© 1997 American Heart Association, Inc.
Articles |
Endothelium-Dependent Vasodilation and Tissue-Type Plasminogen Activator Release in Borderline Hypertension
From the Clinical Experimental Research Laboratory, Sahlgrenska University Hospital/Östra, Heart and Lung Institute, and the Department of Neurology, Institute of Clinical Neuroscience, Sahlgrenska University Hospital/Sahlgrenska (C.J.), Göteborg University, Göteborg, Sweden.
Correspondence to Sverker Jern, MD, Clinical Experimental Research Laboratory, Sahlgrenska University Hospital/Östra, S-416 85 Göteborg, Sweden.
 |
Abstract |
|---|
 Top Abstract IntroductionMethodsResultsDiscussionReferences |
|---|
Abstract We recently showed that muscarinic receptor stimulation causes a marked increase in the net release of tissue-type plasminogen activator (TPA) antigen and activity across the human forearm in vivo, in conjunction with endothelium-dependent vasodilation. Because hypertension has been associated with endothelial dysfunction, the aim of the study was to compare forearm TPA release and vasodilation in response to muscarinic stimulation in normotensive (NC) and borderline hypertensive (BH) subjects. The study was performed in 10 apparently healthy young men with BH and 10 male NC subjects. Methacholine (MCh: 0.1, 0.8, and 4.0 µg/min) and sodium nitroprusside (SNP: 0.5, 2.5, and 10 µg/min) were administered in randomized order as double-blind, stepwise, intrabrachial artery infusions. Forearm blood flow was assessed by plethysmography. Net release/uptake was calculated as the product of the arteriovenous concentration gradient and forearm plasma flow. Vasodilator responses to MCh were similar in both groups (P=NS), whereas the decrease in forearm vascular resistance in response to SNP was somewhat less in BH subjects (P=.005). At rest, both groups showed a significant arteriovenous gradient and net release of TPA antigen across the forearm (P<.05 throughout). However, in contrast to the significant net increment in TPA activity across the forearm in the NC group (P<.018), BH subjects had no basal forearm increment in TPA activity (NC vs BH, P=.006). Arterial and venous plasma levels of plasminogen activator inhibitor 1 (PAI-1) antigen and activity were higher in BH subjects (P
.05 throughout), who in contrast to NC
subjects, also had a significant forearm net release of PAI-1 antigen
(P=.006). Across the whole group, there was a significant
inverse relation between arterial PAI-1 antigen levels and
increment in TPA activity across the forearm (r=-.57,
P=.008) but no relation to TPA antigen release. In response
to MCh infusion, both the net release of TPA antigen and increment in
TPA activity increased markedly and to similar extents in both groups
(P<.01 throughout). SNP infusion had no effect on either
TPA antigen release or increment in TPA activity in the NC group but
elicited a significant net release of TPA antigen and increase in TPA
activity in the BH group (P<.05). Both circulating levels
and local release of PAI-1 antigen were significantly correlated to
fasting plasma insulin. Endothelium-dependent
vasodilation and endothelial TPA release in response to
muscarinic receptor stimulation were preserved in BH subjects. At rest,
BH subjects had higher circulating PAI-1 antigen levels and a
corresponding decrease in circulating levels and local increment of TPA
activity. In contrast to NC subjects, BH subjects responded with a TPA
release also in response to increased flow, which may indicate an
enhanced endothelial cell responsiveness to fluid shear
stress.
Key Words: hypertension • muscarinic receptors • TPA • PAI-1
|
Introduction |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
The vascular endothelium produces a number of agents with effects on vascular smooth muscle cell tone and hemostatic function,1 including the vasodilator NO and the endogenous fibrinolytic activator TPA. Because the particular cluster of agonists that cause acute release of TPA appears to be similar to (or even identical with) the agonists that produce endothelium-dependent vasodilatation by generation of NO (compare with Reference 22 ), it is possible that the release of TPA and NO is mediated by similar intracellular signal transduction pathways.
Muscarinic receptor stimulation has been widely used as a pharmacological tool to stimulate NO release and thereby to induce endothelium-dependent vasodilation (eg, see References 3 and 43 4 ). In isolated animal organ preparations, muscarinic agonists have also been shown to stimulate TPA release ex vivo.5 6 7 We recently applied the perfused-forearm model to study the in vivo release mechanisms of TPA in humans8 9 and found that muscarinic receptor stimulation by MCh, in addition to producing pronounced vasodilation, elicited a marked increase in the net release of TPA antigen and increment of TPA activity across forearm tissues.10
It is known that the vasorelaxant responses to pharmacological probes that stimulate NO release are dependent on the intact functional integrity of the vascular endothelium.11 More importantly, evidence has accumulated in the last few years that not only manifest atherosclerosis but also a number of preatherosclerotic conditions such as hypertension,12 13 diabetes mellitus,14 hypercholesterolemia, and smoking15 are associated with functional impairment of endothelial function and a diminished capacity for endothelium-dependent vasodilation. However, to our knowledge, it has not been investigated whether such dysfunction also entails defective TPA release from the vascular endothelium.
