Beetroot juice lowers blood pressure and improves endothelial function in pregnant eNOS-/- mice: importance of nitrate-independent effects

Maternal hypertension associates with adverse pregnancy outcomes, including fetal growth restriction (FGR), due in part to reductions in nitric oxide (NO) bioavailability. We hypothesized that maternal dietary nitrate administration would increase NO bioavailability to reduce systolic blood pressure (SBP), improve vascular function and increase fetal growth in pregnant endothelial NO synthase knockout (eNOS-/- ) mice, which exhibit hypertension, endothelial dysfunction and FGR. Pregnant wildtype (WT) and eNOS-/- mice were supplemented with nitrate-containing beetroot juice (BRJ+) from gestational day (GD) 12.5. Control mice received an equivalent dose of nitrate-depleted BRJ (BRJ-) or normal drinking water. At GD17.5, maternal SBP was measured; at GD18.5, maternal nitrate/nitrite concentrations, uterine artery (UtA) blood flow and endothelial function were assessed, and pregnancy outcomes determined. Plasma nitrate concentrations were increased in both WT and eNOS-/-mice supplemented with BRJ+ (P<0.001), whereas nitrite concentrations were increased only in eNOS-/-mice (P<0.001). BRJ- did not alter nitrate/nitrite concentrations. SBP was lowered and UtA endothelial function enhanced in eNOS-/-mice supplemented with either BRJ+ or BRJ-, indicating nitrate-independent effects of BRJ. Improvements in endothelial function in eNOS-/-mice were abrogated in the presence of 25mM KCl, implicating enhanced EDH signalling in BRJ treated animals. At GD18.5, eNOS-/- fetuses were significantly smaller than WT animals (P<0.001), however BRJ supplementation did not affect fetal weight. BRJ may be a beneficial intervention in pregnancies associated with hypertension, endothelial dysfunction and reduced NO bioavailability. Our data showing biological effects of non-nitrate components of BRJ have implications for both interpretation of previous findings and in the design of future clinical trials.