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Arginine Flux and Nitric Oxide Production During Human Pregnancy and Postpartum

Department of Obstetrics and Gynecology, Division of Meternal Fetal Medicine, Department of Pediatrics, Children's Nutrition Research Center, Baylor College of Medicine, Houston, Texas; University of Texas Medical Branch, Division of Maternal Fetal Medicine, 301 University Boulevard, Galveston, Texas 77555-0587 lgoodrum{at}utmb.edu

George R. Saade, MD

Michael A. Belfort, MD

Kenneth J. Moise, Jr., MD

Farook Jahoor, PhD

Department of Obstetrics and Gynecology, Division of Meternal Fetal Medicine, Department of Pediatrics, Children's Nutrition Research Center, Baylor College of Medicine, Houston, Texas

Objective: To compare second-trimester, third-trimester, and postpartum arginine flux and nitric oxide production using infusions of the stable isotope L-[¹⁵N₂]-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 µmol/kg of labeled arginine was administered, followed by an infusion at 4.95 µmol/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 midgestation 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 µmol/kg per hour, respectively; p < .01).

Conclusion: Arginine and nitric oxide production is higher in mid gestation. This suggests a role for nitric oxide in early cardiovascular adaptation in human gestations.

Key Words: Nitric oxide • arginine • stable isotopes

Journal of the Society for Gynecologic Investigation, Vol. 10, No. 7, 400-405 (2003)
DOI: 10.1016/S1071-55760300137-0


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