Amniotic fluid nitric oxide metabolite levels and nitric oxide synthase localization in feto-placental tissues are modified in association with humanlabor

Nitric oxide (NO) has a relaxant effect on uterine smooth muscle and may be implicated in maintaining uterine quiescence during pregnancy. In order to investigate the role of nitric oxide in human parturition, we have measure d NO metabolite levels in maternal and fetal compartments in association wi th labor, both at term and preterm. We have also examined the localization and distribution of NO synthase (NOS) isoforms in placentas and fetal membr anes after term and preterm delivery by means of immunohistochemistry. Alth ough no differences were present in maternal and fetal blood and in materna l urine among groups, we found that NO metabolite concentrations were highe r in amniotic fluid collected from women in labor than in non-laboring pati ents, both at term (15.4+/-1.6 vs. 6.8+/-0.6 mu M/mg creatinine) and preter m (16.7+/-2.0 vs. 7.0+/-0.8 mu M/mg creatinine). Ir-bNOS staining appeared to be decreased in fetal membranes collected after spontaneous labor at ter m and preterm. In contrast, a stronger staining for iNOS was detected in tr ophoblast cells of fetal membranes from women in labor than in those from n on-laboring women. We suggest that NOS isoenzymes in fetal placental tissue s are differently regulated and might play different roles during pregnancy . (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.