Download Structural and functional assessment of small arteries in patients

Clinical Science (1999) 97, 671–679 (Printed in Great Britain)
Structural and functional assessment of small
arteries in patients with chronic heart failure
C. HILLIER*, P. J. COWBURN†, J. J. MORTON†, H. J. DARGIE†, J. G. F. CLELAND†,
J. J. V. MCMURRAY† and J. C. McGRATH†
*Department of Biological and Biomedical Sciences, Faculty of Health, Glasgow Caledonian University, Glasgow G4 0BA,
Scotland, U.K., and †MRC Clinical Research Initiative in Heart Failure, University of Glasgow, Glasgow G12 8QQ, Scotland, U.K.
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The physiological response to a chronically failing heart is the implementation of compensatory
mechanisms intended to support blood pressure. These mechanisms, which are not fully
understood, increase peripheral vascular tone, thus increasing the strain on the weakened
myocardium. This study investigated the structure and function of small arteries from heart
failure patients and controls without heart failure in an attempt to identify abnormalities
associated with heart failure which may be related to these mechanisms. Small arteries were
dissected from gluteal biopsies and studied using wire myography. Arterial morphological
parameters were measured and concentration–response curves constructed for a number of
vasoconstrictor and vasodilator agonists. Plasma concentrations of neuroendocrine hormones
were also measured. There were no morphological differences between small arteries from
control subjects and those from patients with chronic heart failure. In heart failure patients,
vasoconstrictor responses to endothelin-1 were significantly reduced, although plasma
endothelin-1 levels were increased. Arteries from heart failure patients also showed evidence of
an impaired neuronal uptake mechanism, since blockade by cocaine had no effect on
noradrenaline-induced vasoconstriction in these vessels. These results suggest that small-artery
structure is not altered in chronic heart failure and so cannot account for the heightened vascular
resistance in this syndrome. However, abnormal neuronal uptake and impaired vasoconstriction
in response to endothelin-1 may be associated with the complex compensatory phenomenon
involved in heart failure.
INTRODUCTION
Chronic heart failure (CHF) due to left-ventricular
systolic dysfunction is characterized by an increase in
resting peripheral vascular resistance [1–3]. This increase
in resistance is thought to reflect, in part, the net vascular
effect of the array of neural and ‘ endocrine ’ vasoconstrictor and vasodilator abnormalities that are found in
CHF [1–3]. An abnormality of small-artery structure in
CHF has also been inferred because maximum metabolic
vasodilation is reduced in this syndrome [2,3]. This is,
perhaps, in keeping with the postulated growth effects of
many of the neural and ‘ endocrine ’ (including autocrine
and paracrine) factors that are produced in abnormal
quantities in CHF, although these effects have never been
confirmed in vivo in humans [4,5].
The major component of peripheral vascular resistance
resides in the small arteries and arterioles [2,3,6], and the
use of wire myography for the ex vivo study of human
subcutaneous fat biopsies has been shown to allow
investigations of small arteries that are not practicable in
vivo [5,7–10]. There have been few previous attempts to
Key words : endothelin-1, heart failure, neuronal uptake, subcutaneous small arteries.
Abbreviations : ACE, angiotensin-converting enzyme ; ANG II, angiotensin II ; CHF, chronic heart failure ; ET-1, endothelin-1 ;
pD and pD , negative log of the concentration of drug (M) required to obtain 50 % and 25 % respectively of the maximum
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response ; PSS, physiological salt solution.
Correspondence : Dr Chris Hillier (e-mail C.Hillier!gcal.ac.uk).
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C. Hillier and others
examine small-artery structure and function in CHF.
