(Circulation. 1996;93:2135-2141.)
© 1996 American Heart Association, Inc.
Articles |
From the Cardiovascular Division, Department of Medicine, University of Minnesota Medical School, Minneapolis.
Correspondence to Thomas S. Rector, PhD, Box 508 UMHC, University of Minnesota Medical School, 420 Delaware St SE, Minneapolis, MN 55455.
| Abstract |
|---|
|
|
|---|
Methods and Results Fifteen subjects were given 6 weeks of oral L-arginine hydrochloride (5.6 to 12.6 g/d) and 6 weeks of matched placebo capsules in random sequence. Compared with placebo, supplemental oral L-arginine significantly increased forearm blood flow during forearm exercise, on average from 5.1±2.8 to 6.6±3.4 mL·min-1·dL-1 (P<.05). Furthermore, functional status was significantly better on L-arginine compared with placebo, as indicated by increased distances during a 6-minute walk test (390±91 versus 422±86 m, P<.05) and lower scores on the Living With Heart Failure questionnaire (55±28 versus 42±26, P<.05). Oral L-arginine also improved arterial compliance from 1.99±0.38 to 2.36±0.30 mL/mm Hg (P<.001) and reduced circulating levels of endothelin from 1.9±1.1 to 1.5±1.1 pmol/L (P<.05).
Conclusions Supplemental oral L-arginine had beneficial effects in patients with heart failure. Further studies are needed to confirm the therapeutic potential of supplemental oral L-arginine and to identify mechanisms of action in patients with heart failure.
Key Words: heart failure endothelium L-arginine
| Introduction |
|---|
|
|
|---|
Endothelial cells produce nitric oxide from
L-arginine via nitric oxide synthase.9 Studies
using tracer amounts of [15N]L-arginine
demonstrated that
1% of dietary L-arginine appears in
the urine as labeled nitrate, but the effect of changes in dietary
L-arginine on vascular nitric oxide formation is not
known.10 Under normal conditions, an excess of
L-arginine is available for endothelial
cells, on the basis of in vitro determinations of nitric oxide synthase
kinetics. However, in vitro formation of nitric oxide in response to
endothelium-dependent vasodilators can be
improved by L-arginine when L-arginine stores
are depleted or in the presence of
L-glutamine.11 12 Furthermore, studies of
patients with abnormal endothelium-dependent
vasodilatation related to atherosclerosis or heart
transplantation have observed significant improvements during
short-term intravenous infusions of
L-arginine.13 14
Intra-arterial L-arginine also enhanced the
forearm vasodilator response to acetylcholine, an
endothelium-dependent vasodilator, in patients with
heart failure.15 These studies suggest that, under some
conditions, supplemental L-arginine may augment nitric
oxide production.
The objective of this investigation was to determine whether supplemental oral L-arginine improves peripheral blood flow in patients with heart failure at rest or when stimulated by exercise, postischemic hyperemia, or an endothelium-dependent vasodilator. In addition, measures of submaximal exercise tolerance and quality of life were examined to determine whether supplemental oral L-arginine might produce clinical benefits.
| Methods |
|---|
|
|
|---|
6.2 mmol/L (240 mg/dL).
|
Seven patients were randomly assigned to placebo followed by L-arginine, and 8 patients were assigned to the opposite sequence of treatments. During the 6-week treatment period, patients were given either 2.8 g L-arginine hydrochloride (Tyson and Associates, Inc) twice daily (n=9) or 4.2 g three times daily (n=6). The initial dose of oral L-arginine was selected to double the estimated average daily dietary intake of L-arginine. However, we did not evaluate the actual dietary intake of L-arginine in these patients. In an attempt to detect a dose effect, we arbitrarily increased the amount of supplemental L-arginine 2.5 times after 10 subjects were enrolled. Significant effects were seen after 10 weeks of oral L-arginine treatment in animals.16 Six-week treatment periods were used in this study to increase the likelihood that these patients with severe heart failure would remain stable for the entire study.
Matching placebo capsules were administered during the 6-week control period to mask the identity of study capsules.