In a recent series of studies, we investigated young subjects with persistent BH, a condition that in a substantial proportion of cases is a forerunner of established essential hypertension.16 17 18 We have shown that BH is a syndrome associated with structural vascular changes,19 20 impaired glucose tolerance,21 and endocrine aberrations, including alterations in sex hormone metabolism.22 These disturbances suggest the presence of a complex web of vascular, metabolic, and hormonal aberrations, which are similar to those found in established hypertension. It was therefore considered of interest to investigate endothelium-dependent vasodilation in BH and to examine the relation between vasodilator responses and the capacity for TPA release from the endothelium.
|
Methods |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
Subjects
The study was conducted in 10 men (age range, 24 to 27 years) with BH and 10 NC subjects (age range, 22 to 25 years). BH subjects were recruited from a population sample of healthy young men who had been summoned to compulsory military enlistment. BH was defined as BP 145 mm Hg systolic (SBP) and/or 85 mm Hg diastolic (DBP) at the screening and an SBP of 140 to 160 mm Hg and/or a DBP of 85 to 95 mm Hg on two subsequent follow-up visits to the Hypertension Center. Secondary hypertension was excluded by standard procedures. NC (SBP <130 mm Hg and DBP <70 mm Hg) subjects were recruited from medical students and hospital employees. All subjects were nonobese (body mass index <30) nonsmokers. None of the subjects was taking any medication, and none had a history of cardiovascular disease, diabetes mellitus, or hypercholesterolemia. Clinical characteristics are shown in Table 1
. One
of the BH subjects was later found to have asymptomatic
fasting hyperglycemia with normal insulin levels. The data were
analyzed both with and without the data from this individual,
and because all conclusions remained identical in both instances, this
individual was included in the final analysis except for the
correlation analyses between insulin and fibrinolytic
factors.
|
The nature, purpose, and potential risks of the study were carefully explained to each subject before informed consent to participate was obtained. The protocol was approved by the Ethics Committee of the University of Göteborg, and the study was conducted according to the Declaration of Helsinki.
Experimental Protocol
Studies were performed after an overnight fast (
10 hours) and
commenced at 7:30 AM. After catheterization
and application of the recording devices, the subjects rested
for 60 minutes in the supine position in a dimly lit and soundproof
room. Thereafter, baseline recordings and blood samples were
obtained twice 15 minutes apart. In randomized order, double-blind
infusions of either SNP or MCh were administered 90 minutes apart as
stepwise intra-arterial infusions in three dose steps over
a total of 15 minutes. Each drug was given in fixed-order, incremental
dosages. Blood samples and forearm blood flow recordings were
obtained at each dose step. The total duration of the two infusion
periods, including the baseline period between the two infusion steps,
was 
2.5 hours.
The BH subjects had participated in an initial hemodynamic study after the screening recruitment 4 to 5 years before the present study.23 This earlier study was performed in the same laboratory by the same staff as in the present study, and the initial evaluation followed an identical protocol except for the drug infusions.
Forearm Perfusion Studies
An arterial polyethylene catheter (Viggo
Products, British Viggo) was introduced
percutaneously by the Seldinger technique into the
brachial artery of the nondominant arm and advanced 10 cm in the
proximal direction. Intra-arterial BP was recorded
continuously by an electrical transducer (EMT 35, Siemens-Elema) and a
Mingograph 82 (Siemens-Elema). MAP was obtained by electrical damping
of the pressure signal. An indwelling cannula (Venflon, Viggo) was
introduced retrogradely into a deep antecubital vein of the same arm
for venous blood sampling from the muscle vascular bed. The ECG was
continuously monitored on the Mingograph 82. Catheters were flushed
with heparinized (5 IU/mL) saline after blood sampling. Venous
occlusion plethysmography with a mercury-in-rubber strain gauge was
used to assess FBF.24 FBF in milliliters per minute and
per 100 mL of tissue was calculated from five to eight separate
recordings at each point of measurement. Resting FVR was
calculated as the ratio of MAP to FBF. FVR was expressed as resistance
units (mm Hgxmin-1x100
mL-1xmL-1). FPF was estimated from FBF and
hematocrit and corrected for trapped plasma.
Drugs
MCh chloride (Apoteksbolaget) was administered in isotonic
saline (Kabi Pharmacia), and the infusion was given in three dosage
steps: 0.1, 0.8, and 4.0 µg/min. SNP (Nipride, F. Hoffman–La Roche
AG) was given in three dosage steps: 0.5, 2.5, and 10.0 µg/min. Each
dose was infused for 5 minutes by means of a syringe infusion pump with
a constant infusion rate of 1.0 mL/min.
Blood Sampling and Biochemical Assays
Simultaneous arterial and venous blood
samples were obtained twice at each preinfusion baseline and after 3
minutes of active infusion at each dose step. Venous blood samples were
obtained from the indwelling venous cannula after the first 3 to 4 mL
of blood had been discarded. For arterial samples, the
following procedure was used to eliminate contamination by the active
drug in the blood sample: The arterial catheter was
connected to a three-way stopcock. At the end of each dose step, the
infusion was stopped and the connection to the drug delivery system
rapidly sealed. The first 3 to 4 mL of arterial blood was
withdrawn through the other connection and discarded (the dead space of
the catheter from the tip to the site where the blood samples were
drawn was 1.5 mL). Thereafter the arterial blood sample was
obtained.
Blood samples were collected in tubes containing a 1/10 volume of 0.13 mol/L sodium citrate (Vacutainer), 1/10 volume of 0.45 mol/L sodium citrate buffer, pH 4.3 (Stabilyte, Biopool AB), and 1/10 volume of platelet-stabilizing buffer (DiatubeH, Diagnostica Stago) for determination of TPA antigen, TPA activity, and PAI-1 antigen, respectively. The platelet-stabilizing buffer contained 0.11 mol/L citric acid, 15 mmol/L theophylline, 3.7 mmol/L adenosine, and 0.198 mmol/L dipyridamole, pH 5.0. The tubes were kept on ice and plasma was isolated within 15 minutes by centrifugation at 4°C and 2000g for 20 minutes. Plasma was immediately frozen and stored at -70°C.
