Muscle sympathetic nerve activity and volume-regulating factors in healthy pregnant and nonpregnant women.

Healthy, normotensive human pregnancies are associated with striking increases in both plasma volume and vascular sympathetic nerve activity (SNA). In nonpregnant humans, volume-regulatory factors including plasma osmolality, vasopressin, and the renin-angiotensin-aldosterone system have important modulatory effects on control of sympathetic outflow. We hypothesized that pregnancy would be associated with changes in the relationships between SNA (measured as muscle SNA) and volume-regulating factors, including plasma osmolality, plasma renin activity, and arginine vasopressin (AVP). We studied 46 healthy, normotensive young women (23 pregnant and 23 nonpregnant). We measured SNA, arterial pressure, plasma osmolality, plasma renin activity, AVP, and other volume-regulatory factors in resting, semirecumbent posture. Pregnant women had significantly higher resting SNA (38 ± 12 vs. 23 ± 6 bursts/min in nonpregnant women), lower osmolality, and higher plasma renin activity and aldosterone (all < 0.05). Group mean values for AVP were not different between groups [4.64 ± 2.57 (nonpregnant) vs. 5.17 ± 2.03 (pregnant), > 0.05]. However, regression analysis detected a significant relationship between individual values for SNA and AVP in pregnant ( = 0.71, < 0.05) but not nonpregnant women ( = 0.04). No relationships were found for other variables. These data suggest that the link between AVP release and resting SNA becomes stronger in pregnancy, which may contribute importantly to blood pressure regulation in healthy women during pregnancy. Sympathetic nerve activity and blood volume are both elevated during pregnancy, but blood pressure is usually normal. Here, we identified a relationship between vasopressin and sympathetic nerve activity in pregnant but not nonpregnant women. This may provide mechanistic insights into blood pressure regulation in normal pregnancy and in pregnancy-related hypertension.