Endothelium-dependent inhibition of ergonovine-induced contraction is impaired in porcine coronary arteries with regenerated endothelium

Pneumonia

Pneumonia is a common acute respiratory infection that affects the alveoli and distal airways; it is a major health problem and associated with high morbidity and short-term and long-term mortality in all age groups worldwide. Pneumonia is broadly divided into community-acquired pneumonia or hospital-acquired pneumonia. A large variety of microorganisms can cause pneumonia, including bacteria, respiratory viruses and fungi, and there are great geographical variations in their prevalence. Pneumonia occurs more commonly in susceptible individuals, including children of <5 years of age and older adults with prior chronic conditions. Development of the disease largely depends on the host immune response, with pathogen characteristics having a less prominent role. Individuals with pneumonia often present with respiratory and systemic symptoms, and diagnosis is based on both clinical presentation and radiological findings. It is crucial to identify the causative pathogens, as delayed and inadequate antimicrobial therapy can lead to poor outcomes. New antibiotic and non-antibiotic therapies, in addition to rapid and accurate diagnostic tests that can detect pathogens and antibiotic resistance will improve the management of pneumonia.

Myocardial Ischemic Syndromes, Heart Failure Syndromes, Electrocardiographic Abnormalities, Arrhythmic Syndromes and Angiographic Diagnosis of Coronary Artery Spasm: Literature Review

In coronary artery spasm (CAS), an excess coronary vasoconstriction causing total or subtotal vessel occlusion could lead to syncope, heart failure syndromes, arrhythmic syndromes, and myocardial ischemic syndromes including asymptomatic myocardial ischemia, stable and unstable angina, acute myocardial infarction, and sudden cardiac death. Although the clinical significance of CAS has been underrated because of the frequent absence of symptoms, affected patients appear to be at higher risk of syncope, serious arrhythmias, and sudden death than those with classic Heberden's angina pectoris. Therefore, a prompt diagnosis has important therapeutic implications, and is needed to avoid CAS-related complications. While a definitive diagnosis is based mainly on coronary angiography and provocative testing, clinical features may help guide decision-making. We perform a literature review to assess the past and current state of knowledge regarding the clinical features, electrocardiographic abnormalities and angiographic diagnosis of CAS, while a discussion of mechanisms is beyond the scope of this review.

Coronary artery spasm: review and update

Coronary artery spasm (CAS), an intense vasoconstriction of coronary arteries that causes total or subtotal vessel occlusion, plays an important role in myocardial ischemic syndromes including stable and unstable angina, acute myocardial infarction, and sudden cardiac death. Coronary angiography and provocative testing usually is required to establish a definitive diagnosis. While the mechanisms underlying the development of CAS are still poorly understood, CAS appears to be a multifactorial disease but is not associated with the traditional risk factors for coronary artery disease. The diagnosis of CAS has important therapeutic implications, as calcium antagonists, not β-blockers, are the cornerstone of medical treatment. The prognosis is generally considered benign; however, recurrent episodes of angina are frequently observed. We provide a review of the literature and summarize the current state of knowledge regarding the pathogenesis of CAS.

A-FABP and oxidative stress underlie the impairment of endothelium-dependent relaxations to serotonin and the intima-medial thickening in the porcine coronary artery with regenerated endothelium

Experiments were designed to determine the cause of the selective dysfunction of G(i) proteins, characterized by a reduced endothelium-dependent relaxation to serotonin (5-hydroxytryptamine), in coronary arteries lined with regenerated endothelial cells. Part of the endothelium of the left anterior descending coronary artery of female pigs was removed in vivo to induce regeneration. The animals were treated chronically with vehicle (control), apocynin (antioxidant), or BMS309403 (A-FABP inhibitor) for 28 days before functional examination and histological analysis of segments of coronary arteries with native or regenerated endothelium of the same hearts. Isometric tension was recorded in organ chambers and cumulative concentration-relaxation curves obtained in response to endothelium-dependent [serotonin (G(i) protein mediated activation of eNOS) and bradykinin (G(q) protein mediated activation of eNOS)] and independent [detaNONOate (cGMP-mediated), isoproterenol (cAMP-mediated)] vasodilators. The two inhibitors tested did not acutely affect relaxations of preparations with either native or regenerated endothelium. In the chronically treated groups, however, both apocynin and BMS309403 abolished the reduction in relaxation to serotonin in segments covered with regenerated endothelium and prevented the intima-medial thickening caused by endothelial regeneration, without affecting responses to bradykinin or endothelium-independent agonists (detaNONOate and isoproterenol). Thus, inhibition of either oxidative stress or A-FABP likely prevents both the selective dysfunction of G(i) protein mediated relaxation to serotonin and the neointimal thickening resulting from endothelial regeneration.

