Loss of endothelial pertussis toxin-sensitive G protein function in atherosclerotic porcine coronary arteries

Improved preservation of coronary endothelial function with Celsior compared with blood and crystalloid solutions in heart transplantation

BACKGROUND

Endothelial injury from preservation solutions has been implicated in acute coronary vasospasm and pathologic activation of the endothelium, which can contribute to the development of graft coronary vasculopathy after heart transplantation. Preservation solutions with a powerful antioxidant capacity may decrease the occurrence of these complications.

MATERIALS AND METHODS

This study was designed to evaluate the effect of Celsior (an anti-oxidant solution specifically designed for cardiac preservation) in a model of heart preservation (4 hours at 4 degrees C to reproduce the situation encountered in clinical heart transplantation) compared two commonly used cardioplegic and preservation strategies on coronary endothelial function. Endothelium-dependent relaxation of normal porcine epicardial coronary arteries to serotonin (5-HT, an agonist that activates 5-HT(1d) receptors coupled to Gi proteins) and bradykinin (BK, which activates B2 receptors coupled to Gq proteins) was studied in standard organ chamber experiments in the following groups: a control group was submitted to immediate excision without cardioplegia and preserved in saline solution (0.9% NaCl) for 4 hours (Group 1); two groups had cardioplegia induced with a crystalloid solution and were stored for 4 hours in saline (Group 2) or 4 hours in Celsior solution (Group 3); and two groups had cardioplegia induced with normothermic blood cardioplegia and were stored for 4 hours in the saline (Group 4), or 4 hours in Celsior solution (Group 5). Finally, two groups underwent cardioplegia with Celsior and were stored for 4 hours in saline (Group 6), or 4 hours in the Celsior solution (Group 7). All cardioplegia solutions were at 4 degrees C (except blood cardioplegia at 37 degrees C) and all preservations solutions were at 4 degrees C.

RESULTS

Endothelium-dependent relaxations to serotonin were significantly decreased in all groups except the Celsior + Celsior group compared with the control group. There were no significant differences in relaxation to bradykinin except in one group. Use of the Celsior solution for induction of cardioplegia and storage better preserved endothelium-dependent G-protein-mediated relaxation compared with the other arrest and preservation strategies.

CONCLUSIONS

The observed effect may be associated with an improvement in both short- and long-term outcome in heart transplantation, especially because these alterations may be further compounded by reperfusion.

Coronary artery endothelial dysfunction after ischemia-reperfusion and acute untreated rejection in a canine heterotopic heart transplantation model

BACKGROUND

Acute rejection is a common problem in heart transplantation and may contribute to the development of cardiac allograft vasculopathy. This study was designed to evaluate the mechanisms of coronary endothelial dysfunction associated with ischemia-reperfusion and acute untreated rejection.

METHODS

Two groups of mongrel dogs (n=7 per group) underwent heterotopic cervical heart transplantation without immunosuppression. Allografts were harvested on posttransplant day 1 (group 1) and day 5 (group 2). A third group of unoperated dogs served as control (group 3). After harvesting, epicardial coronary arteries were studied in organ chamber for endothelium-dependent and independent reactivity.

RESULTS

Group 1 displayed multifocal ischemic damage without any rejection while hearts from group 2 reached grade IV rejection. Immunohistochemical studies for von Willebrand factor showed expression on coronary endothelial cells in all animals with scattered areas of denudation in transplanted groups. Endothelium-dependent responses to acetylcholine, calcium ionophore A23147, and bradykinin were unaffected in groups 1 and 2. Endothelial relaxations to sodium fluoride (Gi-protein activator) was significantly reduced in group 1 and significantly increased in group 2 compared with control. Responses to serotonin and UK14304 (receptors linked to Gi-protein) were significantly increased in group 2. Responses to thrombin were decreased in both groups. Endothelium-independent responses were unaffected.

CONCLUSIONS

In the canine model of heterotopic heart transplantation, the early (24 hr) endothelial dysfunction seen after transplantation is specific to the thrombin receptor and the Gi-protein signaling pathway. Acute untreated rejection did not modify the alteration in endothelial reactivity to thrombin but enhanced the sensibility of the Gi-protein signaling pathways.

Chronic endothelial dysfunction after oversized coronary balloon angioplasty in pigs: a 12-week follow-up of coronary vasoreactivity in vivo and in vitro

Previous studies have reported the development of vasoconstriction immediately after invasive coronary interventions. Other studies in animals have demonstrated that using oversized balloon angioplasty, vasospasm can be suppressed, even in the presence of endothelial denudation due to important structural alteration in vascular smooth muscle. The regenerated endothelium also appears to be impaired chronically by selective attenuation of in vitro endothelial dependent relaxation related to pertussis toxin-sensitive G proteins. The purpose of this investigation was to verify in vivo and in vitro vasoreactivity to bradykinin (BK) and serotonin (5-hydroxytryptamine; 5-HT) (endothelial dependent agonists) as well as to nitroglycerin (NTG) (exogenous nitric oxide donor) at different times after oversized balloon angioplasty intervention ranging from 1 h to 12 weeks, in normal porcine coronary arteries. BK-induced vasodilatation in vivo was impaired acutely, but it was restored after 4 weeks. Serotonin caused vasoconstriction in vivo that was significantly augmented after 12 weeks. Conversely, endothelium-dependent vasodilatation in vitro to BK and 5-HT remained attenuated during the whole period of follow-up. Finally, relaxation elicited by NTG was reduced in the in vivo experiment until the first week after the procedure. Histological analysis showed severe arterial injury, and complete recovery of endothelial coverage after 4 weeks. In conclusion, this experiment supports evidence for the occurrence of the acute attenuation of vasoresponsiveness and chronic endothelial dysfunction following overstretching coronary balloon angioplasty. Abnormal remodeling associated with the severity of injury may contribute to chronic endothelial dysfunction. Differences found between in vivo and in vitro studies also suggest that multiple endogenous influences present in the former can attenuate the greater endothelial dysfunction demonstrated by endothelial assessment in vitro.

Comparison of endothelium-dependent relaxation in carotid arteries from Japanese white and Watanabe heritable hyperlipidemic rabbits

Modifications by atherosclerosis of endothelium-dependent and -independent relaxations were evaluated in carotid arteries isolated from Watanabe heritable hyperlipidemic (WHHL; age 20-29 months) and age-matched Japanese white (JW) rabbits. Marked, patchy atherosclerotic lesions were observed in all WHHL rabbit arteries. Endothelium-dependent relaxations induced by acetylcholine, partly depressed by N(G)-nitro-L-arginine (L-NA), were significantly inhibited in the WHHL rabbit arteries with atherosclerosis, compared with those in the arteries without atherosclerotic lesions from JW and WHHL rabbits. No difference was observed in the relaxation caused by superoxide dismutase in these arteries. Conversely, endothelium-dependent relaxations by substance P were greater in the arteries with and without atherosclerosis from WHHL rabbits than in the arteries from JW rabbits. Endothelium-independent relaxations elicited by sodium nitroprusside and 2,2-(hydroxynitrosohydrazino)bis-ethanamine (NOC18) did not differ in the arteries from JW and WHHL rabbits. The responses to acetylcholine and substance P of JW rabbit arteries with the endothelium were not attenuated by treatment with pertussis toxin. L-NA-resistant, endothelium-dependent relaxations by substance P were almost abolished by charybdotoxin, and atherosclerosis did not alter the response. It is concluded that endothelial functions, evaluated by substance P, in rabbit carotid arteries are not impaired by atherosclerosis and by long exposure to hyperlipidemia in vivo. Dysfunction of muscarinic receptors may be involved in the depressed response to acetylcholine. As far as the arteries used in the present study are concerned, responses mediated possibly by endothelium-derived hyperpolarizing factor (EDHF) are unlikely to be modulated by atherosclerosis.

Contribution of bradykinin receptor dysfunction to abnormal coronary vasomotion in humans

OBJECTIVES

The aim of our study was to investigate coronary vascular kinin receptor function in patients with atherosclerosis or its risk factors.

BACKGROUND

Although acetylcholine (ACH) is used as a probe for testing vascular function in vivo, endogenous bradykinin (BK) regulates resting and flow-mediated epicardial tone.

