α1-Adrenoreceptor activity does not explain lower morning endothelial-dependent, flow-mediated dilation in humans

Early morning reduction in endothelium-dependent, flow-mediated dilation (FMD) may contribute to the high incidence of sudden cardiac death at this time of day. The mechanisms underpinning diurnal variation in FMD are unclear, but potentially relate to a circadian rhythm in sympathetic nerve activity. We hypothesized that blockade of α1-mediated sympathetic nerve activity would act to attenuate the diurnal variation in FMD. In a randomized and placebo-controlled design, we measured brachial artery FMD in 12 participants (mean age = 26 yr, SD = 3) at 0600 and 1600 after ingestion of an α1-blocker (prazosin, 1 mg/20 kg body mass) or placebo. Arterial diameter and shear rate were assessed using edge-detection software. Heart rate and blood pressure were also measured. Data were analyzed using linear mixed modeling. Following placebo, FMD was 8 ± 2% in the morning compared with 10 ± 3% in the afternoon ( P = 0.04). Blockade with prazosin led to a slight but nonsignificant increase in morning FMD ( P = 0.24) and a significant ( P = 0.04) decrease in afternoon FMD, resulting in no diurnal variation ( P = 0.20). Shear rate did not differ in the morning or afternoon under either condition ( P > 0.23). Blood pressure was lower following prazosin compared with placebo ( P < 0.02), an effect that was similar at both times of day ( P > 0.34). Heart rate and norepinephrine levels were higher in the afternoon following prazosin. These data indicate that α1-adrenoreceptor activity does not explain lower morning endothelium-dependent FMD.

Download Full-text

Chemical stimulation of the locus coeruleus: inhibitory effects on blood pressure, heart rate and renal sympathetic nerve activity

Journal of the Autonomic Nervous System ◽

10.1016/0165-1838(92)90064-n ◽

1992 ◽

Vol 41 (3) ◽

pp. 231

Author(s):

Takashi Miyawaki ◽

Hiroshi Kawamura ◽

Michinobu Hatano

Keyword(s):

Blood Pressure ◽

Heart Rate ◽

Sympathetic Nerve ◽

Sympathetic Nerve Activity ◽

Chemical Stimulation ◽

Inhibitory Effects ◽

Nerve Activity ◽

Renal Sympathetic Nerve Activity ◽

Renal Sympathetic ◽

Stimulation Of

Download Full-text

Disruption of phase synchronization between blood pressure and muscle sympathetic nerve activity in postural vasovagal syncope

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.00415.2013 ◽

2013 ◽

Vol 305 (8) ◽

pp. H1238-H1245 ◽

Cited By ~ 12

Author(s):

Christopher E. Schwartz ◽

Elisabeth Lambert ◽

Marvin S. Medow ◽

Julian M. Stewart

Keyword(s):

Blood Pressure ◽

Heart Rate ◽

Sympathetic Nerve ◽

Sympathetic Nerve Activity ◽

Phase Synchronization ◽

Vasovagal Syncope ◽

Muscle Sympathetic Nerve Activity ◽

Nerve Activity ◽

Control Subjects ◽

Late Stages

Withdrawal of muscle sympathetic nerve activity (MSNA) may not be necessary for the precipitous fall of peripheral arterial resistance and arterial pressure (AP) during vasovagal syncope (VVS). We tested the hypothesis that the MSNA-AP baroreflex entrainment is disrupted before VVS regardless of MSNA withdrawal using the phase synchronization between blood pressure and MSNA during head-up tilt (HUT) to measure reflex coupling. We studied eight VVS subjects and eight healthy control subjects. Heart rate, AP, and MSNA were measured during supine baseline and at early, mid, late, and syncope stages of HUT. Phase synchronization indexes, measuring time-dependent differences between MSNA and AP phases, were computed. Directionality indexes, indicating the influence of AP on MSNA (neural arc) and MSNA on AP (peripheral arc), were computed. Heart rate was greater in VVS compared with control subjects during early, mid, and late stages of HUT and significantly declined at syncope ( P = 0.04). AP significantly decreased during mid, late, and syncope stages of tilt in VVS subjects only ( P = 0.001). MSNA was not significantly different between groups during HUT ( P = 0.700). However, the phase synchronization index significantly decreased during mid and late stages in VVS subjects but not in control subjects ( P < .001). In addition, the neural arc was significantly affected more than the peripheral arc before syncope. In conclusion, VVS is accompanied by a loss of the synchronous AP-MSNA relationship with or without a loss in MSNA at faint. This provides insight into the mechanisms behind the loss of vasoconstriction and drop in AP independent of MSNA at the time of vasovagal faint.

