Sex differences in sympathetic neural and limb vascular reactivity to mental stress in humans

Mental stress elicits a robust and consistent forearm vasodilation, but vascular reactivity in the calf remains inconsistent. It has been reported that calf vascular responses to MS may be sex dependent. Muscle sympathetic nerve activity (MSNA) is an important contributor to calf blood flow (CBF), yet the relations between sex, limb blood flow, and MSNA reactivity to mental stress have not been explored. We hypothesized that mental stress would elicit more dramatic vasodilation of the limbs in women and that this might be explained by reduced MSNA reactivity and/or blunted sympathetic vascular transduction. We measured heart rate (HR), mean arterial pressure (MAP), CBF, calf vascular conductance (CVC), forearm blood flow (FBF), forearm vascular conductance (FVC), and MSNA concurrently in 18 men (age: 23 ± 2 yr) and 16 women (age: 24 ± 2 yr) during 5 min of supine baseline and 5 min of mental stress. Mental stress elicited similar increases in MAP (Δ10 ± 1 vs. Δ11 ± 1 mmHg), HR (Δ16 ± 2 vs. Δ17 ± 2 beats/min), FBF (Δ81 ± 16% vs. Δ83 ± 15%), and FVC (Δ62 ± 13% vs. Δ65 ± 13%) in men and women, respectively. In contrast, CBF (Δ16 ± 8% vs. Δ37 ± 9%, P = 0.036) and CVC (Δ4 ± 7% vs. Δ24 ± 8%, P = 0.036) responses were exaggerated in women compared with men. Changes in FVC were significantly correlated with changes in CVC in women (r = 0.681, P = 0.004) but not in men. MSNA reactivity to mental stress was not different between men and women; however, changes in CVC were negatively correlated with increases of MSNA in men (r = -0.411, P = 0.045) but not in women. In conclusion, our data suggest different patterns of calf vascular reactivity to mental stress in men and women that might relate, in part, to altered vascular transduction of MSNA.