Gender-related differences in the sympathetic vasoconstrictor drive of normal subjects

The risk of cardiovascular disease has been linked to sympathetic activation and its incidence is known to be lower in women than in men. However, the effect of gender on the sympathetic vasoconstrictor drive has not yet been established. In the present study, we investigated whether there is a gender difference in MSNA (muscle sympathetic nerve activity) and blood flow, and to determine the mechanisms involved. We examined 68 normal subjects, 34 women and 34 men, matched for age, BMI (body mass index) and waist circumference. MSNA was measured as the mean frequency of single units (s-MSNA) and as multi-unit bursts (m-MSNA) from the peroneal nerve simultaneously with its supplied muscle CBF (calf blood flow). Women had lower (P=0.0007) s-MSNA (24±2.0 impulses/100 cardiac beats) than men (34±2.3 impulses/100 cardiac beats), and a greater baroreceptor reflex sensitivity controlling efferent sympathetic nerve activity than men. The sympathetic activity was inversely and directly correlated respectively, with CBF (P=0.03) and CVR (calf vascular resistance; P=0.01) in men only. The responses of an increase in CVR to cold pressor and isometric handgrip tests were significantly smaller in women (P=0.002) than in men, despite similar increases in efferent sympathetic nerve activity. Women had a lower central sympathetic neural output to the periphery, the mechanism of which involved differences in central and reflex control, as well as a lower vasoconstrictor response to this neural output. It is suggested that this may partly explain the observed lower incidence of cardiovascular events in women compared with men.