JACC Vol. 27, No. 5
April 1996:1207-13
1207
Dietary Supplementation With L-Arginine Fails to Restore Endothelial
Function in Forearm Resistance Arteries of Patients With Severe
Heart Failure
J A Y E P. F. C H I N - D U S T I N G , PHD, D A V I D M. K A Y E , MBBS, F R A C P , PI-ID,
J E F F R E Y L E F K O V I T S , MBBS, F R A C P , J A M E S W O N G , MBBS, F R A C P ,
P E T E R B E R G I N , MBBS, F R A C P , G A R R Y L. J E N N I N G S , MBBS, F R A C P , M D
Victoria, Australia
Objectives. We sought to examine the eOicacyof dietary supplementation of L-arginine on endothelium-dependent vasodilation
in patients with congestive heart failure.
Background. Endothelial dysfunction, as evidenced by a diminished response to such vasodilators as acetylcholine, is well
defined in patients with heart failure. These responses are improved by intraarterial infusion with L-arginine. Because Larginine is a semiessential amino acid, we investigated the effects
of dietary L-arginine on endothelium-dependent vasodilation in
these patients.
Methods. Twenty patients with heart failure (New York Heart
Association functional class III/IV, mean [-+SE] age 51.3 _+ 1.7
years) and seven healthy control subjects (mean age 52.6 -+ 3.3
years) were studied. All patients continued taking their usual
treatment. Responses to acetylcholine and sodium nitroprusside
were determined using forearm plethysmography. Patients with
heart failure received either L-arginine (20 g/day every day for 28
days) or placebo (vehicle syrup in equal amounts) in a double-
blind protocol. The calculated power of the study was between 62%
and 80% to detect a 30% to 40% change in area under the
dose-response (forearm vascular resistance) curve.
Results. Responses to acetylcholine, but not to sodium nitroprusside, were significantly attenuated in patients with heart
failure compared with control subjects (mean area under curve
[AUC], control subjects vs. patients with heart failure: 1,125.4 -+
164.5 vs. 617.3 -+ 116.6 U, p < 0.05, by Student t test). A significant
increase in urea and aspartate transaminase levels in patients
receiving active L-arginine treatment was observed. Responses to
acetylcholine (AUC; before vs. after L-arginine: 641.5 -+ 126.7 vs.
695.9 -+ 151.9 U) and sodium nitroprusside were not affected by
either L-arginine or placebo.
Conclusions. Endothelial dysfunction was apparent in patients
with heart failure despite rigorous vasoactive treatment. Oral
administration with L-arginiue was ineffective in influencing endothelial function in these patients.
(J Am Coil Cardio11996;27:1207-13)
Peripheral vasoconstriction is a characteristic feature of congestive heart failure. This has been attributed to activation of
the sympathetic nervous system (1,2), the renin-angiotensin
system (3) or the pituitary-vasopressin axis (4). However,
recent attention has been directed toward a potential contributory role of the vascular endothelium. Considerable support
has accumulated for abnormal endothelium-dependent vasodilation in heart failure arising from in vivo and in vitro studies
performed both in humans (5-7) and animals with experimental heart failure (8-10). The dysfunction is associated with
diminished vasodilator responses to acetylcholine and attenu-
ated hyperemic responses to exercise and ischemia, both of
which are largely endothelium dependent (11,12).
Recently, several groups have shown that infusion of the
nitric oxide precursor L-arginine can improve endotheliumdependent dilation, previously demonstrated to be diminished,
in hypercholesterolemic humans (13,14). In 1994, Hirooka et
al. (12) reported that intraarterial infusions of L-arginine enhanced the vasodilator action of acetylcholine and ischemia in
patients with heart failure. L-Arginine, a semiessential amino acid
(15) and dietary supplement, is used therapeutically in human
infants born with carbamyl synthetase deficiency (16) and in
children with lysinuria (17). Dietary supplementation with Larginine has also been tested in men for reproductive activity (18).
