This Article Abstract Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Owlya, R. Articles by Scherrer, U. Search for Related Content PubMed PubMed Citation Articles by Owlya, R. Articles by Scherrer, U.

(Circulation. 1997;96:3897-3903.)
© 1997 American Heart Association, Inc.

Articles

Cardiovascular and Sympathetic Effects of Nitric Oxide Inhibition at Rest and During Static Exercise in Humans

Reza Owlya, MD; Laurent Vollenweider, MD; Lionel Trueb, MD; Claudio Sartori, MD; Mattia Lepori, MD; Pascal Nicod, MD; ; Urs Scherrer, MD

From the Department of Internal Medicine B, Centre Hospitalier Universitaire Vaudois, Lausanne (R.O., C.S., M.L., P.N., U.S.), and the Institute of Physiology, University of Lausanne (L.V., L.T.), Switzerland.

Correspondence to Dr Urs Scherrer, Department of Internal Medicine, BH 10.642, CHUV, CH-1011 Lausanne, Switzerland. E-mail Urs.Scherrer{at}chuv.hospvd.ch

	Abstract

Top Abstract Introduction Methods Results Discussion References

 
Background Nitric oxide (NO) regulates vascular tone and blood pressure, and studies in animals suggest that it does so, at least in part, by modulating sympathetic neural outflow. Loss of NO-induced vasodilator tone and restraint on sympathetic vasoconstrictor outflow could lead to exaggerated vasoconstrictor and pressor responses to physical stress in humans.

Methods and Results To determine the role of NO in the modulation of central sympathetic outflow and vascular tone at rest and during a physical stress, we tested effects of systemic inhibition of NO synthase by N^G-monomethyl-L-arginine (L-NMMA) infusion (a stereospecific inhibitor of NO synthase) on sympathetic nerve activity (microneurography), regional vascular resistance, and blood pressure at rest and during static handgrip. The major new findings are that (1) under resting conditions, L-NMMA infusion, which increased mean arterial pressure by 10%, did not have any detectable effect on muscle sympathetic nerve activity, whereas a similar increase in arterial pressure evoked by phenylephrine infusion (an NO-independent vasoconstrictor) decreased the rate of sympathetic nerve firing by 50%; (2) during static handgrip, the exercise-induced sympathetic nerve responses were preserved during L-NMMA infusion but markedly attenuated during phenylephrine infusion; and (3) the L-NMMA–induced loss of vasodilator tone did not result in exaggerated exercise-induced pressor and calf vasoconstrictor responses.

Conclusions These findings indicate that NO is involved in the central regulation of sympathetic outflow in humans and suggest that both neuronal and endothelial NO synthesis may contribute to the regulation of vasomotor tone.

Key Words: nervous system, autonomic • endothelium • exercise • endothelium-derived factors

	Introduction

Top Abstract Introduction Methods Results Discussion References

 
Over the past few years, nitric oxide (NO),¹ which is synthesized from the amino acid L-arginine by the enzyme NO synthase, has emerged as an important regulatory mechanism of vasomotor tone and arterial pressure in both animals and humans.^2–4 Studies in humans using N^G-monomethyl-L-arginine (L-NMMA), which by its action as a competitive stereospecific inhibitor of NO synthase inhibits both basal and stimulated NO synthesis, indicate that NO plays an important role in the regulation of basal vasomotor tone⁵ and in the mediation of vasodilatory responses to a variety of physiological^6,7 and pharmacological^5,8 stimuli. Studies in several animal species suggest that the pressor effects observed during systemic L-NMMA infusion are caused, at least in part, by alterations in sympathetic vasoconstrictor tone.^2,9–15 In the clinical setting, an impairment in NO synthesis and/or release has been demonstrated in hypercholesterolemia,^16,17 atherosclerosis,^18,19 heart failure,^20,21 and hypertension.^22,23 Such a loss of NO-induced vasodilator tone (and sympathoinhibition) could lead to exaggerated vasoconstrictor and pressor responses to mental and physical stress.²⁴

We examined effects of systemic inhibition of NO synthase by L-NMMA infusion on sympathetic nerve activity, regional vascular resistance, and arterial pressure both at rest and during static exercise, an intervention that evokes large increases in arterial pressure that are mediated by decreases in parasympathetic and increases in sympathetic efferent activity,²⁵ and compared these effects with those of phenylephrine infusion (an NO-independent vasoconstrictor).

	Methods

Top Abstract Introduction Methods Results Discussion References

 
Subjects
We studied 15 lean, healthy male volunteers (weight, 71.2±7.4 kg; height, 180±4 cm; body mass index, 22.1±1.9 kg/m²; age, 25±7 years, mean±SD). All subjects were normotensive, were taking no medications, and had no evidence of metabolic or cardiovascular disease. All the studies were performed in the morning after an overnight fast. The subjects were asked to abstain from alcohol, caffeine, and tobacco for at least 24 hours before each study. The experimental protocol was approved by the Institutional Review Board on Human Investigation, and all subjects provided written informed consent.

General Procedures
The subjects were studied in the supine position. Heart rate (ECG), respiratory excursions (pneumobelt), force of muscle contraction (Harpenden handgrip dynamometer, British Indicators Ltd), blood flow in the resting forearm and calf (venous occlusion plethysmography),²⁶ and efferent muscle sympathetic nerve activity (MSNA) were recorded continuously on an electrostatic recorder and a tape recorder (R71, TEAC Corp). Respiratory excursions were monitored to detect inadvertent performance of a Valsalva maneuver or prolonged expiration, because these respiratory maneuvers can markedly stimulate sympathetic outflow.²⁷ Blood pressure was measured with an automated sphygmomanometric system (Datascope Accutorr, Datascope Corp). Intravenous catheters were inserted into a right and a left antecubital vein, one for drug infusion and the other for blood sampling.

