Regulation of local tissue-type plasminogen activator release by endothelium-dependent and endothelium-independent agonists in human vasculature

Intravenous prostaglandin E1 reduces soluble vascular cell adhesion molecule-1 in peripheral arterial obstructive disease

OBJECTIVES

Elevated levels of soluble (s) vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1, pointing to activation of cells involved in vascular inflammation, have been previously reported in peripheral arterial obstructive disease (PAOD). We tested the hypothesis that intravenous prostaglandin E(1) (PGE(1)) treatment, which produces clinical benefits in this condition, might decrease such levels.

METHODS

Ten subjects (age range 58 +/- 10 years, 6 male, 4 female) with characterized Fontaine stage IIa to IV PAOD (ankle/arm pressure index <0.96) were entered into a treatment protocol with twice daily intravenous infusions of PGE(1) (alprostadil) at 120 microg per day, repeated for 10 consecutive days. Preinfusion and postinfusion plasma samples were stored for blind enzyme immunoassays of soluble adhesion molecules and the fibrinolytic marker tissue plasminogen activator, type-1 plasminogen-activator inhibitor, and D -dimer.

RESULTS

Estimates of severity of pain at rest, consumption of analgesics, magnitude of trophic lesions, remission to lower Fontaine stages, and favorable changes in the venoarteriolar reflex documented significant beneficial effects of the treatment. Significant (P <.01) pretreatment and posttreatment reductions of in all soluble markers explored were found. Particularly, sVCAM-1 exhibited a significant decrease after each infusion, which was sustained at the last day of treatment (from 854 +/- 214 ng/mL to 775 +/- 215 ng/mL across the first infusion, from 773 +/- 146 ng/mL to 680 +/- 110 ng/mL across the last infusion).

CONCLUSION

Thus a global decrease of vascular cell activation appears to occur as a result of PGE(1) administration and may contribute to the observed clinical benefits in PAOD.

Bradykinin stimulates the release of tissue plasminogen activator in human coronary circulation: effects of angiotensin-converting enzyme inhibitors

OBJECTIVES

The goal of this study was to determine: 1) whether bradykinin (BK) directly stimulates tissue plasminogen activator (tPA) secretion in human coronary circulation, and 2) whether angiotensin-converting enzyme (ACE) inhibition favorably alters the fibrinolytic balance regulated by BK.

BACKGROUND

Bradykinin is a potent stimulator of tPA secretion in endothelial cells; however, the effect of BK on tPA release in the human coronary circulation has not been studied.

METHODS

Fifty-six patients with atypical chest pain were randomly assigned to two groups: 25 patients were treated with the ACE inhibitor enalapril (ACE inhibitor group), and 31 were not treated with ACE inhibitors (non-ACE inhibitor group). Graded doses of BK (0.2, 0.6, 2.0 microg/min), acetylcholine (ACh) (30 microg/min) and papaverine (PA) (12 mg) were administered into the left coronary artery. Coronary blood flow (CBF) was evaluated by Doppler flow velocity measurement. Blood samples were taken from the aorta (Ao) and the coronary sinus (CS).

RESULTS

Bradykinin induced similar increases in CBF in both groups. The net tPA release induced by BK was dose-dependently increased in both groups, and the extent of that increase in the ACE inhibitor group was greater than that in the non-ACE inhibitor group. Bradykinin did not alter plasminogen activator inhibitor-1 (PAI-1) levels in the Ao or CS in either group. Neither ACh nor PA altered tPA levels or PAI-1 levels in either group.

CONCLUSIONS

Intracoronary infusion of BK stimulates tPA release without causing any change in PAI-1 levels in the human coronary circulation. In addition, this effect of BK is augmented by an ACE inhibitor.

Surgical stress induces acute coronary release of tissue-type plasminogen activator in the pig

BACKGROUND

Tissue-type plasminogen activator (t-PA) is an endothelium derived key enzyme in the initiation of endogenous fibrinolysis. Acute regulated release of active t-PA occurs within minutes in response to threatening thrombotic vessel occlusion. The aim of this study was to investigate the impact of surgical stimulation on the kinetics of t-PA release in the coronary vascular bed in the pig.

METHODS

In anaesthetised pigs (n=16), arterio-venous concentration gradients of t-PA, and plasma flows (retrograde thermodilution) were obtained across the coronary vascular bed before (control) and at 1, 3, 5 and 10 min after sternotomy.

RESULTS

At control, no significant coronary net flux (release or uptake) of t-PA was observed, while sternotomy induced a rapid net release of total t-PA (132.6 ng x min(-1)), with an associated increase in active t-PA (93.6 ng x min(-1)). This response, evident already after 1 min, showed a peak at 5 min and returned towards baseline levels within 10 min. No concurrent alterations in aortic levels of active t-PA were found and haemodynamic variables were unaltered.

CONCLUSION

The rapidly increasing and transient net coronary release of t-PA after sternotomy suggests that the endothelium actively promotes local endogenous fibrinolysis during surgery. Such events could reflect a dynamic responsiveness to protect the coronary circulation during stress.