METHODS

In 53 patients with mild atherosclerosis or its risk factors and 9 control subjects, endothelium-dependent vasomotion was tested with intracoronary ACH (30 microg/min) and BK (62.5 ng/min and 4 microg/min), and endothelium-independent function with sodium nitroprusside. Metabolic vasodilation was assessed during cardiac pacing (n = 19). Correlation with serum angiotensin-converting enzyme (ACE) levels and the ACE insertion/deletion genotype was performed.

RESULTS

There was progressive impairment in ACH-mediated microvascular dilation with increasing numbers of risk factors (p = 0.025, analysis of variance). By contrast, BK- and sodium nitroprusside-mediated microvascular dilation was similar in all groups. Similarly, there was no correlation between epicardial coronary responses to ACH and BK; segments that constricted or dilated with ACH had similar dilator responses with BK. Bradykinin, but not ACH-mediated vasomotion, was depressed in epicardial segments that constricted with pacing. Finally, epicardial BK responses were depressed in patients with high ACE levels and in those with the ACE DD genotype.

CONCLUSIONS

Endothelial dysfunction in atherosclerosis appears to be receptor-specific, involving the muscarinic receptor with relative sparing of the kinin receptor pathways. Abnormal reactivity of epicardial coronary arteries during physiologic stress is better represented by BK and not by ACH responses. Bradykinin activity and, hence, physiologic coronary vasomotion appears to be influenced by serum ACE levels and the ACE insertion/deletion genotype.

Should intensive cholesterol lowering play a role in the management of acute coronary syndromes?

Although several large, well-controlled trials with 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) demonstrate the benefits of cholesterol lowering on cardiovascular morbidity and mortality, these trials excluded patients with recent unstable angina or myocardial infarction. Thus, the potentially beneficial effects that may accrue from early statin therapy have not been apparent. Mechanistic and experimental studies show that benefits from statin therapy may include improved endothelial function, a decrease in platelet thrombus deposition, and a reduction in inflammation at the site of the lesion. Large-scale clinical trials are now under way to determine the effect of aggressive cholesterol lowering in patients with acute coronary syndromes. If the findings of the smaller studies are confirmed, statin therapy should be considered early after infarction or unstable angina.

Time and dose effect of transdermal nicotine on endothelial function

Nicotine patches are available as an over-the-counter medication for aid in smoking cessation. This study was designed to determine how nicotine patch therapy over time and dose ranges used in smoking cessation programs in humans affects endothelium-dependent relaxations. Dogs were treated with nicotine patches (11, 22, or 44 mg/day) for 2 and 5 wk. Circulating nicotine and oxidized products of nitric oxide (NOx) were measured. Coronary arteries were prepared for measurement of isometric force and aortic endothelial cells were prepared for measurement of mRNA or NO synthase (NOS) activity. Circulating nicotine increased with increasing concentrations of nicotine patches. After 5 wk of treatment with 22 mg/day patches, circulating NOx was reduced but NOS activity was increased. NOS mRNA was similar among groups. Only after 5 wk of treatment with 22 mg/day patches were endothelium-dependent relaxations reduced to alpha(2)-adrenergic agonists, ADP, and the calcium ionophore A-23187. These results suggest a time and biphasic dose effect of nicotine treatment on endothelium-dependent responses that may be related to bioavailability of NO. This complex relationship of duration and dose of nicotine treatment may explain, in part, discrepancies in effects of nicotine on endothelium-dependent responses.

Role of pertussis toxin-sensitive G protein in metabolic vasodilation of coronary microcirculation

We have previously demonstrated that pertussis toxin (PTX)-sensitive G protein (G(PTX)) plays a major role in coronary microvascular vasomotion during hypoperfusion. We aimed to elucidate the role of G(PTX) during increasing metabolic demand. In 18 mongrel dogs, coronary arteriolar diameters were measured by fluorescence microangiography using a floating objective. Myocardial oxygen consumption (MVO(2)) was increased by rapid left atrial pacing. In six dogs, PTX (300 ng/ml) was superfused onto the heart surface for 2 h to locally block G(PTX). In eight dogs, the vehicle (Krebs solution) was superfused in the same way. Before and after each treatment, the diameters were measured during control (130 beats/min) and rapid pacing (260 beats/min) in each group. Metabolic stimulation before and after the vehicle treatment caused 8.6 +/- 1. 8 and 16.1 +/- 3.6% dilation of coronary arterioles <100 microm in diameter (57 +/- 8 microm at control, n = 10), respectively. PTX treatment clearly abolished the dilation of arterioles (12.8 +/- 2. 5% before and 0.9 +/- 1.6% after the treatment, P < 0.001 vs. vehicle; 66 +/- 8 microm at control, n = 11) in response to metabolic stimulation. The increases in MVO(2) and coronary flow velocity were comparable between the vehicle and PTX groups. In four dogs, 8-phenyltheophylline (10 microM, superfusion for 30 min) did not affect the metabolic dilation of arterioles (15.3 +/- 2.0% before and 16.4 +/- 3.8% after treatment; 84.3 +/- 11.0 microm at control, n = 8). Thus we conclude that G(PTX) plays a major role in regulating the coronary microvascular tone during active hyperemia, and adenosine does not contribute to metabolic vasodilation via G(PTX) activation.

Effects on coronary endothelial function of the Cohn stabilizer for beating heart bypass operations

BACKGROUND

The effects of different stabilizing methods for minimally invasive beating heart coronary artery bypass grafts (CABG) on coronary endothelial function are unknown.

METHODS

We compared the effects on endothelial function of the Cohn stabilizer (used with proximal snaring by Retract-o-tape silicone air cushion) and a coronary shunt (CTS flow coil shunt) on an in vivo model of beating heart CABG. The two techniques were applied for 15 minutes on porcine epicardial coronary arteries. Control rings were taken from the same coronary artery. Endothelial function of control and instrumented arterial rings was studied in organ chamber experiments. Evaluation of endothelial coverage was performed with silver nitrate staining.

RESULTS

Endothelium-dependent relaxation to serotonin and bradykinin was significantly decreased in the shunt group compared to control, Cohn stabilizer, and snare groups. There were no significant differences in the endothelium-independent relaxation to sodium nitroprusside between groups.

CONCLUSIONS

Greater endothelium-dependent relaxation with the Cohn stabilizer suggests better preservation of endothelial coverage at the site of application and reduced propensity for coronary spasm and later development of intimal hyperplasia.

Low density lipoprotein cholesterol and coronary microvascular dysfunction in hypercholesterolemia

OBJECTIVES

The present study evaluates the impact of total cholesterol (TC) and its subfractions on coronary flow reserve (CFR), an index of the integrated function of the coronary circulation, in asymptomatic subjects.

BACKGROUND

Endothelial dysfunction of the coronary microcirculation has been reported in asymptomatic subjects with hypercholesterolemia.

METHODS

Using oxygen-15-labeled water and positron emission tomography, myocardial blood flow (MBF, in ml/min per g) was measured at rest and during intravenous adenosine (140 microg/kg body weight per min) in 80 asymptomatic nonsmoking men: group 1 (n = 61; age 45 +/- 7 years) had normal TC (< or =6.5 mmol/liter or < or =250 mg/dl) and group 2 (n = 19; age 48 +/- 10 years) had elevated TC.

RESULTS

Total cholesterol were 5.1 +/- 0.8 and 7.2 +/- 0.7 mmol/liter in groups 1 and 2 (p < 0.0005), respectively; low density lipoprotein (LDL) cholesterol levels were 3.2 +/- 0.8 and 4.9 +/- 0.7 mmol/liter (p < 0.0005); high density lipoprotein (HDL) cholesterol levels were 1.1 +/- 0.3 and 1.0 +/- 0.4 mmol/liter (p = NS); and triglyceride levels were 1.8 +/- 1.3 and 3.0 +/- 1.8 mmol/liter (p < 0.005). Groups 1 and 2 did not differ with regard to MBF at rest (0.87 +/- 0.14 vs. 0.84 +/- 0.14), MBF during adenosine (3.63 +/- 1.02 vs. 3.30 +/- 0.86) or CFR (4.23 +/-1.29 vs. 3.95 +/- 0.93). A significant but weak correlation was found between CFR and HDL in group 1 (r = 0.29, p < 0.05), but not in group 2. In contrast, a significant inverse correlation between LDL and CFR was found in group 2 (r = -0.61, p < 0.05), but not in group 1.

CONCLUSIONS

Low density lipoprotein cholesterol but not TC correlated inversely with CFR in hypercholesterolemic subjects. Thus, LDL-induced coronary microvascular dysfunction could play an important role in the pathogenesis of coronary artery disease and its complications.

