Contrasting effects of phentolamine and nitroprusside on neural and cardiovascular variability

Philippe Van De Borne, Mohsen Rahnama, Silvia Mezzetti, Nicola Montano, Alberto Porta, Jean Paul Degaute, Virend K. Somers

Research output: Contribution to journalArticlepeer-review

34 Scopus citations


The relative contributions of a central neural oscillator and of the delay in α-adrenergic transmission within the baroreflex loop in the predominance of low-frequency (LF) cardiovascular variability during sympathetic activation in humans are unclear. We measured R-R interval (RR), muscle sympathetic nerve activity (MSNA), blood pressure (BP), and their variability in 10 normal subjects during sympathetic activation achieved by BP lowering with sodium nitroprusside (SNP) and α-adrenergic blockade using phentolamine. SNP and phentolamine induced comparable reductions in BP (P > 0.25). Despite tachycardia and sympathetic activation with both SNP and phentolamine, LF variability in RR, MSNA, and BP increased during SNP and decreased during phentolamine (SNP: RR +20 ± 6%, MSNA +3 ± 5%, systolic BP +9 ± 6%, diastolic BP +7 ± 5%; phentolamine: RR -2 ± 7%, MSNA -34 ± 6%, systolic BP -16 ± 8%, diastolic BP -13 ± 4%, P < 0.05 except systolic BP, where P = 0.09). Thus LF variability is reduced when sympathetic activation is induced by α-adrenergic blockade. This suggests that α-adrenergic transmission within the baroreflex loop may contribute importantly to the predominance of LF cardiovascular variability associated with sympathetic excitation in humans.

Original languageEnglish (US)
Pages (from-to)H559-H565
JournalAmerican Journal of Physiology - Heart and Circulatory Physiology
Issue number2 50-2
StatePublished - 2001


  • Sympathetic nervous system

ASJC Scopus subject areas

  • Physiology
  • Cardiology and Cardiovascular Medicine
  • Physiology (medical)


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