Study Assessments
The following sequence of measurements was made at the end of
each 6-week treatment period. Medications were withheld on the morning
of these evaluations. First, study nurses read standard instructions
and then asked the patients to complete the Living With Heart Failure
questionnaire to ascertain how their heart failure had affected their
quality of life.17 18 The total distance covered during a
6-minute walk test was used as a measure of exercise tolerance during
daily activities.19 20 A standard set of instructions was
read each time the walk test was done. Patients were told to walk as
far as they could in 6 minutes in an isolated 60-foot hallway. During
the walk test, patients were periodically encouraged to go as far as
they could. Rest stops were allowed if symptoms became too
bothersome.
Vascular function was examined at the end of each 6-week period by a
regionally perfused forearm technique. Forearm blood flow was measured
by venous occlusion plethysmography. Patients rested in the supine
position with their nondominant forearm abducted
30° and raised to
midchest position. A mercury-in-Silastic strain gauge was placed
around the upper forearm and connected to a calibrated plethysmograph
to measure forearm blood flow as the rate of change of forearm volume
(mL·min-1·100
mL-1 forearm volume). Venous occlusion
was induced by rapid inflation of a blood pressure cuff placed around
the upper arm to 40 mm Hg (D.E. Hokanson, Inc). Hand blood flow was
excluded by a wrist cuff inflated to suprasystolic pressure
before each measurement, which was the average of three
recordings. Room temperature was constant during each day of
study and did not vary by more than 1°C between study days. Forearm
volume was calculated as the volume of a truncated cone based on wrist
and upper forearm circumference and forearm length. The average forearm
volume was 1097±169 mL.
After measurement of baseline forearm blood flow, forearm exercise was performed with a hand dynamometer set at 15%, 30%, and 45% of each patient's maximal voluntary contraction as has been previously described.21 The exercise protocol consisted of cycles of 5 seconds of contraction followed by 10 seconds of relaxation. Patients exercised for 2 minutes, then forearm blood flow was measured 5 seconds into each relaxation phase during the third minute of exercise. When flow had returned to baseline, a 5-minute period of forearm ischemia was created by inflation of the cuff around the upper arm to suprasystolic pressure. Flow measurements taken immediately after the pressure occlusion was deflated and after 15, 30, 45, and 60 seconds were used to characterize the amount of reactive hyperemia.
A 20-gauge cannula was then inserted under local lidocaine anesthesia into the brachial artery of the same arm to study responses to intra-arterial administration of an endothelium-dependent vasodilator, methacholine, and an endothelium-independent vasodilator, nitroprusside. Patients rested quietly for 30 minutes after catheter insertion before baseline blood samples, blood pressure, and heart rate were obtained. Baseline forearm blood flow was measured, followed by infusion of methacholine at 0.3, 1.5, and 3.0 µg/min, with measurement of flow at the end of each 90-second infusion. When baseline flow was reestablished, the responses to three doses of nitroprusside, 1, 5, and 10 µg/min, were determined in the same manner. Finally, a competitive inhibitor of nitric oxide synthase, L-N-monomethylarginine, was administered to assess basal nitric oxide activity. First, baseline flow was reestablished, then flow was measured at the end of two cumulative 4-minute infusions of L-N-monomethylarginine (4 and 8 µmol/min).
Vascular smooth muscle relaxation can increase arterial compliance as well as lower arteriolar resistance.22 Arterial compliance was estimated by pulse contour analysis.23 24 Pressure waves were obtained by placing a tonometer sensor array (model N-500, Nellcor) over the radial artery of the nondominant arm. Tonometer dispersions were calibrated by use of synchronized automatic blood pressure cuff measurements taken from the contralateral arm. Pressure waveforms from several stable beats captured over 30 seconds were fit by nonlinear least-squares regression to a modified Windkessel model resulting in two separate compliance indexes based on the exponential decay of the diastolic portion of the wave form (C1) and the superimposed decaying sinusoidal waveform (C2).
The effects of L-arginine on several vasoconstrictor pathways that are often activated in patients with heart failure were also examined because of previous reports suggesting that increased nitric oxide activity may interact with the sympathetic nervous system or endothelin.25 26 27 Plasma endothelin was quantified by radioimmunoassay.28 The rabbit antibody used (Peninsula Laboratories, Inc) had 100% cross-reactivity with endothelin-1, 7% with endothelin-2 and -3, and 17% with big endothelin. The normal range for endothelin in our laboratory is 0.2 to 1.9 pmol/L. Plasma norepinephrine was measured by high-performance liquid chromatography with electrochemical detection.29 Our normal plasma norepinephrine ranges from 0.8 to 1.9 nmol/L. Plasma renin activity was determined by a radioimmunoassay with a normal range from 0.12 to 0.85 nmol·h-1·L-1. The concentration of L-arginine in plasma was determined by our hospital laboratory, in which normal values range from 20 to 180 µmol/L.