Recording of Sympathetic Nerve Activity
Multiunit recordings of postganglionic sympathetic nerve activity were obtained with unipolar tungsten microelectrodes inserted selectively into muscle nerve fasciculi of the peroneal nerve posterior to the fibular head by the microneurographic technique of Vallbo et al.²⁸ The neural signals were amplified 20 000 to 50 000 times, filtered (bandwidth, 700 to 2000 Hz), rectified, and integrated (time constant, 0.1 second) to obtain a mean voltage display of sympathetic activity. A recording of sympathetic activity was considered acceptable when it revealed spontaneous, pulse synchronous bursts of neural activity, with the largest bursts showing a minimal signal-to-noise ratio of 3:1. In each study, we documented that we were recording sympathetic outflow to skeletal muscle by demonstrating that the neural activity did not respond to arousal stimuli (loud noise) or a pinch of the skin but showed a characteristic biphasic response to the Valsalva maneuver.²⁹

For analysis, printed filtered and mean voltage neurograms were visually inspected to identify bursts of sympathetic nerve discharge. The recordings were all analyzed by the same observer who was blinded to the pharmacological intervention assigned to the subject. The intraobserver and interobserver coefficients of variation of the mean in identifying bursts are <6% and <9%, respectively.³⁰ Nerve traffic was expressed both as number of bursts per minute, an index of the frequency of the activity, and as bursts per minute times mean burst amplitude, an index of integrated (total) activity. For quantitative analysis, data were normalized by transcribing nerve recordings from FM tape to a hard copy in such a way that mean burst amplitudes were comparable in all subjects.

Measurement of Muscle Blood Flow
While recording sympathetic outflow to calf muscles in one leg, we simultaneously measured blood flow in the contralateral leg and forearm by venous occlusion plethysmography using mercury-in-Silastic strain gauges. The forearm and the calf were elevated 10 to 15 cm above the level of the right atrium to collapse the veins. Circulation to the hand and foot was arrested by inflating a cuff around the wrist and the ankle during blood flow determinations, which were performed at 15-second intervals over a 5-minute period.

Static Handgrip
At the beginning of each experiment, the subject's maximal voluntary contraction was determined using a handgrip dynamometer. Subjects performed static handgrip at 33% maximal voluntary contraction for 2 minutes, aided by a visual feedback of the force output.

Drugs
Drugs were dissolved in physiological saline immediately before use. L-NMMA and L-arginine were obtained from Clinalfa, phenylephrine from Winthrop Pharmaceuticals, and sodium nitroprusside from Roche.

Experimental Protocols
Protocol 1: Cardiovascular and Sympathetic Effects of L-NMMA Infusion at Rest
Nine subjects participated in this protocol. After instrumentation, the subjects rested quietly for 30 minutes. They then received sequential infusions of normal saline (1 mL/min) for 30 minutes, L-NMMA (50 µg · kg^-1 · min^-1) for 60 minutes, and L-arginine (50 mg · kg^-1 · min^-1) for 10 minutes. Hemodynamic measurements and sympathetic nerve activity were recorded for 5 minutes of each 15-minute period during the 30 minutes of saline and the 60 minutes of L-NMMA infusion and during the last 5 minutes of L-arginine infusion.

To determine the effects of inhibitory baroreflexes (activated by L-NMMA–induced increases in arterial pressure) on L-NMMA–induced sympathetic responses, we performed additional experiments in five of the nine subjects. The subjects received sequential infusions of normal saline for 30 minutes, phenylephrine (titrated at a rate to match the increase in arterial pressure produced by L-NMMA infusion) for 20 minutes, normal saline for 30 minutes, L-NMMA (50 µg · kg^-1 · min^-1) for 45 minutes, and concomitant L-NMMA and sodium nitroprusside (titrated at a rate to offset the L-NMMA–induced increase in arterial pressure) for 15 minutes. Hemodynamic measurements and sympathetic nerve activity were recorded for 5 minutes of each 15-minutes period during the 30-minute baseline period and during the last 10 minutes of phenylephrine, L-NMMA, and L-NMMA plus sodium nitroprusside infusion.

In three additional subjects, phenylephrine was infused over 60 minutes at a rate to mimic the temporal profile of the increase in blood pressure observed during the 60 minutes of L-NMMA infusion.

To examine the effects of time on sympathetic nerve activity, in five subjects we infused saline (1 mL/min) over 2 hours. This infusion did not have any detectable effect on sympathetic nerve activity; values for MSNA burst frequency (total activity) were 15±2 bursts per minute (159±15 U) before the start of infusion and 14±1 bursts per minute (138±13 U) and 15±1 bursts per minute (156±14 U) 60 and 120 minutes after the start of the saline infusion, respectively.

Protocol 2: Cardiovascular and Sympathetic Effects of L-NMMA Infusion During Static Exercise
Eight subjects participated in this protocol. In each subject, we measured hemodynamic and sympathetic responses during 2 minutes of static handgrip: one performed during saline infusion, and one performed 45 minutes after the start of L-NMMA infusion (50 µg · kg^-1 · min^-1).

