Menstrual cycle elicits divergent forearm vascular responses to vestibular activation in humans

The menstrual cycle has been reported to alter mean arterial pressure (MAP), but not muscle sympathetic nerve activity (MSNA), during vestibular activation. Specifically, MAP responses to head-down rotation (HDR) are augmented during the mid-luteal (ML) phase compared to the early follicular (EF) phase in young, eumenorrheic women. The purpose of the present study was to determine if the menstrual cycle influences vestibular-mediated changes in limb blood flow. MSNA, MAP, heart rate, and limb blood flow responses to HDR were measured in 12 healthy women. Resting MSNA, MAP, heart rate, forearm blood flow and calf blood flow were not altered by the menstrual cycle. HDR elicited similar increases in MSNA during the EF (Delta3+/-1 bursts/min; P<0.05) and ML (Delta2+/-1 bursts/min; P<0.05) phase, but only increased MAP during the ML phase (Delta4+/-2 mmHg; P<0.05). HDR did not change heart rate during either the EF or ML phase. HDR elicited similar increases in calf vascular resistance during the EF (Delta6+/-2 mmHg/mL/100 mL/min; P<0.05) and ML (Delta7+/-2 mmHg/mL/100mL/min; P<0.05) phases of the menstrual cycle. In contrast, HDR increased forearm vascular resistance during the ML phase (Delta4+/-2 mmHg/mL/100mL/min; P<0.05), but not the EF phase (Delta0+/-2 mmHg/mL/100mL/min). These findings suggest an increased transduction of sympathetic nerve activity into forearm vascular resistance during the ML phase, and reveal the first recorded divergent vascular response to vestibular excitation in human limbs.