Beneficial effects of fluvastatin on myocardial blood flow at two time-points in hypercholesterolemic patients with coronary artery disease

Hypercholesterolemia is a major risk factor initiating and accelerating atherosclerosis and leading to severe stages of coronary artery disease (CAD) with a high risk of cardiovascular events. We investigated the impact of lipid lowering in patients with hypercholesterolemia and evident CAD on clinically relevant parameters like myocardial perfusion. Myocardial imaging was performed with thallium-201 single photon-emission computed tomography at rest and after maximal bicycle exercise in 22 patients after a 4-week lead-in period, and after 12 and 24 weeks of therapy with fluvastatin. Perfusion defects occurred in all patients, indicating stress-induced myocardial ischemia. After 12 weeks of therapy, the perfusion of the ischemic segments increased by 26% (277+/-99 to 349+/-96 cpm; p < 0.001), whereas the value of the normal segments was augmented only by 4% (478+/-44 to 497+/-28 cpm; p < 0.05). The results slightly improved further after 24 weeks. Moreover, a subgroup analysis elucidated a more pronounced effect in patients without lipid-lowering premedication. This nonpretreated group (n = 11) revealed an improvement of ischemic segments at stress by 42% at week 24. In contrast, pretreated patients had an increase of only 18% (between groups, p < 0.05), indicating a carryover effect of premedication. In conclusion, short-term therapy with fluvastatin acts beneficially on impaired vascular function in hypercholesterolemic patients with CAD.

Oxidized low-density lipoprotein stimulates monocyte adhesion to glomerular endothelial cells

BACKGROUND

Abnormalities in lipid and lipoprotein metabolism have been implicated in the pathogenesis of glomerulosclerosis. Atherogenic lipoproteins [for example, low-density lipoprotein (LDL) and oxidized LDL (ox-LDL)] have been shown to stimulate glomerular monocyte chemoattractants involved in monocyte infiltration. However, the role of LDL and ox-LDL in the early monocyte adhesion to glomerular endothelial cells (ECs) and associated intracellular signaling mechanisms are not clearly understood.

METHODS

In this study, we examined the effect of LDL and ox-LDL on intracellular signaling mechanisms associated with monocyte adhesion to glomerular ECs and intercellular adhesion molecule-1 (ICAM-1) expression.

RESULTS

Ox-LDL, but not LDL, stimulated EC ICAM-1 expression and monocyte adhesion. Ox-LDL elevated protein tyrosine kinase (PTK) activity, and the preincubation of ECs with specific PTK inhibitors blocked ox-LDL-induced ICAM-1 message and monocyte adhesion. Whereas experimental maneuvers that inhibit either protein kinase C activation (by PKC depletion or with inhibitors) or Gi-protein-mediated pathways (pertussis toxin sensitive) had no effect on ox-LDL-induced monocyte adhesion and ICAM-1 expression. cAMP-elevating compounds did not induce ICAM-1 or monocyte adhesion.

CONCLUSIONS

The data indicate that ox-LDL, by stimulating monocyte adhesion to the glomerular endothelium, may regulate monocyte infiltration within the glomerulus, supporting an early pathobiological role for atherogenic lipoproteins in glomerular injury. The results suggest that the activation of specific PTK and associated signaling may, at least in part, play a critical role in ox-LDL-mediated endothelial-monocyte interaction-related events. The data suggest that the interventions aimed at modifying associated intracellular signaling events within the glomerulus may provide potential therapeutic modalities in monocyte/macrophage-mediated glomerular disease.

Clinical importance of coronary endothelial vasodilator dysfunction and therapeutic options

The vascular endothelium plays a key role in the control of vasomotor tone, local haemostasis and vascular wall proliferation processes. These responses are mediated by a variety of substances released from the endothelium in response to physiological stimuli, including prostacyclin, endothelin, and most importantly nitric oxide (NO). NO mediates vasodilation and furthermore inhibits platelet aggregation, expression of adhesion molecules for monocytes and adhesion of neutrophils, and it impairs growth of vascular smooth muscle cells. Risk factors for coronary atherosclerosis, such as hypercholesterolaemia, impair NO bioactivity, mainly due to an oxidative stress by superoxide radicals (O2-), which are able of rapidly inactivating endothelium-derived NO. Impaired NO bioactivity leads to unopposed paradoxical vasoconstriction of epicardial conductance vessels in response to physiological stimuli such as sympathetic activation as well as impaired vasodilator function of coronary resistance vessels. Therefore, endothelial dysfunction contributes to ischaemic manifestation of coronary artery disease. In addition, enhanced paradoxical vasoconstriction and a loss of endothelial antithrombotic activities might unfavourably modulate the course of acute coronary syndromes. Thus, the aim of therapeutic interventions is to increase NO bioavailability by either increasing NO production or decreasing O2- production in the endothelium. This goal can be reached, for example by ACE inhibitors, lipid-lowering drugs, increased shear-stress by physical exercise, oestrogens, and L-arginine, which have already been shown to improve endothelial vasodilator function. Nevertheless, it has to be determined whether ameliorated endothelial function will contribute to improved patients prognosis.

Agonist-specific impairment of coronary vascular function in genetically altered, hyperlipidemic mice

The objectives of the present study were to 1) examine mechanisms involved in endothelium-dependent responses of coronary arteries from normal mice and 2) determine whether vascular responses of coronary arteries are altered in two genetic models of hypercholesterolemia [apolipoprotein E (apoE)-deficient mice (apoE -/-) and combined apoE and low-density lipoprotein receptor (LDLR)-deficient mice (apoE + LDLR -/-)]. Plasma cholesterol levels were higher in both apoE -/- and apoE + LDLR -/- compared with normal mice on normal and high-cholesterol diets (normal chow: normal 110 +/- 5 mg/dl, apoE -/- 680 +/- 40 mg/dl, apoE + LDLR -/- 810 +/- 40 mg/dl; high-cholesterol chow: normal 280 +/- 60 mg/dl, apoE -/- 2,490 +/- 310 mg/dl, apoE + LDLR -/- 3,660 +/- 290 mg/dl). Coronary arteries from normal (C57BL/6J), apoE -/-, and apoE + LDLR -/- mice were isolated and cannulated, and diameters were measured using videomicroscopy. In normal mice, vasodilation in response to ACh and serotonin was markedly reduced by 10 microM Nomega-nitro-L-arginine (an inhibitor of nitric oxide synthase) or 20 microM 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ; an inhibitor of soluble guanylate cyclase). Vasodilation to nitroprusside, but not papaverine, was also inhibited by ODQ. Dilation of arteries from apoE -/- and apoE + LDLR -/- mice on normal diet in response to ACh was similar to that observed in normal mice. In contrast, dilation of arteries in response to serotonin from apoE -/- and apoE + LDLR -/- mice was impaired compared with normal. In arteries from both apoE -/- and apoE + LDLR -/- mice on high-cholesterol diet, dilation to ACh was decreased. In apoE + LDLR -/- mice on high-cholesterol diet, dilation of coronary arteries to nitroprusside was increased. These findings suggest that dilation of coronary arteries from normal mice in response to ACh and serotonin is dependent on production of nitric oxide and activation of soluble guanylate cyclase. Hypercholesterolemia selectively impairs dilator responses of mouse coronary arteries to serotonin. In the absence of both apoE and the LDL receptor, high levels of cholesterol result in a greater impairment in coronary endothelial function.

Endothelium-dependent relaxation by acetylcholine is impaired in hypertriglyceridemic humans with normal levels of plasma LDL cholesterol

OBJECTIVES

Patients with high triglyceride (of which very low density lipoproteins [VLDL] are the main carriers), but with normal low density lipoprotein (LDL) cholesterol levels, were examined for in vivo endothelium function status.

BACKGROUND

Very low density lipoproteins inhibit endothelium-dependent, but not -independent, vasorelaxation in vitro.

METHODS

Three groups were studied: 1) healthy volunteers (n = 10; triglyceride 1.24+/-0.14 mmol/liter, LDL cholesterol 2.99+/-0.24 mmol/liter); 2) hypertriglyceridemic (n = 11; triglyceride 6.97+/-1.19 mmol/liter, LDL cholesterol 2.17+/-0.2 mmol/liter, p < 0.05); and 3) hypercholesterolemic (n = 10; triglyceride 2.25+/-0.29 mmol/liter, LDL cholesterol 5.61+/-0.54 mmol/liter; p < 0.05) patients. Vasoactive responses to acetylcholine, sodium nitroprusside, noradrenaline, N(G)-monomethyl-L-arginine and postischemic hyperemia were determined using forearm venous occlusion plethysmography.

