Sympathetic neural mechanisms in normal and hypertensive pregnancy in humans

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 no rmal pregnancy, when arterial blood pressure can be normal or relatively lo w, 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 dischar ges (MSNA) and from single units with defined vasoconstrictor properties (s -MSNA). The s-MSNA in NP (38 +/-6.6 impulses/100 beats) was greater (P <0.0 5) than in NN women (19 +/-1.8 impulses/100 beats) despite similar age and body weight but less than in PIH women (P <0.001) (146 +/- 23.5 impulses/10 0 beats). MSNA followed a similar trend. Cardiac baroreceptor reflex sensit ivity (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 sympat hetic output occurred despite an insignificant change in blood pressure. Conclusions-Central sympathetic output was increased in women with normal p regnancy and was even greater in the hypertensive pregnant group. The findi ngs suggest that the moderate sympathetic hyperactivity during the latter m onths of normal pregnancy may help to return the arterial pressure to nonpr egnant levels, although when the increase in activity is excessive, hyperte nsion may ensue.