Vasomotor sympathetic nerve activity in men during bed rest and on orthostasis after bed rest

Atsunori Kamiya, Satoshi Iwase, Yoshiki Sugiyama, Tadaaki Mano, Masamichi Sudoh

Research output: Contribution to journalArticle

20 Citations (Scopus)

Abstract

Background: Alterations in autonomic function are commonly seen during and after spaceflight, and its ground-based analog, 6°head-down bed rest (HDBR). They may include peripheral vascular regulation, but vasomotor sympathetic efferent nerve discharges to peripheral vasculatures have not been examined. The aim of our study was to examine changes in vasomotor sympathetic nerve activity during HDBR and under orthostasis after HDBR. Methods: We performed 6 d of HDBR on six male subjects, and measured muscle sympathetic nerve activity (MSNA) together with plasma norepinephrine concentrations in the supine position before HDBR and in 6°head-down position on the sixth day (HDBR6) of HDBR. We also measured MSNA in head-up tilt (HUT) test before and after HDBR. Results: On HDBR6, MSNA burst rate was the same (17 ± 4 bursts · min-1) as that in supine position before HDBR (15 ± 2 bursts, min-1), but plasma norepinephrine concentrations were decreased to 1.14 ± 0.10 pmol · ml-1 compared with the supine value before HDBR (1.56 ± 0.20 pmol · ml-1, p < 0.05). After HDBR, supine MSNA burst rate significantly increased by 55% to 24 ± 4 bursts · min-1. MSNA increment in response to HUT was similar between before (34 ± 3 bursts · min-1 · sin HUT-1) and after (40 ± 6 bursts · min-1 · sin HUT-1) HDBR. Conclusions: Our findings suggest that: a) the relationship between MSNA and plasma norepinephrine concentrations was altered on the sixth day during HDBR; b) the vasomotor sympathetic nerve activity was enhanced after HDBR; and c) the augmentation of vasomotor sympathetic outflow to muscles under orthostasis was preserved after HDBR.

Original languageEnglish
Pages (from-to)142-149
Number of pages8
JournalAviation Space and Environmental Medicine
Volume71
Issue number2
Publication statusPublished - Feb 1 2000
Externally publishedYes

Keywords

  • Bed rest
  • Muscle sympathetic nerve activity
  • Plasma norepinephrine
  • Simulated microgravity

ASJC Scopus subject areas

  • Public Health, Environmental and Occupational Health

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