Inhibitory effect of alkaloids extracted from the stem bark of Hunteria zeylanica on 5-lipoxygenase activity in vitro.

The effects of alkaloid extract from the stem bark of Hunteria zeylanica Gard. (H. zeylanica) on the activities of cyclooxygenase and 5-lipoxygenase in A23187-stimulated rat mast cells were investigated. H. zeylanica alkaloid extract (0.3-300 micrograms/ml) inhibited leukotriene C4 (LTC4) production by 5-lipoxygenase in a concentration-dependent manner and it blocked the production by 50% at 300 micrograms/ml. On the other hand, the extract had no effect on prostaglandin D2 (PGD2) production by cyclooxygenase. Neither (-)-eburnamine nor pleiomutinine, major constituents of H. zeylanica alkaloid extract, inhibited the production of PGD2 and LTC4 in the A23187-stimulated mast cells. The inhibition of arachidonic acid metabolism via 5-lipoxygenase pathway may be due to minute amounts of other components as stated in the Discussion.