Angus et al. [11] studied a small group of patients with
CHF and observed both impaired vasoconstriction and
vasodilation to a small number of agonists, whereas
Heagerty and colleagues [12] could find no vascular
changes in patients with mild CHF following myocardial
infarction. However, the important mechanisms underlying peripheral vascular control in CHF have yet to be
determined. Recent evidence has strongly implicated the
endothelium-derived
vasoconstrictor
endothelin-1
(ET-1) in the increased vascular resistance observed in
CHF patients [13], but this has yet to be supported by in
vitro studies of human tissue. The objectives of the
present study were to investigate if CHF is associated
with changes in small-artery structure or endothelial
function, or with altered responses to important endogenous vasoactive mediators, including ET-1.
METHODS
Patients and control subjects
This study conformed with the principles outlined in the
Declaration of Helsinki and was approved by the local
Committee on Medical Ethics, and all subjects studied
gave prior written, informed consent. A total of 16
patients (13 male ; three female) aged 31–74 years
(meanpS.D. 55p13 years) with chronic ( 6 months
duration) heart failure due to coronary artery disease (12
patients) or idiopathic dilated cardiomyopathy (four
patients) were studied. All had a left-ventricular ejection
fraction of
40 % (mean 27 %), as measured by echocardiography. Twelve patients were receiving chronic
diuretic therapy, and 13 were being treated with an
angiotensin-converting enzyme (ACE) inhibitor.
Although many patients with CHF also have hypertension, no patients with past or present hypertension, or
with diabetes mellitus, were included, since these conditions are known to have specific vascular abnormalities
which would confound the data set and make it difficult
to be sure of effects caused primarily by CHF. In
addition, 12 age-matched (57p14 years ; range 29–71
years) and gender-matched (10 male ; two female) control
subjects were studied. All had normal left-ventricular
systolic function on echocardiograph examination. Eight
had coronary heart disease and four were healthy
volunteers with no past medical history and who did not
take regular medication. There was no difference in
plasma lipid total cholesterol between the patients
(5.63 mmol\l) and the control subjects (5.65 mmol\l).
Further subject details are given in Table 1.
Blood sampling
Venous blood was collected for neuroendocrine measurements after 30 min of supine rest (see below). Blood was
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taken into chilled tubes and centrifuged immediately at
4 mC. Plasma was then separated and stored at k70 mC
until assayed. Plasma atrial natriuretic peptide [14], brain
natriuretic peptide [15], angiotensin II (ANG II) [16],
noradrenaline [17] and ET-1 [18] were measured, as
previously described.
Subcutaneous fat biopsies
In both groups, skin and subcutaneous fat biopsies were
taken, after application of 1 % lidocaine local anaesthesia,
from the right or left gluteal region, as previously
described [9]. Each biopsy measured approx.
2 cmi1 cmi1 cm.
Vessel preparation
Small arteries ( 300 µm) dissected from fat under a
microscope were mounted on two 40 µm stainless steel
wires on a Mulvany\Halpern myograph [11], allowing
isometric force measurements to be made. Two vessels
from each patient were investigated simultaneously under
identical conditions. The mean for the two sets of data
was obtained to form one data set for each patient used
for statistical analysis. The vessels were maintained at
37p0.5 mC in 95 % O \5 % CO at pH 7.4 in physio#
#
logical salt solution (PSS) with the following
composition (mmol\l) : NaCl 118.4, NaHCO 25, KCl
$
4.7, KH PO 1.2, CaCl 2.5, MgSO :7H O 1.2 and
# %
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%
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glucose 11.
Myography studies
The standard myography protocols developed by
Mulvany (see [11]) have been widely published previously. Briefly, following an equilibration period,
measurement of wall thickness and lumen diameter was
performed at three points along each vessel (set to a
minimal resting tension of 0.25 mN) using light microscopy and a filar micrometer eyepiece with a resolution of 1 µm. Wall thickness, rather than media
thickness, was measured, since the media–adventitial
border was not always sufficiently clear to allow accurate
media measurement. Similarly, vessels in which the edge
of the steel wire in the lumen could not be clearly
identified were not measured. Measurements of vessel
length were also obtained. The wall\lumen ratio and the
cross-sectional area (CSA) of the vessel walls were
calculated using the following formulae :
Wall\lumen l m\di100
CSA l π(dmjm#)
where m is wall thickness and d is lumen diameter.
