Pharmacology I · Exam 2 · Class of 2028

Histamine Receptor Actions

Where the H1 and H2 receptors are and what histamine does at each, the reason antihistamines do what they do.

Lecture 5 — Ear, Nose and Throat Drugs 9 rows

H1 blockers (the antihistamines on the comparison chart) act on the H1 rows: itch and pain, swelling from leaky venules, bronchial contraction. The H2 receptors run gastric acid secretion, which is why H2 blockers treat acid, not allergy. The slide puts heart rate on H1 and force of contraction on H2; some references put both on H2. Know the slide’s version for this exam.

Organ or tissue	Receptor	Action	Source
Vascular smooth muscle	H1 and H2	Decreases total peripheral resistance (vasodilation)	L5 slide 28
Postcapillary venules	H1	Increases permeability (swelling)	L5 slide 28
Heart	H1	Increases heart rate	L5 slide 28
Heart	H2	Increases force of contraction	L5 slide 28
Bronchiolar smooth muscle	H1	Contraction	L5 slide 28
Bronchiolar smooth muscle	H2	Relaxation	L5 slide 28
Gastrointestinal smooth muscle	H1	Constriction	L5 slide 28
Gastrointestinal mucosa	H2	Gastric acid and pepsin secretion	L5 slide 28
Cutaneous nerve endings	H1	Pain and itch	L5 slide 28

Every row is checked against the slide it cites by tools/check_pharm_e2.py before this page is written.

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