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Histamine released locally after intradermal antigen challenge in man.

Plasma histamine concentration was measured in venous blood draining the site of antigen-induced wheal and flare responses in the forearm skin of seven atopic volunteers. Concentrations were measured using a double isotope radioenzymatic method. The mean +/- s.e. mean resting plasma concentration was 0.18 +/- 0.01 ng/ml. In all subjects an increase was detected in local plasma histamine concentration after intradermal antigen challenge. The peak histamine concentration occurred between 2 and 15 min after challenge, and represented an increase of three- to 20-fold above the resting concentration. Plasma histamine concentration remained significantly elevated for at least 60 min after challenge. A 30 min incubation at 37 degrees C of blood taken at the time of peak plasma concentration caused a fall in histamine concentration. This suggests that histamine release from basophils during the sampling procedure was not a significant problem. This method is less invasive than skin chamber or blister techniques for the demonstration of mediator release in cutaneous inflammation and allows a simultaneous assessment of tissue response.