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18 Cards in this Set
- Front
- Back
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Where is histamine?
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In vesicular granules of mast cells or basophils (skin, mouth, nose, airways, blood vessles)
Neuronal tissue in the brain Enterochromaffin-like cells of the fundus of the stomach, venoms and sting secretions. |
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What releases histamine?
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type I immediate allergic reaction (IgE)
Venoms, toxins radiation cold temps some drugs mechanical injury |
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H1 receptor
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Smooth muscle, e.g. blood vessels, bronchi, GI tract; endothelium & sensory nerve endings – Gq- coupled to elevation in IP3, Ca2+ and diacylglycerol.
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H2 receptor
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Gastric parietal cells, cardiac and some vascular smooth muscle – Gs- coupled to elevation in cAMP.
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H3 receptor
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Presynaptic nerves in brain & myenteric plexus – Gi- coupled to N-type calcium channels.
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H4
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Blood cells in bone marrow and circulating blood, e.g. eosinophils & neutrophils - Gi- coupled to reduction of cAMP and intracellular Ca2+.
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What cardiovascular effects does histamine have?
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down BP (direct): NO-dependent vasodilation of arterioles & precapillary sphincters. Mainly H1-, but some H2-receptor dependency.
Flushing, sense of warmth & headache: vasodilation. up rate/force of heart contraction (direct & indirect) - H2-receptor dependent. Edema: Endothelial cell contraction in blood vessels of the microcirculation (esp. postcapillary vessels) causing in capillary permeability - H1mediated. Heat, redness & local swelling, a.k.a. urticaria or hives: indicative of histamine release in skin |
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What effects on nerves does histamine have?
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Sensations of pain and itching: H1-mediated direct effect on sensory nerves endings.
Component of the urticarial response & reactions to insect bites and nettle stings. Inhibition of neurotransmitter release: H3-receptors on presynaptic nerves. Clinical importance – yet to be determined. Axon Reflex: Direct action on H1-receptors on sensory nerve endings and/or depolarization of efferent axons. Important component of the ‘triple response’. |
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What is the triple response?
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reddening, wheal and edema, red irregular flare (form vasodilation itch and pain also from histamine)
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What respiratory effects does histamine have?
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Bronchoconstriction: H1- mediated
Not marked in non-asthmatics; asthmatic airways can be 100 to 1000-fold more sensitive. Basis for a provocative test (histamine-challenge) of bronchial hyperreactivity. Watery secretion prominent in submucosal glands of nasal cavity: mostly H1- mediated. |
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What GI effects does histamine have?
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H1- receptors mediate contraction of intestinal smooth muscle.
H2- receptors mediate parietal cell acid production in gastric mucosa. |
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What are H4 receptors looking into treating?
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acute myelogenous leukemia,
hepatitis C infection , malignant melanoma , non-alcoholic steatosis-hepatitis , renal cell cancer |
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What are some physiological antagonists of histamine?
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bronchodilators, vasoconstrictors (epi), degranulation inhibitors, decongestion
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What is the difference between 1st and 2nd generation antihistamines?
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1st block muscarinic receptors, cross the BBB (drowsiness), shorter action (4-6hr vs. 12-24hr), can treat motion sickness, ^ heart rate, thicken secretions
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What effects do antihistamines have on the body?
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1st generation only stuff, dry up secretions(not remove), reverse triple response, local anesthetic effect not due to histamine receptor blockade.
NOT effective in asthma or GI symptoms |
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What are some adverse effects of antihistamines?
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Sedation (1st gen), dry mouth, blurred vision (mostly 1st gen), urinary retention, down GI motility
insomnia, nervousness and tremors in children. |
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Why don't antihistamines made good decongestants?
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They only dry, they don't remove. There are lots of different mediators cause rhinitis symptoms (ie other auticoids)
decongestants block the action instead of the receptor like the antihistamines do. |
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What causes runny nose/congestion?
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vasodilation pushes the stuff out.
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