Following a further equilibration period, the vessel
was stretched in a series of small (2–3 mN) steps at 1 min
intervals, and resting tension was determined for each
stretch. Using Laplace’s equation to relate transmural
Small-artery changes in chronic heart failure
Table 1
Characteristics of CHF patients and control subjects
Abbreviations : NYHA, New York Heart Association ; IHD, ischaemic heart disease ; LV, left-ventricular ; HV, healthy volunteers ;
DCM, dilated cardiomyopathy ; LVEF, left-ventricular ejection fraction ; BNP, brain natriuretic peptide ; ANP, atrial natriuretic
peptide. Values are meanspS.D. Significance of differences compared with controls : *P 0.05.
Sex (male/female)
Age (years)
Aetiology
Controls
CHF patients
10/2
57p14
13/3
55p13
8 IHD (normal LV function) ;
4 HV
12 IHD ;
4 DCM
NYHA class
II
III
IV
–
–
–
11
4
1
LVEF (%)
51p4
27p9
Drug therapy
ACE
Diuretic
Digoxin
Calcium antagonist
Oral nitrate
β-Blocker
Aspirin
0
0
0
1
3
8
7
13
12
7
4
9
3
8
Neuroendocrine levels
ET-1 (pmol/l)
Noradrenaline (nmol/l)
ANG II (pmol/l)
BNP (pmol/l)
ANP (pmol/l)
2.1p0.16
4.8p0.6
7.7p2.4
5.8p1.0
0.7p0.1
2.8p0.27*
6.8p0.6*
32p19.0
16.5p4.0*
1.1p0.17
tension and vessel circumference to the transmural
pressure, the ‘ effective pressure ’ was calculated at each
step until an effective pressure of 13.3 kPa (100 mmHg)
was reached. This gives an estimate of the transmural
pressure that would be needed in vivo to stretch the
relaxed vessel to the given internal circumference. Finally,
each vessel was set to 90 % of its own internal circumference at an effective pressure of 100 mmHg, since
previous studies have shown that a maximal force is
generated at this setting [11].
Drugs and pharmacological protocols
Acetylcholine, ANG II, bradykinin, cocaine hydrochloride, ET-1, noradrenaline and sodium nitroprusside were
obtained from Sigma Chemical Co. (Poole, Dorset,
U.K.). The prostaglandin I analogue Cicaprost was
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obtained from Schering Pharmaceuticals. All drugs were
dissolved in distilled water and diluted to the final bath
concentration with PSS.
Following normalization, the vessels were left for a
further 1 h and then exposed to a high (123 mM)
concentration of potassium (solution identical to PSS
except that sodium was replaced by potassium on an
equimolar basis) for a series of 5 min periods until
repeatable maximal contractions were achieved. A series
of pharmacological protocols that examined either the
contractility or the relaxation of the vessels was then
performed.
All
experiments
were
cumulative
concentration–response curves to various agonists. Contraction curves were carried out with the following
agonists : noradrenaline (10 nM–30 µM) before and after
incubation with cocaine (1 µM) added 30 min before the
curve to inhibit neuronal uptake, ANG II (0.01 nM–
100 nM) and ET-1 (0.01 nM–100 nM). Relaxation studies
were carried out in a different set of vessels preconstricted
to a steady plateau with noradrenaline (10 µM). The
following agonists were used : acetylcholine (10 nM–
0.1 mM),
bradykinin
(0.1 nM–3 µM),
cicaprost
(0.01 nM–0.3 µM) and sodium nitroprusside (1 nM–
0.1 mM). Vessels were left for 30 min between curves.
Preliminary experiments with time controls had shown
that the contraction responses of human vessels to
noradrenaline remain stable over 6 h, and that 30 min
between curves is sufficient to achieve repeatable contraction responses.
