[Study on the morphological changes in the placenta of rats administered nitric oxide synthase inhibitor]

To clarify the roles of nitric oxide synthase (NOS) during pregnancy, histopathological changes in the placenta were observed after the administration of an NOS inhibitor [NG-nitro-L-arginine methyl ester (L-NAME)] to rats. L-NAME was infused subcutaneously from day 12 of gestation at stable concentrations of 3mg/day (group B) or 25mg/day (group C) until day 18 when the placentae were removed. The mean systolic blood pressures in groups B and C were higher than in the controls (group A). By both light and electron microscopy, morphological changes were observed and compared to those of human placenta in preeclampsia. In groups B and C, light microscopy showed that giant cells were vacuolated, degenerated and decreased in number. In the labyrinth, the stroma was extremely edematous, and the intervillous space and fetal vessels were narrowed. Electron microscopy showed that micro-fibrin clots were deposited on the maternal surface of trophoblasts. The endothelial cells of fetal vessels were irregular in shape. In group B the endothelial cells and intermediate filaments were increased. These findings suggest that decreased NO production may cause changes similar to those found in preeclampsia. Treatment with NOS inhibitor may be used in an animal model for preeclampsia.