To determine the effects of inhibitory baroreflexes (activated by L-NMMA–induced increases in arterial pressure) on exercise-induced sympathetic responses, we performed additional experiments in five more subjects. In each subject, we measured hemodynamic and sympathetic responses during three 2-minute bouts of static handgrip: one performed during saline infusion, one performed during phenylephrine infusion (titrated at a rate to match the increase in baseline arterial pressure produced by L-NMMA infusion), and one performed during L-NMMA (50 µg · kg^-1 · min^-1) infusion.

Protocol 3: Cardiovascular and Sympathetic Effects of High-Dose L-NMMA Infusion
To determine whether the differences between the findings of the present study and those of an earlier report³¹ were related to the much higher dose of L-NMMA infused, we performed additional experiments in three subjects in whom L-NMMA was infused at the rate (500 µg · kg^-1 · min^-1 for 15 minutes) used by Hansen et al.³¹ Hemodynamic measurements and sympathetic nerve activity were recorded for 5 minutes of each 15-minute period during the 30 minutes of baseline and during the entire 15-minute period of L-NMMA infusion.

Protocol 4: Cardiovascular Effects of L-Arginine Infusion in the Absence of L-NMMA
To exclude the possibility that in protocol 1, L-arginine was acting as a nonspecific vasodilator (rather than as a stereospecific substrate for NO synthase), in six subjects we examined effects of L-arginine infusion (50 mg · kg^-1 · min^-1 for 10 minutes) alone on arterial pressure and heart rate.

Protocol 5: Sympathetic Effects of Concomitant Infusion of L-NMMA and Nitroprusside From Baseline
To examine whether MSNA increases not only during the rapid reduction of blood pressure to its baseline values induced by adding nitroprusside to L-NMMA (protocol 1) but also when the increase in blood pressure is prevented, in five subjects we coinfused nitroprusside and L-NMMA from baseline. Particular care was taken not to lower blood pressure below the resting baseline level.

Data Analysis
Mean arterial pressure was calculated as diastolic pressure plus one third of the pulse pressure. Vascular resistance in the forearm and calf was determined as mean arterial pressure in millimeters of mercury divided by blood flow in milliliters per minute per 100 millimeters of tissue; it was expressed in units.

The measurements of MSNA, blood flow in the forearm and the calf, blood pressure, and heart rate that were collected over 5-minute periods were averaged to a single value.

Statistical analysis was performed with paired two-tailed t tests and ANOVA with repeated measures followed by Fisher's post hoc test. A value of P<.05 was considered significant. Data are given as mean±SE unless stated otherwise.

	Results

Top Abstract Introduction Methods Results Discussion References

 
Cardiovascular and Sympathetic Effects of L-NMMA Infusion at Rest
L-NMMA infusion, which increased mean arterial pressure progressively by 7±1 mm Hg (P<.001) and decreased heart rate by 3±1 bpm (P=.003), did not have any detectable sympathetic effect throughout the entire infusion period. Mean arterial pressure increased progressively from 78±2 mm Hg at baseline to 81±2, 82±2, and 85±2 mm Hg 15, 30, and 60 minutes, respectively, after the start of L-NMMA infusion, whereas MSNA burst frequency (total activity) remained unchanged: 22±2 bursts per minute (350±38 U) during saline infusion and 21±2, 19±2, and 23±3 bursts per minute (348±49, 321±34, and 371±45 U) during L-NMMA infusion. L-Arginine infusion rapidly reversed the L-NMMA–induced changes in arterial pressure and heart rate without altering MSNA (Tables 1 and 2 and Figs 1 and 2).

View this table: [in this window] [in a new window]   Table 1. Responses to L-NMMA Infusion at Rest

View this table: [in this window] [in a new window]   Table 2. Responses to L-NMMA and L-Arginine Infusion at Rest

View larger version (18K): [in this window] [in a new window]   Figure 1. Segments of representative recordings of muscle sympathetic nerve activity (MSNA) (and corresponding values of mean arterial pressure) in one subject obtained at baseline and during infusion of NG-monomethyl-L-arginine (L-NMMA), L-NMMA plus nitroprusside, or phenylephrine. Each peak represents a spontaneous burst of sympathetic nerve discharge.

View larger version (16K): [in this window] [in a new window]   Figure 2. Mean±SE effects in five subjects of infusion of NG-monomethyl-L-arginine (L-NMMA), phenylephrine (PE), or L-NMMA plus nitroprusside (NP) on heart rate, arterial pressure, and muscle sympathetic nerve activity (MSNA). *P<.05 vs basal.

Phenylephrine infusion and L-NMMA infusion, which increased mean arterial pressure comparably (by 8±1 and 7±1 mm Hg, respectively), evoked directionally opposite effects on MSNA; during phenylephrine infusion, MSNA burst frequency decreased by 8±1 bursts per minute, whereas it increased by 2±2 bursts per minute during L-NMMA infusion (P=.016). When phenylephrine was infused over 60 minutes to mimic the temporal profile of the increase in blood pressure during L-NMMA infusion, MSNA burst frequency decreased from 20±1 bursts per minute (362±40 U) at baseline to 10±2, 8±1, and 8±1 bursts per minute (138±9, 113±7 and 108±22 U) 15, 30, and 60 minutes, respectively, after the start of the phenylephrine infusion.