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C. Hillier and others
Statistical analysis
Contraction responses are expressed as tension\unit
length of vessel (mN\mm), and relaxation data as
percentage change (%) from the maximum noradrenaline-induced contraction. Results are expressed as
meanspS.E.M. For the purposes of analysis, the term
pD has been used to describe the negative log of the
#&
concentration of drug (M) required to obtain 25 % of the
maximum response. This is in keeping with the use of the
ubiquitous term pD to describe the concentration of
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drug required to obtain 50 % of the maximum response.
Statistical comparisons of morphology data, maximum
response and pDx were performed using the unpaired
Student’s t test. Concentration–response curves were
analysed by one-way analysis of variance for repeated
measures, with a P value of
0.05 being considered
statistically significant.
RESULTS
Concentration–response curves to
contractile agonists
Noradrenaline
The responses to noradrenaline did not differ significantly between patients with CHF and controls with
respect to either the size of the maximum contraction or
sensitivity (Figure 1a). The sensitivity of control vessels
to noradrenaline, however, increased following incubation with the neuronal uptake blocker cocaine (Figure
1b). In the control vessels cocaine significantly reduced
pD and pD (P 0.05) (Figure 1, right panels). This
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effect of cocaine on sensitivity was not seen in vessels
from patients with CHF.
Angiotensin II
The responses to exogenous ANG II were noticeably
variable in both groups, and there was no significant
difference in either the maximum response or the pD
#
value between patients with CHF and control subjects
(Figure 2a).
ET-1
Neuroendocrine assays
Plasma concentrations of all the neuroendocrine substances measured were increased in patients with CHF
compared with controls ; however, whereas the increases
in ET-1, noradrenaline and brain natriuretic peptide were
statistically significant, those in ANG II and atrial
natriuretic peptide did not reach statistical significance.
These findings are summarized in Table 1.
Small-artery morphology
There were no morphological differences observed between the two groups in any of the parameters measured
(Table 2). This was true for comparisons of wall
thickness, wall cross-sectional area and wall\lumen ratio.
The mean internal diameters in the two groups were very
similar (controls, 251p12 µm ; CHF patients,
253p14 µm).
Table 2 Morphological characteristics of subcutaneoussmall
arteries from patients with CHF and from control subjects
Wall thickness could only be measured in those vessels in which the lumenal wires
could be clearly identified (n l 9 both groups). Abbreviation : CSA, cross-sectional
area.
Parameter
Controls (n l 12)
CHF patients
(n l 16)
Internal diameter (µm)
Wall thickness (µm)
Wall/lumen ratio ( %)
Wall CSA (µm2)
251p12
33p6
12p3
31 320p6004
253p14
27p8
13p2
21 723p10 477
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Comparison of the concentration–response curves
showed that the contractile response to ET-1 was
significantly reduced in small arteries from patients with
CHF compared with those from control subjects (P
0.05 ; Figure 2b). Similarly, the maximal contraction
obtained was significantly smaller in vessels from CHF
patients compared with those from controls (controls,
2.06p0.21 mN\mm ; CHF, 1.43p0.20 mN\mm ; P
0.05). No comparison of pD values was made, as a true
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maximum contractile response to ET-1 was not obtained
in vessels from patients with CHF.
Concentration–response curves to
vasorelaxant agonists
Acetylcholine
The maximum relaxation obtained with acetylcholine
was significantly reduced in resistance arteries from
patients with CHF compared with those from controls
(CHF, 72p12 % ; controls, 96p15 % ; P 0.05 ; Figure
3a). The sensitivity to acetylcholine did not, however,
differ significantly between the two groups (pD : CHF,
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6.74p0.30 ; controls, 7.39p0.10).
