Oral Contraceptives Do Not Alter Sympathetic Neural Control of Blood Pressure in Young, Healthy Women

Abstract

BackgroundSympathetic nerve activity and its effect on blood pressure are altered by female sex hormones; however, this effect differs between exogenous and endogenous hormones. With oral contraceptive (OC) use, cross‐sectional data has demonstrated higher blood pressure (BP) with no corresponding change in muscle sympathetic nerve activity (MSNA). This results in a higher BP/MSNA ratio with OC use although contributing mechanisms are unclear. The higher BP/MSNA ratio in women on OC suggests OC use may limit the ability of sympathetic baroreflex (sBRS) to suppress MSNA. Alternatively, a “burst” of MSNA could result in a greater change in BP (augmented neurovascular transduction).ObjectiveThe goal of this study was to determine if OCs alter blood pressure control through autonomic mechanisms in young women.HypothesesWe hypothesized (1) sympathetic baroreflex sensitivity would be decreased and (2) neurovascular transduction would be augmented in women on OCs compared to naturally cycling women.MethodsWe conducted a retrospective analysis of data from healthy young women taking OCs (n=30, 25±4yrs) and with natural menstrual cycles (n=23, 27±4yrs). Women were studied during the placebo phase of OC use or early follicular phase of the menstrual cycle. Heart rate (HR, 3‐lead ECG), BP (arterial line or photoplethysmography for both groups), and MSNA (peroneal nerve microneurography) were measured over 5 min of quiet rest and data were analyzed for measures of sBRS and neurovascular transduction (Ensemble, Elucimed Inc., Dunedin, New Zealand).ResultsGroups did not differ in mean BP (Control: 94±9, OC:92±8mmHg, p=0.60), or HR (Control: 61±8, OC: 62±9 bpm, p=0.57), but women on OCs had lower MSNA than controls (Control: 16±6, OC: 12±5 bursts/min, p=0.006). There were no significant differences in TPR (Control: 0.022±0.005, OC: 0.020±0.005 mmHg min/L, p=0.12), however there was a trend toward increased cardiac output in women on OCs (Control: 4.45±0.86, OC: 4.94±1.02 L/min, p=.068). There were no significant group differences in sBRS (Control: −4.3±2.1, OC: −4.0±2.6 bursts ·100 heartbeats−1 ·mmHg−1, p=0.79), or neurovascular transduction (Control: 0.093±0.042, OC: 0.091±0.058 ΔmmHg/% burst area, p=0.87). Furthermore, there were no significant correlations between BP and BRS, MSNA, or transduction in either group.ConclusionsOur data strengthen previous findings which have shown women taking OCs have higher BP for a given MSNA. The analysis we performed build on these results and demonstrate that the increase in BP for a given MSNA in women taking OCs is not due to attenuated sBRS or augmented neurovascular transduction. This work has advanced our understanding of the alteration of blood pressure with OC use in young women.Support or Funding InformationNIH HL083947