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