Vasoconstrictor responses to immersion
of the hand in ice water in the sympathetically denervated forearm
were abolished; during the second minute of the cold pressor
test, vascular resistance had increased by 48±20 percent
in the innervated limb, whereas it had decreased by 17±5
percent in the denervated limb (
P<0.02> limbs).
Figs. 1 and 2
show that
L-NMMA infusion evoked a roughly 3-fold
larger increase in vascular resistance in the denervated forearm
than in the innervated calf. In the forearm, vascular resistance
increased by 58±10 percent during
L-NMMA infusion whereas
in the calf, it increased only by 21±6 percent (
P<0.001,
forearm vs. calf). The
L-NMMA induced vasoconstriction was reversed
by
L-arginine, but not by
D-arginine, infusion (
Table 1). In
contrast to
L-NMMA, infusion of an equipressive dose of phenylephrine
increased the vascular resistance comparably in the denervated
and the innervated limb (by 24±3 and 26±7 percent,
respectively;
P>0.5, forearm vs. calf).
Here we used subjects having undergone thoracic
sympathectomy for hyperhydrosis, to probe the role of the peripheral
sympathetic nervous system in the modulation of the vascular
responsiveness to nitric oxide synthase inhibition. We found
that
sympathectomy markedly potentiated the vasoconstrictor
effect of
L-NMMA infusion. The
L-NMMA induced vasoconstrictor
effect was almost three times larger in the denervated than
in the innervated limb. These findings provide the first evidence
for an important interplay between the peripheral sympathetic
nervous system and the
L-arginine–nitric-oxide system
in the regulation of the vascular tone in humans, and indicate
that sympathetic innervation attenuates the vasoconstrictor
effect of nitric oxide synthase inhibition.
Cardiovascular Research 1999 43(3):739-743; doi:10.1016/S0008-6363(99)00084-X
© 1999 by European Society of Cardiology
, 
Volume 138, Issue 1, Pages 40-45 (July 2005)