Antihistamines Flashcards
Histamine effects in the vascular system
Dilate small blood vessels and increase cap perm
Histamine in the bronchi
Smooth muscle constriction
Histamine in the stomach
Stimulates secretion of acid
Histamine in the CNS
Neurotransmitter.
Produced in posterior hypothalamus and with axonal projections toe the frontal and temporal cortices
Histamine stores in
Skin, GI, lungs but also all tisue
Allergic release of histamine
IgE creates antibodies to allergens, beyond first exposure the allergen and antibody form a bridge, and somehow mobilizes intracellular calcium.
Calcium causes histamine-containing storage granules to fuse with the cell membrane and disgorge contents into extracellular space.
Nonallergic release
Some agents (some drugs, radiocontrast) bind directly to mast cells and trigger histamine release.
No sensitization needed like allergic release
Cell injury can also cause this
H1 effects
Small vessel dilations. increased cap perm, bronchoconstriction (not the cause of asthma), CNS, itching and pain, secretion of mucous
H1 CNS effects
Role in cognition, memory, sleep/wake cycle
H2 effects
Secretion of gastric acid (along with acetylcholine and gastrin to lesser extents)
Mediators of allergic reactions
Histamine prostaglandins, leukotrienes, tryptase
Severity of allergic reactions
Mild caused largely by H1 being triggered by histamine
Anaphylaxis is mostly triggered by leukotrienes
1st/2nd gen anti histamines
1st gen highly sedating
H1 MOA
Do not block H2 receptors
Don’t block release of histamine from mast cells/basophils.
Certain antihistamines also bind and block muscarinic receptors
Antihistamines motion sickness
Gravol works by blocking H1 and muscarinic receptors in neuronal pathway leading from vestibular apparatus of inner ear to vomit center in medulla