Plasma concentrations of TPA and PAI-1 antigen were determined by ELISA (TintElize TPA, (catalog no. 1105, and TintElize PAI-1, catalog no. 210221, Biopool AB). In the TPA assay, free and complexed forms of TPA are detected with equal efficiency.25 The PAI-1 assay detects all molecular forms of PAI-1, although the efficiency in detecting TPA/PAI-1 complexes is somewhat higher compared with that of active PAI-1 and latent PAI-1, which have been reported to be less well detected.26 For determination of TPA activity in plasma, a solid-phase immunosorbent assay was used with trinitrobenzoylated poly-D-lysine as a stimulator.27 The PAI-1 activity assay is based on the quantitative conversion of PAI-1 to a UPA/PAI-1 complex, the concentration of which is determined by an ELISA employing monoclonal anti–PAI-1 as the capture antibody and monoclonal anti–UPA as the detecting antibody.28 Antibodies were purchased from Novo Nordisk. All samples from one experiment were assayed in duplicate on the same microtest plate. Intra-assay coefficients of variation were 4.3%, 3.9%, 4.5%, and 4.5% for TPA activity and antigen and PAI-1 antigen and activity, respectively. Hematocrit was determined in duplicate on arterial and venous blood using a microhematocrit centrifuge (Hettich Haematokrit, Hettich Zentrifugen). Fasting insulin was determined in duplicate by radioimmunoassay (Diagnostic Products Corp).
Arteriovenous concentration gradients for each individual were obtained by subtracting the measured values in simultaneously collected venous and arterial blood. For TPA and PAI-1 antigen, a positive difference (venous minus arterial) indicated a net release and a negative difference, a net uptake. The net release or uptake rate was calculated as the arteriovenous concentration gradient times FPF per unit of time across the forearm.8 For TPA and PAI-1 activity, the term net increment of the respective activity was used to emphasize the fact that changes may not only reflect tissue release/uptake but also possible shifts between the complex-bound and free forms during passage through the forearm.
Statistical Analyses
Standard statistical methods were used. Between-group
comparisons for nonnormally distributed fibrinolytic variables were
performed by the Mann-Whitney U test. The probability that
the arteriovenous concentration gradients or the calculated net
release/uptake indices were different from zero was evaluated by the
nonparametric Wilcoxon signed rank test.
Parametric methods (ANOVA and t test) were used to
evaluate changes in response to infusions. Unless otherwise stated,
data are given as mean and SEM. Responses to intra-arterial
SNP and MCh infusions were evaluated by two-way (group and dose) and
one-way (dose) ANOVA's for repeated measures, with subjects as the
random factor. Owing to the slight baseline differences in FBF between
the groups, FVR responses to the two treatments were evaluated as
relative changes from the preinfusion baseline levels. Degrees of
freedom were corrected according to the conservative Greenhouse and
Geisser procedure for possible violation of the assumption of
sphericity.29 The relation between fasting insulin and TPA
or PAI-1 was evaluated by univariate linear regression
analyses after logarithmic transformation of insulin values. A
similar analysis was used to evaluate the relation between
postischemic vasodilator capacity and
endothelium-dependent vasodilation in response to MCh
and the release of TPA. Univariate linear regression
analyses of the relation between arterial PAI-1
levels and arteriovenous concentration gradients of TPA were performed
on untransformed values. Test results were considered significant at
the P<.05 level (two-tailed test).
|
Results |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
Table 2
summarizes the central and
peripheral hemodynamics of the two groups.
Intra-arterial BP and cardiac output were significantly
higher in BH than in NC subjects. In the BH group, BP levels and
central hemodynamics had remained stable and on similar
levels as those observed at the initial investigation 4 to 5 years
earlier. FBF and FVR were similar at rest and during maximal
vasodilation in both NC and BH subjects. However, resting FBF was
higher at the initial than the present evaluation in BH
subjects.
|
During the preinfusion baseline periods, FVR was somewhat lower in BH
than NC subjects before both SNP (34.7 versus 49.2, P=.05)
and MCh (37.7 versus 47.4, P=.2). As shown in Fig 1, the relative decrease in FVR in
response to SNP was less in BH subjects (ANOVA P=.005),
whereas the response to MCh was of comparable magnitude in both groups
(ANOVA P=NS). Also, the absolute fall in FVR during SNP
infusion was attenuated in the BH group in response to both the 2.5 and
10 µg/min dose steps (t test NC versus BH,
P=.007 and P=.03, respectively). Whereas FVR
responses to the two highest doses of MCh and SNP were similar in NC
subjects, BH subjects had, on average, a 27% and 20% higher response
to MCh than to SNP. There were no significant correlations between the
vasodilatory response to either MCh or SNP and postischemic
vasodilatory capacity, as reflected by the minimal FVR (data not
shown).
|
Table 3 shows the net kinetics of
fibrinolytic factors across the forearm at baseline. Both groups showed
a positive arteriovenous concentration gradient of TPA antigen and a
significant net release of TPA antigen at rest (Wilcoxon's
test, P<.05 throughout). However, in contrast to the
significant arteriovenous step up (P=.013) and the
significant net increment in TPA activity (P=.018) over the
forearm vasculature in the NC group, BH subjects had no increase in TPA
activity across the forearm (Mann-Whitney U test, NC versus
BH, P=.006). Circulating arterial and venous
PAI-1 antigen and activity levels were significantly higher in BH
subjects (Mann-Whitney U test, P.05
throughout). In addition, BH subjects showed a significant net forearm
release of PAI-1 (P=.019), whereas NC subjects showed no
significant step up of PAI-1 across the forearm. Regarding PAI-1
activity, there was an insignificant net decrement across the
forearm.
