The Changes And Significance Of Placental Nitric Oxide Synthase Activities And Plasma Nitric Oxide/Endothelin Levels Of Maternal And Umbilical Blood In Patients With Pregnancy Induced Hypertension

Objective To study whether the activities of placental nitric oxide synthase (NOS) and the plasma nitric oxide (NO)/endothelin (ET) levels of maternal and umbilical blood were changed in patients with pregnancy induced hypertension (PIH) and discuss the effect of NO /ET in the development of PIH.Methods 40 women with PIH ,30 normal late trimester pregnant women were studied. Maternal venous blood and umbilical venous blood were collected from all cases. Plasma NC>2 /NOa ,the stable metabolic end products of NO, were measured with nitrate reductase. Plasma ET and cyclic guanosine monophosphate (cGMP ), a second messenger of NO , were measured with radioimmunoassay. The NOS activities in placental tissues were assayed by spectrophotometry.Results (1) The NOS activities in placental tissues were significantly lower in the PIH group than in the control group (P<0.01) . The activities of placental NOS in moderate or severe patients were lower than those of mild patients respectively (P<0.05, P<0.01). (2) The maternal andumbilical plasma concentration of NO2 /NO3 and cGMP in patients with PIH decreased significantly when compared with those of the control group(P<0.01, P<0.01), while the maternal and umbilical plasma ET levels in patients with PIH were markedly higher than those in the control group(P<0.01) . (3) The ratio of NO2~/NO3~ to ET was significantly lower in the maternal and umbilical plasma of patients with PIH than that of the control group (P<0.01, P<0.01), and it decreased with the severity of the disease. The ratio in moderate or severe patients was lower than that of mild patients respectively (P<0.01, P<0.01) . (4) In PEH group, no significant correlation between the NO2 /NOa and ET levels was found in both maternal and umbilical plasma (r =0.274, P>0.05-, r= 0.220, P>0.05). However, there was a significantly positive correlation between the NO2 /NOa and ET levels in the maternal and umbilical plasma of women from the control group (r =0.642, P<0.01: r=0.529, P<0.01) . (5) NO2~/NO3~ and ET levels of maternal plasma were higher than those of umbilical plasma in both groups (P<0.01, P<0.05) . There was a positive correlation about plasma NO2/NO3 and ET levels between mother and her fetus in both groups (P<0.01). (6) There was a negative correlation between the ratio of NC>2 /NOs to ET in the maternal plasma and the mean arterial blood pressure in PIH group(r = -0.629, P<0.01); There was a positive <|prrelation between the ratio and the weight of the newborn in PIH group (r=0.480, P<0.01). (7) There wasa negative correlation between the NOS activities in placental tissues and the mean arterial blood pressure in PIH group (r=-0.679, P<0.01)-, There was a positive correlation between the NOS activities and the weight of the newborn in PIH group (r=0.524, P<0.01) .Conclusion PIH may be related to decreasing synthesis and release of NO , and increasing ET poduction. The imbalance between NO and ET may be one of the important factors responsible for the development of PIH. The lower NO/ET ratio, the more severe the disease.