Safety measures included clinic visits every 3 weeks; blood tests for electrolytes, glucose, insulin, renal function, liver function; and complete blood counts. Intravenous administration of much higher doses of L-arginine hydrochloride have been associated with hyperinsulinemia and changes in potassium concentrations.30 If similar changes occur during oral L-arginine treatment, endothelium-dependent vasodilatation could be affected. Blood urea nitrogen was also increased by oral L-arginine in a previous animal study.16
Statistical Analysis
Data were summarized as mean±SD except in the figures, in which
standard error bars are shown. Measurements obtained after 6 weeks of
oral L-arginine were compared with those obtained after the
6-week placebo control period by ANOVA for repeated measurements that
included estimates of the effects of treatment sequence and dose of
oral L-arginine. Since treatment sequence and
L-arginine dose did not significantly affect the results,
the data were not presented for subgroups defined by these
factors. If changes in neurohormones followed a skewed distribution, a
Wilcoxon signed rank test was used to compare concentrations
during the oral L-arginine and placebo treatment periods. A
value of P
.05 was considered statistically
significant.
| Results |
|---|
|
|
|---|
|
|
Peripheral Vascular Function
During forearm exercise, forearm blood flow increased
significantly after the L-arginine treatment period
compared with the placebo period (Fig 3
). The average
improvement in forearm blood flow during exercise was 1.5±3.0
mL·min-1·dL-1
(P<.05). Maximum voluntary hand contraction did not change
(35±9 versus 36±10 kg). In contrast to exercise hyperemia,
reactive hyperemia after 5 minutes of arterial
occlusion was not significantly augmented (Fig 4
).
|
|
Methacholine was used to examine the effect of oral
L-arginine on the response of the
endothelial nitric oxide pathway when stimulated to
release increased amounts of nitric oxide. Increases in forearm blood
flow in response to methacholine were on average 1.5±4.2
mL·min-1·dL-1
greater with L-arginine than with placebo (Fig 5
), but this difference did not attain statistical
significance (P=.33). Responses to exogenous nitric oxide
provided by infusion of nitroprusside were similar during the
L-arginine and placebo periods (Fig 6
).
|
|
Vasoconstrictor responses to
L-N-monomethylarginine, an
inhibitor of nitric oxide synthase, were similar during the
L-arginine and placebo treatment periods (Fig 7
), suggesting that basal endothelial
nitric oxide activity was not increased by oral L-arginine
supplementation. This finding is consistent with unchanged
forearm blood flow under basal conditions during L-arginine
administration compared with placebo (3.7±1.1 versus 3.8±1.6
mL·min-1 · dL-1,
respectively).
|
Arterial compliance as assessed by pulse contour analysis was improved by administration of oral L-arginine. Compliance estimated from the exponential decay of the diastolic pressure (C1) improved to 2.36±0.30 from 1.99±0.38 mL/mm Hg (P<.001), and the second compliance term in the modified Windkessel model of the circulation (C2) increased from 0.048±0.024 to 0.064±0.026 mL/mm Hg (P<.05).
Biochemical Assessments
There was a significant increase in mean plasma
L-arginine concentration, from 85±21 to 98±28 µmol/L
(P<.05), during administration of supplemental oral
L-arginine. Other data are summarized in Table 2
. Small increases in blood urea nitrogen were seen,
which may be related to L-arginine metabolism
in the urea cycle. There were no differences in serum electrolytes.
|
Endothelin levels fell significantly, from 1.9±1.1 to 1.5±1.1 pmol/L (P<.05). Plasma norepinephrine and plasma renin activity were not significantly reduced by oral L-arginine.
