Sympathetic activity and baroreflex sensitivity in young women taking oralcontraceptives

Background-We tested sympathetic and cardiovagal baroreflex sensitivity dur ing the placebo or "low-hormone" phase (LH) and 2 to 3 weeks later during t he "high-hormone" phase (HH) of oral contraceptive (OC) use in 9 women. Methods and Results-Sympathetic baroreflex sensitivity was assessed by intr avenous 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 norep inephrine levels. However, sympathetic baroreflex sensitivity was greater a nd mean arterial pressure was higher during the LH than in the HH phase. Si milarly, cardiovagal baroreflex sensitivity was greater in the LH than in t he HH phase. Conclusions-Sympathetic and cardiovagal baroreflex sensitivities change dur ing the 28-day course of OC use. Furthermore, changes in baroreflex sensiti vity with OC differ from changes in baroreflex sensitivity during the norma l menstrual cycle.