The forgotten player of in-stent restenosis: Endothelial dysfunction

Reduced coronary endothelium-dependent vasodilation may play a role in the pathophysiology of in-stent restenosis. Moreover, endothelial dysfunction may cause to progression of athetrosclerosis in coronary arteries in patients undergoing percutaneous coronary intervention, especially stent deployment. We believe that the agents improving endothelial dysfunction and healing-enhanced stents, namely vascular endothelial growth factor (VEGF)-eluting stents, estradiol-eluting stents and stents attracting endothelial cells, might take an important role in the prevention of stent restenosis strategies in the near future.

Presence of asymmetric dimethylarginine gradients across high-grade lesions in patients with coronary artery disease

BACKGROUND

Asymmetric dimethylarginine, an endogenous inhibitor of nitric oxide synthase, is a systemic marker of endothelial dysfunction. Although experimental evidence indicates that asymmetric dimethylarginine may play an important role in atherogenesis, local asymmetric dimethylarginine levels have not been measured in vivo.

OBJECTIVES

We sought to determine whether: (i) asymmetric dimethylarginine is elevated locally at sites of coronary lesions, (ii) systemic asymmetric dimethylarginine concentrations correlate with local levels, and (iii) percutaneous coronary intervention produces immediate local asymmetric dimethylarginine elevation.

METHODS

In patients undergoing percutaneous coronary intervention (n=15), blood samples were obtained from a peripheral venous site, the coronary ostium proximal to the lesion and the coronary vessel distal to the lesion, before percutaneous coronary intervention. Samples were also obtained distal to the coronary lesion immediately after percutaneous coronary intervention and from the peripheral venous line 24 h after percutaneous coronary intervention.

RESULTS

Asymmetric dimethylarginine gradients were present across the coronary bed: local asymmetric dimethylarginine (micromol/l) was significantly higher distal to coronary lesions compared with proximally (2.39+/-1.27 vs. 1.52+/-0.68, P=0.005), and to systemic venous levels (2.39+/-1.27 vs. 1.17+/-0.72, P=0.001). Local asymmetric dimethylarginine did not increase immediately after percutaneous coronary intervention (1.88+/-0.89 vs. 2.39+/-1.27, P=0.11). Peripheral venous percutaneous coronary intervention levels 24 h after percutaneous coronary intervention were similar to baseline values (1.17+/-1.2 vs. 1.17+/-0.72, P=0.98).

CONCLUSION

Asymmetric dimethylarginine gradients exist across coronary lesions, suggesting asymmetric dimethylarginine release at the plaque site. Local asymmetric dimethylarginine accumulation may contribute to the endothelial dysfunction associated with high-grade coronary lesions. Peripheral asymmetric dimethylarginine is a marker of generalized endothelial dysfunction, but our findings highlight its limitation in detecting focal injury.

Decreased vascular lesion formation in mice with inducible endothelial-specific expression of protein kinase Akt

To determine whether endothelial Akt could affect vascular lesion formation, mutant mice with a constitutively active Akt transgene, which could be inducibly targeted to the vascular endothelium using the tet-off system (EC-Akt Tg mice), were generated. After withdrawal of doxycycline, EC-Akt Tg mice demonstrated increased endothelial-specific Akt activity and NO production. After blood flow cessation caused by carotid artery ligation, neointimal formation was attenuated in induced EC-Akt Tg mice compared with noninduced EC-Akt Tg mice and control littermates. To determine the role of eNOS in mediating these effects, mice were treated with N-nitro-L-arginine methyl ester (L-NAME). Neointimal formation was attenuated to a lesser extent in induced EC-Akt Tg mice treated with L-NAME, suggesting that some of the vascular protective effects were NO independent. Indeed, endothelial activation of Akt resulted in less EC apoptosis in ligated arteries. Immunostaining demonstrated decreased inflammatory and proliferative changes in induced EC-Akt Tg mice after vascular injury. These findings indicate that endothelial activation of Akt suppresses lesion formation via increased NO production, preservation of functional endothelial layer, and suppression of inflammatory and proliferative changes in the vascular wall. These results suggest that enhancing endothelial Akt activity alone could have therapeutic benefits after vascular injury.

