ARACHIDONIC-ACID METABOLISM IN CULTURED ASTROCYTES - PRESENCE OF 12-LIPOXYGENASE ACTIVITY IN THE INTACT-CELLS

In our previous study, it was revealed that the exogenous arachidonic acid is mainly metabolized by the lipoxygenase pathway in the cell-free homogenate of cultured astrocytes. This is apparently in contrast with other studies reporting production and release of the cyclooxygenase products (prostaglandins and thromboxanes) by cultured astrocytes. To help specify the reason for this discrepancy, the metabolism of endogenous arachidonic acid in the intact monolayer of cultured astrocytes was examined. When the astrocytes were stimulated with calcium ionophore A23187, a peak coeluted with authentic 12-hydroxyeicosatetraenoic acid (12-HETE) on reverse-phase high-performance liquid chromatography (RP-HPLC) was observed. Formation of this peak was not affected by indomethacin, a specific inhibitor for cyclooxygenase, but completely inhibited by BW755C, an inhibitor for both cyclooxygenase and lipoxygenases. Furthermore, the ultraviolet spectrum of the substance giving this peak agreed well with that of authentic 12-HETE. The amount of 12-HETE formed and released by the astrocytes was estimated to be 293.1 ng/mg protein/1 h. Taken together, these results suggest that the endogenous arachidonic acid is mainly metabolized by 12-lipoxygenase in the intact monolayer of astrocytes.