Questions and Answers
What is the main function of autacoids?
Histamine is synthesized in mammalian tissues by decarboxylation of the amino acid L-histidine.
True
What is the chief site of histamine storage in most tissues?
Mast cell
Histamine is stored in bound form in granules along with heparin, eosinophil chemotactic factor of anaphylaxis (ECF-A), neutrophil chemotactic factor, and various enzymes such as _.
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What causes the rapid release of histamine from mast cells due to loss of storage granules into the extracellular fluid?
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What are the 2 components of histamine response mentioned in the text?
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What are the main reasons behind the fall in blood pressure in histamine shock?
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Histamine shock is mainly due to the injection of exogenous histamine. In contrast, endogenous histamine can be mobilized in the body by taking drugs that release histamine, leading to a similar state. This similarity is known as endogenous histamine __________.
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Histamine can cause itching when introduced into the superficial layers of the skin. True or False?
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Match the following receptors with their actions:
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Study Notes
Inflammation
- Inflammation is a local reaction to injury or invasion, characterized by swelling and pain.
- The inflammatory response, although primarily defensive, often results in tissue damage serious enough to warrant pharmacological intervention.
Tissue Response to Injury
- The response to injury is divided into three phases:
- Acute phase: initial response to tissue injury, involving the release of autocoids.
- Immune response: activation of immunologically competent cells in response to antigenic substances.
- Chronic inflammation: release of numerous cellular mediators.
Autacoids
- Autacoids are a heterogeneous group of pharmacologically active compounds formed by the tissues they act on, functioning as local hormones.
- Autacoids are characterized by brief duration, local action, and non-blood-borne properties.
- Examples of autacoids include histamine, serotonin, AA metabolites, and PAF.
Histamine
- Histamine is a chemical mediator of various cellular responses, including allergic and inflammatory reactions, and gastric acid secretion.
- Biosynthesis: histamine is synthesized in mammalian tissues by decarboxylation of the amino acid L-histidine, catalyzed by histidine decarboxylase.
- Tissue localization: histamine is stored in mast cells and basophils.
Release of Histamine
- Release of histamine can occur through:
- Pharmacologic release: certain chemicals (e.g., morphine, succinylcholine) displace histamine from the heparin-protein complex within mast cells.
- Physical stimuli: scratching the skin, resulting in rapid release of histamine.
- Immunologic release: interaction of antigen with macrophage to produce an antibody, followed by interaction of IgE antibody and antigen with mast cells to release histamine.
Regulation of Histamine Release
- Inhibition of histamine release is produced by:
- Adrenaline and other drugs that activate β-receptors.
- Stimulation of these receptors results in the accumulation of cAMP, which reduces histamine release.
- Histamine reduces its own release by interacting with H2 receptors on mast cells and basophils.
Histamine Receptors
- Histamine binds to four types of receptors:
- H1 receptors: stimulate IP3 and DAG, and are involved in allergic responses.
- H2 receptors: mediate through cAMP, and are involved in gastric acid secretion.
- H3 receptors: autoreceptors that decrease ACh, NE, and serotonin release.
- H4 receptors: mediate mast cell chemotaxis.
Physiological Roles of Histamine
- Histamine is involved in:
- Hypersensitivity and allergic responses.
- Regulation of gastric acid secretion.
- Neurotransmission in the CNS.
- Cardiovascular system: vasodilation, increased capillary permeability, and decreased blood pressure.
Antihistamines
- H1 blockers: competitive antagonists of histamine at H1 receptors.
- H2 blockers: competitive antagonists of histamine at H2 receptors.
- Examples of antihistamines include:
- 1st generation: diphenhydramine, chlorpheniramine.
- 2nd generation: loratadine, fexofenadine, cetirizine.
Side Effects and Contraindications
- Side effects of antihistamines:
- Sedation, headache, gastrointestinal disturbances.
- Anticholinergic effects: dry mouth, urinary retention, etc.
- Cardiovascular effects: hypotension, tachycardia.
- Contraindications: asthma, active ulcer disease, GI bleeding.
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Description
This quiz covers the pharmacology of inflammation, a local reaction to injury or invasion associated with swelling and pain, and its tissue response to injury.