In the present study we examined the efficacy of orally administered supplemental L-arginine to augment endothelial function in
patients with severe heart failure.
From the Alfred and Baker Medical Unit, Alfred Hospital and Baker
Medical Research Institute, Prahran, Victoria, Australia. This study was sup-
ported by an AustralianNationalHealthand MedicalResearchCouncilgrant
awardedto the BakerMedicalResearchInstitute.
ManuscriptreceivedMay9, 1995;revisedmanuscriptreceivedNovember29,
1995,acceptedDecember12, 1995.
Addressfor correspondence:Dr. Jaye P. F. Chin-Dusting,Alfredand Baker
Medical Unit, Baker Medical ResearchInstitute, CommercialRoad, Prahran
3181,Victoria,Australia.
©1996 by the American College of Cardiology
Published by Elsevier Science Inc.
Methods
Subjects. We recruited into our study 20 patients with
severe heart failure (New York Heart Association functional
0735-1097/96/$15.00
SSDI 0735-1097(95)00611-7
1208
CHIN-DUSTING ET AL.
DIETARY L-ARGININE IN HEART FAILURE
Table 1, Profile and AntifailureTreatment of Patients With
Heart Failure
Pt
No.
Age (yr)/
Gender
%
LVEF
Etiology
NYHA
Functional
Class
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
58/M
51/M
35/M
48/M
40/M
54/M
43/M
48/M
57/M
57/F
51/M
61/M
50/M
44/M
47/M
44/M
64/M
46/M
57/M
53/M
26
17
17
23
21
26
31
13
27
22
20
30
19
14
19
33
15
15
12
15
ICM
1CM
DoxCM
ICM
IDCM
ICM
IDCM
IDCM
ICM
ICM
ICM
IDCM
IDCM
ICM
IDCM
VHD
ICM
ICM
ICM
ICM
4
3
3
3
3
4
2
3
3
4
3
3
3
2
4
4
4
3
4
3
Antifailure
Treatment
ACE, D, Di, N
ACE, A, D
ACE, A, D, Di
ACE, A, D, Di, N
ACE, A, D, Di, N
D, Di, A, N
ACE, A, D, Di
ACE, A, D, Di
ACE, D, Di, N
ACE, A, D, Di, N
ACE, A, D, Di, N
ACE, A, D, Di, N
ACE, A, D, Di
ACE, A, D, Di
ACE, D, Di
ACE, D
ACE, A, D, Di, N
ACE, A, D, Di, N
ACE, A, D, Di
ACE, A
A = anticoagulant; ACE = angiotensin-converting enzyme inhibitor; D diuretic; Di = digoxin; DoxCM - doxorubicin cardiomyopathy; ICM -- ischemic
cardiomyopathy; IDCM = idiopathic dilated cardiomyopathy; LVEF = left
ventrieular ejection fraction; N = nitrate; NYHA = New York Heart Association; Pt = patient; VHD = valvular heart disease.
class III/IV, 19 men, 1 woman; mean [_+SE] age 51.3 _+ 1.7
years) and 7 healthy male control subjects (mean age 52.6 _+
3.3 years). All patients with heart failure were awaiting heart
transplantation and maintained their usual medication regimen for the duration of the trial (Table 1). All control subjects
had normal findings on physical examination, as well as routine
hematologic and biochemical blood analyses. Criteria for entry
into the study included nonsmoking status, absence of alcohol
abuse (less than three standard alcohol drinks per day), systolic
blood pressure <140 mm Hg and diastolic blood pressure
<90 mm Hg, total serum cholesterol <5.5 mmol/liter and total
triglyceride <2.0 mmol/liter. Control subjects had no previous
history of major medical illness (including diabetes or any
other cardiovascular-related diseases) and were not receiving
any medication at the time of study.
The study protocol was approved by the Alfred Group of
Hospitals Ethics Committee, and written informed consent
was obtained from all subjects, who were also informed of their
right to withdraw from the protocol at any time during the
course of the study.