When during L-NMMA infusion sodium nitroprusside was coinfused to offset the L-NMMA–induced increase in arterial pressure, the MSNA burst frequency was roughly twofold higher than during saline infusion (37±5 versus18±4 bursts per minute, P=.04). Similarly, when sodium nitroprusside and L-NMMA were coinfused from baseline, the L-NMMA–induced increase in arterial pressure was prevented (mean arterial pressure was 84±5 mm Hg at baseline and 84±5 and 83±6 mm Hg after 30 and 60 minutes, respectively, of L-NMMA/nitroprusside infusion), whereas MSNA burst frequency (and total activity) now increased more than twofold (P<.001) from 11±2 bursts per minute (270±60 U) at baseline to 25±5 bursts per minute (659±90 U) and 29±4 bursts per minute (756±176 U) after 30 and 60 minutes, respectively, of L-NMMA/sodium nitroprusside infusion.

Cardiovascular and Sympathetic Effects of L-NMMA Infusion During Static Exercise
Resting mean arterial pressure was higher during systemic L-NMMA infusion than during saline infusion (93±3 versus 84±3 mm Hg, P=.02), whereas resting MSNA burst frequency was similar under both conditions. Static handgrip evoked increases in mean arterial pressure, heart rate, and MSNA that were comparable in both time course and magnitude during saline infusion and L-NMMA infusion. L-NMMA infusion attenuated the decrease in resting forearm vascular resistance during the first minute of handgrip; it decreased by 24.7±7.4% during saline infusion but by only 9.5±6.6% during L-NMMA infusion (P=.049) (Table 3 and Figs 3 and 4).

View this table: [in this window] [in a new window]   Table 3. Effects of L-NMMA Infusion on Cardiovascular and Sympathetic Responses to Handgrip

View larger version (13K): [in this window] [in a new window]   Figure 3. Mean±SE heart rate, blood pressure, and muscle sympathetic nerve activity (MSNA) responses in five subjects to static handgrip at 33% maximal voluntary contraction performed alone () or during concomitant infusion of either NG-monomethyl-L-arginine (L-NMMA) () or phenylephrine (o). During L-NMMA and phenylephrine infusion, the baseline arterial pressure was significantly (P<.05) higher than during control, but the handgrip-induced increases in arterial pressure were comparable under all three conditions. The handgrip-induced sympathetic activation was preserved during L-NMMA infusion but attenuated during phenylephrine infusion (P<.001 for the comparison of handgrip plus phenylephrine with either handgrip plus L-NMMA or handgrip alone).

View larger version (10K): [in this window] [in a new window]   Figure 4. Mean±SE changes in resting forearm blood flow in eight subjects during the first minute of static handgrip performed during concomitant infusion of either NG-monomethyl-L-arginine (L-NMMA) or saline. *P<.05 saline vs L-NMMA infusion.

Phenylephrine and L-NMMA infusion increased baseline mean arterial pressure similarly by 9±2 mm Hg (P=.016 versus saline infusion) and 9±1 mm Hg (P=.002 versus saline infusion) above the values observed during saline infusion (Fig 3). Static handgrip evoked increases in mean arterial pressure that were similar during infusion of phenylephrine (22±5 mm Hg), L-NMMA (24±7 mm Hg), and saline (25±6 mm Hg). In contrast, the exercise-induced sympathetic activation was markedly attenuated during phenylephrine infusion; during the second minute of handgrip, MSNA burst frequency increased by 18±1 bursts per minute during saline infusion, by 19±3 bursts per minute during L-NMMA infusion, but by only 3±1 bursts per minute (73±20 U) during phenylephrine infusion (F=40.4, P<.0001 versus saline infusion and F=18.9, P<.001 versus L-NMMA infusion).

High-Dose L-NMMA Infusion
In contrast to low-dose L-NMMA infusion (protocols 1 and 2), high-dose L-NMMA infusion rapidly and markedly increased mean arterial pressure and decreased MSNA and heart rate. All three variables had reached a new plateau within 5 minutes of the start of infusion; at the end of the 15 minutes of L-NMMA infusion, mean arterial pressure had increased from 80±3 to 90±2 mm Hg (P=.007), heart rate had decreased from 53±4 to 43±4 bpm (P=.01), MSNA burst frequency had decreased from 22±2 to 7±1 bursts per minute (P=.01), and MSNA total activity had decreased from 302±42 to 95±9 U (P=.01).

Cardiovascular Effects of L-Arginine Infusion in the Absence of L-NMMA
L-Arginine infusion alone (in contrast to infusion after L-NMMA; protocol 1) did not have any detectable effect on mean arterial pressure (72±3 mm Hg at baseline and 71±2 mm Hg at the end of the 10-minute infusion) or heart rate (55±4 and 54±5 bpm, respectively).

	Discussion

Top Abstract Introduction Methods Results Discussion References

 
The major new findings are that (1) under resting conditions, systemic inhibition of NO synthase by L-NMMA infusion, which increased mean arterial pressure by 10%, did not have any detectable effect on MSNA, whereas a similar increase in arterial pressure evoked by phenylephrine infusion decreased the rate of sympathetic nerve firing by roughly 50 percent; (2) during static handgrip, the exercise-induced sympathetic nerve responses were preserved during L-NMMA infusion but markedly attenuated during phenylephrine infusion; (3) the L-NMMA–induced loss of vasodilator tone did not result in exaggerated exercise-induced pressor and calf vasoconstrictor responses; and (4) L-NMMA infusion attenuated the exercise-induced vasodilation in the resting forearm at the beginning of isometric exercise. These results indicate that systemic inhibition of NO synthase has sympathoexcitatory effects in humans and suggest that NO, in addition to its direct vasodilator action, plays a role in the neural regulation of vascular tone. Moreover, these data suggest that in healthy subjects, inhibition of nitric oxide release does not lead to exaggerated vasoconstrictor responses during static exercise.