|
As shown in Fig 2, there was a
significant inverse correlation (r=-.57, P=.008)
between arterial PAI-1 levels and the increment in TPA
activity across the forearm. However, there was no correlation between
arterial PAI-1 levels and TPA antigen release.
|
Fig 3 shows forearm TPA responses to MCh
and SNP infusions. In response to MCh, the net release in TPA antigen
increased markedly in both NC and BH groups (one-way ANOVAs,
P=.006 and P=.0007, respectively), and response
patterns were similar in the two groups (two-way ANOVA,
P=NS). SNP infusion stimulated TPA antigen release in the BH
group (one-way ANOVA, P=.046) but had no significant effect
on TPA antigen net release in the NC group. The increase in TPA
activity during the MCh infusion was similar in the two groups (two-way
ANOVA, dose effect, P=.005 and group effect,
P=NS). In response to SNP, TPA activity fell to a zero net
increment in NC individuals. By contrast, in BH individuals, the
arteriovenous concentration gradients became significantly positive
despite the increase in FPF on the second and third dose step. The
resulting increase in TPA activity across the forearm during SNP was
significant (one-way ANOVA, P=.020). The TPA release in
response to MCh or SNP was not correlated to the
postischemic vasodilatory capacity (minimal FVR, data not
shown).
|
PAI-1 antigen "switched" from a net release to a significant net uptake in the BH group during SNP infusion (one-way ANOVA, P=.046), but PAI-1 release was unchanged in NC subjects. MCh caused no changes in PAI-1 release in either group. No consistent changes in PAI-1 activity across the forearm were observed in response to the two drugs in either group.
Across the entire group (n=19), there were significant direct correlations between fasting insulin and circulating arterial PAI-1 antigen (r=+.50, P=.031) as well as PAI activity levels (r=+.49, P=.034). Furthermore, insulin concentrations were positively correlated with net forearm release of PAI-1 antigen (r=+.51, P=.026). The net increment in TPA activity across the forearm was inversely correlated with plasma insulin levels (r=-.52, P=.026).
|
Discussion |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
The findings of the present study show that endothelium-dependent vasodilation was preserved in young untreated subjects with BH, in whom their BP elevation had persisted over a period of 4 to 5 years. However, BH subjects had a nonspecific attenuation of the vasodilatory response to the NO donor SNP. The observation that the relative vascular response to MCh over SNP was even greater in BH subjects supports the interpretation that the reduced FBF response was not due to a dysfunction of the endothelium per se. Rather, it appears that the functional impairment of the vasorelaxant response may be related to some as-yet-undefined ineffective action of NO on the vascular smooth muscle cells or to structural changes in the vasculature. To test this hypothesis, we also investigated the postischemic vasodilatory capacity, which may reflect structural vascular changes and/or reduced production or action of endogenous vasodilator release during tissue ischemia. However, BH subjects had no evidence of impaired forearm postischemic vasodilation, and there was no significant correlation between the responses to either MCh or SNP and tissue ischemia.
The capacity of the endothelium to synthesize vasodilators such as NO is reduced in both human coronary atherosclerosis and animal models of the disease. More important, functional impairment of endothelium-dependent vasodilation has been observed in patients with preatherosclerotic conditions, such as established hypertension, and it has therefore been suggested that reduced production of the physiological vasodilator NO may contribute to the BP elevation.12 13 The findings of the present study, which to our knowledge is the first on BH, do not support the view that endothelial dysfunction is an obligatory or early finding in hypertensive disease that is not complicated by major metabolic disturbances. Our data are in accordance with those obtained by Cockcroft and coworkers,30 who reported similar findings in untreated patients with mild to moderate hypertension devoid of major lipid metabolic aberrations.30 Taken together, the two studies suggest that the hemodynamic load of a moderate BP elevation does not per se constitute a mechanism for impaired endothelial function. In addition to the synthesis and release of vasoactive substances, the vascular endothelium also produces fibrinolytic activators and inhibitors such as TPA and PAI-1. The inference that endothelial integrity is preserved in BH is further corroborated by the finding that forearm TPA release increased markedly and to a similar extent in both groups in response to muscarinic receptor stimulation by MCh.
