Dept. of Exercise Science, Michigan Technological Univ., 1400 Townsend Drive, Houghton, MI 49931, USA.
Am J Physiol Regul Integr Comp Physiol. 2010 Jan;298(1):R9-R14. doi: 10.1152/ajpregu.00554.2009. Epub 2009 Oct 14.
Recent studies report that the menstrual cycle alters sympathetic neural responses to orthostatic stress in young, eumenorrheic women. The purpose of the present study was to determine whether oral contraceptives (OC) influence sympathetic neural activation during an orthostatic challenge. Based on evidence that sympathetic baroreflex sensitivity (BRS) is increased during the "low hormone" (LH) phase (i.e., placebo pills) in women taking OC, we hypothesized an augmented muscle sympathetic nerve activity (MSNA) response to orthostatic stress during the LH phase. MSNA, mean arterial pressure (MAP), and heart rate (HR) were recorded during progressive lower body negative pressure (LBNP; -5, -10, -15, -20, -30, -40 mmHg; 3 min/stage) in 12 healthy women taking OC (age 22 +/- 1 years). Sympathetic BRS was assessed by examining relations between spontaneous fluctuations of diastolic arterial pressure and MSNA. Subjects were examined twice: once during LH phase and once approximately 3 wk after LH during the "high hormone" phase (randomized order). Resting MSNA (10 +/- 2 vs. 13 +/- 2 bursts/min), MAP (85 +/- 3 vs. 84 +/- 3 mmHg), and HR (62 +/- 2 vs. 65 +/- 3 beats/min) were not different between phases. MSNA and HR increased during progressive LBNP (P < 0.001), and these increases were similar between phases. Progressive LBNP did not change MAP during either phase. Sympathetic BRS increased during progressive LBNP, but these responses were not different between LH and high hormone phases. In conclusion, our results demonstrate that OCs do not alter cardiovascular and sympathetic neural responses to an orthostatic challenge in young, healthy women.
近期研究报告指出，在年轻、月经规律的女性中，月经周期会改变其对直立性应激的交感神经反应。本研究旨在确定口服避孕药（OC）是否会影响直立性挑战期间的交感神经激活。基于在服用 OC 的女性中，交感神经压力反射敏感性（BRS）在“低激素”（LH）期（即安慰剂片）增加的证据，我们假设在 LH 期，对直立性应激的肌肉交感神经活动（MSNA）反应增强。在 12 名健康服用 OC 的女性（年龄 22 ± 1 岁）中，记录了 MSNA、平均动脉压（MAP）和心率（HR）在逐渐进行的下体负压（LBNP；-5、-10、-15、-20、-30、-40mmHg；3 分钟/阶段）期间的变化。通过检查舒张压自发性波动与 MSNA 之间的关系来评估交感神经 BRS。受试者在两次检查中接受了检查：一次是在 LH 期，一次是在大约 3 周后 LH 期的“高激素”期（随机顺序）。在两个阶段之间，静息 MSNA（10 ± 2 与 13 ± 2 爆发/分钟）、MAP（85 ± 3 与 84 ± 3mmHg）和 HR（62 ± 2 与 65 ± 3 次/分钟）没有差异。MSNA 和 HR 在进行性 LBNP 期间增加（P < 0.001），并且这些增加在两个阶段之间相似。在两个阶段中，进行性 LBNP 均未改变 MAP。随着进行性 LBNP，交感神经 BRS 增加，但这些反应在 LH 和高激素期之间没有差异。总之，我们的结果表明，OC 不会改变年轻健康女性对直立性挑战的心血管和交感神经反应。
