Women Have Lower Tonic Autonomic Support of Arterial Blood Pressure and Less Effective Baroreflex Buffering Than Men

Background: Short-term and tonic regulation of arterial blood pressure (BP) differ in premenopausal women and men of similar age. The autonomic nervous system (ANS) plays a critical role in BP regulation.

Methods And Results: To test the hypothesis that women have lower tonic ANS support of BP (reduction in intra-arterial BP during acute ganglionic blockade [GB] with intravenous trimethaphan) and less effective baroreflex buffering (BRB) of BP (potentiation of the systolic BP [SBP] response to bolus phenylephrine during versus before GB) than men, 51 healthy adults, 22 premenopausal women (aged 28+/-1 years, mean+/-SE) and 29 men (aged 27+/-1 years), were studied. Women had lower baseline SBP and plasma catecholamine concentrations than men (P<0.05). Tonic ANS support of BP was approximately 50% to 65% lower in the women (P<0.001). The reductions in BP during GB were related to baseline plasma catecholamine concentrations (r=-0.31 to -0.41, P<0.05). Acute BRB of BP was 47% smaller in the women (3.3+/-0.5 versus 6.3+/-0.9, P=0.006) and was related to the SBP responses to phenylephrine before GB (R2=0.71, P<0.0001). Systemic alpha1-adrenergic vascular responsiveness (SBP response to bolus phenylephrine during GB) was not different (women 21.5+/-2 mm Hg versus men 18.6+/-2 mm Hg, P=0.3).

Conclusions: Premenopausal women have lower tonic sympathoadrenal activity-related ANS support of BP and less effective BRB of BP than men of similar age. The lower tonic ANS support of BP could contribute to the lower chronic BP levels of premenopausal women, whereas attenuated BRB of BP may help explain less effective BP regulation in women in response to vasoactive drugs and acute stress.