Study protocol. Control subjects underwent one forearm
venous occlusion plethysmography session. Patients with heart
failure were randomized to one of two groups--those given
L-arginine or those given the placebo solution. Forearm venous
occlusion plethysmography was performed before and after 4
weeks of treatment in this patient group.
JACC Vol. 27, No. 5
April 1996:1207-13
Dietary L-arginine. Patients were randomly allocated in a
double-blind protocol to receive either L-arginine or placebo.
Randomization and preparation of both the active (L-arginine)
and placebo oral solutions were performed by the pharmacy
department of the Alfred Hospital. Patients were given a
2-week supply at a time of oral solution. The active (L-arginine)
solution was 300 g arginine hydrochloride (courtesy of Ajinomoto Co., Kawasaki, Japan) added to deionized water (400 ml)
and compound hydroxybenzoate solution (5 ml) and made up
to a 900-ml volume with either aromatic or orange syrup. The
preparation for the placebo oral solution was deionized water
(600 ml) and compound hydroxybenzoate solution (5 ml) made
up to a 900-ml volume with either aromatic or orange syrup.
The purity of L-arginine hydrochloride was >98%. Patients
were instructed to self-administer 30 ml oral solution two times
a day.
Rest blood pressure and plasma biochemical analysis.
Weekly blood pressure measurements were obtained by the
same nurse throughout the entire study. Supine blood pressure
measurements were obtained after 10 min of horizontal rest,
whereas standing blood pressure measurements were obtained
after 5 min in the upright position. Blood pressure values were
obtained at the same time, as closely as possible, on the same
day of each week at week 0 (pretreatment) through weeks 1, 2,
3 and 4 (final week of treatment).
After blood pressure measurements had been taken, 10 ml
blood was obtained for plasma analysis of urea, creatinine,
liver function enzymes and electrolyte levels.
Walk test. Each patient performed a walk test (19) before
and after 4 weeks of supplementation with the oral solution.
Patients were instructed to walk on a flat surface at a self-set
pace for 6 rain. They were supervised by a cardiologist or a
trained critical care nurse, both of whom had no knowledge of
the patient's treatment. The distance walked over the 6-rain
period was measured.
Forearm venous occlusion plethysmography. Subjects rested
supine throughout the course of the experiment in a comfortable, relaxing environment maintained at a constant temperature of 22°C. Measurements of forearm blood flow were taken
in all participants before the introduction of any dietary
supplementation (day 1) and in patients with heart failure on
day 29, after 28 days of dietary supplementation with either
L-arginine or placebo.
The protocol for measurement of forearm blood flow has
previously been described (20,21). In summary, forearm blood
flow was measured by venous occlusion plethysmography with
a sealed, alloy-filled (gallium and indium), double-strand strain
gauge (Medasonic). Venous occlusion pressure was 40 to
50 mm Hg at the proximal end (elbow) and cuff occlusion
pressure was -200 mm Hg at the distal end (wrist) to arrest all
circulation to the hand. The distal cuff was inflated before
determination of forearm blood flow and left inflated for the
duration of all measurements. Forearm blood flow was calculated for 10 of every 20 s.
The brachial artery was cannulated (3F, 5-cm catheter,
Cook) for intraarterial blood pressure recordings as well as for
JACC Vol. 27, No. 5
April 1996:1207-13
Figure 1. Top left, Forearm blood flow responses to
acetylcholine relative to forearm basal blood flow
measurements for control (C) and heart failure (HF)
patient groups. *p < 0.05 versus control group by
multivariate analysis of variance followed by Student
t test with Bonferroni correction. Histograms depict
mean area under the acetylcholine dose-response
curve. *p < 0.05 versus control group by Student t
test. Bottom left, Forearm vascular resistance responses calculated for acetylcholine relative to forearm basal resistance measurements for control and
heart failure groups. *p < 0.05 versus control group
using multivariate analysis of variance followed by
Student t test with Bonferroni correction. Histograms depict mean area (given a negative value to
depict a decrease in vascular resistance) under the
acetylcholine dose-response curve. *p < 0.05 versus
control group using Student t test. Top right, Forearm blood flow responses to sodium nitroprusside
relative to forearm basal blood flow measurements
for control and heart failure groups. Histograms
depict mean area under the sodium nitroprusside
dose-response curve. Bottom right, Forearm vascular resistance responses calculated for sodium nitroprusside relative to forearm basal resistance measurements for control and heart failure groups.
