Effect of Syzygium aromaticum extract on immediate hypersensitivity in rats

We investigated the effect of aqueous extract of Syzygium aromaticum (L.) Merr. et Ferry (Myrtaceae) flower bud (SAFE) on immediate hypersensitivity. SAFE inhibited compound 48/80-induced systemic anaphylaxis in rats (IC50 = 31.25 mg/kg, i.p.). SAFE also inhibited local immunoglobulin E (IgE)-mediated passive cutaneous anaphylactic reaction (IC50 = 17.78 mg/kg, i.v.; IC50 = 19.81 mg/kg, p.o.). When SAFE was pretreated at concentrations ranging from 25 to 1000 mg/kg, the serum histamine levels were reduced in a dose-dependent manner. Moreover, SAFE dose-dependently inhibited histamine release from rat peritoneal mast cells (RPMC) by compound 48/80 or anti-dinitrophenyl IgE. When SAFE was added, the level of cAMP in RPMC transiently and significantly increased about 47-fold at 10 s compared with that of basal cells. These results indicate that SAFE inhibits immediate hypersensitivity by inhibition of histamine release from mast cells in vivo and in vitro. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.