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 Somers

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30 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)
JournalAmerican Journal of Physiology - Heart and Circulatory Physiology
Issue number2 50-2
StatePublished - 2001



  • Sympathetic nervous system

ASJC Scopus subject areas

  • Physiology
  • Physiology (medical)

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