Sex differences in sympathetic neurovascular and neurohemodynamic relationships during cold pressor test.

ABSTRACT

Muscle sympathetic nerve activity (MSNA) affects vascular resistance differently in women and men. However, whether this sex difference persists during pronounced increases in MSNA remains unclear. Therefore, the purpose of this study was to examine sex differences in neurovascular transduction during cold pressor test (CPT)-mediated sympathoexcitation. Integrated peroneal MSNA (microneurography) was measured at rest and during a 3-min CPT in young healthy women (n = 11) and men (n = 10). Mean arterial pressure (MAP) was measured beat-by-beat (Finometer), and superficial femoral artery blood flow was measured using duplex ultrasound. Femoral vascular resistance (FVR) was quantified as MAP/femoral blood flow (mmHg/mL/min). Baseline MSNA was similar between women and men (14 ± 9 vs. 15 ± 9 bursts/100 heartbeat, respectively; P = 0.83), whereas MAP was lower (86 ± 7 vs. 92 ± 4 mmHg; P = 0.047), and FVR was greater in women than men (0.54 ± 0.16 vs. 0.36 ± 0.15 mmHg/mL/min; P = 0.02). CPT-induced increases in MSNA were similar between the sexes (19 ± 11 vs. 26 ± 14 bursts/100 heartbeat; P = 0.26) whereas increases in MAP (7 ± 3 vs. 10 ± 3 mmHg; P = 0.03) and FVR (3.2 ± 18.6 vs. 26.8 ± 12.8%; P < 0.01) were smaller in women than in men. Within men, CPT- induced increases in MSNA predicted increases in MAP (R2 = 0.51, P = 0.02) and FVR (R2 = 0.49, P = 0.02). However, MSNA did not predict MAP (R2 = 0.11, P = 0.35) or FVR (R2 = 0.07, P = 0.46) in women. Our findings demonstrate that men experience robust CPT-induced MAP responses that are driven by both neurovascular (MSNA-FVR) and neurohemodynamic (MSNA-MAP) coupling. These relationships were not observed in women, indicating that even during pronounced increases in sympathetic outflow, MSNA is not predictive of vascular nor blood pressure outcomes in young healthy women.