Studies in animals have provided evidence that neuronal NO is involved in the central regulation of sympathetic outflow.^2,9–15 Here, we provide the first such evidence in humans. This interpretation is based on the following observations. First, during L-NMMA infusion, the progressive increase in arterial pressure—in marked contrast to phenylephrine infusion—was not accompanied by any detectable decrease in MSNA, indicating a sympathoexcitatory effect of NO synthase inhibition (as further evidenced by the handgrip studies). Second, when the L-NMMA–induced increase in arterial pressure was either reversed or prevented by concomitant nitroprusside infusion, the rate of sympathetic nerve firing was roughly twofold higher than that observed at the same arterial pressure at baseline. This finding indicates that normally the L-NMMA–induced sympathetic activation is masked by an inhibitory effect of arterial baroreflexes (whose function is preserved³² or even augmented³³ during acute NO synthase inhibition), an interpretation that is consistent with observations made in anesthetized animals.¹⁰ Third, when L-NMMA infusion was followed by L-arginine infusion, the L-arginine–induced decrease in arterial pressure (an effect caused specifically by restoration of NO synthesis as evidenced by protocol 4) did not trigger any detectable increase in MSNA. This observation further strengthens the interpretation that NO is involved in the tonic restraint of sympathetic outflow.^2,9–15

The vascular actions of nitric oxide have been the focus of much interest, and it has been postulated that impaired production and release of NO could lead to exaggerated and paradoxical vasoconstrictor responses to physical stress.²⁵ Our findings challenge this concept and demonstrate that even though baseline arterial pressure was significantly higher during NO synthase inhibition, the exercise-induced increases in blood pressure (and calf vascular resistance) were comparable, not larger than those evoked by handgrip alone. Moreover, our data indicate that the lack of an exaggerated exercise-induced pressor response during L-NMMA infusion cannot be explained on the basis of an attenuated sympathetic nerve response to this form of exercise, because MSNA increased comparably during handgrip performed alone and performed during L-NMMA infusion. The latter finding contrasts with the markedly attenuated exercise-induced sympathetic responses observed during phenylephrine infusion and provides further evidence for a sympathoexcitatory effect of NO synthase inhibition in humans. This observation is consistent with findings in ex vivo and anesthetized in vivo animal preparations^2,9–15 but differs from those of a recent study in humans that provided no evidence for a sympathoexcitatory effect of L-NMMA infusion.³³ This difference appears to be related to the infusion in this earlier study of much larger (up to nine times) doses of L-NMMA over a short period of time (as evidenced by our high-dose L-NMMA infusion studies), a finding that is expected to have important implications on the design of future studies examining the role of NO in the regulation of sympathetic neural outflow in humans. The underlying mechanism(s) for the differential sympathetic and hemodynamic effects of low- and high-dose L-NMMA infusion are not clear but could include different ED₅₀ doses for L-NMMA–induced blockade of neural versus endothelial NO synthesis. Alternatively, the tonic central neural restraint on sympathetic outflow by NO may be to limited, for its withdrawal to counterbalance the baroreflex-mediated sympathoinhibition evoked by the higher blood pressure rise during high-dose L-NMMA infusion.

In the resting forearm, blood flow increases and vascular resistance decreases during the first minute of static handgrip, an observation that has been attributed to stimulation of cholinergic vasodilator mechanisms.³⁴ The present findings suggest that stimulation of NO release through activation of cholinergic³⁵ and/or nonadrenergic noncholinergic³⁶ pathways plays an important role in the mediation of the exercise-induced vasodilation in the resting forearm.

This study shows that NO is involved in the central regulation of sympathetic outflow in humans and suggests that both neuronal and endothelial NO synthesis may contribute to the regulation of vasomotor tone. In these short-term experiments in healthy subjects, inhibition of NO synthase had sympathoexcitatory effects that were masked by an inhibitory effect of the baroreflexes. It is possible that in disease states such as heart failure that are characterized by an impairment in both baroreflex function and NO synthesis and release, the conjunction of these two defects could be one of the factors contributing to sustained sympathetic activation.

	Acknowledgments

 
This work was supported by grants from the Swiss National Science Foundation (32-36280.92 and 32-46797.96), the International Olympic Committee, the Emma Muschamp Foundation, and the Placide Nicod Foundation. We are indebted to Vincent Pichot for help with some of the final studies.

	Footnotes

 
Presented in part at the 67th Scientific Sessions of the American Heart Association, Dallas, Tex, November 14–17, 1994, and at the 68th Scientific Sessions of the American Heart Association, Anaheim, Calif, November 13–16, 1995, and published in abstract form (Circulation. 1994;90[suppl I]:I-316, and Circulation. 1995;92[suppl I]:I-12).

Received April 30, 1997; revision received August 4, 1997; accepted August 20, 1998.

