Arginine flux and nitric oxide production during human pregnancy and postpartum.
OBJECTIVE
To compare second-trimester, third-trimester, and postpartum arginine flux and nitric oxide production using infusions of the stable isotope L-[(15)N(2)]-arginine in normal human gestation.


METHODS
Kinetic measurements were made in pregnant volunteers with uncomplicated singleton gestations in mid gestation, late gestation, and more than 8 weeks postpartum. A bolus of 4.95 micromol/kg of labeled arginine was administered, followed by an infusion at 4.95 micromol/kg per hour for 6 hours. The isotopic enrichment of plasma arginine and nitrite or nitrate (NO(x)) was determined by gas chromatography, mass spectrometry, or both. We used the Kolmogorov-Smirnov test for normality, repeated-measures analysis of variance, and Newman-Keuls test. P <.05 denoted statistical significance.


RESULTS
The rate of turnover of the intravascular NO(x) pool was significantly higher in mid gestation compared with late gestation and almost reached statistical significance when compared with postpartum values (6.2 +/- 0.9 versus 4.3 +/- 0.8 [P <.02] versus 3.7 +/- 2.1% pool/hour; P =.08). Arginine flux was significantly higher in early compared with late gestation and postpartum (107.8 +/- 13.9 versus 72.5 +/- 16.1 versus 82 +/- 8.8 micromol/kg per hour, respectively; P <.01).


CONCLUSIONS
Arginine and nitric oxide production is higher in mid gestation. This suggests a role for nitric oxide in early cardiovascular adaptation in human gestations.
D000293:Adolescent; D000328:Adult; D001120:Arginine / Q000008:administration & dosage / Q000378:metabolism*; D005260:Female; D005865:Gestational Age; D006801:Humans; D007700:Kinetics; D009569:Nitric Oxide / Q000096:biosynthesis*; D009587:Nitrogen Isotopes; D049590:Postpartum Period; D011247:Pregnancy
D009587:Nitrogen Isotopes; D009569:Nitric Oxide; D001120:Arginine