Inhibition of IgE-mediated histamine release from human leukocytes by a new xanthine derivative, D 4026

Pretreatment of human leukocytes with the new xanthine compound, 3,7-dihydro-1,8-dimethyl-3-phenyl-1H-purine-2,6-dione (D 4026), induced a dose-dependent and statistically significant inhibition of immunoglobulin E-mediated histamine release in the concentration interval 0.1-1000 microM. Histamine release elicited with suboptimum amounts of the triggering agent (anti-IgE or antigen) was inhibited to a greater extent than a release initiated with optimum amounts. At a concentration of 10 microM, D 4026 had at least the same inhibitory effect as 100 microM theophylline. When leukocytes were incubated simultaneously with D 4026 and a histamine H-2 receptor-stimulating drug (histamine or clonidine), the two drugs combined induced an inhibition significantly greater than the sum of their individual inhibitory effects. Only pure additive inhibitory effects were, however, obtained during simultaneous treatment of leukocytes with theophylline and histamine.