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48 Cards in this Set

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Sometimes called autocoids, few clinical applications. Selective agonists and atagonists are clinically useful.
Histamines
How are histamines formed?
By decarboxylation of amino acid L-histidine by histidine decarboxylase.
Where are histamines found?
Stored in granules in mast cells or basophils. Bound form is biologically inactive.
Where are mast cells especially rich?
Sites of potential injury
i.e. nose, mouth, feet, internal body surfaces, and blood vessels.
What effects do histamines have on the CNS as a neurotransmitter?
Neuroendocrine control, cardiovascular regulation, thermal and body weight and arousal
What effects does Histamine have on the stomach?
Cells in the fundus of the stomach cause the release of acid from parietal cells of the mucosa.
True or False?
Release of His is energy and calcium required.
True. His, ATP and other mediators are stored together.
Where is negative feedback mediated?
It is mediated by H2 receptors found in mast cells in skin and basophils but not in lung mast cells.
What can displace Histamine from heparin-protein complex?
Amines (morphine, tubocurarine)
What causes degranulation and His release?
Chemical and Mechanical mast cell injury.
What type of release is not associated with mast cell injury or degradation?
Chemical release
What is compound 40/80?
An experimental diamine polymer the induces histamine release from mast cells by exocytotic degranulation requiring energy and calcium.
How many receptor subtypes does histamine have?
Four
What receptors are H1 more similiar to?
Muscarinic receptors
What receptors are H2 more similar to?
Serotonin receptors
Where are H1 receptors found?
Located in smooth muscle, endothelium, and post synaptic membrane in brain.
Where are H2 receptors found?
Found in gastric mucosa, cardiac muscle, mast cells, and post synaptic membrane in brain
True or False?
Only H1 receptors increase intracellular Ca++
False both H1 and H2 receptors increase intracellular Ca++
Where are H3 receptors found?
On dopamine and GABA PRE-synaptic neurons in the basal ganglia
Where are H4 receptors found?
Mainly in bone marrow (eosinophils, neutrophils, CD4 cells) and WBC
What receptors mediate urticarial response to insect and nettle stings and modulate respiration in some mammals?
H1 receptors
What effects does Histamine have on the cardiovascular system?
Decrease in systolic and diastolic BP, vasodilation, tachycardia and reflex tachycardia.
What does direct vasodilation of arterioles and precapillary sphincters cause?
Flushing, warmth, headache
How does Histine-induced edema occur?
H1 mediated in post capillary vessels, actin and myocin contract separating endothelial cells.
What are some cardiac effects of Histamine?
Increase in contractility and pacemaker in some mammals decrease atrial muscle contractility in humans.
Does histamine cause bronchoconstriction?
Yes
What is the only clinical use for histamine?
Diagnose asthma or cystic fibrosis.
True or False?
Histamine has significant effects on smooth muscle of the eye, genitourinary tract, and GI tract.
False except pregnant women and histamine-induced contractions.
At ordinary concentrations, what secretory effects can be seen?
Secretion of gastric acid pepsin, and intrinsic factor modulated by H2 receptors.
At high concentrations what kinds of secretions can histamine cause?
Adrenal medullary discharge.
Which receptor has been linked to obesity through increased food intake and decreased energy expenditure in mice?
H3 receptors
What is the triple resonse?
Intradermal injection causes a "wheal and flare" response.
Three cell types; smooth muscle, capillary or venular dilation and sensory nerve endings cause sense of itching, flare caused by axon reflex, and wheal due to edema
What two drugs have been shown to have analgesic effects similiar to opiods?
Burimamide (H2 blocker)
Improgran (no H1, H2, or H3 activity)
Ethanolomines, Ethylaninediamines, piperazine derivates, alkylating derivatives, Phenothiazine derivatives.
First generation H1 Antagonists
Carbinoxamine (Clistin), Dimenhydrinate (Salt of diphenhydramine; Dramamine), Diphenhydramine (Benadryl), Doxylamine
Ethanolamines
Ethylaminediamines
Pyrilamine (Neo-Antergan), Tripelennamine (PBZ)
Hydroxyzine (Atarax), Cyclizine (Marezine), Meclizine (Bonine)
Piperazine derivatives
Alkylamines derivatives
Brompheniramine (Dimetane), Chlorpheniraine (Chlor-Trimeton)
Phenothiazine derivatives
Promethazine (Phenergan)
What are some characteristics of second generation histamine Blockers (H1)
Less lipid soluble; do not penetrate the BBB readily.
Longer acting such as meclazine (12-24 hrs), Metabolized by the CYP3A4 system
True or False?
H1 receptor antagonists by reversible competitive inhibition?
True
What are some non specific actions of Histamine blockade?
Sedation, antinausea, antiparkinsonism effects, anticholinergic actions, adrenoceptor blockade, serotonin blockade, local anesthesia
True or False?
At toxic doses, antihistamines causes stimulation, agitation, and even convulsion in adults
True
What is the DOC for rhinitis and urticaria?
H1 antagonists
What drug was used for antinausea and vomitting during pregnancy in the 1970s, but is no longer used because of reports of fetal malformation?
Doxylamine
What are some common toxic effects of antihistamines?
Sedation and antimuscarinic action
What are the two mechanisms of action for H2 blockers?
1. ECL HIS blocked from parietal cell H2
2. Gastrin or Ach stimulation of parietal cell
True or False?
H2 blockers have high incidence of side effects.
False
Side effects include diarrhea, headache, fatigue, and constipation and occur in 3% of patients