(Circulation. 1995;91:1981-1987.)
© 1995 American Heart Association, Inc.
Articles |
From the I Clinica Medica, University of Pisa, Pisa, Italy.
Correspondence to Stefano Taddei, MD, I Clinica Medica, University of Pisa, Via Roma, 67, 56100 Pisa, Italy.
| Abstract |
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Methods and Results Within the normotensive or hypertensive group (n=53 and n=57, respectively), subjects were selected with similar blood pressure, plasma cholesterol, and glucose values, and hypercholesterolemic subjects, diabetics, and smokers were excluded. We evaluated forearm blood flow (by strain-gauge plethysmography) modifications induced by intrabrachial acetylcholine (0.15, 0.45, 1.5, 4.5, and 15 µg/100 mL per minute), an endothelium-dependent vasodilator, and sodium nitroprusside (1, 2, and 4 µg/100 mL per minute), an endothelium-independent vasodilator. Acetylcholine caused a dose-dependent vasodilation that was significantly (P<.01) lower in essential hypertensive patients than in normotensive control subjects. However, a significant negative correlation was observed between acetylcholine-induced vasodilation and patient age in both normotensive (r=-.86, P<.001) and hypertensive (r=-.85, P<.001) patients. In contrast, vasodilation to sodium nitroprusside was similar in normotensive control subjects and essential hypertensive patients with a poorer inverse correlation with patient age (normotensive control subjects, r=-.37; hypertensive patients, r=-.36) compared with acetylcholine.
Conclusions The present data indicate that there is a blunted response to acetylcholine with advancing age in both normotensive control subjects and essential hypertensive patients, suggesting that aging is associated with reduced endothelium-dependent vasodilation in humans.
Key Words: acetylcholine endothelium aging hypertension
| Introduction |
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In addition to acetylcholine, many other agonists or physiological stimuli can trigger endothelium-dependent relaxations by releasing endothelium-derived relaxing factor (EDRF),3 4 5 6 recently identified with nitric oxide,7 a labile substance derived from L-arginine degradation.8 Moreover, endothelial cells can activate a cyclooxygenase-dependent pathway and produce endothelium-derived contracting factors (EDCFs)9 10 that, although not yet completely identified, are very likely to be endoperoxides such as thromboxane A211 or prostaglandin H2.12
It is well documented that loss of endothelial function not only is characteristic of diseases such as genetic or secondary hypertension, hypercholesterolemia, and atherosclerosis,13 but also has been associated with advancing age. Experimental data indicate that, independent of the presence of other pathologies, aging alters endothelium-dependent relaxations in both the aorta and small resistance arteries in rats.14 15 16 17 18 These findings have been confirmed in human coronary arteries in vivo.19 20 21 22
However, human coronary arteries can be affected by early atherosclerosis,23 even though angiographically they appear to be free from lesions. Therefore, the present study was designed to evaluate whether age can alter endothelial function in the forearm of normotensive subjects and essential hypertensive patients. Our aim was to assess the role of aging as an independent factor in impairing endothelial function in a vascular district such as the forearm that is usually not affected by atherosclerosis.
| Methods |
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Subjects, defined as healthy according to the absence of familial history of essential hypertension and by blood pressure of <140/90 mm Hg, were characterized by a mean age of 46.7±7.7 years (range, 19 to 79 years), mean blood pressure of 121.6±4.7/79.4±2.6 mm Hg, and mean total plasma cholesterol of 191.6±7.1 mg/dL (4.95±0.18 mmol/L). Essential hypertensive patients were recruited from among the newly diagnosed cases at our outpatient clinic. In all cases, patients reported the presence of positive familial history of essential hypertension, and supine arterial blood pressure (after 10 minutes of rest), as measured by mercury sphygmomanometer three times at 1-week intervals, was consistently found to be >140/90 mm Hg. Patients with secondary forms of hypertension were excluded. Mean age was 49.1±7.8 years (range, 20 to 78 years); blood pressure was 154.8±7.3/101.2±4.4 mm Hg; and mean plasma total cholesterol was 188.6±6.3 mg/dL (4.87±0.16 mmol/L).
Normotensive control subjects and
hypertensive patients were selected
to have comparable hemodynamic and humoral variables along all aging
profiles (Table 1
).
