Previous human studies have shown that large-artery stiffness contributes to an age-related decrease in cardiovagal baroreflex sensitivity. Whether this is also true with sympathetic baroreflex sensitivity is unknown. We tested the hypothesis that sympathetic baroreflex sensitivity is associated with the stiffness of baroreceptor segments (the carotid artery and the aorta) in elderly individuals, and that sex affects this relationship. Sympathetic baroreflex sensitivity was assessed from the spontaneous changes in beat-by-beat diastolic pressure and corresponding muscle sympathetic nerve activity (microneurography) during supine rest in 30 men [69±1 (mean±SEM) years] and 31 women (68±1 years). Carotid artery stiffness (B-mode ultrasonography) and aortic stiffness (magnetic resonance imaging) were also determined. We found that elderly women had lower sympathetic baroreflex sensitivity than elderly men (–2.33±0.25 vs. –3.32±0.25 bursts·100 beats–1·mmHg–1; P=0.007). β-stiffness indices of the carotid artery and the aorta were greater in elderly women than in men (6.68±0.48 vs. 5.10±0.50 and 4.03±0.47 vs. 2.68±0.42; both P<0.050). Sympathetic baroreflex sensitivity was inversely correlated with carotid artery stiffness in both men and women (r=0.49 and 0.50, both P<0.05), while this relation was shifted in parallel upward (towards a reduced sensitivity) in women with no changes in the slope (0.26 vs. 0.24 a.u.). Sympathetic baroreflex sensitivity and aortic stiffness showed similar trends. Thus, barosensory artery stiffness seems to be one independent determinant of sympathetic baroreflex sensitivity in elderly men and women. The lower sympathetic baroreflex sensitivity in elderly women may predispose them to an increased prevalence of hypertension.
Key points• Sympathetic activity has been reported to increase in normotensive pregnant women, and to be even greater in women with gestational hypertension and preeclampsia at term.• Whether sympathetic overactivity develops early during pregnancy, remaining high throughout gestation, or whether it only occurs at term providing the substrate for hypertensive disorders is unknown.• We found that vasomotor sympathetic activity was markedly greater, diastolic pressure trended lower, total peripheral resistance decreased, sympathetic vascular transduction was blunted, and renin and aldosterone both were higher during early pregnancy (i.e. ≤8 weeks of gestation) than pre-pregnancy.• It is suggested that sympathetic activation is a common characteristic of early pregnancy in normotensive women.• These results help us better understand blood pressure control mechanisms during normal pregnancy in humans.Abstract Sympathetic activity has been reported to increase in normotensive pregnant women, and to be even greater in women with gestational hypertension and preeclampsia at term. Whether sympathetic overactivity develops early during pregnancy, remaining high throughout gestation, or whether it only occurs at term providing the substrate for hypertensive disorders is unknown. We tested the hypothesis that sympathetic activation occurs early during pregnancy in humans. Eleven healthy women (29 ± 3 (SD) years) without prior hypertensive pregnancies were tested during the mid-luteal phase (PRE) and early pregnancy (EARLY; 6.2 ± 1.2 weeks of gestation). Muscle sympathetic nerve activity (MSNA) and haemodynamics were measured supine, at 30 deg and 60 deg upright tilt for 5 min each. Blood samples were drawn for catecholamines, direct renin, and aldosterone. MSNA was significantly greater during EARLY than PRE (supine: 25 ± 8 vs. 14 ± 8 bursts min −1 , 60 deg tilt: 49 ± 14 vs. 40 ± 10 bursts min −1 ; main effect, P < 0.05). Resting diastolic pressure trended lower (P = 0.09), heart rate was similar, total peripheral resistance decreased (2172 ± 364 vs. 2543 ± 352 dyne s cm −5 ; P < 0.05), sympathetic vascular transduction was blunted (0.10 ± 0.05 vs. 0.36 ± 0.47 units a.u.−1 min −1 ; P < 0.01), and both renin (supine: 27.9 ± 6.2 vs. 14.2 ± 8.7 pg ml −1 , P < 0.01) and aldosterone (supine: 16.7 ± 14.1 vs. 7.7 ± 6.8 ng ml −1 , P = 0.05) were higher during EARLY than PRE. These results suggest that sympathetic activation is a common characteristic of early pregnancy in humans despite reduced diastolic pressure and total peripheral resistance. These observations challenge conventional thinking about blood pressure regulation during pregnancy, showing marked sympathetic activation occurring within the first few weeks of conception, and may provide the substrate for pregnancy induced cardiovascular complications.
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