Influence of the Menstrual Cycle on Sympathetic Activity, Baroreflex Sensitivity, and Vascular Transduction in Young Women

TLDR

The study aimed to assess sympathetic and cardiovagal baroreflex sensitivity and sympathetic transduction into vascular resistance across early follicular and midluteal menstrual phases. Sympathetic and cardiovagal baroreflex sensitivities were quantified as slopes between MSNA and diastolic blood pressure, and R‑R interval and systolic blood pressure, respectively, while vascular transduction was measured as the slope between MSNA and calf vascular resistance during handgrip exercise and post‑exercise ischemia. Resting sympathetic activity and norepinephrine were higher in the midluteal phase, and sympathetic baroreflex sensitivity was greater, whereas cardiovagal baroreflex sensitivity and vascular transduction did not differ between phases.

Abstract

Background —Our goal was to test sympathetic and cardiovagal baroreflex sensitivity and the transduction of sympathetic traffic into vascular resistance during the early follicular (EF) and midluteal (ML) phases of the menstrual cycle. Methods and Results —Sympathetic baroreflex sensitivity was assessed by lowering and raising blood pressure with intravenous bolus doses of sodium nitroprusside and phenylephrine. It was defined as the slope relating muscle sympathetic nerve activity (MSNA; determined by microneurography) and diastolic blood pressure. Cardiovagal baroreflex sensitivity was defined as the slope 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 baroreflex sensitivity was greater during the ML than the EF phase in every subject (MSNA/diastolic blood pressure slopes: EF, −4.15; FL, −5.42; P =0.005). No significant differences in cardiovagal baroreflex sensitivity or vascular transduction were observed. Conclusions —The present study suggests that the hormonal fluctuations that occur during the normal menstrual cycle may alter sympathetic outflow but not the transduction of sympathetic activity into vascular resistance.