Furthermore, in the BH group, flow stimulation by SNP elicited a significant forearm release of TPA antigen and a net increase in TPA activity, an effect that was absent in NC subjects. Available evidence indicates that there is no direct effect of NO on TPA release in either animal models or humans.6 31 However, fluid mechanical shear stress may increase both TPA protein secretion and expression of TPA mRNA in cultured human endothelial cells.32 33 There is circumstantial evidence that shear stress may also induce acute TPA release. It has been shown that increased shear stress elevates intracellular inositol triphosphate levels in endothelial cells,34 and there are data to show that activation of the phosphoinositide system mediates TPA release.35
Whether this mechanism may be operative during
physiological blood flow conditions in humans has
not been studied previously, but in a recent study, we showed that SNP
was effective in stimulating minor forearm TPA release in normotensive
subjects only when high FBF levels (ie, 13 mL/minx100
mL-1 tissue) were reached.10 Although we have
recently found that BH is associated with an enhanced TPA release
capacity in response to venous occlusion,36 the close
similarity of the TPA responses to MCh in BH and NC subjects argues
against the interpretation that the response to SNP was due solely to a
greater releasable TPA pool in BH subjects. Rather, since the effect of
SNP on TPA release was already observed at the two lower-dose steps of
SNP (ie, in the flow range of 4 to 7 mL/minx100 mL-1
tissue) in the BH group, the most likely explanation would be that some
BH subjects have an augmented responsiveness to fluid shear stress
compared with NC subjects. An increased mechanical flow responsiveness
would also be consistent with the fact that a stimulatory
effect on TPA release was evident throughout the SNP infusion, despite
the fact that the SNP-induced vasodilation was less at all three dose
steps in the BH compared with the NC subjects. If this interpretation
is correct, then the observation is of potential
pathophysiological importance because shear stress
also is known to mediate the expression and release of various growth
factors from the vascular
endothelium.37
A somewhat intriguing finding was the fact that even though SNP
stimulated an average TPA antigen release in the BH group of the same
order of magnitude as did MCh, the net increase in TPA activity across
the forearm was considerably smaller with SNP than MCh. Furthermore,
the similarity between the average TPA antigen response to SNP and MCh
in BH subjects might be interpreted to indicate that flow stimulation
alone (which was provoked to the same extent by both agents) could be
responsible for the TPA response in this group. However,
analysis of individual data showed that the TPA response to SNP
was quite variable among BH subjects, in particular at the highest
dose step (Fig 3
). The TPA response was particularly marked in 3 BH
individuals. In fact, in the remaining 7 BH subjects, TPA responses to
SNP were only moderately more pronounced than those observed in NC
subjects. Thus, the degree to which the two pathways activated
by flow and muscarinic receptor stimulation are involved in stimulating
the TPA secretory response appears to vary among individuals and
particularly so in BH. Furthermore, high-flow responders also had a
higher mean arterial PAI-1 level. Our observation (Fig 2)
that higher PAI-1 levels in arterial blood tend to
complex/bind more of the locally released TPA may explain the lesser
enhancement of average net TPA activity increment across the forearm in
the BH group with SNP than MCh, since the TPA response to the latter
stimulus was more uniform among subjects.
In addition to these alterations in stimulated TPA release, we also found some notable differences in basal fibrinolytic function between the two groups. Although both groups had a significant and roughly similar net release rate of TPA antigen at rest, BH subjects had no increment in TPA activity across the forearm in contrast to the marked increase in TPA activity observed in NC subjects. This was explained by the significantly higher circulating arterial PAI-1 antigen levels in BH subjects. The inverse relation between arterial PAI-1 and the arteriovenous concentration gradient of free but not of total TPA forearm release indicated that the higher the PAI-1 concentration in inflowing arterial blood, the more of the released TPA would complex/bind to the inhibitor. Thus, due to the higher PAI levels in BH subjects, the forearm did not contribute to any significant increment in TPA activity. Despite slightly higher circulating arterial levels of TPA antigen in BH subjects, they had only about half of the arterial TPA activity of NC subjects. This finding indicates that the "consumption" of free TPA by the high circulating PAI-1 levels was not confined to the forearm vasculature only but was also operating in other vascular districts of the body. It is also worth notice that there was a significant production of PAI-1 antigen across the forearm in BH but not in NC subjects. This finding further supports the notion that some stimulatory influence acting on the vascular endothelium to enhance constitutive PAI-1 release was present in BH subjects.
Thus, it appears that enhanced PAI-1 secretion is a primary pathophysiological aberration in hypertension that is already detectable in very early and mild forms of the disease. In established phases of essential hypertension, previous studies have consistently found increased PAI activity and decreased TPA activity in patients in comparison with normotensive subjects.38 39 40 41 42 Increased TPA antigen levels in hypertension have been reported by some41 42 43 but not other39 44 investigators. The mechanism behind the elevated PAI-1 levels in BH is not clear. There is a well established direct relation between metabolic factors and PAI levels. It has been proposed that hyperinsulinemia, which is a characteristic feature of both obesity and essential hypertension,45 is the underlying factor behind the elevated PAI concentrations.46 In support of and further extending this view, we observed a direct relation not only between fasting insulin and circulating PAI-1 antigen levels but also between fasting insulin and net forearm PAI-1 release. Conversely, there was an inverse correlation between insulin and the net increment in TPA activity across the forearm. Unfortunately, in most previous studies on fibrinolytic function in hypertension, metabolic data have not been presented.40 41 42 43 However, in a recent population-based study of young borderline hypertensives, from our laboratory we also confirmed the strong statistical correlation between hyperinsulinemia (or obesity) and PAI-1 antigen levels in the very early phases of BP elevation.36 We also observed that when nonobese BH subjects were compared with normotensive subjects of similar body mass index and fasting insulin levels, there were no between-group differences in PAI-1 or TPA activity levels. However, BH subjects were found to have higher TPA antigen concentrations than NC subjects. In the present study, a nonsignificant trend toward a similar elevation of both circulating TPA antigen levels and unstimulated net release was observed in borderline hypertensives, but due to the wide interindividual variation in fibrinolytic variables, the power of the present study was probably not strong enough to detect significant between-group differences.