Download Full-text

Abstract 529: Muscle Sympathetic Nerve Activity is Higher in Winter than Other Seasons

Hypertension ◽

10.1161/hyp.62.suppl_1.a529 ◽

2013 ◽

Vol 62 (suppl_1) ◽

Author(s):

Jian Cui ◽

Matthew D Muller ◽

Allen R Kunselman ◽

Cheryl Blaha ◽

Lawrence I Sinoway

Keyword(s):

Blood Pressure ◽

Heart Rate ◽

Sympathetic Nerve ◽

Sympathetic Nerve Activity ◽

Muscle Sympathetic Nerve Activity ◽

Epidemiological Data ◽

Repeated Measurements ◽

Nerve Activity ◽

Cardiovascular Morbidity And Mortality ◽

Significant Difference

Epidemiological data suggest that blood pressure tends to be higher in winter and lower in summer, particularly in the elderly. Moreover, hospitalization and mortality rates due to cardiovascular disease have higher rates in winter than summer. Whether autonomic adjustment including muscle sympathetic nerve activity (MSNA) varies with season is unclear. To test the hypothesis that resting MSNA varies along the seasons, we retrospectively analyzed the supine baseline (6 min) MSNA and heart rate (from ECG) of 57 healthy subjects (33M, 24F, 29 ± 1 yrs, range 22-64 yrs) from studies in our laboratory (room temperature ~23 °C). Each of these subjects from central Pennsylvania was studied during 2 or more seasons (total 231 visits). A linear-mixed effects model, which is an extension of the analysis of variance model accounting for repeated measurements (i.e. season) per subject, was used to assess the association of season with the cardiovascular outcomes. The Tukey-Kramer procedure was used to account for multiple comparisons testing between the seasons. MSNA burst rate in winter (21.3 ± 1.0 burst/min) was significantly greater than in summer (13.7 ± 1.0 burst/min, P < 0.001), spring (17.5 ± 1.6 burst/min, P = 0.04) and fall (17.0 ± 1.2 burst/min, P < 0.002). There was no significant difference in MSNA in other comparisons (spring vs. summer, P = 0.12; spring vs. fall, P = 0.99; summer vs. fall, P = 0.054). Heart rate (63.6 ± 1.1 vs. 60.8 ± 1.2 beats/min, P = 0.048) was significantly greater in winter compared to summer. Blood pressure (automated sphygmomanometry of the brachial artery) was not significantly different between seasons. The results suggest that baseline sympathetic nerve activity varies along the seasons, with peak levels evident in winter. We speculate that the seasonal MSNA variation may contribute to seasonal variations in cardiovascular morbidity and mortality.

Download Full-text

Measurement of sympathetic nerve activity in the unanesthetized rat

Journal of Applied Physiology ◽

10.1152/jappl.1989.67.1.250 ◽

1989 ◽

Vol 67 (1) ◽

pp. 250-255 ◽

Cited By ~ 14

Author(s):

J. P. Fluckiger ◽

G. Gremaud ◽

B. Waeber ◽

A. Kulik ◽

A. Ichino ◽

...

Keyword(s):

