Page 993 - Veterinary Immunology, 10th Edition

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FIG. 30.2 The basic mechanisms of anaphylaxis. The proximal
cause of death in most but not all species results from extreme
constriction of the bronchial smooth muscle and subsequent
asphyxiation.

In sheep, pulmonary signs predominate in anaphylaxis as a result
of constriction of the bronchi and pulmonary vessels. Smooth
muscle contraction also occurs in the bladder and intestine with

predictable results. The major mediators of type I hypersensitivity
in sheep are histamine, serotonin, leukotrienes, and kinins.
In pigs, anaphylaxis is largely the result of systemic and
pulmonary hypertension, leading to dyspnea and death. In some

pigs the intestine is involved, whereas in others no gross intestinal
lesions are observed. The most significant mediator identified in
this species is histamine.
Dogs differ from the other domestic mammals in that the major

shock organ is not the lung but the liver, specifically the hepatic
veins. Dogs undergoing anaphylaxis show initial excitement
followed by vomiting, defecation, and urination. As the reaction

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