In conclusion, stimulation of endothelial cells by the muscarinic receptor agonist MCh showed that BH subjects had a "preserved" endothelium-dependent vasodilator response similar to that observed in NC subjects. Furthermore, the stimulatory effect on TPA release was similar in NC and BH subjects. Thus, the observations of the present study argue against the presence of any functional impairment of vasodilator or local fibrinolytic responses of the vascular endothelium in the forearm in this form of early hypertension. By contrast, the present data suggest that the responsiveness of endothelial cells to fluid shear stress may be enhanced in some individuals with BH. Furthermore, BH is associated with higher levels of PAI-1 antigen and an enhanced constitutive forearm production of PAI-1 antigen. High arterial levels of PAI-1 antigen lead to a consumption of locally released TPA and thereby significantly decrease the increment in fibrinolytic activity across the forearm vasculature of BH subjects. Insulin may, on a long-term basis, be involved in the regulation of local PAI-1 release in BH subjects.
|
Selected Abbreviations and Acronyms |
|---|
|
|
Acknowledgments |
|---|
This study was supported by grants from the Swedish Medical Research Council (09046 and 7324), The Swedish Heart-Lung Foundation, The Bank of Sweden Tercentenary Foundation, The Swedish Hypertension Society, and The Swedish Medical Association. The authors wish to thank Annika Johansson, Hannele Korhonen, and Kristina Jansson for excellent technical assistance throughout the study.
Received March 8, 1995; accepted May 21, 1997.
|
References |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
1. Davies MG, Hagen P-O. The vascular endothelium: a new horizon. Ann Surg.. 1993;218:593-609.[Medline] [Order article via Infotrieve]
2. Emeis JJ. Mechanisms involved in short-term changes in blood levels of tissue-type plasminogen activator. In: Kluft C, ed. Tissue-Type Plasminogen Activator (t-PA): Physiological and Clinical Aspects. Boca Raton, Fla: CRC Press; 1988;2:21-35.
3. Furchgott RF, Zawadski JV. The obligatory role of endothelial cells in the relaxation of arterial smooth muscle by acetylcholine. Nature.. 1980;288:373-376.[Medline] [Order article via Infotrieve]
4. Vallance P, Collier J, Moncada S. Effects of endothelium-derived nitric oxide on peripheral arteriolar tone in man. Lancet.. 1989;334:997-1000.
5. Klöcking H-P. Release of plasminogen activator by acetylcholine from the isolated perfused pig ear. Thromb Res.. 1979;16:261-264.[Medline] [Order article via Infotrieve]
6. Nakajima K. Pharmacological observations of plasminogen activator release caused by vasoactive agents in isolated perfused pig ears. Thromb Res.. 1983;29:163-174.[Medline] [Order article via Infotrieve]
7. Emeis JJ. Perfused rat hindlegs: a model to study plasminogen activator release. Thromb Res.. 1983;30:195-203.[Medline] [Order article via Infotrieve]
8. Jern C, Selin L, Jern S. In vivo release of tissue-type plasminogen activator across the human forearm during mental stress. Thromb Haemost.. 1994;72:285-291.[Medline] [Order article via Infotrieve]
9. Jern C, Selin L, Jern S. Application of the perfused-forearm model to study release mechanisms of tissue-type plasminogen activator in man. Fibrinolysis. 1994;8(suppl 2):13-15.
10. Jern S, Selin L, Bergbrant A, Wall U, Jern C. Release of tissue-type plasminogen activator in response to muscarinic receptor stimulation in human forearm. Thromb Haemost.. 1994;72:588-594.[Medline] [Order article via Infotrieve]
11. Moncada S, Palmer RMJ, Higgs EA. Nitric oxide: physiology, pathophysiology, and pharmacology. Pharmacol Rev.. 1991;43:109-142.[Medline] [Order article via Infotrieve]
12. Panza JA, Quyyumi AA, Brush JJ, Epstein SE. Abnormal endothelium-dependent vascular relaxation in patients with essential hypertension. N Engl J Med.. 1990;323:22-27.[Abstract]
13.
Linder L, Kiowski W, Buhler FR, Luscher TF.
Indirect evidence for release of
endothelium-derived relaxing factor in human forearm
circulation in vivo: blunted response in essential
hypertension. Circulation.. 1990;81:1762-1767.
14. Calver A, Collier J, Vallance P. Inhibition and stimulation of nitric oxide synthesis in the human forearm arterial bed of patients with insulin-dependent diabetes. J Clin Invest.. 1992;90:2548-2554.
15. Celermajer DS, Sorensen KE, Gooch VM, Spiegelhalter DJ, Miller OI, Sullivan ID, Lloyd JK, Deanfield JE. Non-invasive detection of endothelial dysfunction in children and adults at risk of atherosclerosis. Lancet.. 1992;340:1111-1115.[Medline] [Order article via Infotrieve]
16. Julius S, Harburg E, McGinn NF, Keyes J, Hoobler SW. Relation between casual blood pressure readings in youth and at age 40: a retrospective study. J Chronic Dis.. 1964;17:397-404.[Medline] [Order article via Infotrieve]
17.
Paffenbarger RS, Thorne MC, Wing AL. Chronic
disease in former college students, VIII: characteristics in youth
predisposing to hypertension in later years. Am J
Epidemiol.. 1968;88:25-32.
18.
Saige A, Larson MG, Levy D. The natural history
of borderline isolated systolic hypertension.
N Engl J Med.. 1993;329:1912-1917.
19. Jern S. Psychological and hemodynamic factors in borderline hypertension. Acta Med Scand. 1982;(suppl 662):1-54.
20.
Bergbrant A, Hansson L, Jern S. Interrelation
between cardiac and vascular structure in borderline
hypertension. Eur Heart J.. 1993;14:1304-1314.