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Experimental Procedure
All studies were performed at 8
AM after an
overnight fast with the subjects lying supine in a quiet
air-conditioned room (22° to 24°C). A polyethylene cannula (21
gauge, Abbot) was inserted into the brachial artery with the
participant under local anesthesia (2% lidocaine) and was connected
through stopcocks to a pressure transducer (model MS20, Electromedics)
for systemic mean blood pressure (
pulse pressure
plus
diastolic pressure) and heart rate (model VSM1, PhysioControl)
monitoring and for intra-arterial infusions. Forearm blood flow (FBF)
was measured in both forearms (experimental and contralateral forearms)
by strain-gauge venous plethysmography (LOOSCO, GL
LOOS).23 Circulation to the hand was prohibited 1 minute
before each sampling or FBF measurement by inflating a pediatric cuff
around the wrist at suprasystolic blood pressure. Details concerning
the sensitivity and reproducibility of the method as performed in our
laboratory have been published.24
Drug infusion rates were normalized for 1 dL of tissue by adjusting the speed of infusion to the desired infusion rates. Drugs were infused at systemically ineffective rates through separate ports via three-way stopcocks.
Experimental Design
Endothelium-dependent vasodilation was
estimated with a
dose-response curve to intra-arterial acetylcholine (cumulative
increase of the infusion rates: 0.15, 0.45, 1.5, 4.5, and 15 µg/100
mL forearm tissue per minute for 5 minutes at each dose).
Endothelium-independent vasodilation was assessed with a dose-response curve to intra-arterial sodium nitroprusside, a direct smooth muscle cellrelaxant compound25 (cumulative increase by 1, 2, and 4 µg/100 mL forearm tissue per minute for 5 minutes at each dose). These rates were selected to induce vasodilation comparable to that obtained with acetylcholine.
The sequence of infusion of the two drugs was randomized, and 45 minutes of recovery were allowed between the two experimental steps.
Statistical Analysis
Because arterial pressure did not change
significantly during
the study, all data were analyzed in terms of FBF; FBF increments were
taken as evidence of local vasodilation. Raw data were analyzed by two-
or three-way ANOVA, and Duncan's test was applied for multiple
comparison testing. Wilcoxon's test was used to check the statistical
significance of the difference between nonparametric values. The global
FBF response to the dose-response curve for acetylcholine and sodium
nitroprusside was also analyzed as the slope of the percent increase in
FBF above basal level induced by both agonists, calculated using a
linear regression analysis (y axis: percent
increase in FBF; x axis: logdoses] [µg/min] of
acetylcholine or sodium nitroprusside). The correlation coefficient was
.91±.09 (range, .75 to .99). Interactions between age and forearm
vasodilation to acetylcholine and sodium nitroprusside (considered in
terms of either maximum effect or slope) were calculated by a
multivariate analysis, using a multiple stepwise regression, to
exclude the effects of blood pressure and plasma cholesterol. Results
were expressed as mean±SD.
Drugs
Acetylcholine HCl (Farmigea S.P.A.) and sodium
nitroprusside
(Malesci) were obtained from commercially available sources and diluted
to the desired concentration by adding normal saline; fresh solutions
were made for each experiment. Sodium nitroprusside was dissolved in
glucosate solution and protected from light with aluminum foil.
| Results |
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Response to Intrabrachial Acetylcholine
Fig 1
shows the percent increase in FBF above basal
level induced by acetylcholine in normotensive control subjects divided
into four subgroups according to age. It is evident that the
vasodilating response to acetylcholine declines progressively with
increasing age. Thus, FBF increased from 3.5±0.7 to 34.1±6.2
mL/100
mL forearm tissue per minute in the <30-year-old subgroup, from
3.5±0.7 to 28.3±5.8 mL/100 mL forearm tissue per minute in the
31- to
45-year-old subgroup, from 3.6±0.8 to 20.4±6.4 mL/100 mL forearm
tissue per minute in the 41- to 60-year-old subgroup, and from 3.2±0.4
to 10.8±1.8 mL/100 mL forearm tissue per minute in the oldest subjects
(>60 years old). In essential hypertensive patients, acetylcholine
caused a dose-dependent relaxation that was found to be significantly
(P<.001) reduced compared with normotensive control
subjects (Fig 2
). However, within the hypertensive group
(Fig 3
), the vascular response to acetylcholine
progressively declined with age (<30 years, from 3.2±0.4 to
25.9±3.7
mL/100 mL forearm tissue per minute; 31 to 45 years, from 3.6±0.7 to
17.6±6.5 mL/100 mL forearm tissue per minute; 46 to 60 years, from
3.5±0.9 to 15.0±3.4 mL/100 mL forearm tissue per minute; >60
years,
from 3.7±0.7 to 9.4±2.3 mL/100 mL forearm tissue per minute).
