Influence of the menstrual cycle on sympathetic activity, baroreflex sensitivity, and vascular transduction in young women

Background-Our goal was to test sympathetic and cardiovagal baroreflex sens itivity and the transduction of sympathetic traffic into vascular resistanc e during the early follicular (EF) and midluteal (ML) phases of the menstru al cycle. Methods and Result-Sympathetic baroreflex sensitivity was assessed by lower ing and raising blood pressure with intravenous bolus doses of sodium nitro prusside and phenylephrine, It was defined as the slope relating muscle sym pathetic nerve activity (MSNA; determined by microneurography) and diastoli c blood pressure. Cardiovagal baroreflex sensitivity was defined as the slo pe relating R-R interval and systolic blood pressure. Vascular transduction was evaluated during ischemic handgrip exercise and postexercise ischemia, and it was defined as the slope relating MSNA and calf vascular resistance (determined by plethysmography). Resting MSNA (EF, 1170 +/- 151 U/min; ML, 2252 +/- 251 U/min, P<0.001) and plasma norepinephrine levels (EF, 240 +/- 21 pg/mL; ML, 294 +/- 25 pg/mL; P=0.025) were significantly higher in the ML than in the EF phase. Furthermore, sympathetic bal orc flex sensitivity was greater during the ML than the EF phase in every subject (MSNA/diastoli c blood pressure slopes: EF, -4.15; FL, -5.42; P=0.005), No significant dif ferences in cardiovagal baroreflex sensitivity or vascular transduction wer e observed. Conclusions-The present study suggests that the hormonal fluctuations that occur during the normal menstrual cycle may alter sympathetic outflow but n ot the transduction of sympathetic activity into vascular resistance.