Today's Veterinary Practice

JUL-AUG 2017

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55 JULY/AUGUST 2017 ■ TVPJOURNAL.COM CONTINUING EDUCATION Mast cell activation and granule release GI Tract: Increased fluid secretion Increased peristalsis Expulsion of the GI tract contents (vomiting and diarrhea) Congestion and blockage of airway (wheezing, coughing, phlegm) Swelling and mucus secretion Increased fluid in tissues causing increased lymph flow, fluid shifts to the interstitium Airway: Decreased diameter Increased mucus secretion Blood Vessels: Increased blood flow Increased permeability more antigen exposure and do not result in the release of histamine as a mediator. Furthermore, IgE-independent reactions do not require initial allergen exposure. 2,3 Anaphylactoid Reaction: Nonimmunologic Anaphylaxis Nonimmunologic reactions may occur via degranulation of mast cells and basophils without immunoglobulins. They may be triggered by external influences, such as physical factors, drugs, and external toxins. 2,3 CHEMICAL MEDIATORS Mediators stored in mast cells and basophils (ie, histamine, heparin, proteases such as tryptase and chymase, and cytokines) are released during degranulation ( Figure 1 ), which causes an increased production of phospholipase A and thus arachidonic acid and its metabolites. Downstream activation of this cascade leads to an increase in newly synthesized mediators, such as prostaglandins, leukotrienes, and plasma activating factor. These newly synthesized mediators induce an inflammatory response. The release of inflammatory and vasoactive mediators leads to shock. 10,12 Histamine Once an antigen has bound to the primed IgE receptors, histamine is released. Histamine is the principal mediator stored in granules of mast cells and basophils. It is released quickly during anaphylaxis and can be found in elevated concentrations in circulating plasma less than 1 minute after allergen interaction. 3 FIGURE 1. Effect of mast cell degranulation. 11 GI, gastrointestinal.

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