RESUMO
OBJECTIVE: To determine the relationship between gestational age or the Liley index (the severity of fetal hemolysis) and the amniotic fluid total nitrite (NOx), cyclic guanosine 3',5 'monophosphate (cGMP) and dimethylarginine (DMA) concentrations. We hypothesized that the concentrations of these components change because of fetal growth or adaptation to fetal anemia. STUDY DESIGN: Amniotic fluids (n=64) were obtained between 23 and 37 weeks from fifty-three patients at risk for alloimmunization. Amniotic fluids from the pregnancies with a Liley index=1 were considered as controls (n=17). Creatinine (C, microMol) was determined with the Jaffé reagent, nitrite (NOx, microMol) with the Griess reagent, cGMP (nMol) by an enzyme immunoassay and DMA (microMol) after HPLC. Multiple regression analysis was used for separating the effects of growth and the estimated degree of anemia. RESULTS: The concentration of NOx, cGMP and DMA was not related to the Liley index or whether or not the fetuses needed blood transfusions. The concentrations of creatinine (C), NOx and cGMP increased during pregnancy (in weeks;W) (C=-69.2+6.28W; r2=0.532; P<0.0001, NOx=-17.6+1.29W; r2=0.106; P=0.01, cGMP=-20.9+1.05W; r2=0.414; P<0.0001). The DMA concentration (3.8+/-0.8(SD) and the NOx/creatinine ratio (181+/-110 mM/M) did not change with gestational age. The cGMP/creatinine ratios (microM/M) increased (cGMP/C=-41.8+4.31W; r2=0.134; P=0.007) whereas the DMA/creatinine ratio (mM/M) declined during pregnancy (DMA/C=73.1-1.34W; r2=0.278; P=0.0002). Consequently, the NOx/DMA and cGMP/DMA ratios increased (NOx/DMA=-6.96+0.43W; r2=0.105; P=0.02, cGMP/DMA=-5.9+0.29W; r2=0.391; P<0.0001). CONCLUSIONS: The concentrations in amniotic fluid of cGMP and NOX, but not of DMA increase during gestation. The cGMP/creatinine ratio increases also whereas that of DMA decreases. The changes in products of the NO-cGMP pathway are independent of mild to moderate fetal hemolysis and may result from fetal growth as well as from reduced inhibition of NO synthase by DMA. Gestational age related effects should be taken into account when analyzing nitric oxide metabolites in amniotic fluids.