	References

Top Abstract Introduction Methods Results Discussion References

 

1. Palmer RMJ, Ashton DS, Moncada S. Vascular endothelial cells synthesize nitric oxide from L-arginine. Nature. 1988;333:664-666.[Medline] [Order article via Infotrieve]
   
2. Zanzinger J, Czachurski J, Seller H. Inhibition of sympathetic vasoconstriction is a major principle of vasodilation by nitric oxide in vivo. Circ Res. 1994;75:1073-1077.[Abstract/Free Full Text]
   
3. Moncada S, Higgs A. The L-arginine-nitric oxide pathway. N Engl J Med. 1993;329:2002-2012.[Free Full Text]
   
4. Haynes WG, Noon JP, Walker BR, Webb DJ. Inhibition of nitric oxide synthesis increases blood pressure in healthy humans. J Hypertens. 1993;11:1375-1380.[Medline] [Order article via Infotrieve]
   
5. Vallance P, Collier J, Moncada S. Effects of endothelium-derived nitric oxide in peripheral arteriolar tone in man. Lancet. 1989;2:997-1000.[Medline] [Order article via Infotrieve]
   
6. Pohl U, Busse R. Hypoxia stimulates the release of endothelium-derived relaxant factor (EDRF). Am J Physiol. 1989;256:H1595-H1600.[Abstract/Free Full Text]
   
7. Scherrer U, Randin D, Vollenweider P, Vollenweider L, Nicod P. Nitric oxide accounts for insulin's vascular effects in humans. J Clin Invest. 1995;94:2511-2515.
   
8. Tagawa T, Imaizumi T, Endo T, Shiramoto M, Hirooka Y, Ando S, Takeshita A. Vasodilatory effect of arginine vasopressin is mediated by nitric oxide in human forearm vessels. J Clin Invest. 1993;92:1483-90.
   
9. Harada S, Tokunaga S, Momohara M, Masaki H, Tagawa T, Imaizumi T, Takeshita A. Inhibition of nitric oxide formation in the nucleus tractus solitarius increases renal sympathetic nerve activity in rabbits. Circ Res. 1993;72:511-516.[Abstract/Free Full Text]
   
10. Sakuma I, Togashi H, Yoshioka M, Saito H, Yanagida M, Tamura M, Kobayashi T, Yasuda H, Gross SS, Levi R. N^G-methyl-L-arginine, an inhibitor of L-arginine-derived nitric oxide synthesis, stimulates renal sympathetic nerve activity in vivo. Circ Res. 1992;70:607-611.[Abstract/Free Full Text]
    
11. Tagawa T, Imaizumi T, Harada S, Endo T, Shiramoto M, Hirooka Y, Takeshita A. Nitric oxide influences neuronal activity in the nucleus tractus solitarius of rat brainstem slices. Circ Res. 1994;75:70-76.[Abstract/Free Full Text]
    
12. Toda N, Kitamura Y, Okamura T. Neural mechanism of hypertension by nitric oxide synthase inhibitor in dogs. Hypertension. 1993;21:3-8.[Abstract/Free Full Text]
    
13. Togashi H, Sakuma I, Yoshioka M, Kobayashi T, Yasuda H, Kitabatake A, Saito H, Gross SS, Levi R. A central nervous system action of nitric oxide in blood pressure regulation. J Pharmacol Exp Ther. 1992;262:343-347.[Abstract/Free Full Text]
    
14. Togashi H, Yoshioka M, Sakuma I, Matsumoto M, Saito H, Kitabatake A, Levi R. Central sympathectomy attenuates the hypertensive response to the acute and chronic administration of nitric oxide synthase inhibitors. Circulation. 1994;90(suppl I):I-33. Abstract.
    
15. Yoshida K, Okamura T, Kimura H, Bredt DS, Snyder SH, Toda N. Nitric oxide synthase-immunoreactive nerve fibers in dog cerebral and peripheral arteries. Brain Res. 1993;629:67-72.[Medline] [Order article via Infotrieve]
    
16. Creager MA, Cooke JP, Mendelsohn ME, Gallagher SJ, Coleman SM, Loscalzo J, Dzau VJ. Impaired vasodilation of forearm resistance vessels in hypercholesterolemic humans. J Clin Invest. 1990;86:228-234.
    
17. Casino PR, Kilcoyne CM, Quyyumi AA, Hoeg JM, Panza JA. Role of nitric oxide in the endothelium-dependent vasodilation of hypercholesterolemic patients. Circulation. 1993;88:2541-2547.[Abstract/Free Full Text]
    
18. Ludmer PL, Selwyn AP, Shook TL, Wayne RR, Mudge GH, Alexander RW, Ganz P. Paradoxical vasoconstriction induced by acetylcholine in atherosclerotic coronary arteries. N Engl J Med. 1986;315:1046-1051.[Abstract]
    
19. Zeiher AM, Drexler H, Wollschläger H, Just H. Modulation of coronary vasomotor tone in humans: progressive endothelial dysfunction with different early stages of coronary atherosclerosis. Circulation. 1991;83:391-401.[Abstract/Free Full Text]
    
20. Kubo SH, Rector TS, Bank AJ, Williams RE, Heifetz SM. Endothelium-dependent vasodilation is attenuated in patients with heart failure. Circulation. 1991;84:1589-1596.[Abstract/Free Full Text]
    
21. Drexler H, Hayoz D, Münzel T, Hornig B, Just H, Brunner HR, Zelis R. Endothelial function in chronic congestive heart failure. Am J Cardiol. 1992;69:1596-1601.[Medline] [Order article via Infotrieve]
    
22. Panza J, Quyyumi AA, Brush JE, Epstein SE. Abnormal endothelium-dependent vascular relaxation in patients with essential hypertension. N Engl J Med. 1990;323:22-27.[Abstract]
    
23. Linder L, Kiowski W, Bühler FR, Lüscher TF. Indirect evidence for release of endothelium-derived relaxing factor in the human forearm circulation in vivo: blunted response in essential hypertension. Circulation. 1990;81:1762-1767.[Abstract/Free Full Text]
    
24. Ånggard E. Nitric oxide: mediator, murderer, and medicine. Lancet. 1994;343:1199-206.[Medline] [Order article via Infotrieve]
    
25. Martin CE, Shaver JA, Leon DF, Thompson ME, Reddy PS, Leonard JJ. Autonomic mechanisms in hemodynamic responses to isometric exercise. J Clin Invest. 1974;54:104-115.
    
