Preserved alpha-adrenergic tone in the leg vascular bed of spinal cord-injured individuals.
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 alpha-adrenergic contribution to the increased vascular tone in the lower extremity in patients without central sympathetic control of leg circulation.


RESULTS
Upper-leg vascular resistance responses to local infusion of incremental doses of phentolamine (a competitive antagonist of the alpha-adrenoceptor) into the femoral artery were determined in 10 spinal cord-injured individuals (SCI) and 8 healthy age-matched control subjects during local beta-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 alpha-adrenoceptor-mediated vascular tone in the leg is preserved in spinal cord-injured individuals without sympathetic supraspinal control.
Kooijman
Miriam
M
Department of Physiology, Department of Physiology, University Medical Center Nijmegen, The Netherlands . m.kooijman@fysiol.umcn.nl
Rongen
Gerard A
GA
Smits
Paul
P
Hopman
Maria T E
MT
D000317:Adrenergic alpha-Antagonists; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000328:Adult; D001794:Blood Pressure; D003080:Cold Temperature; D005260:Female; D006801:Humans; D006940:Hyperemia / Q000503:physiopathology; D007866:Leg / Q000098:blood supply*; D008297:Male; D008875:Middle Aged; D010646:Phentolamine; D011433:Propranolol / Q000494:pharmacology; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D013119:Spinal Cord Injuries / Q000503:physiopathology*; D014655:Vascular Resistance; D014661:Vasoconstriction
D000317:Adrenergic alpha-Antagonists; D000319:Adrenergic beta-Antagonists; D011942:Receptors, Adrenergic, alpha; D011433:Propranolol; D010646:Phentolamine