An 8-year-old girl with asthma presents with respiratory distress. She has a history of allergies and upper respiratory tract infections. She also has history of wheezes associated with exercise. Which of the following preformed substances is released from mast cells and platelets, resulting in increased vascular permeability in the lungs of the patient?

Histamine. When IgE-sensitized mast cells are stimulated by antigen, preformed mediators of inflammation are secreted into the extracellular tissues. Histamine binds to specific H1 receptors in the vascular wall, inducing endothelial cell contraction, gap formation, and edema. Massive release of histamine may cause circulatory collapse (anaphylactic shock). Bradykinin (choice A) and Hageman factor (choice B) are plasma-derived mediators. The other choices are not preformed molecules but are synthesized de novo following cell activation.Diagnosis: Asthma