Page 992 - Veterinary Immunology, 10th Edition

Bronchial and bronchiolar constriction leads to coughing, dyspnea,
VetBooks.ir and eventually apnea. On necropsy, severe pulmonary emphysema

and peribronchiolar edema are commonly seen. In addition to the
lung lesions, edematous hemorrhagic enterocolitis may cause

severe diarrhea. The major mediators of anaphylaxis in horses are
probably histamine and serotonin.
In cattle the major shock organs are the lungs (Fig. 30.2).
Anaphylaxis is characterized by profound systemic hypotension

and pulmonary hypertension. The pulmonary hypertension results
from constriction of the pulmonary vein and leads to pulmonary
edema and severe dyspnea. The smooth muscle of the bladder and
intestine contract, causing urination, defecation, and bloating. The

main mediators of anaphylaxis in cattle are serotonin, kinins, and
the leukotrienes. Histamine is of lesser importance. Dopamine
enhances histamine and leukotriene release from the lung, thus
exerting a form of positive feedback. Because of the anticoagulant

properties of heparin from mast cells, blood from affected animals
may not coagulate. In cattle, in contrast to the other species, β-
stimulants such as isoproterenol potentiate histamine release from
leukocytes, whereas α-stimulants such as norepinephrine inhibit

histamine release. Epinephrine also potentiates histamine release in
cattle. The significance of these anomalous effects is unclear.

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