Inhibitory effect of MY-1250 on histamine release from rat peritoneal mast cells and guinea pig lung fragments: the elucidation of the mechanism.

When the effect of MY-1250 (5,6-dihydro-7,8-dimethyl-4,5-dioxo-4 H-pyrano [3,2-c] quinoline-2-carboxylic acid) on histamine release from rat peritoneal mast cells induced by compound 48/80 was studied, MY-1250 caused a significant inhibition of histamine release at concentrations higher than 3 microM. Furthermore, the compound inhibited not only 45C a uptake into the mast cells but also Ca2+ release from the intracellular Ca store at a concentration of 10 microM in both cases. By contrast, MY-1250 did not affect either histamine release from permeabilized mast cells induced by TPA, IP3 and GTP gamma S or Ca2+ release from the endoplasmic reticulum induced by IP3. In the chopped lung preparations, MY-1250 at doses of 10 and 100 microM caused a significant inhibition in histamine release from the pieces of actively sensitized guinea pigs exposed to antigen and simultaneously prevented a decrease in intracellular cAMP contents taking place in association with antigen-antibody reaction. No significant changes were effected by MY-1250 in alpha-chymotrypsin activity and phospholipase A2 activity. Also, no antagonistic effects on LTD4 and PAF were observed.