Heterogeneous responses of human limbs to infused adrenergic agonists: A gravitational effect?

James Anthony Pawelczyk, Benjamin D. Levine

Research output: Contribution to journalArticle

80 Citations (Scopus)

Abstract

Unlike quadrupeds, the legs of humans are regularly exposed to elevated pressures relative to the arms. We hypothesized that this "dependent hypertension" would be associated with altered adrenergic responsiveness. Isoproterenol (0.75-24 ng·100 ml limb volume-1·min-1) and phenylephrine (0.025-0.8 μg·100 ml limb volume-1·min-1) were infused incrementally in the brachial and femoral arteries of 12 normal volunteers; changes in limb blood flow were quantified by using strain-gauge plethysmography. Compared with the forearm, baseline calf vascular resistance was greater (38.8 ± 2.5 vs. 26.9 ± 2.0 mmHg·100 ml·min·ml-1; P < 0.001) and maximal conductance was lower (46.1 ± 11.9 vs. 59.4 ± 13.4 ml·ml-1·min-1·mmHg-1; P < 0.03). Vascular conductance did not differ between the two limbs during isoproterenol infusions, whereas decreases in vascular conductance were greater in the calf than the forearm during phenylephrine infusions (P < 0.001). With responses normalized to maximal conductance, the half-maximal response for phenylephrine was significantly less for the calf than the forearm (P < 0.001), whereas the half-maximal response for isoproterenol did not differ between limbs. We conclude that α1- but not β-adrenergic-receptor responsiveness in human limbs is non-uniform. The relatively greater response to α1-adrenergic-receptor stimulation in the calf may represent an adaptive mechanism that limits blood pooling and capillary filtration in the legs during standing.

Original languageEnglish (US)
Pages (from-to)2105-2113
Number of pages9
JournalJournal of Applied Physiology
Volume92
Issue number5
DOIs
StatePublished - Jan 1 2002

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Adrenergic Agonists
Extremities
Phenylephrine
Isoproterenol
Forearm
Adrenergic Receptors
Blood Vessels
Leg
Plethysmography
Brachial Artery
Femoral Artery
Vascular Resistance
Adrenergic Agents
Healthy Volunteers
Arm
Hypertension
Pressure

All Science Journal Classification (ASJC) codes

  • Physiology
  • Physiology (medical)

Cite this

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title = "Heterogeneous responses of human limbs to infused adrenergic agonists: A gravitational effect?",
abstract = "Unlike quadrupeds, the legs of humans are regularly exposed to elevated pressures relative to the arms. We hypothesized that this {"}dependent hypertension{"} would be associated with altered adrenergic responsiveness. Isoproterenol (0.75-24 ng·100 ml limb volume-1·min-1) and phenylephrine (0.025-0.8 μg·100 ml limb volume-1·min-1) were infused incrementally in the brachial and femoral arteries of 12 normal volunteers; changes in limb blood flow were quantified by using strain-gauge plethysmography. Compared with the forearm, baseline calf vascular resistance was greater (38.8 ± 2.5 vs. 26.9 ± 2.0 mmHg·100 ml·min·ml-1; P < 0.001) and maximal conductance was lower (46.1 ± 11.9 vs. 59.4 ± 13.4 ml·ml-1·min-1·mmHg-1; P < 0.03). Vascular conductance did not differ between the two limbs during isoproterenol infusions, whereas decreases in vascular conductance were greater in the calf than the forearm during phenylephrine infusions (P < 0.001). With responses normalized to maximal conductance, the half-maximal response for phenylephrine was significantly less for the calf than the forearm (P < 0.001), whereas the half-maximal response for isoproterenol did not differ between limbs. We conclude that α1- but not β-adrenergic-receptor responsiveness in human limbs is non-uniform. The relatively greater response to α1-adrenergic-receptor stimulation in the calf may represent an adaptive mechanism that limits blood pooling and capillary filtration in the legs during standing.",
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Heterogeneous responses of human limbs to infused adrenergic agonists : A gravitational effect? / Pawelczyk, James Anthony; Levine, Benjamin D.

In: Journal of Applied Physiology, Vol. 92, No. 5, 01.01.2002, p. 2105-2113.

Research output: Contribution to journalArticle

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T2 - A gravitational effect?

AU - Pawelczyk, James Anthony

AU - Levine, Benjamin D.

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