Histograms depict mean area (given a negative value
to depict a decrease in vascular resistance) under the
sodium nitroprusside dose-response curve. Open
circles = control group (n = 7); solid circles = heart
failure group (n = 20).
1209
CHIN-DUSTING ET AL.
D I E T A R Y L-ARGININE IN H E A R T F A I L U R E
120
2500
240
20
~o 100
2000
200
15
160
12 o
°
8
8o
1500
120
60
~
40
~
20
1000
$"
500
0
10
20
30
80
40
0
0
8
8
4
0
40
0
0.0 0.4 0.8 1.2 1.6 2.0
C
C HF
0
° \TI
0
-200
"~ -10
0
-10
-20
-10
-20
-30 ~"
600
~
-3o
-40
-800
~"
-40
-50
-400
'
HF
-1000
-50
-1200
-60
-1400
-70
o
60
-70
-50
i
0
10
20
30
40
acetylcholine (mcg/min)
local, sequential infusions of acetylcholine (4.6, 9.25, 18.5
and 37 /xg/min) and sodium nitroprusside (0.2, 0.4, 0.8 and
1.6 /zg/min). Basal blood flow (the average of three flow
measurements before each drug infusion) was obtained after
an equilibration period of 40 to 60 s. Each drug was infused at
2 ml/min over a maximum of 5 rain or until the response over
three flow measurements reached a plateau (usually by 3 rain).
Rest periods of 5 min between concentrations and of 15 rain
between drugs were observed. At the concentrations used,
neither systemic blood pressure, recorded with a disposable
physiologic pressure transducer (Model CMS-327, Biosensors), nor heart rate, recorded with a lead II electrocardiogram
(Spacelabs Inc.) was affected.
Forearm vascular resistance (FVR) was calculated as follows: FVR (R units) = Mean arterial pressure (ram Hg)/
Forearm blood flow (ml/dl per min).
Other drugs. Acetylcholine chloride (BDH Chemicals
Ltd.) was diluted under sterile conditions with 0.9% saline.
Sodium nitroprusside (David Bull Laboratories) was diluted
under sterile conditions in 5% dextrose.
Statistical analysis. Unless otherwise stated, all results are
expressed as mean value _+ SE. Analysis of variance
([ANOVA] one or two way or repeated measures where appropriate) followed by a Student t test (paired, where appropriate)
was used. Analysis was performed using SigmaStat Statistical
Software (Jandel Scientific), which inherently analyzes data for
normality before performing parametric analysis. Where data
failed to meet normality criteria, nonparametric analysis (Kruskal
-90
0.0
0.4
0.8
1.2
1,6
sodium nitroprusside (mcg/min)
Wallis nonparametric test) was applied. In addition, analysis for
each dose-response curve was undertaken by calculation of the
area under each individual dose-response curve, which was used
as a single-value summary for that data set (22).
Results
Forearm venous occlusion plethysmography: patients with
heart failure versus control subjects. Mean basal forearm
blood flow did not differ (1.93 _+ 0.18 vs. 2.57 -~ 0.47 ml/dl per
rain, p > 0.05) but mean basal arterial pressure was significantly lower in patients with heart failure than control subjects
(78.86 _+ 1.75 vs. 93.03 _+ 2.15 mm Hg, p < 0.05 by Student t
test). Mean arterial pressures were not significantly altered in
the presence of the agonists used (p > 0.05, ANOVA).
We previously showed (20) a high intrasubject coefficient of
variation on basal forearm blood flow and vascular resistance.