RESULTS

Responses to acetylcholine (37 microg/min) were significantly dampened both in hypercholesterolemic (% increase in forearm blood flow: 268.2+/-62) and hypertriglyceridemic patients (232.6+/-45.2) when compared with controls (547.8+/-108.9; ANOVA p < 0.05). Responses to sodium nitroprusside (at 1.6 microg/min: controls vs. hypercholesterolemics vs. hypertriglyceridemic: 168.7+/- 25.1 vs. 140.6+/-38.9 vs. 178.5+/-54.5% increase), noradrenaline, N(G)-monomethyl-L-arginine and postischemic hyperemic responses were not different among the groups examined.

CONCLUSIONS

Acetylcholine responses are impaired in patients with pathophysiologic levels of plasma triglycerides but normal plasma levels of LDL cholesterol. The impairment observed was comparable to that obtained in hypercholesterolemic patients. We conclude that impaired responses to acetylcholine normally associated with hypercholesterolemia also occur in hypertriglyceridemia. These findings identify a potential mechanism by which high plasma triglyceride levels may be atherogenic independent of LDL cholesterol levels.

Impaired endothelial regulation of vascular tone in patients with systemic arterial hypertension

The discovery of the endothelium as a major regulator of vascular tone triggered intense research among basic and clinical investigators to unravel the physiologic and pathophysiologic significance of this phenomenon. Importantly, endothelial modulation of the contractile state of vascular smooth muscle has been shown to be impaired in atherosclerosis and in several conditions known to be associated with the premature development of atherosclerosis. Studies in several different animal models of arterial hypertension, and in patients with both essential and secondary hypertension, have demonstrated an association between elevated systemic blood pressure and impaired endothelium-dependent vascular relaxation. More recently, a diminished bioavailability of nitric oxide (NO) has been identified as a mechanism responsible for endothelial dysfunction in hypertensive patients. Different processes may, in turn, explain this decreased vascular activity of NO. The present review focuses on those clinical studies that are aimed at identifying the precise abnormality responsible for reduced NO-dependent vasodilation in patients with essential hypertension. Understanding of the basic mechanisms of this process may prove to be beneficial for the development of more specific therapies and ultimately for the outcome of hypertensive patients.

Improvement in the endothelium-dependent relaxation in hypercholesterolemic rabbits treated with vitamin E

The authors studied the time course of the vitamin E mediated improvement in endothelium-dependent relaxation in hypercholesterolemic rabbits. A total of 40 male New Zealand white rabbits were randomly assigned to hypercholesterolemic (control) and vitamin E treated groups. The latter group was further divided in three subgroups in accordance with the duration of the vitamin E treatment (2, 4 or 6 days) at the end of the experiment. The dose of vitamin E utilized was 50 IU/day administered once a day by gavage. All the rabbits were fed a diet supplemented with cholesterol (0.5%) and coconut oil (2%) for 4 weeks. At the end of this period, the animals were sacrificed and the aorta removed for determination of the cholesterol and malondialdehyde (MDA) contents. The relaxation of the aortic strips in response to acetylcholine was also studied. In addition, the cholesterol and MDA contents of native and oxidized LDL were measured. At the end of the 4th week, the MDA level was significantly reduced in native and oxidized LDL in the rabbits treated with vitamin E for 2 days, while in aortic tissue a reduction was seen after 4 days of treatment. Endothelium-dependent relaxation improved significantly after 6 days of vitamin E administration, and there was a reduction in the total plasma and aortic cholesterol levels during this same period. We conclude that vitamin E at a dose of 50 IU/day for 6 days improves the endothelium-dependent relaxation seen in hypercholesterolemic rabbits. This effect may be mediated through an antioxidant action on LDL particles and on the aortic arterial wall.

Endothelial dysfunction in human intramyocardial small arteries in atherosclerosis and hypercholesterolemia

Vascular responses of human intramyocardial small arteries were examined in vitro to assess the influence of atherosclerosis and risk factors for coronary artery disease on endothelium-dependent relaxation. Recipient hearts were obtained from patients with ischemic (n = 14) and nonischemic (n = 13) cardiomyopathy undergoing heart transplantation. Small intramyocardial coronary arteries (mean internal diameter 313 +/- 11 micrometers) were mounted on a wire myograph for measurement of morphology and isometric tension. Vasodilation was examined after preconstriction with U-46619, a thromboxane A2 analog. Endothelium-dependent relaxation to acetylcholine and bradykinin was impaired in patients with ischemic compared with nonischemic cardiomyopathy (P < 0.01 and P < 0.001, respectively). Endothelium-independent relaxation to sodium nitroprusside was preserved. Incubation with L-arginine (3 mmol/l) did not improve endothelium-dependent relaxation to acetylcholine or bradykinin. With the use of stepwise multivariate analysis, hypercholesterolemia, but no other risk factor for atherosclerosis, was independently associated with impaired endothelium-dependent relaxation to acetylcholine (r = -0.50, P = 0.05) but not to bradykinin. Endothelial dysfunction in intramyocardial small arteries may predispose patients with nonobstructive epicardial atherosclerosis and hypercholesterolemia to myocardial ischemia.

Restoration of nitric oxide function in human hyperlipidaemia, congestive heart failure and liver cirrhosis

1. There is accumulating evidence for a range of abnormalities in the nitric oxide (NO) signalling cascade in human cardiovascular disorders. 2. In the present review we assess the literature detailing such evidence in early (hyperlipidaemia) and end-stage (heart failure) disease, with emphasis on the mechanisms by which the disturbances are thought to occur. 3. Strategies for the correction of disturbed NO signalling in these states are reviewed and include both prescribed pharmacological interventions, such as lipid-lowering therapy and novel uses of angiotensin-converting enzyme inhibitors, as well as non-pharmacological interventions, such as exercise and dietary supplementation with L-arginine and n-3 polyunsaturated fatty acids. 4. In addition to a decreased production/function of NO, the possible detrimental effects of a chronic elevation in NO production in patients with liver cirrhosis, together with a novel use of antibiotics to correct this perturbation, is outlined.

Role of nitric oxide in cardiovascular disease: focus on the endothelium

Nitric oxide is a soluble gas continuously synthesized by the endothelium. This substance has a wide range of biological properties that maintain vascular homeostasis, including modulation of vascular dilator tone, regulation of local cell growth, and protection of the vessel from injurious consequences of platelets and cells circulating in blood. A growing list of conditions, including those commonly associated as risk factors for atherosclerosis such as hypertension and hypercholesterolemia, are associated with diminished release of nitric oxide into the arterial wall either because of impaired synthesis or excessive oxidative degradation. Diminished nitric oxide bioactivity may cause constriction of coronary arteries during exercise or during mental stress and contribute to provocation of myocardial ischemia in patients with coronary artery disease. Additionally, diminished nitric oxide bioactivity may facilitate vascular inflammation that could lead to oxidation of lipoproteins and foam cell formation, the precursor of the atherosclerotic plaque. Numerous therapies have been investigated to assess the possibility of reversing endothelial dysfunction by enhancing the release of nitric oxide from the endothelium, either through stimulation of nitric oxide synthesis or protection of nitric oxide from oxidative inactivation and conversion to toxic molecules such as peroxynitrite. Accordingly, causal relationships between improved endothelial function and reduction in myocardial ischemia and acute coronary events can now be investigated.

Oxidative stress and lipids in diabetes: a role in endothelium vasodilator dysfunction?

Endothelial dysfunction is a key feature of diabetes mellitus and is thought to be the major cause of vascular complications associated with the disease. The vascular endothelium demonstrates impaired synthesis of vasodilators and increased release of procoagulants and vasoconstrictors, defects which theoretically could explain the increased incidence of atherosclerosis and hypertension found within this patient group. The pathways mediating endothelial cell layer dysfunction are unknown, although many candidates have been proposed. This review concentrates on the hypothesis that increased oxidative stress combined with abnormal plasma lipid composition leads to reduced synthesis of endothelial vasodilators and hence endothelial dysfunction. Free radical generation is undoubtedly raised in diabetes but the evidence for decreased antioxidant status is debatable. The role of antioxidant and lipid-lowering therapy is considered, but few studies have directly investigated the effect of treatment on vascular function. Concern arises from individual studies of vitamin E in diabetic animals which have proved deleterious. Current literature implies that a combination therapy of vitamin E and vitamin C may be beneficial, but this needs to be investigated further in both animal and human diabetes.