Adverse Effects
One patient experienced diarrhea during the placebo period. Two
patients, one in each treatment period, had acute episodes of gout
during the trial. End-point assessments were avoided during these
attacks. No other potential adverse effects were noted.
| Discussion |
|---|
|
|
|---|
Previous studies in animals and humans with heart failure have indicated that short-term administration of L-arginine can restore vasodilator responses to an endothelial nitric oxidedependent vasodilator.15 31 This was the first study to examine the effects of oral L-arginine administered over several weeks. Three different assessments were used to determine whether supplemental oral L-arginine could improve peripheral blood flow in patients with heart failure when nitric oxide activity was stimulated. Both forearm exercise and release of a brachial artery occlusion increase shear stress in the forearm vasculature, which can lead to increased formation of nitric oxide from L-arginine.32 33 Muscarinic agonists have served as a pharmacological stimulus to examine the functional status of the endothelial nitric oxide pathway ever since the seminal study of Furchgott and Zawadzki.34 Significant enhancement of exercise hyperemia was observed during L-arginine administration and may have been related to increased nitric oxide activity. However, additional investigations using inhibitors of nitric oxide synthase during exercise are needed to determine whether the observed increase in exercise hyperemia was indeed mediated via the nitric oxide pathway. The effect of supplemental oral L-arginine on methacholine-induced vasodilation was, on average, similar to the increase in exercise hyperemia, but the changes in methacholine responses were more variable than changes in exercise hyperemia. Given greater variation in the effect of L-arginine on methacholine responses, a much larger sample size would be needed to achieve statistical significance and provide a precise estimate of any effect of L-arginine. Postischemic hyperemia was not significantly increased by oral L-arginine. Although peripheral blood flow tended to improve during all three interventions used to stimulate the nitric oxide pathway, the results were somewhat inconsistent, perhaps because of differences in the extent to which nitric oxide contributes to the total vasodilator responses to these three interventions. Overall, these results can neither establish nor preclude the possibility that supplemental L-arginine may be converted to nitric oxide in patients with heart failure when activity of the nitric oxide synthase pathway is increased by different stimuli.
Lack of significant increases in the vasoconstrictor response to L-N-monomethylarginine, an inhibitor of nitric oxide synthase, suggests that oral L-arginine did not substantially enhance basal nitric oxide formation in the forearm vasculature. Resting vasoconstrictor tone as measured by forearm vascular resistance also was not reduced, since basal forearm blood flow did not increase and mean blood pressure was only slightly decreased. Similar responses to nitroprusside during the L-arginine and placebo treatment periods suggest that L-arginine did not alter nitric oxideinduced smooth muscle relaxation.
Indexes of vascular compliance were also significantly improved during the L-arginine treatment period. Reduced vascular compliance has been documented in patients with heart failure by pulse contour analysis as well as other methods.35 36 37 Theoretically, improvements in peripheral vascular compliance could decrease reflection of pressure waves from the periphery, thereby reducing impedance to left ventricular outflow. In addition, better arterial compliance may improve arterial baroreceptor function and decrease sympathetic activity in patients with heart failure. Other studies have suggested that endothelial nitric oxide can attenuate sympathetic nervous system activity.25 38 However, mean plasma norepinephrine concentration was not reduced by L-arginine. This observation, in conjunction with the lack of change in basal forearm vascular resistance, suggests that compliance was not improved by reductions in sympathetic vasoconstrictor tone.
Few reports were found in the literature describing structural alterations in arteries from patients with heart failure. Theoretically, increased circulating levels of growth-promoting factors such as norepinephrine, angiotensin II, and endothelin may alter vascular structure. In infarcted rats, increased medial thickness of intramuscular resistance vessels and increased carotid artery stiffness associated with increased collagen content and adventitial thickness have been demonstrated.39 40 It is possible that L-arginine could have improved vascular compliance via structural changes related to antigrowth activity of nitric oxide and barrier functions of intact endothelium.41 Indexes of arterial compliance based on pulse contour analysis cannot be used to isolate the contributions of hemodynamic versus structural changes. L-Arginine had only minimal effects on blood pressure that would not be expected to greatly improve vascular compliance through a decrease in distending pressure. Nitric oxide has been shown to inhibit the positive inotropic effect of ß-adrenergic stimulation.42 Since our measures of arterial compliance vary in direct proportion to the cardiac output and cardiac output was not directly measured, it is possible that the compliance estimates were confounded by changes in cardiac output. More in-depth investigation of changes in compliance with L-arginine is needed.