Nebivolol and its 4-keto derivative increase nitric oxide in endothelial cells by reducing its oxidative inactivation

OBJECTIVES

The objective of the present study was to elucidate the vasodilator mechanisms of nebivolol, a high selective beta(1)-receptor antagonist with antioxidant properties.

BACKGROUND

Oxidative inactivation of nitric oxide (NO) is regarded as an important cause of its decreased biological activity.

METHODS

Oxidative stress was induced through the binding of oxidized (ox)-low-density lipoprotein (LDL) to its specific endothelial receptor, called "lectin-like oxidized LDL receptor-1" (LOX-1), in bovine and human endothelial cells and in Chinese hamster ovary cells stably expressing bovine LOX-1 (BLOX-1-CHO cells). Reactive oxygen species (ROS), superoxide (O(2)(*-)), and NO were measured in cells by flow cytometry.

RESULTS

Nebivolol and its 4-keto derivative prevented in a dose-dependent manner the increase of ROS (p < 0.001) and O(2)(*-) (p < 0.001) in bovine aortic endothelial cells (BAECs), human umbilical vein endothelial cells (HUVECs), and BLOX-1-CHO cells stimulated with ox-LDL. Atenolol had no effect. The incubation of HUVECs and BAECs with ox-LDL reduced basal and bradykinin-induced NO and nitrite concentration (p from <0.001 to <0.01). Nebivolol and its 4-keto derivative prevented the reduction of basal and stimulated NO and nitrite concentration (p from <0.001 to <0.01) while atenolol had no effect. The preincubation of BAECs with blocking anti-LOX-1 monoclonal antibody (LOX-1 mAb) significantly counteracted the effect of ox-LDL on stimulated generation of NO (p < 0.001), but the effect was significantly lower than that of nebivolol and its 4-keto derivative alone (p < 0.01).

CONCLUSIONS

In conclusion, the findings of the present study indicate that nebivolol increases NO also by decreasing its oxidative inactivation.

Mechanisms underlying attenuated contractile response of aortic rings to noradrenaline in fructose-fed mice

We hypothesized that an impairment of endothelial dysfunction and an increased response to alpha-adrenoceptor agonists may occur in fructose-fed, insulin-resistant mice. The aim of the present study was to assess the relationship between endothelial dysfunction and agonist-induced contractile responses in such mice. The acetylcholine-induced relaxation was significantly attenuated in streptozotocin-diabetic and fructose-fed mice. The contractile response to noradrenaline was significantly weaker than the control in fructose-fed but not in streptozotocin-diabetic mice; treatment with N(G)-nitro-L-arginine effectively restored this response. Incubating aortic rings with noradrenaline increased the NO(x) [nitrite (NO(2)(-)) and nitrate (NO(3)(-))] level and this level was significantly higher in fructose-fed mice than in control mice. Clonidine induced a dose-dependent relaxation in aortic rings pre-contracted with prostaglandin F(2alpha) that was completely abolished by N(G)-nitro-L-arginine; this relaxation was markedly enhanced in fructose-fed mice. In both control and fructose-fed mice, the clonidine-induced relaxation was significantly attenuated and the noradrenaline-induced contraction augmented by pertussis toxin. These results suggest that endothelial function is attenuated in both fructose-fed and streptozotocin-diabetic mice. It is suggested that the decreased noradrenaline contractile response in fructose-fed mice (compared to both controls and streptozotocin-diabetic mice) may be due to an increase in nitric oxide formation mediated by endothelial GTP-binding-coupled alpha(2)-adrenoceptors.

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.

