Sympathetic activity and baroreflex sensitivity in young women taking oral contraceptives

Background - We tested sympathetic and cardiovagal baroreflex sensitivity during the placebo or 'low-hormone' phase (LH) and 2 to 3 weeks later during the 'high-hormone' phase (HH) of oral contraceptive (OC) use in 9 women. Methods and Results - Sympathetic baroreflex sensitivity was assessed by intravenous doses of sodium nitroprusside and phenylephrine and defined as the slope relating muscle sympathetic nerve activity (by microneurography) and diastolic blood pressure. Cardiovagal baroreflex sensitivity was defined as the slope relating R-R interval and systolic blood pressure. No difference was observed for resting muscle sympathetic nerve activity or plasma norepinephrine levels. However, sympathetic baroreflex sensitivity was greater and mean arterial pressure was higher during the LH than in the HH phase. Similarly, cardiovagal baroreflex sensitivity was greater in the LH than in the HH phase. Conclusions - Sympathetic and cardiovagal baroreflex sensitivities change during the 28-day course of OC use. Furthermore, changes in baroreflex sensitivity with OC differ from changes in baroreflex sensitivity during the normal menstrual cycle.