PLACENTAL NITRIC-OXIDE METABOLISM

There is increasing evidence that nitric oxide (NO) has a role in preg nancy. NO is synthesized from L-arginine by NO synthase (NOS), which c an exist either as a calcium-dependent or a calcium-independent isofor m of the enzyme. Both isoforms are present in placental villi and the authors have measured NOS activities in tissues from early and term no rmal, pre-eclamptic and growth-retarded pregnancies. Higher activities were seen in first trimester placental villi than at term. An impairm ent of NO metabolism occurred in placental villi from pre-eclamptic an d growth-retarded pregnancies. Smoking also results in decreased NOS a ctivities in the placental villi, suggesting that problems attributed to smoking during pregnancy could be linked to NO metabolism. Polyamin es, arginine and citrulline (all of which are important metabolites in the NO pathway) were also measured in placental villous tissues. The data presented in this review article are from work carried out in the authors' laboratories and suggest that alterations in the placental a rginine-NO pathway may not only play a role in the physiological chang es of advancing gestation but may also contribute to the pathophysiolo gy of pre-eclampsia and fetal growth retardation.