α -adrenoreceptor activity does not explain lower morning endothelial-dependent, flow-mediated dilation in humans

Research output: Contribution to journalArticle

Authors

  • H. Jones
  • N.C.S. Lewis
  • D.J. Green
  • G. Atkinson
  • P.N. Ainslie
  • E.J.M. Grant
  • Y.-C. Tzeng

Colleges, School and Institutes

External organisations

  • Liverpool John Moores University
  • The University of Western Australia
  • University of British Columbia
  • Department of Surgery and Anaesthesia, University of Otago

Abstract

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 a1-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 a 1 -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 a1-adrenoreceptor activity does not explain lower morning endothelium-dependent FMD.

Details

Original languageEnglish
Pages (from-to)1437-1442
Number of pages6
JournalAJP Regulatory Integrative and Comparative Physiology
Volume300
Issue number6
Publication statusPublished - 1 Jun 2011