Sodium nitroprusside
In contrast, the concentration–relaxation response curves
to sodium nitroprusside were similar in patients with
CHF and controls (Figure 3b)
Bradykinin
The maximum relaxation in response to bradykinin was
similar in CHF patients and controls. Although comparison of the pD values between groups did not reach
#
statistical significance (controls, 8.57p0.37 ; CHF,
Small-artery changes in chronic heart failure
Figure 1
Effects of noradrenaline on isolated resistance arteries from control subjects (#) and patients with CHF ($)
Concentration–response curves were constructed before (Figure 1a) and after (Figure 1b) incubation with 1 µM cocaine for 30 min. The right-hand panels show the
concentration of noradrenaline (norepinephrine) required to produce contractions equivalent to 10 % (pD10), 25 % (pD25) and 50 % (pD2) of maximum in controls before
cocaine () and after cocaine (#), and in CHF patients before cocaine (
) and after cocaine ($). Significance of differences : *P 0.05.
Figure 2
($)
Effects of ANG II (a) and ET-1 (b) on isolated resistance arteries from control subjects (#) and patients with CHF
Significance of differences : *P
0.05.
Figure 3 Effects of acetylcholine (a) and sodium nitroprusside (b) on isolated resistance arteries from control subjects (#)
and patients with CHF ($)
Significance of differences : *P
0.05.
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Figure 4 Effects of bradykinin (a) and cicaprost (b) on isolated resistance arteries from control subjects (#) and patients
with CHF ($)
Significance of differences : *P
0.05.
7.23p0.23) comparison of the complete curves showed
that, for patients with CHF, the concentration–response
curve was shifted significantly to the right (P 0.05 ;
Figure 4a).
Cicaprost
The concentration–response curve to the prostacyclin
analogue cicaprost was excessively shifted to the right in
CHF patients. Furthermore, pD responses were also
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significantly different. (CHF, 8.04p0.18 ; controls,
9.27p0.34 ; P 0.05 ; Figure 4b), indicating decreased
sensitivity to the vasodilator action of this agent in
patients with CHF compared with controls. The maximum relaxation achieved with cicaprost did not differ
between the two groups.
DISCUSSION
This study shows that subcutaneous small arteries from
patients with CHF have blunted responses to a number
of important vasoactive agents. Specifically, this is seen in
(a) reduced responses to the endothelium-dependent
agonists acetylcholine and bradykinin ; (b) reduced
responses to the endothelium-independent agonist
cicaprost ; (c) a failure of the neuronal noradrenaline
uptake mechanism ; and (d) a significantly reduced
vasoconstrictor response to ET-1.
The importance of ET-1 as a mediator of vasoconstriction in vivo is still not clear. In the present study,
healthy control subjects showed a pharmacological
threshold for ET-1 that was ten times lower than that for
ANG II (ET-1, 3 pM ; ANG II, 30 pM). Even these small
contractile responses seen at such low ET-1 concentrations could have large physiological effects in vivo,
particularly since our measured plasma concentrations of
ET-1 are within this range. Local vascular concentrations
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are presumably much greater. ET-1 was also the most
powerful vasoconstrictor, partly because of the commonly observed phenomenon of tachyphylaxis seen at
higher concentrations of ANG II in vitro [19,20]. This
tissue was least sensitive to noradrenaline, although this
agent proved to be a powerful vasoconstrictor at high
concentrations. These data suggest that the circulating
concentrations of ANG II, ET-1 and noradrenaline
found during exercise and in certain disease states, such as
CHF, are at least potentially capable of having a systemic
vascular effect, assuming that the responsiveness of
vessels is maintained in these states [21,22]. An interesting
finding from the study of vasodilator agonists in control
vessels is the demonstration that the human subcutaneous
bed is exquisitely sensitive to the epoprostenol analogue
cicaprost compared with bradykinin, acetylcholine or
sodium nitroprusside, indicating the potential potency of
cAMP-dependent prostaglandin-induced vasorelaxation
in this vascular bed.
In agreement with previous in vitro studies [11,12], our
data suggest that small-artery structure is not altered in
CHF and that a structural component to the increased
vascular resistance is unlikely, even with high systemic
and local concentrations of potential mitogens such as
ET-1, ANG II and noradrenaline. On the other hand, the
reduction in maximum hyperaemia in the arm and leg
following ischaemia or vigorous muscle contraction has
been said to indicate the presence of structural arterial
abnormality in CHF [2,3]. A number of possibilities may
explain this discrepancy. A structural abnormality may
exist in vascular beds other than the subcutaneous one.