Hence, responses to both acetylcholine and sodium nitroprusside were normalized for basal forearm flow (or resistance)
(i.e., that obtained immediately before each drug addition).
Both forearm blood flow (area under curve [AUC], control vs.
heart failure group: 2,019.8 _+ 441.7 vs. 969.0 _+ 238.3 U, p <
0.05 by Student t test) and forearm vascular resistance (AUC,
control vs. heart failure group: 1,125.4 _+ 164.5 vs. 617.3 +
116.6 U, p < 0.05 by Student t test) responses to acetylcholine
(Fig. 1), but not to sodium nitroprusside (AUC [forearm blood
flow], control vs. heart failure group: 173,486 _ 23,657 vs.
1210
80
=
C H I N - D U S T I N G E T AL.
DIETARY L-ARGININE IN HEART FAILURE
20
0
c
'~
25
1500
200
20 o
1000
150
15 §
100
10 g
' 500
0
0
10
20
30
0
-200
-10
-~
o= -2o
-30
~o -40
10
20
30
0
0.00.40.81.2
40
acetylcholine (mcg/min)
1.5
o
-10
-20
..30 x
0
-10
-20
~
-400
-~o
-4o
-800
-40
-5o g
-800
-80
-80
-70
-10OO
0
5
50
40
0
3O
300
250
j•2000
6040 !l
J A C C Vol. 27, No. 5
April 1996:1207-13
-80 ~
J
0.0 014 018 1.2 1.6
sodium nitroprusside (ng/min)
147,768 _ 26,555 U; p > 0.05 by Student t test), were
significantly depressed in patients with heart failure.
Dietary L-arginine. Adverse events. After randomization
into one of the two groups, three patients withdrew from the
dietary protocol. One patient (Patient 1, Table 1) was receiving
the active oral u-arginine supplement, whereas the other two
(Patients 11 and 12) were receiving the placebo. Patient 1
developed unstable angina 3 to 4 days after commencement of
the active supplement. Blood pressure dropped from
120/80 mm Hg to 90/60 mm Hg during this time. Patient 11
withdrew from the study to undergo heart transplantation.
Patient 12 developed atrial flutter (slow 200 beats/min with
2:1 atrioventricular block) 3 days after commencement of the
oral supplement. He also complained of lightheadedness,
nausea, lethargy and postural dizziness. Thus, a total of 17
patients completed the L-arginine trial--9 receiving active
supplement and 8 receiving placebo.
Of the nine patients who remained on the L-arginine
supplement, one complained of diarrhea, nausea and malaise;
another of diarrhea and stomach cramps; and a third of
diarrhea. Of the eight patients who remained on the placebo,
one complained of muscle pain in the back and abdominal
areas; one of nausea and diarrhea; another of nausea; and a
fourth of gastrointestinal upset leading to flatus. Two patients
on the oral L-arginine supplement claimed to feel much better,
as did two patients on the placebo.
Plasma biochemistry. Plasma urea levels increased significantly in heart failure patients receiving L-arginine supplementation. These levels increased from pretreatment levels of
-70
1 -80
-90
Figure 2. Top left, Forearm blood flowresponses to
acetylcholine relative to forearm basal blood flow
measurements for heart failure group before and
after dietary supplementation with 20 g/day Larginine. Histograms depict mean area under the
acetylcholine dose-response curve. Bottom left,
Forearm vascularresistance responses calculatedfor
acetylcholine relative to forearm basal resistance
measurements for heart failure group before and
after dietary supplementation with 20 g/day Larginine. Histograms depict mean area (given a
negative value to depict a decrease in vascular resistance) under the acetylcholinedose-response curve.
