IMMUNOHISTOCHEMICAL LOCALIZATION OF INDUCIBLE NITRIC-OXIDE SYNTHASE ON HUMAN FETAL AMNION IN INTRAAMNIOTIC INFECTION

OBJECTIVES: Amniotic fluid levels of nitric oxide metabolites are sign ificantly elevated in intra-amniotic infection. We hypothesized that f etal amnion is a possible site for the production of nitric oxide. Bec ause inducible nitric oxide synthase is the key enzyme responsible for the generation of nitric oxide in patients with intra-amniotic infect ion, we used immunohistochemistry to localize it on human fetal amnion . STUDY DESIGN: Human fetal amnions were obtained from patients with a nd without intra-amniotic infection (n = 5, respectively). Intra-amnio tic infection was diagnosed by positive amniotic fluid cultures and pl acental pathologic features. Human fetal amniotic membranes were proce ssed into tissue blocks and embedded in paraffin. A rabbit polyclonal antibody against human inducible nitric oxide synthase was used as the primary antibody followed by avidin-biotin immunoperoxidase localizat ion. Normal rabbit serum was used as a negative control and ovarian ca rcinoma cells were used as the positive control. RESULTS: Anti-inducib le nitric oxide synthase labeling of human fetal amniotic membranes in patients with intra-amniotic infection showed positive immunostaining of epithelial cells, specifically in the cytoplasm of the perinuclear area. In contrast, no anti-inducible nitric oxide synthase immunostai ning on human fetal amniotic membranes could be identified in patients without intra-amniotic infection. CONCLUSIONS: Our data provide impor tant evidence that inducible nitric oxide synthase can be induced on h uman fetal amnion in intra-amniotic infection. These findings strongly support our hypothesis that human fetal amnion may be a possible site for the synthesis of nitric oxide after inducible nitric oxide syntha se is induced in response to infectious products in intra-amniotic inf ection.