21. Wall U, Bergbrant A, Jern S. Impaired glucose tolerance in young men with borderline hypertension. Blood Press.. 1996;5:138-146.
22. Bergbrant A, Wall U, Jern S. Lower levels of male sex hormones in borderline hypertension are related to impaired glucose tolerance. Submitted for publication 1997.
23. Bergbrant A, Hansson L, Jern S. Correspondence between screening and intra-arterial blood pressures in young men with borderline hypertension. J Intern Med.. 1993;234:201-209.[Medline] [Order article via Infotrieve]
24. Whitney RJ. The measurement of volume changes in human limbs. J Physiol (Lond).. 1953;121:1-27.
25. Rånby M, Nguyen G, Scarabin PY, Samama M. Immunoreactivity of tissue plasminogen activator and of its inhibitor complexes. Thromb Haemost.. 1989;61:409-414.[Medline] [Order article via Infotrieve]
26. Huisman LGM, Meijer P, van Griensven J, Kluft C. Evaluation of the specificity of antigen assays for plasminogen activator inhibitor 1: comparison of two new commercial kits. Fibrinolysis. 1992;6(suppl 3):87-88.
27. Petersen LC, Handest P, Brender J, Selmer J, Jørgensen M, Thorsen S. A sensitive solid-phase immunosorbent assay for tissue-type plasminogen activator activity in plasma using trinitrobenzoylated poly-D-lysine as a stimulator for plasminogen activation. Thromb Haemost.. 1987;57:205-211.[Medline] [Order article via Infotrieve]
28. Philips M, Juul A-G, Selmer J, Lind B, Thorsen S. A specific immunologic assay for functional plasminogen activator inhibitor 1 in plasma: standardized measurements of the inhibitor and related parameters in patients with venous thromboembolic disease. Thromb Haemost.. 1992;68:486-494.[Medline] [Order article via Infotrieve]
29. Vasey MW, Thayer JF. The continuing problem of false positives in repeated measures ANOVA in psychophysiology: a multivariate solution. Psychophysiology.. 1987;24:479-486.[Medline] [Order article via Infotrieve]
30.
Cockcroft JR, Chowienczyk PJ, Benjamin N, Ritter JM.
Preserved endothelium-dependent vasodilation in
patients with essential hypertension. N Engl J
Med.. 1993;330:1036-1040.
31. Rosing DR, Redwood DR, Brakman P, Astrup T, Epstein SE. The fibrinolytic response of man to vasoactive drugs measured in arterial blood. Thromb Res.. 1978;13:419-428.[Medline] [Order article via Infotrieve]
32.
Diamond SL, Eskin SG, McIntire LV. Fluid flow
stimulates tissue plasminogen secretion by cultured human
endothelial cells. Science.. 1989;243:1483-1485.
33. Diamond SL, Sharefkin JB, Dieffenbach C, Fraiser-Scott K, McIntire LV, Eskin SG. Tissue plasminogen activator messenger RNA levels increase in cultured human endothelial cells exposed to laminar shear stress. J Cell Physiol.. 1990;143:364-371.[Medline] [Order article via Infotrieve]
34. Nollert MU, Eskin SG, McIntire LV. Shear stress increases inositol trisphosphate levels in human endothelial cells. Biochem Biophys Res Commun.. 1990;170:281-287.[Medline] [Order article via Infotrieve]
35. Tranquille N, Emeis JJ. The involvement of products of the phospholipase pathway in the acute release of tissue-type plasminogen activator. Eur J Pharmacol.. 1992;213:285-292.[Medline] [Order article via Infotrieve]
36.
Wall U, Jern C, Bergbrant A, Jern S. Enhanced
levels and release capacity of tissue-type plasminogen
activator in borderline hypertension.
Hypertension.. 1995;26:796-800.
37.
Resnick N, Collins T, Atkinson W, Bonthron DT, Dewey CF
Jr, Gimbrone MA Jr. Platelet-derived growth factor B chain
promoter contains a cis-acting fluid shear-stress-responsive
element. Proc Natl Acad Sci U S A.. 1993;90:4591-4594.
38. Landin K, Tengborn L, Smith U. Elevated fibrinogen and plasminogen activator inhibitor (PAI-1) in hypertension are related to metabolic risk factors for cardiovascular disease. J Intern Med.. 1990;227:273-278.[Medline] [Order article via Infotrieve]
39. Jansson J-H, Johansson B, Boman K, Nilsson TK. Hypofibrinolysis in patients with hypertension and elevated cholesterol. J Intern Med.. 1991;229:309-316.[Medline] [Order article via Infotrieve]
40. Gleerup G, Winther K. Decreased fibrinolytic activity and increased platelet function in hypertension: possible influence of calcium antagonist. Am J Hypertens.. 1991;4:168S–171S.[Medline] [Order article via Infotrieve]
41. Donders SH, Lustermans FA, van Wersch JW. Low order of correlation of lipoprotein (a) with other blood lipids and with coagulation and fibrinolysis parameters in hypertensive and diabetic patients. Blood Coagul Fibrinolysis.. 1992;3:249-256.[Medline] [Order article via Infotrieve]
42. van Wersch JW, Rompelberg-Lahaye J, Lustermans Fath. Plasma concentration of coagulation and fibrinolysis factors and platelet function in hypertension. Eur J Clin Chem Clin Biochem.. 1991;29:375-379.[Medline] [Order article via Infotrieve]
43. Palermo A, Bertalero P, Pizza N, Amelotti R, Libretti A. Decreased fibrinolytic response to adrenergic stimulation in hypertensive patients. J Hypertens. 1989;7(suppl 6):S162–S163.