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Multivariate analysis showed a highly significant inverse
correlation between age and acetylcholine-induced forearm vasodilation,
in terms of either maximum FBF response or slope of the FBF relation to
the muscarinic agonist, in both normotensive subjects (maximum FBF
response, r=-86, P<.001; slope of FBF
response,
r=-.83, P<.001; Fig 4
) and
essential hypertensive patients (maximum FBF response,
r=.85, P<.001; slope of FBF response,
r=-.83, P<0.001; Fig 5
). It
is
noteworthy that younger (<40 years) normotensive and
hypertensive subjects showed a significant and similar inverse
correlation between age and vasodilation to acetylcholine, whereas
older subjects (>60 years) showed no correlation (Table 2
).
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In agreement with the inclusion criteria, no correlation was found between the response to acetylcholine and plasma cholesterol (normotensive subjects, r=-.28; hypertensive patients, r=-.21) or mean blood pressure values (normotensive subjects, r=-.13; hypertensive patients, r=-.26) in either group.
Response to Intrabrachial Sodium Nitroprusside
Fig
1
shows the percent increase in FBF above basal level induced
by sodium nitroprusside in normotensive control subjects. Forearm
vasodilation in response to the highest dose of sodium nitroprusside
was greatest in the youngest persons compared with the other subgroups,
whereas the vascular effects of the lower and intermediate doses of the
compound were similar in all subjects. In essential hypertensive
patients, the response to sodium nitroprusside was similar to that of
normotensive control subjects (Fig 2
); thus, the vasodilating
effect of
the highest dose of the compound was shown to be increased in the
youngest hypertensive patients compared with older subgroups (Fig
3
).
However, in both normotensive subjects and essential hypertensive
patients, multivariate analysis showed only a slight correlation
between the maximum blood flow (normotensive subjects,
r=-.37, P<.01; hypertensive patients,
r=-.36, P<.01) and the slope of the FBF
relation to sodium nitroprusside (normotensive subjects,
r=-.37, P<.01; hypertensive patients,
r=-.30, P<.05) and advancing age (Figs
6
and 7
). Finally, although
younger (<40 years) essential hypertensive patients showed an inverse
correlation between age and vascular response to sodium nitroprusside,
no correlation was found in younger (<40 years) normotensive subjects
and in older (>60 years) control subjects and hypertensive patients
(Table 2
).
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| Discussion |
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The present study was designed to evaluate the role of advancing age as an independent factor that can alter endothelial function. Therefore, the major aim was to discriminate between the effect of aging and that of the several clinical conditions that can impair endothelial responsiveness, such as hypertension, hypercholesterolemia, and atherosclerosis.13 To achieve this goal, we followed two different approaches. First, we selected a group of healthy control subjects and hypertensive patients, ensuring that older and younger subjects were matched for blood pressure values and had comparable, normal range values of total, HDL, and LDL plasma cholesterol; plasma glucose; and body mass index. Second, we recruited a group of essential hypertensive patients to test whether aging exerts an unfavorable effect on endothelial function even in the presence of another factor that has been clearly shown to impair endothelium-dependent relaxations in humans.26 27 28
It should be noted that in the two groups of patients, both the maximum effect and the slope of the flow response to acetylcholine, the latter being an integrated index representing the complete vascular effect of the dose-response curve to the muscarinic agonist, show an inverse correlation with advancing age. These findings strongly suggest that aging is associated with impairment of endothelial function. The alternative possibility of a generalized defect in the ability of smooth muscle cell to relax appears to be much less likely, considering both the much poorer correlation between aging and the maximum or the slope of the FBF response to sodium nitroprusside compared with acetylcholine. However, the finding that in both normotensive and hypertensive younger subjects the maximum dose of sodium nitroprusside caused greater vasodilation compared with the other subgroups suggests that a certain amount of impairment in smooth muscle celldependent vascular reactivity is associated with advancing age, although to a much lesser extent.29
It is important to observe that in both normotensive control subjects and essential hypertensive patients, the forearm vascular response to acetylcholine showed an inverse correlation with age in younger subjects (<40 years), whereas no correlation was found in older subjects (>60 years). Thus, age-related impairment in endothelial function is an early event that progressively curtails vascular function up to 60 years, when the derangement appears to stop. This latter finding can tentatively be explained as follows. First, in old age, endothelial cells could already be maximally altered; and second, an alternative explanation could be represented by the recruitment of older subjects in good health, a clinical condition not common at that age, which could have determined selection of a study population with a vascular bed in particularly good condition.
In agreement with previous reports,26 27 28 the present results demonstrating impaired vasodilating response to acetylcholine but not to sodium nitroprusside in patients with essential hypertension compared with normotensive control subjects of the same age confirm the presence of impaired endothelial function in essential hypertension. However, it is important to observe that, even in hypertensive patients, aging still exerts a negative effect on endothelium-dependent relaxations, further indicating that advancing age appears to be an independent factor that, by itself, causes progressive derangement of endothelium-dependent vascular control.