26. Greenfield ADM, Whitney RJ, Mowbray JF. Methods for investigation of peripheral blood flow. Br Med Bull. 1963;19:101-109.[Free Full Text]
    
27. Delius W, Hagbarth K-E, Hongell A, Wallin BG. Maneuvers affecting sympathetic outflow in human muscle nerves. Acta Physiol Scand. 1972;84:82-94.[Medline] [Order article via Infotrieve]
    
28. Vallbo AB, Hagbarth K-E, Torebjörk HE, Wallin BG. Somatosensory, proprioceptive, and sympathetic activity in human peripheral nerves. Physiol Rev. 1979;59:919-957.[Free Full Text]
    
29. Randin D, Vollenweider P, Tappy L, Jéquier E, Nicod P, Scherrer U. Suppression of alcohol-induced hypertension by dexamethasone. N Engl J Med. 1995;332:1733-1737.[Abstract/Free Full Text]
    
30. Vollenweider P, Tappy L, Randin D, Schneiter P, Jéquier E, Nicod P. Differential effects of hyperinsulinemia and carbohydrate metabolism on sympathetic nerve activity and muscle blood flow in humans. J Clin Invest. 1993;92:147-154.
    
31. Hansen J, Jacobsen TN, Victor RG. Is nitric oxide involved in the tonic inhibition of central sympathetic outflow in humans? Hypertension. 1994;24:439-444.[Abstract/Free Full Text]
    
32. Miyano H, Kawada T, Matsuura W, Sato T, Sunagawa K. Nitric oxide blockade increases sympathetic nerve activities without changing dynamic property of baroreflex. Circulation. 1995;92(suppl I):I-13. Abstract.
    
33. Liu J-L, Murakami H, Zucker IH. Nitric oxide affects the arterial baroreflex control of renal sympathetic nerve activity in conscious rabbits. Circulation. 1995;92(suppl I):I-13. Abstract.
    
34. Sanders JS, Mark AL, Ferguson DW. Evidence of cholinergically mediated vasodilation at the beginning of isometric exercise in humans. Circulation. 1989;79:815-824.[Abstract/Free Full Text]
    
35. Loke KE, Sobey CG, Dusting GJ, Woodman OL. Cholinergic neurogenic vasodilation is mediated by nitric oxide in the dog hindlimb. Cardiovasc Res. 1994;28:542-547.[Abstract/Free Full Text]
    
36. Rand MJ. NANC transmission: nitric oxide as a mediator of non-adrenergic, non-cholinergic neuro-effector transmission. Clin Exp Pharmacol Physiol. 1992;19:147-169.[Medline] [Order article via Infotrieve]
    

This article has been cited by other articles:

				K. Ramasubbu, J. Estep, D. L. White, A. Deswal, and D. L. Mann Experimental and clinical basis for the use of statins in patients with ischemic and nonischemic cardiomyopathy. J. Am. Coll. Cardiol., January 29, 2008; 51(4): 415 - 426. [Abstract] [Full Text] [PDF]

				P. A. Kaufmann, O. E. Rimoldi, T. Gnecchi-Ruscone, T. F. Luscher, and P. G. Camici Systemic nitric oxide synthase inhibition improves coronary flow reserve to adenosine in patients with significant stenoses Am J Physiol Heart Circ Physiol, October 1, 2007; 293(4): H2178 - H2182. [Abstract] [Full Text] [PDF]

				J. Sugawara, H. Komine, K. Hayashi, M. Yoshizawa, T. Otsuki, N. Shimojo, T. Miyauchi, T. Yokoi, S. Maeda, and H. Tanaka Systemic {alpha}-adrenergic and nitric oxide inhibition on basal limb blood flow: effects of endurance training in middle-aged and older adults Am J Physiol Heart Circ Physiol, September 1, 2007; 293(3): H1466 - H1472. [Abstract] [Full Text] [PDF]

				D. Gentilcore, R. Visvanathan, A. Russo, R. Chaikomin, J. E. Stevens, J. M. Wishart, A. Tonkin, M. Horowitz, and K. L. Jones Role of nitric oxide mechanisms in gastric emptying of, and the blood pressure and glycemic responses to, oral glucose in healthy older subjects Am J Physiol Gastrointest Liver Physiol, June 1, 2005; 288(6): G1227 - G1232. [Abstract] [Full Text] [PDF]

				M. Lindqvist, A. Melcher, and P. Hjemdahl Hemodynamic and sympathoadrenal responses to mental stress during nitric oxide synthesis inhibition Am J Physiol Heart Circ Physiol, November 1, 2004; 287(5): H2309 - H2315. [Abstract] [Full Text] [PDF]

				P. A. Kaufmann, O. Rimoldi, T. Gnecchi-Ruscone, R. S. Bonser, T. F. Luscher, and P. G. Camici Systemic Inhibition of Nitric Oxide Synthase Unmasks Neural Constraint of Maximal Myocardial Blood Flow in Humans Circulation, September 14, 2004; 110(11): 1431 - 1436. [Abstract] [Full Text] [PDF]

