Histamine, Bradykinin, And Their Antagonists

Question 1

Histamine

Answer 1

H1: Gq bronchoconstriction and vasoconstriction
H2: Gs gastric parietal cells, heart, mast cells, brain
H3: Gi CNS and gastric mucosa

Question 2

Antihistamines

Answer 2

Stabilize inactive conformation of H1 and shift equilibrium to inactive state
Most effective prophylaxis than after ax rxn has started
-amines: cross BBB, drowsiness and sedation
-dine or zine: do not cross BBB, unpleasant taste, ha, nose bleed
Azelastine and Olopatadine: not BBB, dry/burning eyes

Question 3

H2 receptor Antagonists

Answer 3

Act reversibly and competitively inhibit binding of histamine to H2 receptors on parietal cells
Tx: uncomplicated GERD, ulcers, dec nocturnal acid
AE: diarrhea, ha, muscle pain, thrombocytopenia, confusion, hallucinations
DI: may dec absorption of meds that require acid for absorption (ketoconazole, Ca carbonate)

Question 4

Cimetidine

Answer 4

Inhibits p450 (lidocaine, phenytoin, guidine, theophylline, warfarin)
AE: androgenic effects

Question 5

CNS actions

Answer 5

N/V
Chemosensory organ for emesis
Receives from medulla, CTZ, cortex, visceral afferent of pharynx and GI
H1 receptors: histamine, acts on vestibular afferents and within brainstem to trigger emesis center, NT for inner ear/cerebellar transmission (motion sickness)