Alternatively, subtle histological alterations, not leading
to gross morphological changes detectable by our techniques, may be present in the arteries we studied. Also, it
is known that vigorous diuresis can substantially restore
post-ischaemic hyperaemia, suggesting that excessive
vascular or perivascular sodium and water retention, and
not intrinsic arterial morphological alterations, may
account for impaired vasorelaxation in CHF [23]. Finally,
Small-artery changes in chronic heart failure
it is possible that the presence of ACE inhibitors and βblockers, which are able to reverse some vascular changes,
may have ‘ normalized ’ vascular structural changes.
Indeed, if ACE inhibition was begun early enough in the
history of the disease, then structural changes may not
even have had the opportunity to occur.
A previous in vivo study involving intravenous infusion of noradrenaline suggested the presence of a
reduced haemodynamic response to exogenous agonist,
probably due to ‘ down-regulation ’ of α -adrenoceptors
"
[24]. In the present study, blockade of neuronal noradrenaline re-uptake with cocaine enhanced sensitivity to
noradrenaline in arteries from control subjects, but had
no such effect in vessels from patients with CHF [25].
This may simply reflect reduced sensitivity to noradrenaline in these vessels and, therefore, no further
contraction in response to the increment in local concentration of the agonist brought about by the action of
cocaine. Alternatively, the cocaine-sensitive neuronal
uptake mechanism may not function fully in CHF. If
confirmed, this may be important, as it would tend to
potentiate increased sympathetic neuronal traffic in
CHF, leading to increased synaptic noradrenaline concentrations [26,27].
In contrast with the effects of noradrenaline, the
concentration–response curve to ET-1 in CHF patients
was significantly shifted to the right, with a reduction in
sensitivity to the agonist. This is in keeping with
observations in experimental heart failure and in humans,
at least with one dose of ET-1 infused into the brachial
artery [28], suggesting that, in the case of ET-1, subcutaneous vessels behave similarly to muscle (forearm)
arteries. Also, although the contractile response to ET-1
was diminished in CHF, ET-1 was still the most potent
constrictor agonist of the series studied, suggesting that it
may be an important therapeutic target in CHF.
Concentrations of ANG II as low as 10 pM were able
to elicit the contraction of small arteries from patients
with CHF. This is potentially a very important finding,
as the majority of our patients with CHF were taking
what is conventionally regarded as a maximum dose of an
ACE inhibitor. Despite this treatment, they had plasma
ANG II concentrations that could have a vasoconstrictor
action in the systemic circulation. Others have made
similar observations [29]. Synergistic interactions between ANG II and other vasoconstrictors could
potentiate this effect [30]. This suggests that alternative or
additional approaches to inhibition of the renin–
angiotensin system in CHF may be of value [31].
In keeping with previous in vivo [32–35] and in vitro
studies [11,32,33] in humans, the responses to acetylcholine in CHF were reduced in both sensitivity and
maximum response. However, given that most of our
patients were receiving treatment with an ACE inhibitor,
it was surprising that the vasorelaxant effect of
bradykinin was also attenuated in CHF. In experimental
models and in humans in vivo, ACE inhibitors have been
shown to augment the vasodilator action of bradykinin
[36,37]. As with ET-1, this reduced response may be due
to down-regulation of receptors in the presence of high
plasma levels. ET-1 levels in these patients were clearly
raised, whereas it is probable that the use of ACE
inhibition may have potentiated at least local levels of
bradykinin via inhibition of ACE kininase activity.
Finally, we also found that the prostacyclin analogue
cicaprost is a very potent relaxant of preconstricted
human small arteries, and that this effect was greatly
attenuated in CHF. The potential role of prostanoid
vasodilator pathways in CHF has been generally
neglected, although the suggestion that acetylsalicylic
acid (aspirin) may attenuate the beneficial actions of ACE
inhibitors has generated some interest [38].
