β-receptor agonist activity of phenylephrine in the human forearm

Klaus D. Torp, Michael E. Tschakovsky, John R. Halliwill, Christopher T. Minson, Michael J. Joyner

Research output: Contribution to journalArticlepeer-review

36 Scopus citations

Abstract

β-Receptor agonist activity of phenylephrine in the human forearm. J Appl Physiol 90: 1855-1859, 2001. - Phenylephrine is generally regarded as a "pure" α1-agonist. However, after treatment of the forearm with the α-adrenergic-blocking drug phentolamine, brachial artery infusion of phenylephrine can cause transient forearm vasodilation. To determine whether this response was β-receptor mediated, phenylephrine, phentolamine, and propranolol were infused into the brachial arteries of six healthy volunteers. Forearm vascular conductance (FVC) was also calculated and expressed as arbitrary units (units). Infusion of phenylephrine by itself (0.5 μg·dl forearm volume-1·min-1) caused a sustained decrease (P < 0.05) in FVC from 3.5 ± 0.7 to 0.9 ± 0.2 units (P < 0.05). Infusion of the α-blocker phentolamine increased (P < 0.05) baseline FVC to 5.7 ± 1.3 units. Subsequent infusion of phenylephrine after α-blockade caused FVC to increase (P < 0.05) for ∼ 1 min from 5.7 ± 1.3 to a peak of 13.1 ± 1.8 units. Propranolol had no effect on baseline flow, and subsequent phenylephrine infusion after α- and β-blockade caused a small, but significant, sustained decrease in FVC from 5.1 ± 1.0 to 3.6 ± 0.8 units. There were no systemic effects from the infusions, and saline infusion at the same rate (1-2 ml/min) had no forearm vasoconstrictor or dilator effects. These data indicate that in humans phenylephrine can exert transient β2-vasodilator activity when its predominant α-constrictor effects are blocked.

Original languageEnglish (US)
Pages (from-to)1855-1859
Number of pages5
JournalJournal of applied physiology
Volume90
Issue number5
DOIs
StatePublished - 2001

Keywords

  • Adrenergic receptors
  • Blood flow
  • Vasoconstriction

ASJC Scopus subject areas

  • Physiology
  • Physiology (medical)

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