This possibility is in agreement with several observations based on studies on animals involving both large vessels or small resistance arterioles14 15 16 17 18 and with similar results obtained in epicardial and in resistance coronary arteries in humans in vivo.19 20 21 22 However, this vascular district can be characterized by early atherosclerosis even in the presence of angiographically normal coronary arteries,20 a possibility that is much more unlikely in forearm vessels.
With respect to the mechanism(s) responsible for the age-associated impairment of endothelial function, different possibilities can be considered based on animal studies, but at the present time, no data are available in humans. Experimental data indicate that advancing age may be characterized by a derangement of endothelial cells that leads to a decrease in EDRF (nitric oxide) production.17 30 Moreover, it has been demonstrated that aging is associated with the accumulation of glycosylation end-products that reduce nitric oxide activity and cause impaired endothelium-dependent relaxations.31 32 In addition, another possible mechanism is suggested by the finding that in the aorta of Wistar-Kyoto rats, the age-associated impaired endothelial response to acetylcholine is determined by the production of a cyclooxygenase-dependent EDCF; normal response to the muscarinic agonist can be restored by indomethacin.33 This unidentified constrictor substance is the same as that characterizing the blunted endothelium-dependent relaxations in animal genetic hypertension.9 10
In humans, different lines of observations characterize the complexity of mechanisms involved in the reduced endothelial function demonstrated in different pathologies such as hypercholesterolemia or hypertension. Hypercholesterolemic subjects show a blunted forearm34 and coronary35 blood flow response to acetylcholine that can be normalized by the administration of L-arginine.35 Therefore, in these patients it is likely that impairment of endothelial function could be mediated by reduced production of nitric oxide. In addition, essential hypertension, which corresponds to the genetic form of hypertension in animals, appears to be characterized by the simultaneous presence of a defect in the L-argininenitric oxide pathway36 37 and production of a cyclooxygenase-dependent EDCF.28 Consequently, a decrease in nitric oxide release, production of EDCF(s), or both can be taken into account to explain the mechanism that determines the age-associated impairment of endothelial function in humans. Therefore, further studies are needed to explore these possibilities.
However, apart from the mechanisms involved, impairment of endothelial function appears to characterize advancing age in both normotensive subjects and essential hypertensive patients independent of other conditions such as hypercholesterolemia or atherosclerosis that can be associated with reduced endothelium-dependent relaxations. This finding could have important clinical relevance since endothelial cells play a key role both in local control of vascular reactivity and in protecting the arterial wall against the series of events that lead to atherosclerosis. Thus, endothelium-derived substances represent one of the principal mechanisms in maintaining the autoregulation capacity of important vascular districts such as the cerebral,38 cardiac,39 and renal40 districts. Moreover, the endothelium releases factors involved in coagulation and thrombus formation41 and in growth inhibition or stimulation.42 Normally, substances such as nitric oxide, which maintain blood flow and inhibit platelet aggregation or smooth muscle growth, are dominant, but alterations in endothelial anatomy, function, or both may contribute to the pathogenesis as well as to the progression and complications of cardiovascular disease.
Finally, the possibility of, at least in part, reversing endothelial dysfunction by drug treatment in essential hypertensive patients remains debated. Experimental data obtained in large conduit arteries43 44 and in resistance arteries45 of hypertensive rats demonstrate that appropriate antihypertensive treatment with several drugs (calcium antagonists, angiotensin-converting enzyme (ACE) inhibitors, angiotensin II receptor antagonists, diuretics) can restore normal endothelium-dependent responsiveness. In contrast, results in patients with essential hypertension46 indicate that up to 12 weeks of treatment with ACE inhibitors (either captopril or enalapril) was ineffective in reversing endothelial dysfunction. In addition, other negative results were obtained by Panza et al47 in hypertensive patients receiving treatment with different drugs and for different periods of time. However, the discrepancy between data in animals and humans could be related to the possibility that essential hypertensive patients may require a prolonged period of treatment to obtain an improvement in endothelial function. Therefore, further studies are needed to evaluate whether prolonged antihypertensive treatment (for several months or even 1 year) can improve endothelium-dependent vasodilation.
In conclusion, the present results show that endothelial dysfunction is associated with advancing age in both normotensive and hypertensive persons. It is tempting to speculate that this alteration could be a possible explanation of the higher cardiovascular risk associated with old age.48
| Acknowledgments |
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Received March 8, 1994; revision received August 15, 1994; accepted November 11, 1994.
| References |
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