Assessment of endothelial nitric oxide synthase activity and stable nitric oxide metabolite levels in pregnant women with hypertensive disorders

The aim. To evaluate nitric oxide system parameters in pregnant women with hypertensive disorders by assessing the levels of stable NO metabolites and the activity of endothelial NO synthase. Materials and methods. A prospective controlled study included 65 pregnant women in the third trimester of pregnancy. The main group comprised 35 patients with gestational hypertension or preeclampsia, while the control group included 30 women with physiological pregnancies. Endothelial NO synthase (eNOS) activity was assessed spectrophotometrically by the stoichiometric oxidation of NADPH during the conversion of L-arginine to NO. The concentration of stable NO metabolites: nitrates and nitrites (NOx) was determined spectrophotometrically using the Griess reagent with preliminary reduction of nitrates to nitrites. For statistical analysis, the Mann-Whitney U test and Spearman’s rank correlation coefficient were applied. Results. In women with hypertensive disorders, eNOS activity was more than 3.5 times lower compared to the control group: 16.70 [16.10-17.60] vs. 60.45 [59.55-62.25] nmol/mg protein/min (p < 0.05). The NOx concentration was also nearly halved: 18.60 [17.80-19.25] vs. 34.80 [32.90-36.80] µmol/L (p < 0.05). A positive correlation was found between eNOS activity and NOx concentration (ρ = 0.72; p < 0.05), confirming their physiological interrelation. Conclusions. Pregnant women with hypertensive disorders demonstrated a marked decrease in eNOS activity and stable NO metabolite levels, indicating significantly reduced NO bioavailability. These findings are consistent with current concepts regarding the role of endothelial dysfunction and oxidative stress in the pathogenesis of preeclampsia. Assessment of these biomarkers may have promising value for early diagnosis, prognosis of pregnancy complications, and may provide a rationale for novel preventive strategies