Heagerty and colleagues [12] have already shown that
the blunted responses we report here are not found in
mild heart failure, indicating a time-dependent effect of
CHF. During the time period during which CHF
develops, fundamental abnormalities in second messenger systems or calcium handling may occur. Indeed, it
may be inferred that smooth muscle cAMP-mediated
pathways are abnormal (noradrenaline, cicaprost),
whereas the actions of smooth muscle cGMP-dependent
agonists (e.g. sodium nitroprusside) are better preserved.
Only endothelial, as opposed to smooth muscle, abnormalities are unlikely (i.e. impaired responsiveness to
acetylcholine and bradykinin, but preserved response to
sodium nitroprusside), since cicaprost is an endotheliumindependent vasodilator. Also, enhanced basal nitric
oxide release could account for some of our findings [35] ;
however, this is difficult to study without a flow system
to generate endothelial shear stress stimulation of nitric
oxide synthase.
There is a general attenuation of responses observed
throughout these studies, of which only specific agonist
responses have been shown to be statistically significant.
However, since the variability of myograph responses is
agonist-dependent, it is possible that, with the group
sizes we have used, a type II statistical error is present,
and that a greater sample size would have shown more
specific differences between CHF patients and control
subjects.
It is not known whether the subcutaneous bed is any
more, or less, important than the other large resistance
beds of the body (i.e. the skeletal muscle and mesenteric
beds) in the pathology of CHF. In other human disorders
(hypertension, peripheral vascular disease, diabetes) these
beds have been shown to reflect pathological changes in
both structure and function consistent with the accepted
knowledge of haemodynamic changes. In CHF, the
technique of venous occlusion plethysmography, which
minimizes the effect of the skin, has shown previously
that the skeletal muscle vasculature is depressed [2,3], but
little is known about the changes occurring in the
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C. Hillier and others
subcutaneous bed. The findings of attenuated responses
to ET-1 and endothelial dysfunction in the subcutaneous
bed correspond to similar findings in the skeletal muscle
bed [28,32,34]. Therefore studying the subcutaneous bed
may reflect peripheral changes occurring throughout the
resistance system. Moreover, the gluteal biopsy technique
allows small arteries from both control subjects and CHF
patients to be studied comprehensively.
We have not studied an untreated placebo control
group in the present investigation. Such an approach may
have elucidated the effects of therapy and allowed a more
detailed description of the effects of CHF alone. Also,
our study used a mixed control group with both normal
subjects and ischaemic heart disease patients, which
allowed the opportunity to observe changes due to heart
failure and not simply vascular disease changes per se.
The ejection fraction of the control group averaged 51 %,
measured using the Simpson’s Biplane method. This
method generally gives a ‘ low ’ ejection fraction value.
However, this is the same technique used in a recent
study of left-ventricular function in our population, in
which the average left-ventricular ejection fraction was
measured to be 47 %. Therefore, within this framework,
our control group provides a realistic and useful comparison with CHF patients [39].
In summary, small-artery morphology is not grossly
altered in CHF. Generally, CHF seems to be characterized by reduced responses to ET-1 and, among
vasodilators, to cicaprost, acetylcholine and bradykinin.
Neuronal re-uptake of noradrenaline also seems to be
altered in CHF. Despite these differences, ET-1 remains
the most powerful vasoconstrictor and cicaprost the most
powerful vasodilator in CHF ; these observations have
obvious therapeutic implications. Circulating and local
concentrations of ANG II and ET-1 in patients with
CHF treated with an ACE inhibitor are probably high
enough to have a physiological action in the systemic
circulation.
ACKNOWLEDGMENTS
This work was supported by the Medical Research
Council.
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Received 7 May 1999/23 July 1999; accepted 10 September 1999
# 1999 The Biochemical Society and the Medical Research Society
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