Neural control of blood pressure during pregnancy in humans

Abstract

Purpose: Previous microneurographic studies found that muscle sympathetic nerve activity (MSNA) increased in normotensive pregnant women and was even greater in women with gestational hypertension and preeclampsia during the third trimester. It is possible that sympathetic activation during the latter months of normal pregnancy helps return arterial pressure to non-pregnant levels. However, when the increase in sympathetic activity is excessive, hypertension ensues. The key question that must be addressed is whether sympathetic activation develops early during pregnancy and remains high throughout gestation, or whether this sympathetic overactivity only occurs at term, providing the substrate for preeclampsia and other pregnancy-associated cardiovascular complications.

Methods: This was a literature review of autonomic neural control during pregnancy.

Results: Recent work from our laboratory and other laboratories showed that in healthy women resting MSNA increased in early pregnancy, increased further in late pregnancy, and returned to the pre-pregnancy levels shortly after delivery. We found that women who exhibited excessive sympathetic activation during the first trimester, before any clinical signs and symptoms appeared, developed gestational hypertension at term. We also found that the level of corin, an atrial natriuretic peptide-converting enzyme, was increased in the maternal circulation, especially during late pregnancy, as a homeostatic response to elevated sympathetic activity.

Conclusion: These findings provide important insight into the neural mechanisms underlying hypertensive disorders during pregnancy. With this knowledge, early prevention or treatment targeted to the appropriate pathophysiology may be initiated, which may reduce maternal and fetal death or morbidity, as well as cardiovascular risks in women later in life.

Keywords: Blood pressure; Hemodynamics; Muscle sympathetic nerve activity; Pregnancy.

Conflict of interest statement

Competing Interests

There is no conflict of interest to disclose.

Figures

Fig. 1

Time-course changes in resting MSNA during normotensive pregnancy in 21 healthy women. Sympathetic activity increased during early pregnancy, further increased during late pregnancy, and returned to prepregnancy levels 6–10 weeks after delivery. Values are means ± SEM. * Significant difference vs. pre-pregnancy at P

Fig. 2

Time-course changes in a) systolic blood pressure, b) diastolic blood pressure and c) heart rate at rest in normal pregnancy. Values are means ±SEM. * Significant difference vs. pre-pregnancy at P

Fig. 3

MSNA responses to upright tilt in women before, during and after normotensive pregnancy. Values are mean ±SEM * Significant difference vs. pre and post-pregnancy at P

Fig. 4

Sympathetic baroreflex sensitivity during pre and early pregnancy in healthy women in the supine position and during 30-degree and 60-degree head-up tilt. Values are means ± SD (manuscript in preparation)

Fig. 5

Changes in a) limb (forearm) vascular resistance, b) plasma norepinephrine concentration, c) direct renin concentration and d) aldosterone concentration during normal pregnancy in Caucasian and Asian women. Values are means ± SEM. * Significant difference vs. Caucasian women at P