Aortic stiffness in young patients with heterozygous familial hypercholesterolemia

BACKGROUND

Dyslipidemia is a primary risk factor for the development of atherosclerosis. Aortic distensibility is an important determinant of left ventricular function and coronary blood flow whose possible alterations in patients with dyslipidemia have not been fully investigated.

METHODS

To assess the effect of dyslipidemia on the elastic properties of the aorta, we studied 60 patients (mean age 37+/-11 years) with heterozygous familial hypercholesterolemia and no manifest arterial disease and compared them with 20 of their normolipidemic siblings (mean age 34+/-10 years). Two indexes of the aortic elastic properties were measured: aortic distensibility was calculated by use of the formula: 2 x (AoS-AoD)/PP x AoD, and aortic stiffness index was calculated by use of the formula: In (SBP/DBP)/(AoS-AoD)/AoD, where AoS and AoD are aortic root end-systolic and end-diastolic diameters, respectively, SBP and DBP are systolic and diastolic arterial pressure, respectively, and PP is pulse pressure. Internal aortic root diameters were measured at 3 cm above the aortic valve by use of two-dimensional guided M-mode transthoracic echocardiography, and arterial pressure was measured simultaneously at the brachial artery by sphygmomanometry.

RESULTS

The mean aortic systolic and diastolic diameter index did not differ significantly between the two groups. In contrast, aortic distensibility was found to be significantly reduced in subjects with isolated familial hypercholesterolemia compared with that in the control group (2.15+/-1.72 cm2.dynes(-1).10(-6) vs 3.18+/-1.58 cm2.dynes(-1).10(-6), p < 0.02). In addition, the mean aortic stiffness index was double in patients with familial hypercholesterolemia compared with that in normolipidemic subjects.

CONCLUSIONS

Severe dyslipidemia does not overtly influence aortic dimensions but leads to impairment of aortic elastic properties before the occurrence of clinical manifestations of atherosclerotic disease.

[The role of endothelial function for ischemic manifestations of coronary atherosclerosis]

The vascular endothelium controls vasomotor tone by releasing a number of substances like nitric oxide (NO). NO has been shown to play a very important role, because it mediates vasodilation and furthermore inhibits platelet aggregation, expression of adhesion molecules for monocytes and adhesion of neutrophils and it impairs growth of vascular smooth muscle cells. An increased oxidative stress, decreasing the bioavailability of NO, is mainly responsible for a blunted endothelium dependent vasoreactivity. Risk factors for endothelial dysfunction are coronary artery disease, hypertension, hypercholesterolemia, smoking, and aging. Endothelial dysfunction in the presence of these risk factors might contribute to the occurrence of myocardial ischemia, aggravate acute coronary syndromes and accelerate progression of coronary artery disease. Amelioration of blunted endothelial function appears to be a major therapeutical goal to reduce ischemia and clinical events and might even retard progression of coronary artery disease.

ACE inhibition, endothelial function and coronary artery lesions. Role of kinins and nitric oxide

In healthy coronary arteries, the endothelium plays an important role in the regulation of vascular smooth muscle growth and contractility. Furthermore, the endothelium inhibits overt platelet aggregation and prevents the adhesion of white blood cells to, and their infiltration into, the vascular wall. Among the mediators of these functions of endothelial cells, nitric oxide (NO) plays a central role. Moreover, the presence of local kinin-generating enzymatic systems associated with endothelial cells, vascular smooth muscle, platelets, neutrophils and monocytes suggests that bradykinin stimulates endothelial cells to release NO locally. The activation of endothelial cells by bradykinin is inhibited by kininase II, best known as angiotensin converting enzyme (ACE). Hence, ACE inhibitors, in addition to reducing the levels of angiotensin II (a potent stimulus to vascular smooth muscle growth and contraction), cause an amplification of the release of NO and other endothelial mediators that is induced by bradykinin. Independent risk factors for coronary artery disease such as hypertension, diabetes and hypercholesterolaemia reduce the NO-dependent regulation of vascular smooth muscle contractility and growth in otherwise normal coronary arteries. This endothelial dysfunction probably also affects the inhibitory role of NO with regard to platelet aggregation and monocyte infiltration into the vascular wall. In atherosclerotic vessels, the role of NO is severely reduced. In animal models, as well as in patients with coronary artery disease, endothelial dysfunction is improved by treatment with ACE inhibitors. Although in humans the mechanism of the restoration of endothelial function is not known, in animals endogenous kinins and NO are involved. However, it is clear that this process is multifactorial, and thus probably involves both the prevention of the deleterious actions of angiotensin II and the potentiation of bradykinin.

Preeclampsia selectively impairs endothelium-dependent relaxation and leads to oscillatory activity in small omental arteries

The vascular pathophysiology of preeclampsia, a hypertensive disorder unique to human pregnancy, has been postulated to be due to endothelial dysfunction, primarily manifest as deficient nitric oxide (NO) synthesis. We evaluated contraction (KCl and arginine vasopressin [AVP]) and dilation (acetylcholine and bradykinin) in small resistance-size omental arteries obtained during surgery from women with preeclampsia, postulating that these vessels would exhibit augmented contraction and diminished endothelium-dependent relaxation, most likely due to decreased NO synthesis. For comparison, vessels were also obtained from normotensive gravidas, pregnant women with chronic hypertension, or with chronic hypertension and superimposed preeclampsia, as well as from premenopausal nonpregnant controls. Vessels of approximately 200 micron in internal diameter were studied in vitro using a Mulvany-Halpern myograph. Maximal contraction due to either KCl or AVP was significantly augmented in vessels from women with preeclampsia; these vessels all exhibited endothelium- and cyclooxygenase-dependent phasic oscillations while vessels from all other groups exhibited only tonic contractions. Acetylcholine and bradykinin both led to dose- and endothelium-dependent relaxation which was unaffected by inhibitors of NO synthesis. Responses to bradykinin were similar in vessels from normal pregnant and preeclamptic women while those to acetylcholine were absent in vessels from women with preeclampsia. These data suggest specific defects in resistance-artery endothelium from women with preeclampsia.

Morphological heterogeneity with normal expression but altered function of G proteins in porcine cultured regenerated coronary endothelial cells

1. Experiments were designed to investigate whether the pertussis toxin-dependent endothelial dysfunction following balloon injury is due to a reduced expression or an insufficient function of G-proteins. 2. Endothelium-dependent responses of porcine coronary arteries were examined in vitro by use of conventional organ chambers. Morphological analysis was performed by isolating and culturing the endothelial cells from these arteries. The expression of Gi-proteins in regenerated endothelial cells was measured by Western blots and immunolabelling. The function of G-proteins was assessed by measuring the GTPase activity of cultured endothelial cells. 3. Eight days following denudation, endothelial regrowth was confirmed by histological examination and by demonstrating the presence of endothelium-dependent relaxations to bradykinin and 5-hydroxytryptamine (5-HT). In primary culture, the regenerated endothelial cells displayed a 'cobblestone' pattern as seen with native endothelial cells. 4. Twenty eight days after denudation, the endothelium-dependent relaxations induced by 5-HT were impaired, but those to bradykinin were maintained. However, the latter were reduced when endothelium-dependent hyperpolarization was prevented. 5. Twenty eight days after denudation, multinucleated giant cells were present in the regenerated but not in the native cultured endothelial cell populations. These regenerated endothelial cells incorporated less tritiated thymidine than native endothelial cells. 6. The intensities of the bands on the immunoblot of the regenerated endothelial cells, when several antibodies against Gi alpha 1/alpha 2/alpha 3 were used, were the same as those obtained in native endothelial cells. The immunolabelling with the same antibodies was similar between the giant cells and the regenerated endothelial cells of normal size. The hydrolysis of GTP was lower in regenerated than in native endothelial cell membranes. 7. In conclusion, endothelium-dependent relaxations mediated by Gi-proteins are impaired in balloon denuded coronary arteries. This dysfunction following regeneration cannot be explained by a reduced expression of Gi proteins but rather reflects an abnormal function of the G-proteins in the regenerated endothelium.