Testing for endothelial dysfunction

Endothelial health is a key factor in normal cardiovascular homeostasis, and recent studies have revealed several important functions of the vascular endothelium that protect against atherothrombosis. These include control over arterial tone, coagulation, fibrinolysis, and vascular growth. Consequently, endothelial dysfunction has been implicated as an important event in the pathogenesis of atherosclerosis, coronary vasoconstriction, hypertension, and myocardial ischaemia. Therefore, there has been considerable research interest in diagnostic assays for the assessment of endothelium. This review outlines the current status of markers of endothelial dysfunction, particularly those related to vasomotor control, as well as circulating markers of vascular health.

Angiotensin-converting enzyme inhibitor prevents plasminogen activator inhibitor-1 expression in a rat model with cardiovascular remodeling induced by chronic inhibition of nitric oxide synthesis

Plasminogen activator inhibitor-1 (PAI-1) may participate in the development of cardiovascular remodeling by inhibiting extracellular matrix turnover and fibrinolysis. However, little is known about physiological regulators of PAI-1 in vivo. Angiotensin II has been shown to stimulate PAI-1 in vitro. We previously reported that long-term inhibition of nitric oxide (NO) synthesis with Nomega-nitro-L-arginine methyl ester (L-NAME) causes cardiovascular remodeling (vascular medial thickening and fibrosis) associated with increased tissue angiotensin-converting enzyme (ACE) activity. In the present study, we examined whether treatment with an ACE inhibitor modulates the cardiovascular PAI-1 expression in this model in vivo. Wistar-Kyoto rats were treated with either no drugs, L-NAME (100 mg/kg x day), or L-NAME plus the ACE inhibitor imidapril (20 mg/kg day). Marked increases in PAI-1 mRNA and protein levels in the aorta and left ventricle were observed after the first and fourth weeks of PAI-1 treatment. PAI-1 immunoreactivity was increased in the endothelium and the media of the aorta and coronary arteries after treatment of L-NAME. This increase in PAI-1 levels was associated with an increase in ACE activity of the aorta and left ventricle. ACE inhibition with imidapril significantly prevented both the increases in PAI-1 levels and the development of cardiovascular remodeling. These findings suggest that the local renin-angiotensin system regulates PAI-1 expression, and that the increased PAI-1 levels may contribute to the cardiovascular remodeling in this model.

Vasoactive substances in the interstitium of contracting skeletal muscle examined by microdialysis

In the study of the regulation of skeletal muscle blood flow during exercise it is useful to obtain information regarding the concentrations of vasoactive substances in the muscle interstitium, a site where the compounds act on the vascular and skeletal muscle cells. The microdialysis technique is a useful tool for measuring interstitial substances in the muscle at rest and during exercise in human subjects, and the technique can also be used to study the effect of both systemic and local interventions in a specific area of an exercising muscle. Probe recovery, which represents the relative amount of a substance that is diffusing to the dialysis membrane, changes from rest to exercise and can be determined by the internal-standard technique which allows for a relatively high time resolution (min). Furthermore, the use of electrodes at the microdialysis outlet makes it possible to perform continuous measurements of interstitial substances. The present review gives examples of how the microdialysis technique has been applied to study potentially important vasodilators such as adenosine, NO and K+ in human skeletal muscles and highlights areas for future research to establish the functional importance of these compounds.

Bradykinin stimulates tissue plasminogen activator release in human vasculature

Bradykinin stimulates tissue plasminogen activator (tPA) release in isolated perfused animal tissues. The present study tests the hypothesis that bradykinin increases tPA release in humans through local effects on the vasculature. Graded doses of sodium nitroprusside (0.8 to 3.2 micrograms/min), acetylcholine (ACh) (7.5 to 60 micrograms/min), and bradykinin (100 to 400 ng/min) were administered intra-arterially in random order in 10 salt-depleted (10 mmol/d of Na) normotensive volunteers. None of the drugs altered mean arterial pressure or heart rate. Forearm blood flow (FBF) was measured by strain-gauge plethysmography. All 3 drugs caused a dose-dependent increase in FBF, although ACh was less potent than either nitroprusside or bradykinin (maximum FBF 7.5+/-2.4 versus 10.0+/-1.5 and 11.9+/-2.1 mL. 100 mL-1. min-1, respectively). Bradykinin caused a significant, dose-dependent increase in venous (effect of dose F=9. 9, P=0.028 by ANOVA), but not arterial (F=0.154, P=0.92) tPA antigen in the infused arm. Thus, net tPA release increased significantly in response to bradykinin (50.6+/-13.3 at the highest dose versus 0. 9+/-0.4 ng. 100 mL-1. min -1 at baseline, P=0.014). In contrast, bradykinin did not affect plasminogen activator inhibitor antigen. Neither nitroprusside nor ACh altered plasma levels of tPA or plasminogen activator inhibitor antigen. Bradykinin increased tPA release across the forearm in the absence of systemic effects. This effect could not be attributed to changes in blood flow because doses of equivalent potency of the vasodilator nitroprusside did not increase tPA. These data demonstrate that bradykinin stimulates tPA release in the human vasculature.