Immunohistochemical reagents included murine COX-1 monoclonal antibody to sheep seminal vesicle COX-1, murine COX-2 monoclonal antibody to a polypeptide sequence from human COX-2, rabbit 5-LO polyclonal antibody to a peptide from human 5-LO, rabbit polyclonal antibody to murine 12-LO, and sheep 15-LO polyclonal antibody to rabbit reticulocyte 15-LO (Cayman Chemical, Ann Arbor, Mich). Five-micron tissue sections were mounted on charged glass slides (Superfrost Plus; Fisher Scientific, Pittsburgh, Pa) and baked overnight at 60°C. Deparaffinization with xylene and rehydration through a graded alcohol series was followed by blocking of endogenous peroxidase activity with 3.0% hydrogen peroxide for 15 minutes. Antigen retrieval was performed by heating in a decloaking chamber (Biocare Medical, Walnut Creek, Calif) in citrate buffer (20 mmol/L; pH, 6.0) at 120°C for 10 minutes. Staining was performed using an autostainer (DakoCytomation, Carpinteria, Calif). An indirect avidin-biotin immunoperoxidase method (Vector Laboratories, Burlingame, Calif) was used according to the manufacturer's protocol for all cases except 15-LO, for which a biotinylated anti–sheep IgG (Sigma-Aldrich, St Louis, Mo) replaced the Vector IgG, which is specific for mouse and rabbit antibodies. For COX-1, ovarian carcinoma tissue was used as the control, and the final dilution was 5 μg/mL. For COX-2, prostate adenocarcinoma was used, with a final dilution of 1 μg/mL. Colon adenocarcinoma was used as the control for 5-LO and 15-LO, with final dilutions of 1:1500 and 1:250, respectively. The control tissue used for 12-LO was prostate adenocarcinoma, with a final antibody dilution of 1:1000. Paired serial sections were incubated at room temperature for 45 minutes with each particular antibody. Negative controls were performed on all sections using equivalent concentrations of subclass-matched IgG1 (Becton Dickinson Pharmigen, San Jose, Calif) generated against unrelated antigens for COX-1 and COX-2, rabbit serum for 5-LO and 12-LO, and anti–sheep IgG for 15-LO. Enzyme expression was visualized by development with 3,3′-diaminobenzidine (DakoCytomation), counterstained with hematoxylin, dehydrated in graded alcohols, and coverslipped.