Top right, Forearm blood flowresponses to sodium
nitroprusside relative to forearm basal blood flow
measurements for heart failure group before and
after dietary supplementation with 20 g/day Larginine. Histograms depict mean area under the
sodium nitroprusside dose-response curve. Bottom
right, Forearm vascular resistance responses calculated for sodium nitroprusside relative to forearm
basal resistance measurements for heart failure
group before and after dietarysupplementationwith
20 g/day L-arginine. Histograms depict mean area
(given a negative value to depict a decrease in
vascular resistance) under the sodium nitroprusside
dose-response curve. Analysisby repeated-measures
two-wayanalysisof variance or Student paired t test
where appropriate. Open circles = before L-arginine
(n = 9); solid circles = after L-arginine.
8.33 + 1.06 to 12.82 _+ 1.75 mmol/liter in week 1 and remained
elevated throughout the 4 weeks of supplementation. Plasma
urea levels were not altered by placebo supplementation.
Neither plasma glucose nor plasma electrolyte (sodium,
potassium, chloride and bicarbonate) levels were altered during the 4 weeks of treatment with either t:arginine or placebo.
There was a small but significant increase in aspartate transaminase levels in the L-arginine group (from 25.90 _+ 2.49 U/liter
in week 0 to 32.00 _+ 2.59 U/liter in week 3), but not in the
placebo group. Protein levels fluctuated significantly during the
4 weeks in both the L-arginine and placebo groups.
Rest blood pressure. Neither dietary L-arginine nor placebo
supplementation had an effect on supine systolic or diastolic or
standing systolic or diastolic blood pressures.
Forearm venous occlusion plethysmography. Figure 2 shows
forearm blood flow and calculated vascular resistance responses to acetylcholine in patients with congestive heart
failure. Dietary L-arginine had no effect on either of these
values or on responses to sodium nitroprusside (AUC [forearm
blood flow] before vs. after L-arginine: 152,604 _+ 49,636 vs.
183,461 _+ 65,881 U; p > 0.05 by Student paired t test).
Likewise, the placebo supplement had little effect on mean
basal blood flow and vascular resistance and on responses to
acetylcholine and sodium nitroprusside.
Intergroup comparisons were also undertaken (i.e., responses of patients after placebo vs. patients after L-arginine
supplementation). There was no difference in basal values or
responses to acetylcholine or sodium nitroprusside between
JACC Vol. 27, No. 5
April 1996:1207-13
CHIN-DUSTING ET AL.
D I E T A R Y L-ARGININE IN H E A R T F A I L U R E
these two groups. Formal analysis of results was described in
the Statistical Analysis section previously.
Six-minute walk test. Dietary L-arginine had little effect on
the capacity of the patients to perform the walk test. The
distance walked in 6 min after I_-arginine supplementation was
500.0 _+ 79.6 m compared with 467.4 _+ 54.3 m before
supplementation (p > 0.05 by paired t test). The distance
walked before and after placebo supplementation was 396.5 _+
67.0 and 401.2 _+ 68.1 m, respectively (p > 0.05 by paired t
test).
Discussion
The two primary findings are that 1) endotheliumdependent vasodilation, as assessed by responses to acetylcholine, is impaired in patients with severe heart failure despite
vigorous conventional vasoactive medication, and 2) dietary
supplementation of the nitric oxide precursor, L-arginine 20
g/day for 28 days, has no effect on this dysfunction in these
patients.
Since the original report (5) that endothelium-dependent
vasodilation is defective in patients with heart failure, several
authors have pursued and confirmed this finding (6,12,23,24).
In all previous studies, however, vasoactive treatment was
withheld for several days before the day of study. Our study
shows that this impairment is still present despite conventional
vasoactive medication in patients with end-stage heart failure.
Causes of endothelial dysfunction in heart failure. Although it is accepted that heart failure is associated with
impaired endothelium-dependent dilation, the cause of this
dysfunction is not well described. It is reported not to be
associated with age, plasma levels of norepinephrine or renin
activity in this patient group (5). It is unlikely to be associated
with atherosclerosis because upper limb vessels, such as those
in the forearm, are seldom involved, or with hypercholesterolemia because impaired endothelium-dependent dilation has
been reported in heart failure patients despite normal plasma
total cholestol levels (mean 188.4 + 8.82 mg/dl) (12). Much of
the human data has been limited to muscarinic stimulation of
endothelium nitric oxide release, confirming an impaired response to either acetylcholine or methacholine (5,6,12,24).
