Published Online
on October 13, 2003

A more recent version of this article appeared on November 11, 2003

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Submitted on October 29, 2002
Revised on July 29, 2003
Accepted on August 1, 2003

Preserved -Adrenergic Tone in the Leg Vascular Bed of Spinal Cord-Injured Individuals

Miriam Kooijman MD^*, Gerard A. Rongen MD, PhD, Paul Smits MD, PhD, and Maria T.E. Hopman MD, PhD

From the Department of Physiology, University Medical Center Nijmegen, the Netherlands (M.K., M.T.E.H.); and the Department of Pharmacology-Toxicology, University Medical Center Nijmegen, the Netherlands (G.A.R., P.S.).

^* To whom correspondence should be addressed. E-mail: m.kooijman{at}fysiol.umcn.nl.

Background--Supraspinal sympathetic control of leg vascular tone is lost in spinal cord-injured individuals, but this does not result in a reduced leg vascular tone: Leg vascular resistance is even increased. The aim of this study was to assess the -adrenergic contribution to the increased vascular tone in the lower extremity in patients without central sympathetic control of leg circulation.

Methods and Results--Upper-leg vascular resistance responses to local infusion of incremental doses of phentolamine (a competitive antagonist of the -adrenoceptor) into the femoral artery were determined in 10 spinal cord-injured individuals (SCI) and 8 healthy age-matched control subjects during local -adrenergic receptor blockade with propranolol. Basal leg vascular resistance was higher in SCI than in control subjects (41±6 arbitrary units [AU] versus 24±4 AU; P=0.034). The same accounts for minimal leg vascular resistance, assessed during reactive hyperemia, which was higher in SCI compared with control subjects (6.9±1.0 AU versus 2.5±0.2 AU; P<0.01). The maximal phentolamine-induced reduction in leg vascular resistance normalized to each individual’s minimal resistance did not differ between the groups (68±17% and 51±4% for SCI and control subjects, respectively; P>0.1). A decline in mean arterial pressure was observed in both groups with increasing dosage of phentolamine. In response, baroreceptor-mediated vasoconstriction was observed in the noninfused leg of the control subjects, whereas in SCI individuals this reaction was absent.

Conclusions--These results indicate that the -adrenoceptor-mediated vascular tone in the leg is preserved in spinal cord-injured individuals without sympathetic supraspinal control.

Key words: blood flow • vasodilation • nervous system, sympathetic • receptors, adrenergic, alpha

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