Vascular effects of cyclosporin A and acute rejection in canine heart transplantation

BACKGROUND

Alteration of coronary vascular regulation during acute rejection may induce graft dysfunction and promote the occurrence of coronary atherosclerosis in transplant recipients. We studied the effects of treated and untreated acute rejection on coronary vascular regulation.

METHODS

Two groups of mongrel dogs (n = 7) underwent heterotopic heart transplantation (cervical position) and received either no treatment (group 1) or cyclosporin A (CyA), 10 mg.kg-1.day-1 (group 2). On day 7, recipient native and transplanted hearts were harvested and studied in organ chambers for coronary vascular reactivity.

RESULTS

Transplanted hearts from group 1 displayed grade IV histologic rejection, whereas those from group 2 displayed grade IIIA to IV rejection. Intimal hyperplasia was found in the coronary arteries of both groups. Immunoperoxidase staining revealed the presence of factor VIII and of immunoglobulin M and G antibodies on the endothelium of both groups. Coronary relaxation to thrombin was impaired in transplanted hearts compared with native hearts (p < 0.05), and this was not influenced by CyA treatment. Conversely, endothelium-dependent relaxation to 5-hydroxytryptamine was enhanced in both CyA-treated (p < 0.01) and untreated groups (p < 0.05). A facilitating effect of CyA on 5-hydroxytryptamine also was seen in transplanted hearts in group 1 versus group 2 (p < 0.05), suggesting an intrinsic effect of CyA. Endothelium-independent relaxation to sodium nitroprusside and the contractile response to prostaglandin F2 alpha were not affected.

CONCLUSIONS

In our model, acute rejection did not specifically impair cyclic guanosine monophosphate-mediated relaxation, but it did affect, in a receptor-specific manner, endothelium-dependent relaxation. Cyclosporin A appeared to enhance coronary endothelial sensitivity to 5-hydroxytryptamine.

G-protein-mediated signaling in cholesterol-enriched arterial smooth muscle cells. 1. Reduced membrane-associated G-protein content due to diminished isoprenylation of G-gamma subunits and p21ras

Mechanisms contributing to altered heterotrimeric G-protein expression and subsequent signaling events during cholesterol accretion have been unexplored. The influence of cholesterol enrichment on G-protein expression was examined in cultured smooth muscle cells that resemble human atherosclerotic cells by exposure to cationized LDL (cLDL). cLDL, which increases cellular free and esterified cholesterol 2-fold and 10-fold, respectively, reduced the cell membrane content of Galphai-1, Galphai-2, Galphai-3, Gq/11, and Galphas. The following evidence supports the premise that the mechanism by which this occurs is due to reduced isoprenylation of the Ggamma-subunit. First, the inhibitory effect of cholesterol enrichment on the membrane content of Galphai subunits was found to be post-transcriptional, since the mRNA steady-state levels of Galphai(1-3) were unchanged following cholesterol enrichment. Second, the membrane expression of alpha and beta subunits was mimicked by cholesterol and 17-ketocholesterol, both of which inhibit HMG-CoA reductase. Third, inhibition of Galphai and Gbeta expression in cholesterol-enriched cells was overcome by mevalonate, the immediate product of HMG-CoA reductase. Fourth, pulse-chase experiments revealed that cholesterol enrichment did not reduce the degradation rate of membrane-associated Galphai subunits. Fifth, cholesterol enrichment also reduced membrane expression of Ggamma-5, Ggamma-7upper; these gamma subunits are responsible for trafficking of the heterotrimeric G-protein complex to the cell membrane as a result of HMG-CoA reductase-dependent post-translational lipid modification (geranylgeranylation) and subsequent membrane association. Cholesterol enrichment did not alter expression of G-gamma-5 mRNA, as assessed by reverse transcriptase polymerase chain reaction, supporting a post-transcriptional defect in Ggamma subunit expression. Fifth, cholesterol enrichment also reduced the membrane content of p21ras (a low molecular weight G-protein requiring farnesylation for membrane targeting) but did not alter the membrane content of the two proteins that do not require isoprenylation for membrane association&sbd;PDGF-receptor or p60-src. Reduced G-protein content in cholesterol-laden cells was reflected by reduced G-protein-mediated signaling events, including ATP-induced GTPase activity, thrombin-induced inhibition of cyclic AMP accumulation, and MAP kinase activity. Collectively, these results demonstrate that cholesterol enrichment reduces G-protein expression and signaling by inhibiting isoprenylation and subsequent membrane targeting. These results provide a molecular basis for altered G-protein-mediated cell signaling processes in cholesterol-enriched cells.

G-protein-mediated signaling in cholesterol-enriched arterial smooth muscle cells. 2. Role of protein kinase C-delta in the regulation of eicosanoid production

PGI2 generation by the vessel wall is an agonist for cyclic-AMP-dependent cholesteryl ester hydrolysis. The process of enhanced PGI2 synthesis is stimulated, in part, by G-protein-coupled receptor ligands. Cellular cholesterol enrichment has been hypothesized to alter G-protein-mediated PGI2 synthesis. In the studies reported herein, cells generated PGI2 in response to AlF4-, GTPgammaS, and ATP in a dose-dependent manner. G-protein agonists stimulated eicosanoid production principally by activating phospholipase A2, but not phospholipase C. This is in contrast to PDGF, which stimulated phospholipase A2 and PLCgamma activities. Galphai subunits mediate G-protein agonist-induced PGI2 synthesis, since ATP- and PDGF-induced PGI2 synthesis was inhibited by pertussis toxin. Although cholesterol enrichment reduced arachidonic acid- and PDGF-induced PGI2 synthesis, cholesterol enrichment enhanced PGI2 release in response to AlF4-, GTPgammaS, and ATP. The enhancement of PGI2 release in cholesterol-enriched cells was augmented by mevalonate, which inhibits the ability of cholesterol enrichment to reduce membrane-associated G-protein subunits. Since cholesterol enrichment inhibited PDGF and AlF4--induced MAP kinase activity [Pomerantz, K., Lander, H. M., Summers, B., Robishaw, J. D., Balcueva, E. A., & Hajjar, D. P. (1997) Biochemistry 36, 9523-9531] (the major mechanism by which phospholipase A2 is activated), these results suggest that cholesterol enrichment induces other alternative signaling pathways leading to phospholipase A2 activation. A PKC-dependent pathway is described herein that is involved in enhanced eicosanoid production in cholesterol-enriched cells. This conclusion is supported by two observations: (1) G-protein-linked PGI2 production is inhibited by calphostin, and (2) cholesterol enrichment augments the specific translocation of the delta-isoform of PKC from the cytosol to the plasma membrane following treatment of cells with phorbol ester. These data support the concept that, in cells possessing normal levels of cholesterol, MAP-kinase-dependent pathways mediate eicosanoid synthesis in response to G-protein activation; however, under conditions of high cellular cholesterol levels, augmented G-protein-linked eicosanoid production results from enhanced PKCdelta activity.

Snaring of the target vessel in less invasive bypass operations does not cause endothelial dysfunction

BACKGROUND

Minimally invasive coronary artery bypass grafting aims to achieve less patient discomfort and a more rapid return to active life. Most approaches have used maintenance of the beating heart and control of the target coronary vessel by different hemostatic devices. The purpose of this study was to assess the effects of commonly used coronary artery snares and of the occlusion of the coronary vessel necessary for minimally invasive coronary artery operations on coronary endothelial function.

METHODS

Coronary artery bypass grafting with an internal mammary artery to left anterior descending artery anastomosis was performed in a porcine model with a 30-minute period of ischemia and a subsequent 30-minute period of reperfusion, using snares on either side of the anastomotic site to achieve hemostasis of the operative field. Endothelium-dependent relaxation to serotonin was studied in conventional organ chamber experiments with rings taken from the left anterior descending artery at the proximal snare site, the anastomotic site in the segment that underwent the ischemia-reperfusion cycle, the distal snare site, and at a control segment. Responses to potassium chloride and bradykinin were also compared.

RESULTS

There were no significant differences in endothelium-dependent relaxation values among the four sites studied.

CONCLUSIONS

These results confirm that snaring of the coronary artery for achieving hemostasis at the anastomotic site when performing coronary artery bypass grafting on the beating heart does not cause endothelial dysfunction.

