Inhibition of histamine release from rat peritoneal mast cells by MY-1250, an active metabolite of Repirinast (MY-5116).

MY-1250, an active metabolite of Repirinast (MY-5116), strongly and dose-dependently inhibited the in vitro histamine release from rat peritoneal mast cells induced by antigen. The IC50 value of MY-1250 for histamine release was in the order of 0.3 microM. Moreover MY-1250 strongly inhibited calcium ion mobilization from the intracellular Ca2+ store. In the presence of 3.6 x 10(-5) M of MY-1250, the initial rise in [Ca2+]i reached a maximum of only 13 nM, and the inhibitory effect was 81% for the initial rise. The IC50 value for this event was 0.25 microM. The inhibitory effect of MY-1250 on the initial rise in [Ca2+]i was closely correlated with that on histamine release.