Plasma histamine after methacholine, allergen, and aspirin challenges

Plasma histamine levels were measured by radio-enzymatic technique in seven patients following 10 challenges: five methacholine challenge tests, four antigen inhalation challenge tests, and one oral aspirin challenge test. Baseline plasma histamine was the same in all patients except in the aspirin-challenged patient, who had a higher baseline histamine level. There was no statistical change in the level of histamine throughout the test in either the methacholine-challenged or the antigen-challenged patients, whereas there was a marked increase in histamine levels in the aspirin challenged patient. A possible explanation is that methacholine and antigen are inhaled and therefore have primarily local effects on the lung, whereas oral aspirin has a systemic effect with consequently systemic changes in histamine which are detectable as changes in plasma level.