Murine peritoneal lavage cells express an arachidonate 12-LOX. Peritoneal lavage in mice was performed as described in Material and Methods. The cells were spun down, washed, and resuspended in 1 mL of PBS. After addition of arachidonic acid (100 μmol/L final concentration), the cells were disrupted and the lysate was incubated for 15 minutes at 37°C. The reaction was stopped by acidification to pH 3, and the lipids were extracted with 1 mL of ethylacetate. The solvent was evaporated, the remaining lipids were reconstituted in 200 μL of methanol, and aliquots were analyzed by RP-HPLC as described in Materials and Methods. Upper trace, incubation with cells; lower trace, control incubation (no cells). Cells alone do not contain significant amounts of hydroxy fatty acids. Inset, ultraviolet-spectrum of the hydroxy fatty acids indicating the presence of conjugated dienes.