Cellular and molecular mechanisms of coronary artery spasm: lessons from animal models

Coronary artery spasm plays an important role in the pathogenesis of a wide variety of ischemic heart diseases, especially in the Japanese population. Because coronary artery spasm can be induced by a variety of stimuli with different mechanisms of action, the occurrence of the spasm appears to be due to the local hyperreactivity of the coronary artery rather than to an enhanced stimulation with a single mechanism of action. Several lines of evidence indicate that coronary artery spasm is caused primarily by smooth muscle hypercontraction whereas the contribution of endothelial dysfunction may be minimal. In order to elucidate the cellular and molecular mechanisms of the spasm, porcine models of the spasm were developed. In the first model with balloon injury and high-cholesterol feeding, a close topological correlation between the early atherosclerotic lesions and the spastic sites was noted, whereas in the second model with an inflammatory cytokine the potential importance of coronary inflammatory changes, especially at the adventitia, was noted. Subsequent studies in vivo and in vitro demonstrated that protein kinase C (PKC) and Rho-kinase are substantially involved in the intracellular mechanism of the spasm, resulting in increases in the mono- and diphosphorylations of myosin light chain (MLC). Furthermore, molecular biological analyses demonstrated that Rho-kinase is upregulated at the spastic site (at all levels, including mRNA, protein, and activity), resulting in the inhibition of MLC phosphatase through the phosphorylation of its myosin binding subunit and thereby causing the increase in MLC phosphorylations. Preliminary results also suggest that the long-term inhibition of Rho-kinase is effective in inhibiting the development of arteriosclerotic vascular lesions in several porcine models. Thus, Rho-kinase could be regarded as a novel therapeutic target for coronary arteriosclerosis in general and coronary artery spasm in particular.

Long-term endothelial dysfunction after coronary artery stenting

OBJECTIVES

We assessed the endothelial-dependent vasomotor function in nonrestenotic coronary arteries more than six months following stent implantation, balloon angioplasty (BA), and directional atherectomy (DCA).

BACKGROUND

Catheter-based coronary interventions are associated with extensive arterial injury. Endothelial function has been shown to remain chronically abnormal after vascular injury. The long-term effects of different percutaneous coronary interventions on endothelial function are not known.

METHODS

Thirty-nine patients treated at least six months earlier with a coronary intervention for isolated proximal left anterior descending (LAD) stenosis, with no evidence of restenosis, were studied. Twelve patients had been stented, 15 had been treated with BA, and 12 had undergone DCA. Changes in diameter of the intervened LAD, and the unintervened circumflex coronary artery (Cx), in response to intracoronary acetylcholine infusions were assessed by quantitative angiography.

RESULTS

The groups had similar angiographic characteristics and risk factors for endothelial dysfunction. The LAD constricted significantly more (p = 0.02) in previously stented patients (-21.8+/-4.3%), as compared to patients previously treated with BA (-9.5+/-2.8%) or with DCA (-9.1+/-3.6%). In contrast, acetylcholine infusion resulted in mild constriction in the Cx, which was similar in the three groups (p = 0.47). By multiple regression analysis, previous implant of a stent was the only significant predictor of LAD constriction (p = 0.008).

CONCLUSIONS

More severe endothelial dysfunction was observed long term after stenting as compared to BA or DCA. These findings may have implications with respect to the progression of atherosclerosis in coronary arteries subjected to percutaneous interventions.

Influence of the endothelium, nitric oxide and serotonergic receptors on coronary vasomotor responses evoked by ergonovine in conscious dogs