Plasma endothelin levels were significantly reduced during the L-arginine treatment period compared with the placebo period. This study did not examine whether decreased formation or increased clearance of endothelin from the circulation could explain this observation. Interestingly, changes in the availability of nitric oxide have been associated with the regulation of endothelin production in vitro.26 27 Since endothelin is a potent vasoconstrictor and mitogenic factor, reduced production of endothelin may be beneficial in patients with heart failure. A recent study of an endothelin receptor antagonist administered to patients with severe heart failure observed significant hemodynamic improvements.43 These investigators also confirmed a strong relationship between plasma endothelin and mean pulmonary vascular resistance. More research is needed to determine whether this potential mechanism accounts for some of the effects of oral L-arginine.
Others have shown that oral L-arginine can improve responses to an endothelium-dependent vasodilator in patients and animals with hypercholesterolemia in the absence of heart failure.16 44 Since the precise degree of elevation of cholesterol or its derivatives, such as oxidized LDL cholesterol, that are needed to alter the activity of the nitric oxide pathway have not been established, it is possible that the effects of L-arginine seen in this study were related to cholesterol.45 However, L-arginine did not change total circulating cholesterol and had similar effects on exercise blood flow, methacholine-induced vasodilation, 6-minute walk test, and quality of life when subgroups defined by the median cholesterol level (4.7 mmol/L, or 180 mg/dL) or a history of ischemic coronary artery disease were examined (data not shown).
Oral L-arginine, 7 g three times a day for 3 days, did not enhance endothelium-dependent forearm vasodilatation in normal subjects who had relatively high cholesterol levels (mean, 5.4 mmol/L).46 Interestingly, platelet aggregation was inhibited by oral L-arginine. The effect of L-arginine on platelet aggregation could be blocked with L-N-monomethylarginine, suggesting that nitric oxide synthase mediated this effect. Platelet aggregation was not evaluated in our study.
Although this investigation was limited to a small sample from a single medical center, the observation of multiple improvements, including increased quality of life, submaximal exercise performance, forearm exercise hyperemia, arterial compliance, and reduced plasma endothelin, warrant further investigations of supplemental oral L-arginine in patients with heart failure. The optimal dosage regimen was not established by this study, and longer studies are needed to determine whether the L-arginine effects persist. A mechanism of action for oral L-arginine could not be established on the basis of these data, which were focused primarily on the forearm vasculature and indirect measures of the nitric oxide pathway. If therapeutic effects can be confirmed by other investigations, studies to identify the mechanism of action may provide valuable insight into the biology of L-arginine.
| Acknowledgments |
|---|
Received October 10, 1995; revision received December 28, 1995; accepted January 2, 1996.
| References |
|---|
|
|
|---|
This article has been cited by other articles:
![]() |
R. H. Boger The Pharmacodynamics of L-Arginine J. Nutr., June 1, 2007; 137(6): 1650S - 1655S. [Abstract] [Full Text] [PDF] |
||||
![]() |
G. K. Grimble Adverse Gastrointestinal Effects of Arginine and Related Amino Acids J. Nutr., June 1, 2007; 137(6): 1693S - 1701S. [Abstract] [Full Text] [PDF] |
||||
![]() |
R. D. Peluffo L-Arginine currents in rat cardiac ventricular myocytes J. Physiol., May 1, 2007; 580(3): 925 - 936. [Abstract] [Full Text] [PDF] |
||||
![]() |
