Background/objectives: Nitric oxide (NO) has been proposed as a mediator of vascular expansion during pregnancy. Inability to increase NO synthesis and/or production of its precursor, arginine, may be a contributor to pregnancy-induced hypertension or preeclampsia. Because maternal weight is associated with blood pressure and risk of preeclampsia during pregnancy, it may also influence arginine and/or NO production. The purpose of this study was to determine the in vivo arginine production and NO synthesis rate in pregnant women with normal (n=10) and low (n=10) body mass indices (BMIs).
Subjects/methods: Arginine flux and NO synthesis rate were measured in the postabsorptive state with constant infusions of 15N2-arginine and 13C,2H4-citrulline. Plasma concentrations of arginine and NO metabolites were also measured. Kinetic parameters were correlated to maternal variables, gestational age, birth weight and blood pressure.
Results: Endogenous arginine flux was significantly faster in the low-BMI compared with normal-BMI women in the first trimester (63.1+/-3.4 vs 50.2+/-2.0 micromol/kg per h, P<0.01), but not in the second. Plasma NO concentration was higher (44.7+/-5.3 vs 30.4+/-1.9 micromol/l, P=0.03) and its rate of synthesis trended faster in the low-BMI compared with normal-BMI group in the second trimester. Maternal weight and BMI were negatively correlated with arginine flux in both trimesters and NO synthesis in the second trimester.
Conclusions: These findings suggest, but do not prove, that maternal BMI may be a factor in the ability to produce NO during pregnancy and may be one way by which BMI influences blood pressure during pregnancy.