Adrenergic vasoconstriction augments tissue O2 extraction during reductions in O2 delivery

L. A. Maginniss, H. Connolly, R. W. Samsel, P. T. Schumacker*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

25 Scopus citations


When systemic O2 delivery is reduced, increases in systemic O2 extraction are facilitated by sympathetically mediated increases in vascular resistance that limit blood flow to regions with low metabolic demand. Local metabolic vasodilation competes with this vasoconstriction, thereby effecting a balance between tissue O2 supply and demand. This study examined the role of sympathetically mediated vasoconstriction on the critical level of O2 extraction in hindlimb and whole body during progressive reductions in O2 delivery. In anesthetized dogs, the left hindlimb was vascularly isolated and its O2 delivery was decreased in stages by reducing the speed of an occlusive pump. In a normovolemic group (n = 6), blood volume was maintained to minimize sympathetic tone while flow to the hindlimb was reduced. In a hypovolemic group (n = 6), blood volume was removed in stages to augment sympathetic tone progressively while flow to the limb was reduced simultaneously. A phenoxybenzamine group (n = 6) was identical to the hypovolemic group, except that α-adrenergic effects were inhibited with phenoxybenzamine (3 mg/kg). The systemic critical O2 extraction ratio in the phenoxybenzamine group (0.60 ± 0.06) was less than for the hypovolemic group (0.71 ± 0.04; P = 0.004). In the hindlimb, critical O2 extractions were significantly less in the normovolemic (0.46 ± 0.17) and phenoxybenzamine (0.49 ± 0.10) groups compared with the hypovolemic group (0.72 ± 0.10; P ≤ 0.008). These findings demonstrate a significant contribution of α- adrenergic vasoconstrictor tone to the critical O2 extraction in whole body and hindlimb during progressive hypoxia and underscore the significance of an active sympathetic response for efficient tissue O2 utilization, especially in states in which O2 delivery to an isolated region is reduced.

Original languageEnglish (US)
Pages (from-to)1454-1461
Number of pages8
JournalJournal of applied physiology
Issue number4
StatePublished - 1994


  • autonomic nervous system
  • blood flow
  • dogs
  • hypoxia
  • ischemia
  • oxygen consumption
  • phenoxybenzamine

ASJC Scopus subject areas

  • Physiology (medical)
  • Physiology


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