Triple response of histamine Dr. Raz Mohammed Lab.5 25. 04. 016

Histamine belongs to a group of compounds called autacoids, that includes (in addition to histamine) prostaglandin and serotonin. These autacoids differ from circulating hormones in that they are produced by many tissues rather than in specific endocrine glands.

Histamine Histamine is a chemical messenger that mediates: Allergic and inflammatory reactions, gastric acid secretion, and neurotransmission in parts of the brain.

inflammatory reaction of histamine

Release of histamine: Stimuli causing the release of histamine from tissues include the destruction of cells as a result of cold, bacterial toxins, bee sting venoms, or trauma.

Types of histamine receptor H1 receptor H2 receptor H3 receptor H4 receptor.

H1 receptor antagonists Non- sedative: Cetrizine Loratadine Terfenadine Desloratadine fexofenadine

Sedative antihistamines Chlorpheniramine Promethazine Diphenhydramine Clemastine Cyproheptadine Triploridine hydroxyzine

H2 receptor antagonists These are a class of drugs used to block the action of histamine on parietal cells in the stomach, decreasing the production of acid by these cells. Nizatidine Ranitidine Cimetidine Famotidine

Actions of Histamine Smooth muscle: Histamine causes contraction of the smooth muscle of the ileum, bronchi and bronchioles, and uterus. Blood vessels: Histamine causes vasodilation. Capillary permeability also increases causing edema.

3. Skin: histamine release in the skin cause itching, because it stimulates sensory nerve endings. 4. Gastric secretion: Histamine stimulates the secretion of gastric acid by action on H2 receptors.

Triple response: If histamine is injected intradermally or when the skin is exposed to a physical trauma a triple response will be elicited. That consists of: Localized red spot: immediate redness of the skin, extending for a few (mm) around the site of injection, that appears within few seconds and recovers maximally in a bout minute (direct vasodilation) due to capillary dilation.

Triple response: 2. Bright red flush (Flare): red and irregular extending a bout (1 cm) beyond the original red spot and developes slowly. Results in itching and pain, due to arteriolar dilatation. 3. Wheal (edema): It occurs in 1 or 2 minutes. Occupying the same area at the original red spot of injection site. Due to increased capillary permeability and due to exudation of fluid from capillaries and venules.