, which of the following statements is true?

a. If curve A represents the effect of drug A given alone, curve C represents the effect of drug A after treatment with an irreversible competitive antagonist

b. If curve C represents the effect of drug C given alone, curve D represents the effect of drug C after treatment with an irreversible competitive antagonist

c. If curve C represents the effect of drug C given alone, curve D represents the effect of drug C in the presence of a reversible competitive antagonist

d. If curve C represents the effect of drug C given alone, curve D represents the effect of drug C given in the presence of a non-competitive antagonist

e. Two of the above statements are true

IV. If curve C represents the increase of motility of isolated stomach after acetylcholine was administered alone, which curve represents the effect of acetylcholine in a preparation pretreated with physostigmine?

a. Curve A

b. Curve B

c. Curve C

d. Curve D

e. None of the above

V. If curve C represents the increased heart rate of an isolated heart after treatment with norepinephrine, which curve might represent the effect of isoproterenol in the same preparation?

a. Curve A

b. Curve C

c. Curve D

d. Curve E

e. None of the above

VI. If curve C represents the vasoconstriction after norepinephrine was given alone, which curve represents the effect of norepinephrine in a preparation pretreated with cocaine?

a. Curve A

b. Curve B

c. Curve C

d. Curve D

e. None of the above

VII. If curve C represents the increased heart rate of an isolated heart after norepinephrine was given alone, which curve represents the effect of norepinephrine in a preparation pretreated with phentolamine?

a. Curve A

b. Curve E

c. Curve C

d. Curve D

e. None of the above

VIII. If curve C represents contraction of an isolated skeletal muscle after acetylcholine was administered alone, which curve represents the effect of acetylcholine in a preparation pretreated with succinylcholine?

a. Curve A

b. Curve C

c. Curve D

d. Curve E

e. None of the above

IX. If curve C represents contraction of an isolated blood vessel after phenylephrine was administered alone, which curve represents the effect of phenylephrine in a preparation pretreated with phenoxybenzamine?

a. Curve E

b. Curve B

c. Curve C

d. Curve D

e. None of the above

X. If curve C represents contraction of an isolated skeletal muscle after acetylcholine administration, which curve represents the effect of acetylcholine in a preparation pretreated with d-tubocurarine?

a. Curve A

b. Curve B

c. Curve C

d. Curve D

e. Curve E

PART B

An experiment was set up to record the blood pressure and heart rate of a cat, anesthetized with pentobarbital and maintained at plane III surgical anesthesia. The right vagus nerve was isolated and separated from its central connections. A pair of stimulating electrodes was placed around the distal vagus for stimulation when desired. Both carotids were isolated in the neck (below the carotid sinus) and were readily available for occlusion when desired. Doses of different drugs were administered intravenously or the nerves were stimulated for a period of two to three seconds. Blood pressure was measured with a pressure transducer, and heart rate was recorded as increased (+) or decreased (-) with respect to the base line represented as 0.

Use the information above to answer the following questions:

XI. Which procedure or drug would induce the changes of the blood pressure and heart rate observed 3 min after the beginning of the experiment?

a. Vagus nerve stimulation

b. Acetylcholine administration

c. Histamine administration

d. Two of the above

e. None of the above

XII. Which drug or procedure would induce the changes of the blood pressure and heart rate observed 6 min after the beginning of the experiment?

a. Phenylephrine administration

b. Administration of a low dose of epinephrine

c. Occlusion of carotid arteries below the carotid sinus

d. Two of the above

XIII. Which of the following in the same dose would diminish and/or abolish the blood pressure changes resulting from both distal vagal nerve stimulation and carotid occlusion?

a. Atropine

b. Phentolamine

c. Propranolol

d. Hexamethonium

e. Two of the above

XIV. Which drug or drug combinations would induce the changes of the blood pressure and heart rate observed 12 min after the beginning of the experiment?

a. Administration of an average dose of epinephrine

b. Administration of a large dose of norepinephrine in a preparation pretreated with phentolamine

c. Histamine administration

d. Two of the above

e. All of the above

XV. Which drugs would induce the changes of the blood pressure and heart rate observed 15 min after the beginning of the experiment?

a. Tyramine administration

b. Albuterol administration

c. Prasozin Administration

d. Two of the above

e. None of the above

XVI. Which of the following could induce the changes of the blood pressure and heart rate observed 18 min after the beginning of the experiment?

a. Administration of epinephrine to a patient treated chronically with propranolol

b. Administration of methoxamine

c. Ingestion of cheese in a patient treated chronically with phenelzine (an MAO inhibitor)

d. Two of the above

e. All of the above

XVII. Which treatment would induce the changes of the blood pressure and heart rate observed 21 min after the beginning of the experiment?

a. Isoproterenol administration

b. Carotid occlusion

c. Administration of epinephrine in a preparation pretreated with phentolamine

d. Two of the above

e. All of the above

XVIII. If phenoxybenzamine were administered to the animal and the test procedures were repeated, you might expect which of the following?

a. The change in blood pressure resulting from carotid occlusion would be greater than that seen in the control period

b. The change in blood pressure resulting from the administration of isoproterenol would be less than that seen in the control period

c. The change in blood pressure resulting from the administration of a low dose of epinephrine would be greater than that seen in the control period

d. Two of the above

e. All of the above

XIX. Which treatment would induce the changes of the blood pressure and heart rate observed 24 minutes after the beginning of the experiment?

a. Vagus nerve stimulation

b. Acetylcholine administration

c. Histamine administration

d. Two of the above

e. All of the above