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Chapter 16: Histamine, Serotonin, Drugs Used in Obesity, & the Ergot Alkaloids

Your 37-year-old patient has been diagnosed with a rare metastatic carcinoid tumor. This neoplasm is releasing serotonin, bradykinin, and several unknown peptides. The effects of serotonin in this patient are most likely to include

(A) Constipation

(B) Episodes of bronchospasm

(C) Hypersecretion of gastric acid

(D) Hypotension

(E) Urinary retention

Serotonin causes bronchospasm, but the other effects listed are not observed. Carcinoid is associated with diarrhea and hypertension. The answer is B.

A 23-year-old woman is admitted to the emergency department with difficulty breathing. Examination reveals significant laryngeal edema. Past medical history indicates that she suffers from recurrent episodes of angioneurotic edema with release of histamine and other mediators. Which of the following drugs is the most effective physiologic antagonist of histamine in smooth muscle?

(A) Epinephrine

(B) Loratadine

(C) Ondansetron

(D) Ranitidine

(E) Sumatriptan

The smooth muscle effects of histamine are mediated mainly by H1 receptors. Loratadine is a pharmacologic antagonist of histamine at these receptors. Ondansetron is a 5-HT3 antagonist used to prevent postsurgical and chemotherapy-induced vomiting. Sumatriptan is a 5-HT1D/1B agonist. Ranitidine is a pharmacologic histamine antagonist that blocks the H2 receptor in the stomach and the heart, not H1 receptors in smooth muscle. Epinephrine has a physiologic antagonist action that reverses histamine’s effects on smooth muscle. The answer is A.

A 20-year-old woman is taking over-the-counter diphenhydramine for severe hay fever. Which of the following adverse effects is she most likely to report?

(A) Muscarinic increase in bladder tone

(B) Nausea

(C) Nervousness, anxiety

(D) Sedation

(E) Vertigo

H1 blockers do not activate muscarinic receptors, mediate vasoconstriction, or cause vertigo. Some relieve vertigo or motion sickness. They do not cause nervousness or anxiety. Diphenhydramine is a potent sedative with H1- and M3-blocking actions. The answer is D.

A laboratory study of new H2 blockers is planned. Which of the following will result from blockade of H2 receptors?


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