Which substance's excessive production is most likely caused by the patient's symptoms? A 22-year-old man comes to the physician because of a 2-year history of episodes of shortness of breath and wheezing. His respirations are 12/min. Physical examination shows no abnormalities. It is found that the symptoms occur after he takes certain over-the-counter medications containing aspirin. Laboratory studies show a serum IgE concentration within the reference range and no eosinophilia.