Sympathetic Neural Mechanisms in Normal and Hypertensive Pregnancy in Humans

Abstract

Background-Direct recordings from peripheral sympathetic nerves have shown an increased sympathetic drive in pregnancy-induced hypertension (PIH) and preeclampsia (PE). It is unknown whether sympathetic drive is altered in normal pregnancy, when arterial blood pressure can be normal or relatively low. The aim of this study was to measure and compare peripheral sympathetic discharge, its vasoconstrictor effect and its baroreceptor control, during pregnancy and postpartum in women with normal pregnancy (NP) and PIH and in normotensive nonpregnant (NN) women. Methods and Results-Twenty-one women with NP, 18 women with PIH, and 21 NN women had muscle sympathetic nerve activity assessed from multiunit discharges (MSNA) and from single units with defined vasoconstrictor properties (s-MSNA). The s-MSNA in NP (38Ϯ6.6 impulses/100 beats) was greater (PϽ0.05) than in NN women (19Ϯ1.8 impulses/100 beats) despite similar age and body weight but less than in PIH women (PϽ0.001) (146Ϯ23.5 impulses/100 beats). MSNA followed a similar trend. Cardiac baroreceptor reflex sensitivity (BRS) was impaired in NP and PIH women relative to NN. After delivery, sympathetic activity decreased to values similar to those obtained in NN, and there was an increase in BRS. In women with NP, the decrease in sympathetic output occurred despite an insignificant change in blood pressure. Conclusions-Central sympathetic output was increased in women with normal pregnancy and was even greater in the hypertensive pregnant group. The findings suggest that the moderate sympathetic hyperactivity during the latter months of normal pregnancy may help to return the arterial pressure to nonpregnant levels, although when the increase in activity is excessive, hypertension may ensue. (Circulation. 2001;104:2200-2204.)

Effect of changes in body posture on vasoactive hormones in pre-eclamptic women

“…There is evidence for perturbations in neurohormonal indices, particularly activation of the sympathetic nervous system. [5][6][7] If indeed there are important neurohormone alterations in pre-eclampsia, we hypothesized that these abnormalities might become more obvious with some body positions than in others. Accordingly, we studied our women in different body positions with careful attention to matching and time of day to avoid the effect of diurnal patterns.…”

“…[1][2][3][4] Support for a role of the sympathetic nervous system in the development and maintenance of hypertension in pre-eclampsia has increased in recent years. In particular, recordings of sympathetic outflow to skeletal muscle 5,6 and measurements of plasma norepinephrine levels through 24 h 7 have both pointed to heightened sympathetic activity in the pre-eclamptic state. We decided to test the hypothesis that changes in body posture might magnify differences in neurohormonal indices, especially plasma norepinephrine, between preeclamptic women and controls.…”

Longitudinal changes in QT interval variability and rate adaptation in pregnancies with normal and abnormal uterine perfusion

“…[3][4][5] Multiple factors might be involved in the arrhythmogenesis, including increased hemodynamic stress on the cardiovascular system. Ventricular repolarization might be altered during pregnancy because of changes in circulating hormones, electrolyte levels 6 and increased sympathetic neural outflow, 7 thereby inducing ventricular arrhythmias. Ventricular repolarization dynamics can be assessed globally through QT interval (variability) in the body surface electrocardiograph (ECG).…”

Relaxin increases sympathetic nerve activity and activates spinally projecting neurons in the paraventricular nucleus of nonpregnant, but not pregnant, rats

“…These adaptations are consistent with increased orthostatic hypotension in P women and greater sensitivity to the hypotensive effects of hemorrhage in pregnancy (3). However, even though the RVLM is under greater GABAergic inhibition, baseline SNA is elevated in conscious P rats (31) and women (17,20).Parvocellular presympathetic neurons in the PVN receive input from the SFO (9) and send excitatory projections to preganglionic sympathetic neurons in the intermediolateral cell column of the spinal cord (IML), either directly or indirectly via a pathway that includes a synapse in the RVLM (1,46). In other physiological and also pathophysiological states, such as dehydration, hypertension, and heart failure, activation of presympathetic parvocellular neurons in the PVN likely contribAddress for reprint requests and other correspondence: C. M. Heesch,…”

“…These adaptations are consistent with increased orthostatic hypotension in P women and greater sensitivity to the hypotensive effects of hemorrhage in pregnancy (3). However, even though the RVLM is under greater GABAergic inhibition, baseline SNA is elevated in conscious P rats (31) and women (17,20).…”