Normotensive Blood Pressure in Pregnancy

Abstract

Abstract-A successful pregnancy requires an accommodating environment. Salt and water availability are critical for plasma volume expansion. Any changes in sodium intake would alter aldosterone, a hormone previously described beneficial in pregnancy. To date, it remains ambiguous whether high aldosterone or high salt intake is preferable. We hypothesized that increased aldosterone is a rescue mechanism and appropriate salt availability is equally effective in maintaining a normotensive blood pressure (BP) phenotype in pregnancy. We compared normotensive pregnant women (n=31) throughout pregnancy with young healthy female individuals (n=31-62) and performed salt sensitivity testing within the first trimester. Suppression of urinary tetrahydro-aldosterone levels by salt intake as measured by gas chromatography-mass spectrometry and urinary sodium excretion corrected for creatinine, respectively, was shifted toward a higher salt intake in pregnancy (P<0.0001). In pregnancy, neither high urinary tetrahydro-aldosterone nor sodium excretion was correlated with higher BP. In contrast, in nonpregnant women, systolic BP rose with aldosterone (P<0.05). Testing the impact of salt on BP, we performed salt sensitivity testing in a final cohort of 19 pregnant and 24 nonpregnant women. On salt loading, 24-hour mean arterial pressure rose by 3.6±1.5 and dropped by -2.8±1.5 mm Hg favoring pregnant women (P<0.01; χ 2 =6.04; P<0.02). Our data suggest first that salt responsiveness of aldosterone is alleviated in conditions of pregnancy without causing aldosterone-induced hypertension. Second, salt seems to aid in BP lowering in pregnancy for reasons incompletely elucidated, yet involving renin suppression and potentially placental sensing mechanisms. and Blood Pressure in Pregnancy 363a homozygous loss-of-function mutation of the CYP11B2 on salt supplementation. 13To date, it remains uncertain whether high aldosterone levels and high salt intake are preferable in pregnancy. Given the current evidence, we hypothesized first that increased aldosterone is a rescue mechanism to maintain a BP reasonable for pregnancy, and second that appropriate salt availability is required to maintain a normotensive BP phenotype in pregnancy. As a corollary, inappropriately low aldosterone levels for a given gestational age might be counterbalanced by increased salt availability, thus substituting for the missing aldosterone effect. To verify our hypothesis, we have first studied the BP in women along pregnancy as related to salt intake and aldosterone levels and then compared first trimester salt sensitivity in pregnant women with young female nonpregnant individuals. Methods PatientsA first set of pregnant women from the Bernese pregnancy registry and nonpregnant women matched for age with a complete prospective sampling of serum and urine was used for the study. Clinical data were collected prospectively including standardized measurement of office BP and pregnancy outcome. Only normotensive pregnant women were included in the analysis. Visits we...

Physiological and Molecular Responses to Altered Sodium Intake in Rat Pregnancy

“…While nonpregnant HS rats tended to increase their BP, pregnant ones demonstrated a reduced BP. These findings in a rat model confirm our recent observations in pregnant women10 in a model with accurate Na + balance.…”

“…The enhanced spontaneous Na + intake is again in line with findings by our group in human pregnancy 10. Although exposed to an excessive Na + load, even pregnant animals of the HS group overall retained Na + .…”

“…The Na + intake was higher in pregnant animals in NS conditions resembling human behavior 10. No such differences regarding the Na + intake were present for the other diets.…”

“…As both high aldosterone levels and enhanced Na + intake have been linked to improved pregnancy outcome and reduced BP, it is unclear whether Na + or aldosterone is primarily responsible 7, 8, 9, 10, 11. A beneficial role of an increased Na + uptake during pregnancy was postulated,10 yet to what extent of Na + intake remains to be elucidated.…”

“…A beneficial role of an increased Na + uptake during pregnancy was postulated,10 yet to what extent of Na + intake remains to be elucidated. This information is relevant to advise national health authorities as to an appropriate Na + intake in pregnancy,12 while lowering Na + intake in pregnancy may even present a risk of adverse outcomes in healthy pregnancies to mothers and to their offspring 13, 14.…”