				L. Stoner, M. Sabatier, K. Edge, and K. McCully Relationship between blood velocity and conduit artery diameter and the effects of smoking on vascular responsiveness J Appl Physiol, June 1, 2004; 96(6): 2139 - 2145. [Abstract] [Full Text] [PDF]

				K. F. Harris and K. A. Matthews Interactions Between Autonomic Nervous System Activity and Endothelial Function: A Model for the Development of Cardiovascular Disease Psychosom Med, March 1, 2004; 66(2): 153 - 164. [Abstract] [Full Text] [PDF]

				F. Mallamaci, G. Tripepi, R. Maas, L. Malatino, R. Boger, and C. Zoccali Analysis of the Relationship between Norepinephrine and Asymmetric Dimethyl Arginine Levels among Patients with End-Stage Renal Disease J. Am. Soc. Nephrol., February 1, 2004; 15(2): 435 - 441. [Abstract] [Full Text] [PDF]

				J. Cui, R. Zhang, T. E. Wilson, S. Witkowski, C. G. Crandall, and B. D. Levine Nitric oxide synthase inhibition does not affect regulation of muscle sympathetic nerve activity during head-up tilt Am J Physiol Heart Circ Physiol, November 1, 2003; 285(5): H2105 - H2110. [Abstract] [Full Text] [PDF]

				G. Cotter, E. Kaluski, O. Milo, A. Blatt, A. Salah, A. Hendler, R. Krakover, A. Golick, and Z. Vered LINCS: L-NAME (a NO synthase inhibitor) In the treatment of refractory Cardiogenic Shock: A prospective randomized study Eur. Heart J., July 2, 2003; 24(14): 1287 - 1295. [Abstract] [Full Text] [PDF]

				N. Toda and T. Okamura The Pharmacology of Nitric Oxide in the Peripheral Nervous System of Blood Vessels Pharmacol. Rev., June 1, 2003; 55(2): 271 - 324. [Abstract] [Full Text] [PDF]

				R. U. Pliquett, K. G. Cornish, J. D. Peuler, and I. H. Zucker Simvastatin Normalizes Autonomic Neural Control in Experimental Heart Failure Circulation, May 20, 2003; 107(19): 2493 - 2498. [Abstract] [Full Text] [PDF]

				J. Tank, A. Diedrich, C. Schroeder, M. Stoffels, G. Franke, A. M. Sharma, F. C. Luft, and J. Jordan Limited Effect of Systemic {beta}-Blockade on Sympathetic Outflow Hypertension, December 1, 2001; 38(6): 1377 - 1381. [Abstract] [Full Text] [PDF]

				M. Lepori, C. Sartori, H. Duplain, P. Nicod, and U. Scherrer Interaction between cholinergic and nitrergic vasodilation: a novel mechanism of blood pressure control Cardiovasc Res, September 1, 2001; 51(4): 767 - 772. [Abstract] [Full Text] [PDF]

				J. Jordan, J. Tank, M. Stoffels, G. Franke, N. J. Christensen, F. C. Luft, and M. Boschmann Interaction between {beta}-Adrenergic Receptor Stimulation and Nitric Oxide Release on Tissue Perfusion and Metabolism J. Clin. Endocrinol. Metab., June 1, 2001; 86(6): 2803 - 2810. [Abstract] [Full Text] [PDF]

				R. Bergholm, J. Westerbacka, S. Vehkavaara, A. Seppälä-Lindroos, T. Goto, and H. Yki-Järvinen Insulin Sensitivity Regulates Autonomic Control of Heart Rate Variation Independent of Body Weight in Normal Subjects J. Clin. Endocrinol. Metab., March 1, 2001; 86(3): 1403 - 1409. [Abstract] [Full Text]

				B. Martínez-Nieves and J. C. Dunbar The Effect of Diabetes and Sex on Nitric Oxide-Mediated Cardiovascular Dynamics Experimental Biology and Medicine, January 1, 2001; 226(1): 37 - 42. [Abstract] [Full Text]

				B. A. KINGWELL Nitric oxide-mediated metabolic regulation during exercise: effects of training in health and cardiovascular disease FASEB J, September 1, 2000; 14(12): 1685 - 1696. [Abstract] [Full Text]

				S. Chowdhary, J. C. Vaile, J. Fletcher, H. F. Ross, J. H. Coote, and J. N. Townend Nitric Oxide and Cardiac Autonomic Control in Humans Hypertension, August 1, 2000; 36(2): 264 - 269. [Abstract] [Full Text] [PDF]

				C. Sartori, L. Trueb, P. Nicod, and U. Scherrer Effects of Sympathectomy and Nitric Oxide Synthase Inhibition on Vascular Actions of Insulin in Humans Hypertension, October 1, 1999; 34(4): 586 - 589. [Abstract] [Full Text] [PDF]

				C. SARTORI, M. LEPORI, T. BUSCH, H. DUPLAIN, W. HILDEBRANDT, P. BÄRTSCH, P. NICOD, K. J. FALKE, and U. SCHERRER Exhaled Nitric Oxide Does Not Provide a Marker of Vascular Endothelial Function in Healthy Humans Am. J. Respir. Crit. Care Med., September 1, 1999; 160(3): 879 - 882. [Abstract] [Full Text]

				M. Lepori, C. Sartori, H. Duplain, P. Nicod, and U. Scherrer Sympathectomy potentiates the vasoconstrictor response to nitric oxide synthase inhibition in humans Cardiovasc Res, August 15, 1999; 43(3): 739 - 743. [Abstract] [Full Text] [PDF]