1. The respective contributions of coronary vascular endothelium, nitric oxide (NO) and serotonergic receptors to the effects of ergonovine on large and small coronary arteries were investigated in conscious dogs. 2. In seven dogs with an endothelium intact, ergonovine (30 - 1000 microg, i.v.) induced a biphasic response on large coronary artery with an early and transient vasodilatation (up to +2.9+/-0.5% from 3310+/-160 microm, P<0.01) followed by a sustained vasoconstriction (down to -4.9+/-0.5%, P<0.001) which occurred simultaneously with a sustained increase in coronary blood flow (CBF) (up to +100+/-26% from 28+/-4 ml min(-1), P<0.001). After endothelium removal (balloon angioplasty), the ergonovine-induced vasodilatation was abolished and vasoconstriction potentiated (-6.4+/-0.9% after vs -4.9+/-0.5% before endothelium removal, P<0.01). 3. After blockade of NO synthesis by Nomega-nitro-L-arginine (30 mg kg(-1)) in four other dogs, the early vasodilatation induced by ergonovine was abolished but the delayed vasoconstriction as well as the increase in CBF remained unchanged. 4. Both ketanserin and methiothepin (0.3 mg kg(-1)) abolished the early vasodilatation and reduced the delayed vasoconstriction induced by ergonovine. Ketanserin decreased and methiothepin abolished the reduction in coronary resistance induced by ergonovine. 5. Thus, the complex interactions between vascular endothelium and serotonergic receptors to ergonovine-induced constriction of large coronary arteries might explain the induction of coronary spasms in patients with endothelial dysfunction.

Long-term endothelial dysfunction is more pronounced after stenting than after balloon angioplasty in porcine coronary arteries

OBJECTIVE

To compare percutaneous transluminal coronary angioplasty (PTCA) and stent implantation with respect to the long-term changes they induce in the newly formed endothelium in porcine coronary arteries by studying both morphological and functional parameters of the endothelium at 2 weeks and 3 months after intervention.

BACKGROUND

Problems affecting PTCA or stent implantation have been overcome to a large extent by means of better techniques and the availability of new drugs. Late problems, however, still exist in that restenosis affects a large number of patients. With an increasing number of patients being treated with stents, the problem of in-stent restenosis is of even greater concern, as this seems difficult to treat. A functional endothelial lining is thought to be important in controlling the growth of the underlying vascular tissue. We hypothesized that the enhanced neointimal hyperplasia observed after stenting is associated with a more pronounced and prolonged endothelial dysfunction.

METHODS

Arteries were analyzed using a dye-exclusion test and planimetry of permeable areas. Thereafter, the arteries were processed for light and scanning electron microscopy for assessment of morphology and proliferative response.

RESULTS

Leakage of the endothelium for molecules such as Evans blue-albumin as well as prolonged endothelial proliferation is observed as late as 3 months after the intervention, and is more pronounced after stenting. Permeability is associated with distinct morphologic characteristics: endothelial retraction, the expression of surface folds, and the adhesion of leukocytes.

CONCLUSIONS

Stenting especially decreases long-term vascular integrity with respect to permeability and endothelial proliferation, and is associated with distinct morphologic characteristics.

Altered endothelial and smooth muscle cell reactivity caused by University of Wisconsin preservation solution in human saphenous vein

PURPOSE

We have investigated the effect of University of Wisconsin (UW) solution at different temperatures on endothelial and smooth muscle cell function of the human saphenous vein to define the efficacy of UW solution as a preservation solution for saphenous vein conduits.

METHODS

Saphenous vein segments from 38 patients undergoing coronary artery bypass surgery were examined with an isolated organ bath technique to monitor changes in vessel reactivity.

RESULTS

Endothelial-dependent relaxations to acetylcholine were attenuated after incubation in UW solution at both 4 degrees C and 28 degrees C (p < 0.05, n = 10). In contrast, relaxations to sodium nitroprusside were unchanged after incubation in UW solution at both temperatures (n = 8). The responses to 90 mmol/L KCl were increased at both 4 degrees C and 28 degrees C, respectively. Tyrode's: 27.2% +/- 3.1% and 23.8% +/- 3.0%, UW: 64.7% +/- 8.0% and 73.1% +/- 11% (p < 0.001). In addition, the responses to 5-HT were enhanced at 4 degrees C and 28 degrees C (p < 0.05). In contrast, responses to noradrenaline were enhanced only at 28 degrees C compared with the responses after incubations in Tyrode's solution (p < 0.05, n = 6). Furthermore U46619 (0.3 nmol/L to 1 nmol/L) responses were augmented at 4 degrees C (p < 0.05, n = 7). The potency (pD2) values for each agonist were not significantly different after incubations in UW solution.

CONCLUSIONS

We conclude that UW solution produces attenuation of acetylcholine relaxations and temperature-dependent increased reactivity of smooth-muscle cell function in the isolated human saphenous vein. These studies document the complex interactions brought about by UW solution on the different components of the vascular wall that need to be elucidated further if this solution is to attain a place in vascular preservation.

