Abstract
Background. During pregnancy, systemic vascular resistance as well as vascular sensitivity to vasoconstrictive agents decreases in pregnant women. Methods and materials. The vascular resistance of the fetus is also maintained in the presence of low blood pressure. We believe that the main factors in this phenomenon are nitric oxide (NO), along with prostaglandin. NO is an unstable compound with a short half-life; it is easily converted to nitrite (NO2) and nitrate (NO3). Since NO cannot be precisely quantified, we measured the NO2 concentration in maternal blood just before and after delivery and compared it with the values of non-pregnant women. Results. NO2. concentrations in the 13 women who received cesarean deliveries under epidural anesthesia were not significantly changed by the anesthesia. Before anesthesia the NO2 concentration was 216 ± 115 pmol/mg protein, and after the induction of anesthesia, but before surgery, it was 218 ± 112 pmol/mg protein. The NO2 concentration then fell significantly after the surgery to 174 ± 75 pmol/mg protein (P < 0.05). In addition, after vaginal delivery, in 17 other patients we observed marked decreases in NO2 concentration, falling from 160 ± 82 to 125 ± 61 pmol/mg protein (p < 0.05). These values were significantly higher than those of nonpregnant women (3.4 ± 2.1 μM. 33 ± 22 pmol/mg protein) (p < 0.000I) Conclusion. These results suggest that NO contributes to the low vascular resistance observed in the mother and fetus during pregnancy.