α-adrenergic vascular responsiveness to sympathetic nerve activity is intact after head-down bed rest in humans

Atsunori Kamiya, Daisaku Michikami, Satoshi Iwase, Junichiro Hayano, Toru Kawada, Masaru Sugimachi, Kenji Sunagawa

Research output: Contribution to journalArticle

16 Citations (Scopus)

Abstract

Spaceflight and its ground-based simulation model, 6° head-down bed rest (HDBR), cause cardiovascular deconditioning in humans. Because sympathetic vasoconstriction plays a very important role in circulation, we examined whether HDBR impairs α-adrenergic vascular responsiveness to sympathetic nerve activity. We subjected eight healthy volunteers to 14 days of HDBR and before and after HDBR measured calf muscle sympathetic nerve activity (MSNA; microneurography) and calf blood flow (venous occlusion plethysmography) during sympathoexcitatory stimulation (rhythmic handgrip exercise). HDBR did not change the increase in total MSNA (P = 0.97) or the decrease in calf vascular conductance (P = 0.32) during exercise, but it did augment the increase in calf vascular resistance (P = 0.0011). HDBR augmented the transduction gain from total MSNA into calf vascular resistance, assessed as the least squares linear regression slope of vascular resistance on total MSNA (0.05 ± 0.02 before HDBR, 0.20 ± 0.06 U·min-1·burst -1 after HDBR, P = 0.0075), but did not change the transduction gain into calf vascular conductance (P = 0.41). Our data indicate that α-adrenergic vascular responsiveness to sympathetic nerve activity is preserved in the supine position after HDBR in humans.

Original languageEnglish
Pages (from-to)R151-R157
JournalAmerican Journal of Physiology - Regulatory Integrative and Comparative Physiology
Volume286
Issue number1 55-1
Publication statusPublished - Jan 1 2004
Externally publishedYes

Keywords

  • Microgravity
  • Spaceflight
  • Vascular contractility
  • Vasoconstriction

ASJC Scopus subject areas

  • Physiology
  • Physiology (medical)

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