(VP099) SEX DIFFERENCES IN THE NEURO-VASCULAR CONTROL OF BLOOD PRESSURE

Background:

Background: Premenopausal females typically present with lower blood pressures than similarly aged males. The neuro-vascular pathway, by which muscle sympathetic nerve activity (MSNA) elicits changes in peripheral blood flow to regulate blood pressure, has been implicated in this sex difference. However, potential sex differences in the neuro-vascular control of blood pressure during acute stress remain incompletely understood. Thus, we tested the hypothesis that stress-induced changes in blood pressure are blunted in females relative to males due to a reduction in neuro-vascular coupling in females.

METHODS AND RESULTS: We tested young healthy males (n=8) and females (n=8; 26±4yrs vs 23±2 years respectively). Mean arterial pressure (MAP; Finometer Midi, FMS), MSNA (microneurography; NeuroAmp, ADI) and peripheral blood flow (duplex ultrasound at the superficial femoral artery; [mL/min]) were measured continuously during 10 minutes of supine rest, a 6-minute cold pressor test (CPT), and 6-minute recovery period (REC). CPT and REC data were assessed in 60s bins; peak (i.e., during CPT) and nadir (i.e., during REC) MSNA bins were extracted for analysis. Blood flow data are quantified as the change relative to the previous condition.

At rest, MAP was higher in males than females (100±8 vs 90±7mmHg, respectively; P=0.03), whereas resting MSNA was not different between the sexes (14±7 vs 11±6bursts/100hb, P=0.44). Additionally, resting femoral blood flow was greater in males than females (244±57 vs 166±44mL/min, P=0.02). During the CPT, there was no effect of sex on MAP during peak MSNA (105±4 vs 98±7mmHg, P=0.20), nor was peak MSNA different between males and females (28±12 vs 27±15bursts/100hb, P=0.98). Decreases in femoral blood flow during peak MSNA were observed in males but not in females (-28±19 vs +7±21mL/min, P=0.02). During REC, MAP during nadir MSNA was not different between the sexes (101±6 vs 94±6mmHg, P=0.15), nor was nadir REC MSNA (16±7 vs 21±6bursts/100hb, P=0.28). However, during nadir MSNA, an increase in femoral blood flow was observed in males but not females (+22±16 vs +5±17mL/min, P=0.08).

Conclusion: In males, the neuro-vascular control of blood pressure was as expected: peak and nadir MSNA were each associated with decreases and increases in femoral blood flow, respectively, and ultimately increases and decreases in MAP. However, in females, the discordant changes in blood pressure and femoral blood flow indicate that blood pressure regulation occurs through mechanisms independent of the sympathetic neuro-vascular system.