Augmented endothelium-dependent constriction to hypoxia early and late following reperfusion of the canine coronary artery

1. Canine coronary arteries with intact endothelium respond to hypoxaemia or serotonin infusion with dilatation, but when the endothelium is injured or dysfunctional, these stimuli can cause constriction. The present studies investigated whether or not regional ischaemia and reperfusion alter endothelium-dependent responsiveness of canine coronary arteries in vivo and in vitro. 2. In organ chamber experiments, isolated control and reperfused coronary artery rings were contracted with prostaglandin F2 alpha and exposed to hypoxia (PO2 less than 5 mmHg). 3. Hypoxia augmented the response of reperfused arteries more than that of controls. The hypoxic augmentation was blocked by NG-monomethyl-L-arginine, an inhibitor of nitric oxide synthesis from L-arginine. 4. These findings demonstrate that early following coronary reperfusion the hypoxic augmentation, which is mediated by a nitric oxide-dependent pathway in the endothelium, is facilitated. 5. In vivo studies revealed hyperconstriction of reperfused arteries in response to hypoxaemia (PO2 = 30-40 mmHg) and administration of either serotonin or ergonovine. 6. Twelve weeks following reperfusion injury, coronary arteries still exhibited augmented endothelium-dependent hypoxic augmentations in vitro, which were inhibited by NG-monomethyl-L-arginine. 7. Furthermore, resting coronary segments with endothelium displayed hypoxia-induced contractions that could not be inhibited by indomethacin, the lipoxygenase inhibitor AA861, superoxide dismutase plus catalase, deferoxamine, ouabain, or NG-monomethyl-L-arginine. 8. These endothelium-dependent hypoxic response may play a role in the pathogenesis of hyperconstriction (vasospasm) following coronary reperfusion.

Mechanisms of ergonovine-induced hyperconstriction of coronary artery after x-ray irradiation in pigs

Mechanisms of ergonovine-induced coronary hyperconstriction were examined in vivo and in vitro in miniature pigs. To provoke coronary hyperconstriction, the endothelium of a segment of a major branch of the left coronary artery was denuded in 19 Göttingen miniature pigs (4 to 6 months of age). In Group I (n = 12), the denuded site of the coronary artery was selectively irradiated with 15Gy of x-ray twice, 3 and 4 months after endothelial denudation. The remaining 7 pigs were not irradiated (Group II). The vasoconstrictive effect of intracoronary administration of ergonovine (1 to 1000 microgram) was examined angiographically 3 months (just before irradiation in group I) and 5 months after denudation in the two groups. After the angiographical study, the vessels were isolated and isometric tensions were measured in an organ chamber. In the in vivo studies, ergonovine-induced vasoconstriction at the denuded and x-ray irradiated site in Group I was significantly greater than that at the control site or that at the denuded site in Group II. Pretreatments with serotonin receptor blockers (ketanserin or methysergide) significantly attenuated ergonovine-induced hyperconstriction, while an alpha-adrenergic receptor blocker (prazosin) did not (% inhibition; ketanserin 74 +/- 9%, p < 0.01, methysergide 60 +/- 10%, p < 0.01, prazosin 9 +/- 5%, NS). In the in vitro studies, ergonovine produced significantly greater tension at the denuded and x-ray irradiated site (Group I) than at the control site or at the denuded site (Group II). Ergonovine-induced endothelium-dependent relaxation was impaired at the denuded site in both groups to a similar extent. These results suggest that ergonovine-induced hyperconstriction at the denuded and x-ray irradiated coronary artery resulted mainly from the hyperreactivity of medial smooth muscle mediated by serotonin receptors.

