Effects of muscle metabolites on responses of muscle sympathetic nerve activity to mechanoreceptor(s) stimulation in healthy humans

Jian Cui, Vernon Mascarenhas, Raman Moradkhan, Cheryl Blaha, Lawrence I. Sinoway

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Abstract

Based on animal studies, it has been speculated that muscle metabolites sensitize muscle mechanoreceptors and increase mechanoreceptor-mediated muscle sympathetic nerve activity (MSNA). However, this hypothesis has not been directly tested in humans. In this study, we tested the hypothesis that in healthy individuals passive stretch of forearm muscles would evoke significant increases in mean MSNA when muscle metabolite concentrations were increased. In 12 young healthy subjects, MSNA, ECG, and blood pressure were recorded. Subjects performed static fatiguing isometric handgrip at 30% maximum voluntary contraction followed by 4 min of postexercise muscle ischemia (PEMI). After 2 min of PEMI, wrist extension (i.e., wrist dorsiflexion) was performed. The static stretch protocol was also performed during 1) a freely perfused condition, 2) ischemia alone, and 3) PEMI after nonfatiguing exercise. Finally, repetitive short bouts of wrist extension were also performed under freely perfused conditions. This last paradigm evoked transient increases in MSNA but had no significant effect on mean MSNA over the whole protocol. During the PEMI after fatiguing handgrip, static stretch induced significant increases in MSNA (552 ± 74 to 673 ± 90 U/min, P < 0.01) and mean blood pressure (102 ± 2 to 106 ± 2 mmHg, P < 0.001). Static stretch performed under the other three conditions had no significant effects on mean MSNA and blood pressure. The present data verified that in healthy humans mechanoreceptor(s) stimulation evokes significant increases in mean MSNA and blood pressure when muscle metabolite concentrations are increased above a certain threshold.

Original languageEnglish (US)
Pages (from-to)R458-R466
JournalAmerican Journal of Physiology - Regulatory Integrative and Comparative Physiology
Volume294
Issue number2
DOIs
StatePublished - Feb 1 2008

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Mechanoreceptors
Muscles
Ischemia
Wrist
Blood Pressure

All Science Journal Classification (ASJC) codes

  • Physiology
  • Physiology (medical)

Cite this

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title = "Effects of muscle metabolites on responses of muscle sympathetic nerve activity to mechanoreceptor(s) stimulation in healthy humans",
abstract = "Based on animal studies, it has been speculated that muscle metabolites sensitize muscle mechanoreceptors and increase mechanoreceptor-mediated muscle sympathetic nerve activity (MSNA). However, this hypothesis has not been directly tested in humans. In this study, we tested the hypothesis that in healthy individuals passive stretch of forearm muscles would evoke significant increases in mean MSNA when muscle metabolite concentrations were increased. In 12 young healthy subjects, MSNA, ECG, and blood pressure were recorded. Subjects performed static fatiguing isometric handgrip at 30{\%} maximum voluntary contraction followed by 4 min of postexercise muscle ischemia (PEMI). After 2 min of PEMI, wrist extension (i.e., wrist dorsiflexion) was performed. The static stretch protocol was also performed during 1) a freely perfused condition, 2) ischemia alone, and 3) PEMI after nonfatiguing exercise. Finally, repetitive short bouts of wrist extension were also performed under freely perfused conditions. This last paradigm evoked transient increases in MSNA but had no significant effect on mean MSNA over the whole protocol. During the PEMI after fatiguing handgrip, static stretch induced significant increases in MSNA (552 ± 74 to 673 ± 90 U/min, P < 0.01) and mean blood pressure (102 ± 2 to 106 ± 2 mmHg, P < 0.001). Static stretch performed under the other three conditions had no significant effects on mean MSNA and blood pressure. The present data verified that in healthy humans mechanoreceptor(s) stimulation evokes significant increases in mean MSNA and blood pressure when muscle metabolite concentrations are increased above a certain threshold.",
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AU - Mascarenhas, Vernon

AU - Moradkhan, Raman

AU - Blaha, Cheryl

AU - Sinoway, Lawrence I.

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