Histamine, Seratonin, and Antagonists

Question 1

What is the physiologic effect of histamine on the cardiovascular system?

Answer 1

Immediate fall in BP due to peripheral vasodilation (H1 and H2)

• also, increase in vascular permeability (H1) and increased contractility and HR (H2)

Question 2

What is the physiologic effect of histamine on the bronchiolar smooth muscle?

Answer 2

Broncoconstriction via H1

Question 3

What is the physiologic effect of histamine on the GI tract?

Answer 3

• contraction of smooth muscle and diarrhea (H1)

- stimulation of gastric acid, pepsin, and intrinsic factor secretion (H2)

Question 4

What is the physiologic effect of histamine on the nervous system?

Answer 4

• stimulation of sensory nerve endings: pain and itching (H1)
• feedback inhibition of synthesis and release of histamine (H3)

Question 5

What are three strategies for pharmacological antagonism of histamine?

Answer 5

• induce opposite actions of histamine via different receptors
• inhibit the degranulation of mast cells
• direct histamine receptor antagonism

Question 6

What is the use of diphenhydramine (H1 receptor antagonist) and what are the major side effects?

Answer 6

• allergic reactions (benadryl)

- SE: anti muscarinic and sedating

Question 7

What is the use of tripelennamine (H1 receptor antagonist)?

Answer 7

• OTC sleep aid

Question 8

What is the use of cyclizine (H1 receptor antagonist)?

Answer 8

• motion sickness

Question 9

What is the use of promethazine (H1 receptor antagonist) and what are the major side effects?

Answer 9

• antiemetic

- SE: anti muscarinic, sedating

Question 10

What is the use of chlorpheniramine (H1 receptor antagonist)? How is it different than other 1st gen antagonists?

Answer 10

• component of cold meds

- less sedating!

Question 11

What is the use of loratadine and fexofenadine (2nd gen H1 receptor antagonists)? What are the rare but important side effects?

Answer 11

• used for allergic rhinitis

- SE: no sedation but CV effects are possible with high doses

Question 12

What are the uses of azelastine (2nd gen H1 receptor antagonist)?

Answer 12

• allergic rhinitis and allergic conjunctivitis

Question 13

What is the use of cetirizine (2nd gen H1 receptor antagonist)?

Answer 13

• allergic rhinitis

Question 14

What is the clinically relevant use of H2 receptor antagonists?

Answer 14

blocks gastric acid secretion from parietal cells; used for dyspepsia and gastric or duodenal ulcers

Question 15

What are the important side effects of cimetidine (H2 receptor antagonist)?

Answer 15

• antiandrogen (impotence and gynecomastia)

- inhibits P450 enzymes and can increase serum concentrations of other drugs

Question 16

Name the four H2 receptor antagonists

Answer 16

cimetidine, ranitidine, famotidine, nizatidine

Question 17

What is a general side effect possible with H2 receptor antagonists?

Answer 17

CNS dysfunction

Question 18

What is serotonin made from? What can it be made into?

Answer 18

• made from tryptophan

- can be made into 5-hydroxyindolacetic acid or melatonin

Question 19

What are the actions of 5HT in the GI tract?

Answer 19

• contraction of GI smooth muscle to increase tone and peristalsis
• can be released as a carcinoid syndrome and causes severe diarrhea

Question 20

What are the actions of 5HT on the cardiovascular system?

Answer 20

• smooth muscle: vasoconstriction

- skeletal muscle: vasodilation

Question 21

What are the actions of 5HT on the nervous system?

Answer 21

• pain and itching on periphery

- centrally involved in mood, food intake, sleep

Question 22

How does cyproheptadine work and what are its uses?

Answer 22

• works as an antihistamine and antiserotinergic agent

- used for skin allergies and to treat diarrhea of carcinoid syndrome

Question 23

How does ketanserin work and what are its uses?

Answer 23

• selective 5HT2A,2C antagonist, α1 antagonist, H1 antagonist
• used as an antihypertensive and as an inhibitor of platelet aggregation

Question 24

What receptor does odansetron antagonize and what is it used for?

Answer 24

• 5HT3 antagonist

- used for anti nausea/vomiting in chemo

Question 25

What are triptans used for and what receptors do they work on?

Answer 25

• used for acute migraine

- selective 5-HT1b,d agonists (induces cerebral vasoconstriction)