Blood Pressure ◽

Heart Rate ◽

Arterial Pressure ◽

Sympathetic Nerve ◽

Sympathetic Nerve Activity ◽

Blood Pressure Reduction ◽

Response Curves ◽

Nerve Activity ◽

Dose Dependent

A new system was developed in our laboratory to continuously monitor intra-arterial pressure, heart rate, and sympathetic nerve activity in unanesthetized rats. The animals were prepared 24 h before the start of the experiments. Sympathoneural traffic was measured at the level of splanchnic nerve. The amplitude of the spikes recorded at this level was utilized to express sympathetic nerve activity. The amplitude of the residual electroneurogram signal present 30 min after the rats were killed was 32 +/- 2 mV (mean +/- SE; n = 11). For analysis, these background values were subtracted from values determined in vivo. The nerve we studied contains postganglionic fibers, since electrical activity decreased in response to ganglionic blockade with pentolinium (1.25 mg/min iv for 4 min). The amplitude of spikes fell by 43 +/- 4% (n = 4). Sympathetic nerve activity was highly reproducible at a 24-h interval (104 +/- 26 vs. 111 +/- 27 mV for the amplitude of spikes; n = 11). Dose-response curves to the alpha 1-stimulant methoxamine and to bradykinin were established in four rats. The increase in blood pressure induced by methoxamine caused a dose-dependent fall in sympathetic nerve activity, whereas the blood pressure reduction resulting from bradykinin was associated with a dose-dependent activation of sympathetic drive. These data therefore indicate that it is possible with out system to accurately measure sympathetic nerve activity in the awake rat, together with intra-arterial pressure and heart rate.

Download Full-text

Effects of SK&F64139, a PNMT inhibitor, on blood pressure, heart rate and sympathetic nerve activity in rats

European Journal of Pharmacology ◽

10.1016/0014-2999(90)92653-z ◽

1990 ◽

Vol 183 (3) ◽

pp. 835-836

Author(s):

M. Minami ◽

H. Matsuda ◽

H. Sato ◽

N. Yamazaki ◽

H. Togashi ◽

...

Keyword(s):

Blood Pressure ◽

Heart Rate ◽

Sympathetic Nerve ◽

Sympathetic Nerve Activity ◽

Nerve Activity

Download Full-text

Changes in heart rate, arterial blood pressure and sympathetic nerve activity following administration of aliphatic amines in rats

Journal of Japanese Society for Dialysis Therapy ◽

10.4009/jsdt1985.22.1069 ◽

1989 ◽

Vol 22 (10) ◽

pp. 1069-1073

Author(s):

Akihide Matsumoto ◽

Kenichi Yonemuma

Keyword(s):

Blood Pressure ◽

Heart Rate ◽

Arterial Blood Pressure ◽

Sympathetic Nerve ◽

Sympathetic Nerve Activity ◽

Aliphatic Amines ◽

Nerve Activity ◽

Arterial Blood

Download Full-text

Baroreflex modulation of sympathetic nerve activity to muscle in heat-stressed humans

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00337.2001 ◽

2002 ◽

Vol 282 (1) ◽

pp. R252-R258 ◽

Cited By ~ 45

Author(s):

Jian Cui ◽

Thad E. Wilson ◽

Craig G. Crandall

Keyword(s):

Blood Pressure ◽

Heart Rate ◽

Heat Stress ◽

Sympathetic Nerve ◽

Sympathetic Nerve Activity ◽

Whole Body ◽

Arterial Baroreflex ◽

Nerve Activity ◽

Arterial Blood ◽

The Relationship

To identify whether whole body heating alters arterial baroreflex control of muscle sympathetic nerve activity (MSNA), MSNA and beat-by-beat arterial blood pressure were recorded in seven healthy subjects during acute hypotensive and hypertensive stimuli in both normothermic and heat stress conditions. Whole body heating significantly increased sublingual temperature ( P < 0.01), MSNA ( P < 0.01), heart rate ( P< 0.01), and skin blood flow ( P < 0.001), whereas mean arterial blood pressure did not change significantly ( P > 0.05). During both normothermic and heat stress conditions, MSNA increased and then decreased significantly when blood pressure was lowered and then raised via intravenous bolus infusions of sodium nitroprusside and phenylephrine HCl, respectively. The slope of the relationship between MSNA and diastolic blood pressure during heat stress (−128.3 ± 13.9 U · beats−1 · mmHg−1) was similar ( P = 0.31) with normothermia (−140.6 ± 21.1 U · beats−1 · mmHg−1). Moreover, no significant change in the slope of the relationship between heart rate and systolic blood pressure was observed. These data suggest that arterial baroreflex modulation of MSNA and heart rate are not altered by whole body heating, with the exception of an upward shift of these baroreflex curves to accommodate changes in these variables that occur with whole body heating.

Download Full-text