44. Arik N, Akpolat T, Özdemir O, Özebe O, Dündar S, Yasavul Ü, Turgan Ç, Çaglar S. Tissue plasminogen activator in essential hypertension. Acta Haematol.. 1992;87:110-111.[Medline] [Order article via Infotrieve]
45.
Lucas CHP, Estigarribia JA, Darga LL, Reaven GM.
Insulin and blood pressure in obesity.
Hypertension.. 1985;7:702-706.
46. Vague P, Juhan-Vague I. Insulin and the fibrinolytic system: a link between metabolism and thrombogenesis. In Smith U, Bruun NE, Hedner T, Hökfelt B, eds. Hypertension as an Insulin-Resistant Disorder. Amsterdam, Netherlands: Elsevier Publishers; 1991:321-334.
This article has been cited by other articles:
 |
|
 |
|
  G. P. Van Guilder, G. L. Hoetzer, J. J. Greiner, B. L. Stauffer, and C. A. DeSouza Metabolic syndrome and endothelial fibrinolytic capacity in obese adults Am J Physiol Regulatory Integrative Comp Physiol, January 1, 2008; 294(1): R39 - R44. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 G. P. Van Guilder, G. L. Hoetzer, D. T. Smith, H. M. Irmiger, J. J. Greiner, B. L. Stauffer, and C. A. DeSouza Endothelial t-PA release is impaired in overweight and obese adults but can be improved with regular aerobic exercise Am J Physiol Endocrinol Metab, November 1, 2005; 289(5): E807 - E813. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 G. L Hoetzer, B. L Stauffer, H. M Irmiger, M. Ng, D. T Smith, and C. A DeSouza Acute and chronic effects of oestrogen on endothelial tissue-type plasminogen activator release in postmenopausal women J. Physiol., September 1, 2003; 551(2): 721 - 728. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J.-A. Bjorkman, S. Jern, and C. Jern Cardiac Sympathetic Nerve Stimulation Triggers Coronary t-PA Release Arterioscler. Thromb. Vasc. Biol., June 1, 2003; 23(6): 1091 - 1097. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. T Smith, G. L Hoetzer, J. J Greiner, B. L Stauffer, and C. A DeSouza Effects of ageing and regular aerobic exercise on endothelial fibrinolytic capacity in humans J. Physiol., January 1, 2003; 546(1): 289 - 298. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
G. L. Hoetzer, B. L. Stauffer, J. J. Greiner, Y. Casas, D. T. Smith, and C. A. DeSouza Influence of oral contraceptive use on endothelial t-PA release in healthy premenopausal women Am J Physiol Endocrinol Metab, January 1, 2003; 284(1): E90 - E95. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. A. S. Muldowney III and D. E. Vaughan Tissue-type plasminogen activator release: New frontiers in endothelial function J. Am. Coll. Cardiol., September 4, 2002; 40(5): 967 - 969. [Full Text] [PDF]
|
|
|
|
 |
|
 J. P.J. Halcox, W. H. Schenke, G. Zalos, R. Mincemoyer, A. Prasad, M. A. Waclawiw, K. R.A. Nour, and A. A. Quyyumi Prognostic Value of Coronary Vascular Endothelial Dysfunction Circulation, August 6, 2002; 106(6): 653 - 658. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. Pretorius, D. A. Rosenbaum, J. Lefebvre, D. E. Vaughan, and N. J. Brown Smoking Impairs Bradykinin-Stimulated t-PA Release Hypertension, March 1, 2002; 39(3): 767 - 771. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. O. Toikka, H. Laine, M. Ahotupa, A. Haapanen, J. S. A. Viikari, J. J. Hartiala, and O. T Raitakari Increased Arterial Intima-Media Thickness and In Vivo LDL Oxidation in Young Men With Borderline Hypertension Hypertension, December 1, 2000; 36(6): 929 - 933. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
L. S. Sjogren, R. Doroudi, L.-m. Gan, L. Jungersten, T. Hrafnkelsdottir, and S. Jern Elevated Intraluminal Pressure Inhibits Vascular Tissue Plasminogen Activator Secretion and Downregulates Its Gene Expression Hypertension, April 1, 2000; 35(4): 1002 - 1008. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. Bertuglia and A. Colantuoni Protective effects of leukopenia and tissue plasminogen activator in microvascular ischemia-reperfusion injury Am J Physiol Heart Circ Physiol, March 1, 2000; 278(3): H755 - H761. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
N. J. Brown, J. V. Gainer, C. M. Stein, and D. E. Vaughan Bradykinin Stimulates Tissue Plasminogen Activator Release in Human Vasculature Hypertension, June 1, 1999; 33(6): 1431 - 1435. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 G. Dell'Omo, L. Ferrini, M. Morale, F. De Negri, E. Melillo, F. Carmassi, and R. Pedrinelli Acetylcholine-Mediated Vasodilatation and Tissue-type Plasminogen Activator Release in Normal and Hypertensive Men Angiology, April 1, 1999; 50(4): 273 - 282. [Abstract] [PDF]
|
|
|
|
|
|
C. Jern, P. Ladenvall, U. Wall, and S. Jern Gene Polymorphism of t-PA is Associated With Forearm Vascular Release Rate of t-PA Arterioscler. Thromb. Vasc. Biol., February 1, 1999; 19(2): 454 - 459. [Abstract] [Full Text] [PDF]
|
|
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||