Vasorelaxant and antiaggregatory properties of the endothelium: a comparative study in normocholesterolaemic and hereditary and dietary hypercholesterolaemic rabbits

1. A comparison of the effects of dietary and genetically-induced hypercholesterolaemia on the vasodilator and antiaggregatory capacity of the endothelium was made in rabbit isolated subclavian artery rings. 2. Dietary-induced hypercholesterolaemia in NZW rabbits decreased the maximum relaxation to carbachol (0.01-10 microM) and calcimycin (0.01-0.1 microM) in vessel rings precontracted with 5-hydroxytryptamine (5-HT), 0.1 microM), when compared to responses observed in rings obtained from control normocholesterolaemic NZW rabbits. The relaxant responses to SIN-1 (3-(4-morpholinyl)-sydnonimine hydrochloride) were attenuated but were not significantly different from controls. In Froxfield genetically hypercholesterolaemic (FHH) rabbits, the maximum relaxations to carbachol, calcimycin and SIN-1 were all reduced significantly. 3. Neither genetic nor dietary-induced hypercholesterolaemia modified the contractile responses of vessel rings to either KCl (10-100 mM) or 5-HT (0.01-10 microM). 4. Endothelium-dependent inhibition of collagen-induced platelet aggregation in whole blood was demonstrated by stimulation of a vessel ring, incorporated into the blood sample, with carbachol (10 microM, final blood concentration). This effect was inhibited by NG-nitro-L-arginine (L-NOARG, 100 microM). SIN-1 (10 microM, final blood concentration) also decreased whole blood platelet aggregation, but only in the presence of an unstimulated vessel ring, and this was unaffected by L-NOARG. Superoxide dismutase (150 u ml-1) did not influence the inhibition of aggregation by either a carbachol-stimulated vessel ring or by SIN-1. 5. Carbachol-stimulated artery rings from FHH rabbits inhibited platelet aggregation to a similar extent to that seen with rings from control normocholesterolaemic rabbits. Rings from hypercholesterolaemic NZW rabbits, however, did not significantly inhibit platelet aggregation when stimulated with carbachol. SIN-1 inhibited platelet aggregation in the presence of rings from either group of hypercholesterolaemic rabbits. 6. Hypercholesterolaemia induced by dietary modification induces changes in endothelial function which are characteristically different from those seen in genetically hypercholesterolaemic rabbits. It appears that dietary-induced hypercholesterolaemia primarily decreases NO release from the endothelium, while in genetically-induced hypercholesterolaemic vessel rings NO is released but there is a decreased responsiveness of the vascular smooth muscle cells to NO. This may reflect differences in the age and severity of the atherosclerotic lesions in the two groups of rabbits.

Vascular endothelium: vasoactive mediators

In most blood vessels, the endothelium generates both vasodilator and growth-stabilizing mediators under normal physiological circumstances. The vasodilator influence of the endothelium modulates the vasoconstriction induced by adrenergic nerves, bloodborne substances, and local autacoids. Nitric oxide (NO) is a major endothelium-derived vasodilator, along with prostacyclin. A third substance called endothelium-derived hyperpolarizing factors (EDHF) mediates vasodilatation in certain conduit arteries and in most resistance vessels. EDHF may be a cytochrome P-450 metabolite of arachidonic acid. NO acts mostly through an elevation of cyclic guanosine monophosphate in vascular smooth muscle, whereas prostacyclin stimulates adenylate cyclase. The mode of action of EDHF involves the activation of K+ channels. The multiplicity of the factors released by the endothelium, as well as the complexity of the interactions among these factors and those with other nonendothelial mediators, determine the extent of vasomotor control exerted locally by the endothelium.

Analysis of lysophophatidylcholine-induced endothelial dysfunction

Endothelial dysfunction caused by the early atherosclerotic process or by endothelial exposure to atherogenic lipids, including lysophosphatidylcholine (lysoPC), is characterized by a selective impairment of responses mediated by the pertussis toxin-sensitive Gi-2 protein. Experiments were performed to analyze the mechanisms underlying this effect. Bradykinin (BK: Gi-2 protein-independent), serotonin (5-HT: Gi-2 protein-dependent), or direct activation of the G(i-2)-protein by mastoparan increased the release of endothelium-derived nitric oxide (EDNO) from porcine arterial endothelial cells (EC). LysoPC decreased the release of EDNO caused by 5-HT, but did not affect the response to BK or mastoparan. LysoPC did not increase production of superoxide radicals detected by lucigenin-enhanced chemiluminescence. Western blot analysis showed no difference in the level of immunoreactive Gi alpha-2 between control and lysoPC-treated cells. Activation of the Gi-2 protein by serotonergic or alpha 2-adrenoceptor stimulation decreased the pertussis toxin-catalyzed ADP-ribosylation of Gi alpha-2 protein in membranes from control but not lysoPC-treated cells. However, direct activation of the Gi-2 protein by mastoparan inhibited the ADP-ribosylation in membranes from control and lysoPC-treated cells. The toxin-catalyzed reaction was reduced in lysoPC-treated cells or lysoPC-treated membranes. LysoPC reduced the ability of endothelin to increase GTP gamma S binding to the Gi-2 protein but did not affect the activity of mastoparan. These results suggest that lysoPC inhibits a pertussis toxin-sensitive signaling pathway in EC by an effect consistent with receptor:Gi-2-protein uncoupling.

Coronary vasomotor responses in cyclosporine-treated piglets

Chronic treatment with cyclosporine A (Cx) seems to produce a decreased ability of the endothelium to secrete nitric oxide. However, its effect on the coronary arterial system remains controversial. Therefore, coronary arteries isolated from piglets treated by intramuscular injections of Cx (10 mg/kg/day, IM, for 22 days) were studied in organ baths and compared with those isolated from control animals (IM injections of the Cx solvent). Depolarization-induced contractions (KCl 120 mM) were similar in both groups, whereas the acetylcholine-induced contractions (percent of 120 mM KCl) were enhanced: The area under the curve (AUC) was 245 +/- 51 in the Cx group versus 110 +/- 15 in the control group (p < 0.05). Removal of the endothelium did not significantly modify the acetylcholine-induced contractions in both groups and, therefore, did not attenuate the enhanced responsiveness to acetylcholine in the Cx group. On unrubbed rings contracted with prostaglandin F2 alpha, the endothelium-dependent relaxations from serotonin (in the presence of 1 microM ketanserin) were reduced: The AUC was 479 +/- 24 in the Cx group versus 385 +/- 22 in the control group (p < 0.02). Larger AUC values were also found for bradykinin and substance P in the Cx group: 158 +/- 18 versus 55 +/- 17 (in the control group, p < 0.01) and 198 +/- 8 versus 145 +/- 12 (p < 0.01), respectively. Nevertheless, no alteration in calcium ionophore-induced relaxations was observed: The AUC was 217 +/- 10 in the Cx group and 224 +/- 18 in the control group (NS). Indomethacin incubation (10 microM) did not prevent the impairment in endothelium-dependent relaxations and did not attenuate the cyclosporine-induced augmentation of acetylcholine-induced contractions. Thus, chronic administration of cyclosporine to piglets impairs the coronary endothelial function and produces functional changes in smooth muscle cells. These alterations may play a role in the occurrence of cardiac graft vasculopathy.

Endothelial Gi protein expression is markedly low in human coronary microvessels

Gi protein functionally mediates endothelium-dependent relaxations in large epicardial coronary arteries but not in small coronary arteries, which suggests a different involvement of Gi protein in the endothelium-dependent relaxations between large and small coronary arteries. We previously showed that endothelial Gi protein is present in human epicardial coronary artery. In the present study, we examined the expression of endothelial Gi protein in human coronary microvessels. Immunohistochemical staining with a specific antibody against human Gi protein was performed in intramyocardial coronary microvessels and vasa vasorum from 34 autopsy cases. The immunoreactive levels of the endothelial Gi protein were semiquantitated into four grades (none, 0; slight, +1; moderate, +2; high, +3), and the mean value of the ratings of all endothelial cells was then used as an index of the endothelial Gi protein expression of the vessel. The immunoreactive levels of the endothelial Gi protein were extremely low in intramyocardial coronary microvessels and in vasa vasorum, irrespective of the age of the patients, the presence or absence of coronary risk factors, or the influence of medical treatments. These results may therefore explain in part why endothelium-dependent relaxations in coronary microvessels are not functionally mediated by Gi protein.