N. Thengchaisri, R. Shipley, Y. Ren, J. Parker, and L. Kuo Exercise Training Restores Coronary Arteriolar Dilation to NOS Activation Distal to Coronary Artery Occlusion: Role of Hydrogen Peroxide Arterioscler. Thromb. Vasc. Biol., April 1, 2007; 27(4): 791 - 798. [Abstract] [Full Text] [PDF] |
||||
![]() |
I. H. Zucker Novel Mechanisms of Sympathetic Regulation in Chronic Heart Failure Hypertension, December 1, 2006; 48(6): 1005 - 1011. [Full Text] [PDF] |
||||
![]() |
X. Sun and D. D. Ku Allicin in garlic protects against coronary endothelial dysfunction and right heart hypertrophy in pulmonary hypertensive rats Am J Physiol Heart Circ Physiol, November 1, 2006; 291(5): H2431 - H2438. [Abstract] [Full Text] [PDF] |
||||
![]() |
S. P. Schulman, L. C. Becker, D. A. Kass, H. C. Champion, M. L. Terrin, S. Forman, K. V. Ernst, M. D. Kelemen, S. N. Townsend, A. Capriotti, et al. L-Arginine Therapy in Acute Myocardial Infarction: The Vascular Interaction With Age in Myocardial Infarction (VINTAGE MI) Randomized Clinical Trial JAMA, January 4, 2006; 295(1): 58 - 64. [Abstract] [Full Text] [PDF] |
||||
![]() |
G. K. McConell, N. N. Huynh, R. S. Lee-Young, B. J. Canny, and G. D. Wadley L-Arginine infusion increases glucose clearance during prolonged exercise in humans Am J Physiol Endocrinol Metab, January 1, 2006; 290(1): E60 - E66. [Abstract] [Full Text] [PDF] |
||||
![]() |
L. G. Olsson, K. Swedberg, A. L. Clark, K. K. Witte, and J. G.F. Cleland Six minute corridor walk test as an outcome measure for the assessment of treatment in randomized, blinded intervention trials of chronic heart failure: a systematic review Eur. Heart J., April 2, 2005; 26(8): 778 - 793. [Abstract] [Full Text] [PDF] |
||||
![]() |
S. G. West, A. Likos-Krick, P. Brown, and F. Mariotti Oral L-Arginine Improves Hemodynamic Responses to Stress and Reduces Plasma Homocysteine in Hypercholesterolemic Men J. Nutr., February 1, 2005; 135(2): 212 - 217. [Abstract] [Full Text] [PDF] |
||||
![]() |
H. L. Gornik and M. A. Creager Arginine and Endothelial and Vascular Health J. Nutr., October 1, 2004; 134(10): 2880S - 2887S. [Abstract] [Full Text] [PDF] |
||||
![]() |
M. M. Parnell, J. P. F. Chin-Dusting, J. Starr, and D. M. Kaye In vivo and in vitro evidence for ACh-stimulated L-arginine uptake Am J Physiol Heart Circ Physiol, July 1, 2004; 287(1): H395 - H400. [Abstract] [Full Text] [PDF] |
||||
![]() |
S.E.S. Miner, A. Al-Hesayen, S. Kelly, T. Benson, J.J. Thiessen, V.R. Young, and J.D. Parker L-Arginine Transport in the Human Coronary and Peripheral Circulation Circulation, March 16, 2004; 109(10): 1278 - 1283. [Abstract] [Full Text] [PDF] |
||||
![]() |
J. Pernow, F. Bohm, E. Beltran, and A. Gonon L-Arginine protects from ischemia-reperfusion-induced endothelial dysfunction in humans in vivo J Appl Physiol, December 1, 2003; 95(6): 2218 - 2222. [Abstract] [Full Text] |
||||
![]() |
R. H Boger The emerging role of asymmetric dimethylarginine as a novel cardiovascular risk factor Cardiovasc Res, October 1, 2003; 59(4): 824 - 833. [Abstract] [Full Text] [PDF] |
||||
![]() |
C. R. Morris, S. M. Morris Jr., W. Hagar, J. van Warmerdam, S. Claster, D. Kepka-Lenhart, L. Machado, F. A. Kuypers, and E. P. Vichinsky Arginine Therapy: A New Treatment for Pulmonary Hypertension in Sickle Cell Disease? Am. J. Respir. Crit. Care Med., July 1, 2003; 168(1): 63 - 69. [Abstract] [Full Text] [PDF] |
||||
![]() |
K. Nakamura, S. Al-Ruzzeh, A. H. Chester, A. Dewar, S. Rothery, N. J. Severs, M. H. Yacoub, and M. Amrani Age-related changes in the protective effect of chronic administration of L-arginine on post-ischemic recovery of endothelial function Eur. J. Cardiothorac. Surg., April 1, 2003; 23(4): 626 - 632. [Abstract] [Full Text] [PDF] |
||||
![]() |
E. B. Feldman The Scientific Evidence for a Beneficial Health Relationship Between Walnuts and Coronary Heart Disease |