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Blunted increases in leg vascular conductance to carotid baroreflex activation in young women

      The arterial baroreflex plays a critical role in the beat-to-beat regulation of arterial blood pressure (BP) primarily via reflex modulation of sympathetic nerve activity and vascular conductance. Limited studies focusing on sex differences have reported similar sympathetic baroreflex sensitivity at rest between young normotensive men and women. These data are interesting given recent evidence suggesting that resting arterial BP is differentially regulated in young men and women. Importantly, while the overall baroreflex control of muscle sympathetic nerve activity is critical, the actual vascular response evoked by baroreflex-mediated alterations in sympathetic nerve activity is essential for the ultimate control of BP. Consequently, we sought to examine possible sex-related differences in arterial baroreflex control of leg vascular conductance (LVC) in humans. To begin to address this question, mean BP, femoral blood flow, and LVC responses to carotid baroreflex activation were characterized in five young men and six young women at rest using 5 s pulses of neck suction (−60 Torr). In response to neck suction, increases in LVC were significantly greater in men compared to women (+20±5% men vs. +5±3% women, P<0.05). Likewise, men exhibited greater increases in femoral blood flow to neck suction when compared to women (+13±4% men vs. +1±4% women, P<0.05). Interestingly, despite the blunted increase in LVC, mean BP responses to neck suction were significantly greater in women compared to men. These preliminary findings suggest that the ability of the carotid baroreflex to regulate vascular conductance appears to be reduced in young women compared to men. The lack of a concomitant reduction in carotid baroreflex mediated BP responses in women suggests inherent sex differences in the mechanisms by which the arterial baroreflex regulates BP.
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