Endothelial control of vasomotion and nitric oxide production: a potential target for risk factor management

During the past 15 years, new concepts have arisen regarding regulation of vasomotor control. It is now clear that the vascular endothelium modulates vascular tone via the release of a variety of substances. Of these, nitric oxide is predominant in modulating vasodilation. Nitric oxide also has a number of other roles that are clearly antiatherogenic. Importantly, a number of disease processes alter the release of nitric oxide and in fact may serve as risk factors in part via this mechanism. In this review, the mechanisms through which hypercholesterolemia alters vasomotion are discussed, and interventions that may improve endothelial function are considered.

The role of oxidized lipoproteins in atherogenesis

This article reviews our current understanding of the mechanisms of low-density lipoprotein (LDL) oxidation and the potential role of oxidized lipoproteins in atherosclerosis. Studies in hypercholesterolemic animal models indicate that oxidation of LDL is likely to play an important role in atherogenesis. Epidemiological investigations further suggest that the dietary intake of antioxidants is inversely associated with the risk of vascular disease, suggesting that oxidized LDL may be important in human atherosclerosis. By activating inflammatory events, oxidized lipoproteins may contribute to all stages of the atherosclerotic process. Lipoprotein oxidation is promoted by several different systems in vitro, including free and protein-bound metal ions, thiols, reactive oxygen intermediates, lipoxygenase, peroxynitrite, and myeloperoxidase. Intracellular proteins that bind iron or regulate iron metabolism might also play an important role. The physiologically relevant pathways have yet to be identified, however. We assess recent findings on the effects of antioxidants in vivo and suggest potential strategies for inhibiting oxidation in the vessel wall.

Nitric oxide: an overview

Nitric oxide (NO), a paracrine-acting gas enzymatically synthesized from L-arginine, is a unique biologic mediator that has been implicated in a myriad of physiologic and pathophysiologic states. It is an important regulator of vascular tone and may be the mediator of the hemodynamic changes involved in sepsis and cirrhosis. In addition, there is increasing evidence that NO is involved in coagulation, immune function, inhibitory innervation of the gastrointestinal tract, protection of gastrointestinal mucosa, and the hepatotoxicity of cirrhosis. It has already been speculated that NO may represent a point of control or intervention in a number of disease states. The purpose of this paper is to provide the surgeon with a broad overview of the scientific and clinical aspects of this important molecule.

Vascular function in the forearm of hypercholesterolaemic patients off and on lipid-lowering medication

To study whether vascular dysfunction in hypercholesterolaemia is reversible, we investigated patients without overt arterial disease who were taking maintenance treatment for hypercholesterolaemia. Medication was stopped for 2 weeks, reinstituted for 12 weeks, and again stopped for 6 weeks. During both maintenance treatment and the 12 weeks of step-up medication the lipid profile was improved but did not return to normal. Dose-response curves for serotonin-induced vasodilatation, an index of nitric oxide-dependent vasodilatation, showed a comparable and significant rightward shift after a medication-free period of 2 and 6 weeks compared with control subjects, indicating endothelial dysfunction, which was already maximum after 2 weeks. After 12 weeks of lipid-lowering medication, the difference in endothelial function between controls and patients had disappeared. Co-infusion of L-arginine, the substrate for nitric oxide synthase, returned the impaired serotonin response during hypercholesterolaemia to normal, but had no effect on this response in controls or in patients while on lipid-lowering medication. Neither endothelium-independent vasorelaxation, assessed by sodium nitroprusside infusion, nor vasoconstriction induced by the nitric oxide blocker L-NMMA, were different between controls and patients, whether the latter were on or off lipid-lowering medication. Our results show an L-arginine-sensitive, impaired nitric-oxide-mediated vascular relaxation of forearm resistance vessels in hypercholesterolaemia which is reproducible, and reversible after short-term lipid-lowering therapy. Demonstration of such changes in this readily accessible vascular bed will allow larger trials assessing vascular function during lipid-lowering therapy to be done.

Impaired endothelial function in patients with nephrotic range proteinuria

Proteinuria is associated with increased cardiovascular morbidity and mortality. Release of nitric oxide by the endothelium has been advanced as an important defense mechanism against vessel-wall damage. In the present study we therefore tested the hypothesis that proteinuria is associated with a defect in nitric oxide-dependent vasodilation, by using venous occlusion plethysmography of the forearm in nine patients with nephrotic range proteinuria (> 3.5 g/24 hr) and normal renal function (creatinine 83.1 +/- 8.7 mumol/liter), eight patients with active glomerulonephritis but normal renal function (creatinine 81.2 +/- 5.4 mumol/liter) and low range proteinuria (< 1.0 g/24 hr), and ten healthy volunteers. We infused L-NMMA (2 mg/min) to inhibit basal nitric oxide production, serotonin (0.1, 0.3 and 1.0 ng/kg/min) as an endothelium-dependent vasodilator, and nitroprusside (1, 10, 30 and 100 ng/kg/min) as an endothelium-independent vasodilator into the brachial artery. Administration of L-NMMA decreased basal forearm vascular resistance (FVR) by 30 +/- 4% in the nephrotic subjects, 38 +/- 4% in the non-nephrotic patients and by 37 +/- 2% in the healthy controls (P = 0.15). Upon the highest dose of serotonin FVR decreased in nephrotic subjects by 40 +/- 5%, which was less than in non-nephrotic patients (56 +/- 3%; P < 0.05) or in healthy controls (55 +/- 3%; P < 0.05). The maximal decrease in FVR upon nitroprusside infusion was not different between the groups (respectively 84 +/- 2, 84 +/- 3 and 84 +/- 2%). The impaired serotonin-induced vasodilation could be attributed to a defect in nitric oxide production, since L-NMMA almost completely prevented serotonergic vasodilation.(ABSTRACT TRUNCATED AT 250 WORDS)

Is endothelial dysfunction reversible?

To date, the published database concerning the impact of therapy on endothelial function in essential hypertension and hypercholesterolemia is small and incomplete. Chronic antihypertensive therapy had not yet been proven to restore endothelial function in patients with essential hypertension. In contrast, chronic lipid-lowering therapy is effective in restoring endothelial function of the coronary and peripheral circulation in patients with hypercholesterolemia. A beneficial effect was already documented after 3 months of therapy with fluvastatin but full restoration may last more than 1 year.

Gi proteins and the response to 5-hydroxytryptamine in porcine cultured endothelial cells with impaired release of EDRF

1. The receptor-mediated release of endothelium-derived relaxing factor(s) (EDRF) requires the presence of different functional G proteins in endothelial cells. Release of EDRF in response to 5-hydroxytryptamine (5-HT), which involves activation of pertussis toxin-sensitive Gi proteins, is impaired in both regenerated endothelium of the coronary artery following balloon catheterization and in porcine cultured endothelial cells. This study used porcine cultured endothelial cells as a model of regenerated endothelium to determine if the abnormal release of EDRF in response to 5-HT may be associated with the loss of functional pertussis toxin-sensitive Gi proteins. 2. Binding studies on porcine cultured endothelial cells demonstrated specific binding sites for [3H]-5-HT. Scatchard analyses revealed a single binding site for [3H]-5-HT with Kd of 7.2 +/- 3.5 nM and maximal binding (Bmax) of 121.4 +/- 51.3 fmol mg-1 protein. Binding of [3H]-5-HT was displaced by methiothepin (5-HT1 and 5-HT2 antagonist; Ki = 6.2 +/- 1.2 nM), but not by ketanserin (preferential 5-HT2 antagonist). 3. Gi alpha 1 protein was expressed in cultured but not in native endothelial cells. Gi alpha 2 and Gi alpha 3 proteins were expressed to significant levels in porcine native and cultured endothelial cells, as detected by Northern and Western blot analysis. 4. In membranes from cultured endothelial cells, two bands of 40 and 41 kDa, which corresponded to the Gi alpha 2 and the combination of Gi alpha 3-Gi alpha 1 proteins, respectively, were ADP-ribosylated by pertussis toxin. The labelling intensity was Gi alpha 2>Gi alpha 3-Gi alpha l and the amount of ADP-ribosylation was not different between porcine native and cultured endothelial cells. Stimulation of the cultured cells with 5-HT (3 x 10-6 M; 4 min) decreased significantly further ADP-ribosylation of Gi alpha 2 by pertussis toxin, but not that of Gi alpha 3 and/or Gi alpha l.5. The present results suggest that porcine endothelial cell culture may lead to the abnormal expression of Gi alpha l protein and that the dysfunctional release of EDRF from cultured porcine endothelial cells in response to 5-HT is not associated with the loss of Gi alpha proteins or the absence of 5-HT binding sites.