However, responses to substance P, another endotheliumdependent vasodilator, have been reported not to be altered in
patients with heart failure (24), leading to the suggestion that
muscarinic receptors or the postreceptor mechanism coupled
with muscarinic receptors are selectively altered in this disease
state. In contrast, responses to reactive hyperemia are blunted
in these patients (12). This supports our findings in a rabbit
model of heart failure, where responses to adenosine, the
major metabolite released during ischemia, were similarly
blunted (10). Although the mechanism by which adenosine
causes vasodilation remains controversial, with evidence for
endothelium-dependent vasorelaxation (25) as well as direct,
endothelium-independent, smooth muscle vasodilatory properties (26,27), it is unlikely that the endothelial dysfunction
seen in heart failure is limited to the muscarinic receptor.
1211
Because only forearm vascular responses to acetylcholine were
used for the evaluation of endothelial function in the current
study, it is not known whether other vascular responses would
have been affected by L-arginine supplementation. However,
because intraarterial infusions of this amino acid improved
both responses to acetylcholine as well as to reactive hyperemia (12), it is unlikely that other indexes of endothelial
function would have been influenced in the present study.
Supplementation with L-arginine. Because intraarterial infusion with the nitric oxide precursor, L-arginine (28), effectively reverses the blunted endothelium-dependent vasodilation in the forearm arteries of patients with heart failure (12),
it may be construed that regardless of the underlying cause,
loading the endothelium with exogenous substrate can overcome the impairment. Whether this effect is simply due to
repleting a limited substrate pool is controversial because
infusions of L-arginine augment acetylcholine responses in the
forearms of healthy humans (29). Because the intracellular
concentration of L-arginine is estimated to be -100/~mol/liter
(30) and the Km of nitric oxide synthase for L-arginine is
<10 /~mol/liter (31), the hypothesis regarding repletion of
substrate is arguable. Regardless, the failure of oral L-arginine
to influence acetylcholine responses in the current study
reflects not on the ineffectiveness of L-arginine itself because
intraarterial infusions of L-arginine have been proved effective
(12), but on the ineffectiveness of the oral route of administration.
Effects of dietary L.arginine in heart failure. Although it is
arguable whether dietary arginine is indispensable in adult
humans, Rose's (15) classification of L-arginine as a semiessential amino acid is still commonly used. In infants with
carbamyl phosphate synthetase deficiency, an argininedeficient syndrome (16), growth retardation can be overcome
by the addition of 400 mg arginine to the daily diet. Similarly,
children with lysinuria (17) or argininosuccinase deficiency
(32) require dietary arginine for normal growth and development. Dietary supplementation of L-arginine has also been
used in clinical trials for improvement of male spermatogenesis
(18,33). Although evidence to date suggests that high doses of
arginine supplementation (30 to 60 g) are well tolerated in
humans (17), two cases of severe hyperkalemia, one leading to
fatal arrhythmia (34), after supplementation at these doses
have been reported. Both patients, however, had renal and
hepatic insufficiency. In light of this and in view of a chronic
oral supplementation, the dose of 20 g/day was chosen for the
current study.
There is a paucity of data available on the metabolic fate of
intragastric L-arginine in humans. The uptake of arginine by
the liver from the systemic circulation is reported to be
relatively poor owing to the low activity of the transport system
responsible for transmembrane passage of the cationic amino
acids arginine, lysine and ornithine in hepatocytes (35). Intestinal absorption of arginine also shares a transport system with
lysine, ornithine and cysteine (36) and may likewise be relatively poor. Also, the conversion of dietary arginine within the
splanchnic region accounts for 16% of daily NO 3 formation
1212
CHIN-DUSTING ET AL.
