The Effect of time-of-day and sympathetic α(1)-blockade on orthostatic tolerance

Hdl Handle:
http://hdl.handle.net/10149/243664
Title:
The Effect of time-of-day and sympathetic α(1)-blockade on orthostatic tolerance
Authors:
Lewis, N. C. S. (Nia); Ainslie, P. N. (Philip); Atkinson, G. (Greg); Jones, H. (Helen); Grant, E. J. M. (Emily); Lucas, S. J. E. (Samuel)
Affiliation:
Teesside University. Health and Social Care Institute.
Citation:
Lewis, N.C.S., Ainslie, P.N., Atkinson, G., Jones, H., Grant, E.J.M. and Lucas, S.J.E. (2012) 'The Effect of time-of-day and sympathetic α(1)-blockade on orthostatic tolerance', Chronobiology international, 29(7), pp.882-890.
Publisher:
Informa Healthcare
Journal:
Chronobiology international
Issue Date:
Aug-2012
URI:
http://hdl.handle.net/10149/243664
DOI:
10.3109/07420528.2012.699121
PubMed ID:
22823871
Abstract:
Tolerance time to a standardized orthostatic stressor is markedly reduced in normotensive individuals in the morning. However, the physiological mechanisms that underpin this phenomenon are unknown. The purpose of this study was to examine the role of α(1)-adrenergic activity on orthostatic tolerance and associated cardiorespiratory and cerebrovascular responses, and to determine whether its endogenous modulation is important in the diurnal variation of orthostatic tolerance. In a four-trial, randomized placebo-controlled crossover experiment, 12 normotensive volunteers (aged 25 ± 1 yrs; mean ± SE) completed a 60° head-upward tilt (HUT; 15 min or until onset of presyncope) at 06:00 and 16:00 h, 90 min after the administration of either α(1)-blockade (prazosin, 1 mg/20 kg body weight) or placebo. Continuous beat-to-beat measurements of middle cerebral blood flow velocity (transcranial Doppler), blood pressure (Finometer), heart rate, stroke volume, cardiac output, and end-tidal carbon dioxide were obtained. Independent of time-of-day, α(1)-blockade markedly reduced the ability to tolerate a 15-min 60° HUT; tolerance time was 229% shorter compared with the placebo condition (p ≤ .0001). Moreover, a marked diurnal variation in orthostatic tolerance was evident following α(1)-adrenergic blockade; e.g., tolerance time in the morning (176 ± 30 s) was lower than in the afternoon (354 ± 75 s; p = .04). These findings highlight an important role of α(1)-sympathetic vasoconstrictor activity in acutely regulating blood pressure and offsetting syncope, especially in the early morning.
Type:
Article
Language:
en
Keywords:
α1-Adrenoreceptor; blood pressure; cerebral blood flow; diurnal; head-up tilt; syncope
ISSN:
1525-6073
Rights:
Subject to restrictions author can archive post-print (ie final draft post-refereeing). For full details see http://www.sherpa.ac.uk/romeo/ [Accessed 12/09/2012].
Citation Count:
0 [Scopus, 12/09/2012]

Full metadata record

DC FieldValue Language
dc.contributor.authorLewis, N. C. S. (Nia)en_GB
dc.contributor.authorAinslie, P. N. (Philip)en_GB
dc.contributor.authorAtkinson, G. (Greg)en_GB
dc.contributor.authorJones, H. (Helen)en_GB
dc.contributor.authorGrant, E. J. M. (Emily)en_GB
dc.contributor.authorLucas, S. J. E. (Samuel)en_GB
dc.date.accessioned2012-09-12T15:46:01Z-
dc.date.available2012-09-12T15:46:01Z-
dc.date.issued2012-08-
dc.identifier.citationChronobiology international; 29 (7) :882-890en_GB
dc.identifier.issn1525-6073-
dc.identifier.pmid22823871-
dc.identifier.doi10.3109/07420528.2012.699121-
dc.identifier.urihttp://hdl.handle.net/10149/243664-
dc.description.abstractTolerance time to a standardized orthostatic stressor is markedly reduced in normotensive individuals in the morning. However, the physiological mechanisms that underpin this phenomenon are unknown. The purpose of this study was to examine the role of α(1)-adrenergic activity on orthostatic tolerance and associated cardiorespiratory and cerebrovascular responses, and to determine whether its endogenous modulation is important in the diurnal variation of orthostatic tolerance. In a four-trial, randomized placebo-controlled crossover experiment, 12 normotensive volunteers (aged 25 ± 1 yrs; mean ± SE) completed a 60° head-upward tilt (HUT; 15 min or until onset of presyncope) at 06:00 and 16:00 h, 90 min after the administration of either α(1)-blockade (prazosin, 1 mg/20 kg body weight) or placebo. Continuous beat-to-beat measurements of middle cerebral blood flow velocity (transcranial Doppler), blood pressure (Finometer), heart rate, stroke volume, cardiac output, and end-tidal carbon dioxide were obtained. Independent of time-of-day, α(1)-blockade markedly reduced the ability to tolerate a 15-min 60° HUT; tolerance time was 229% shorter compared with the placebo condition (p ≤ .0001). Moreover, a marked diurnal variation in orthostatic tolerance was evident following α(1)-adrenergic blockade; e.g., tolerance time in the morning (176 ± 30 s) was lower than in the afternoon (354 ± 75 s; p = .04). These findings highlight an important role of α(1)-sympathetic vasoconstrictor activity in acutely regulating blood pressure and offsetting syncope, especially in the early morning.en_GB
dc.language.isoenen
dc.publisherInforma Healthcareen_GB
dc.rightsSubject to restrictions author can archive post-print (ie final draft post-refereeing). For full details see http://www.sherpa.ac.uk/romeo/ [Accessed 12/09/2012].en_GB
dc.subjectα1-Adrenoreceptoren_GB
dc.subjectblood pressureen_GB
dc.subjectcerebral blood flowen_GB
dc.subjectdiurnalen_GB
dc.subjecthead-up tilten_GB
dc.subjectsyncopeen_GB
dc.titleThe Effect of time-of-day and sympathetic α(1)-blockade on orthostatic toleranceen
dc.typeArticleen
dc.contributor.departmentTeesside University. Health and Social Care Institute.en_GB
dc.identifier.journalChronobiology internationalen_GB
ref.citationcount0 [Scopus, 12/09/2012]en_GB
or.citation.harvardLewis, N.C.S., Ainslie, P.N., Atkinson, G., Jones, H., Grant, E.J.M. and Lucas, S.J.E. (2012) 'The Effect of time-of-day and sympathetic α(1)-blockade on orthostatic tolerance', Chronobiology international, 29(7), pp.882-890.en_GB
dc.description.noteErratum: The effect of time-of-day and sympathetic α1-blockade on orthostatic tolerance (Chronobiology International 29:7 (882-890)) published in Chronobiology International 29(8) p.1151en_GB

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