DIETARY L-ARGININE IN HEART FAILURE
(37), suggesting a significant first-pass disappearance. The fate
of supranormal doses of dietary supplementation of this amino
acid, such as that used in this study, is not known. However,
underscoring the importance of the liver urea cycle and rapid
portal vein absorption of arginine through intraperitoneal or
intrasplenic injections was efficacious against ammonia toxicity
in rats, whereas oral administration offered minimal protection
(38). Hence, although plasma urea levels were significantly
elevated in the current study, it is possible that there was not a
proportional increase in plasma arginine owing to its significant first-pass metabolism in the liver.
Plasma L-arginine concentrations were not obtained in the
current study. In a recent study (39), oral L-arginine given to
healthy individuals (7 g three times daily for 3 days) resulted in
elevated plasma L-arginine levels, from 129 _+ 7 to 303
/xmol/liter. Although platelet aggregation was significantly
inhibited in that study, endothelium-dependent vasodilation
was not affected in those healthy volunteers. The lack of
confirmatory medication compliance in the absence of plasma
L-arginine measurements in the current study is deflected in
part by the significant increase in plasma urea levels seen in
patients administered the active supplement, but not the
placebo. At 20 g/day, L-arginine increased plasma urea levels
significantly in this patient group from the first week of
treatment. These levels remained high throughout the duration of the study, exceeding the maximal normal value of 8.5
mmol/liter. Plasma liver enzyme levels of aspartate transaminase also increased significantly with L-arginine treatment,
although these did not extend beyond normal values. Plasma
electrolyte levels, including potassium, were not affected by
either treatment. Hence, although plasma L-arginine levels
were not measured in the current study, which makes it difficult
to know if the patients were taking effective amounts of
arginine supplementation in terms of reversal of endothelial
dysfunction, it is likely that 20 g/day k-arginine is close to the
maximal clinically tolerable dose in these patients, since higher
dose would be expected to further exacerbate plasma urea and
aspartate transaminase levels. The patients' ability to perform
physical exercise, as assessed by the walk test, was unaltered by
either treatment. Other adverse signs and symptoms were not
formally assessed.
Conclusions. Although endothelium-dependent vasodilation is markedly impaired in patients with heart failure despite
vigorous conventional vasoactive treatment, oral supplementation with L-arginine, aimed at restoring endothelium nitric
oxide function, was unsuccessful. Although it is possible that
insufficient e-arginine was given in the current study owing to
inadequate dosing, poor absorption or a large first-pass disappearance, a daily dose of 20 g/day appears to be close to the
maximal clinically tolerated dose in these patients. The relatively small number of patients studied in this placebocontrolled study also raises the question of the adequacy of
statistical power. The calculated power of the study (placebocontrolled, paired data, n = 9) is between 62% and 80% to
detect a 30% to 40% change in (derived) area under the dose
(acetylcholine)-response (forearm vascular resistance) curve.
JACC Vol. 27, No. 5
April 1996:1207-13
This calculation is based on the findings of Hirooka et al. (12),
who found a 30% to 40% increase in this parameter after
intraarterial e-arginine, and on our calculated standard deviation of 35% for this parameter. It is acknowledged that the
statistical power of this study is weaker than the ideal, and that
the negative outcome must therefore be accepted with some
caution. Another point for consideration is the previous finding that the degree of endothelial function improvement by
k-arginine is inversely proportional to the severity of the
disease (40). All the patients studied in this trial had end-stage
heart failure and were awaiting transplantation. Had a patient
group with mild heart failure been studied, the endothelial
dysfunction may well have been reversible with the treatment
regimen given. Nevertheless, on the basis of the current
findings, we conclude that oral supplementation with karginine is unlikely to be of practical clinical benefit to patients
with severe heart failure.
We are grateful to Sisters Leonie Johnston and Sue Tamblyn for their nursing
assistance. L-Arginine monohydrochloride was generously donated by Ajinomoto
Co., Kawasaki, Japan,
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