The endothelium: a key to the future

The vascular endothelium is a complex modulator of a variety of biological systems and may well be the key to definitive success in the treatment of cardiovascular disorders. Surgically-induced endothelial injury may occur preoperatively during cardiac catheterization and intraoperatively from mechanical manipulation, ischemia, hypothermia, and exposure to cardioplegic solutions. The normal endothelium is antithrombogenic and yet promotes platelet aggregation and coagulation if injured. Vasospasm, occlusive intimal hyperplasia, and accelerated arteriosclerosis can also all occur as a result of endothelial injury. Furthermore, endothelial injury is harmful even in the absence of disruption of its monolayer integrity. Thus, preservation of the endothelium should be an additional objective for all cardiovascular surgeons. Synthetic vascular grafts, cardiac valves, and artificial ventricles do not spontaneously endothelialize and thus usually require some form of anticoagulation to maintain patency. Hence, endothelialization of prosthetic implants became an attractive concept. A number of different methods of obtaining an endothelial lining of prosthetic material has since been developed; these include facilitated endothelial cell migration, and endothelial cell seeding by using either venous or microvascular endothelial cells. Manipulating the endothelium might well provide the next major advancement for therapeutic and preventive measures for cardiovascular disease.

Removal of venous endothelium with air

Much research on the activity and half-life of endothelium-derived substances has entailed the removal of endothelium from arteries by mechanical or enzymatic processes. It has been observed that the technique used for the removal of arterial endothelium may profoundly affect smooth muscle function and release of prostanoids by the vessel wall. The function and patterns of regeneration of arterial endothelium have been extensively described, but there is a relative paucity of information about the venous endothelium, due in part to the difficulty of its removal. We developed a technique for removal of the endothelium of rabbit femoral veins by passing a stream of air through the lumen of the vessel to dry and remove the endothelium. The effectiveness of endothelium removal was verified by the lack of in vitro reactivity to endothelium-dependent relaxing substances, examination of frozen sections of vessels, labeled with fluorescent-tagged acetylated low-density lipoprotein, with fluorescent light microscopy and scanning electron microscopy of vessel segments. Air drying effectively removed the endothelium and abolished mechanical responses to endothelium-dependent vasodilators but did not affect the function of the smooth muscle. We propose the use of air to remove endothelium from veins to be used to study endothelium-derived factors since this method achieves complete removal of endothelium without causing detectable damage (morphological or functional) to the remainder of the vessel wall.

Platelet-leukocyte-endothelial interactions in coronary artery disease

It is generally recognized that formation of a platelet-fibrin-rich thrombus in an atherosclerotic coronary artery is the basis of unstable angina and acute myocardial infarction. Platelet hyperactivity has been identified in coronary risk factors such as hyperlipidemia and diabetes mellitus. Persistent activation of these cells results in release of growth factors that may contribute to the progression of atherosclerosis. Several recent studies show that endothelium, by generating or metabolizing a host of vasoactive substances, plays a critical role in the modulation of vascular tone. Important among these substances are prostacyclin (PGI2) and endothelium-derived relaxing factor (EDRF). The endothelium-dependent modulation of coronary artery tone correlates with the severity of atherosclerosis and the number of coronary risk factors. Procedures such as angioplasty and coronary bypass surgery injure the endothelium. The loss of endothelial smooth muscle relaxant function may contribute to the vasoconstriction and thrombosis often observed soon after these procedures. Thrombolysis (and subsequent reperfusion of the coronary artery) is also associated with severe endothelial dysfunction, with a resulting vasoconstrictor influence on the coronary vascular bed. Activation of leukocytes and their presence in the reperfused myocardium contribute to progression of myocardial injury by release of oxygen free radicals and proteolytic enzymes. Thus, it seems that a perturbation in this delicate equilibrium in cellular interactions relates to genesis and progression of myocardial ischemia.

Oversensitivity to serotonin of the collateralized vascular bed in rat hindquarters: mechanisms of increased vasoconstriction

A buffered solution was perfused at a constant flow rate (2 ml/min) through both iliac arteries in rat hindquarters. Perfusion pressures were measured in normal and collateralized vascular beds of the left and right hind-leg, respectively. Bolus injections of various agonists produced concentration-dependent increases in perfusion pressure in both collateralized and normal circulatory beds. Serotonin, in particular, and noradrenaline, to a lesser extent, produced more pronounced vasoconstriction on the collateral side than on the normal side. The difference in vasoreactivity to serotonin was related to a difference in both vascular structure and sensitivity of both types of vascular bed. Vasoconstriction induced by serotonin was inhibited by 5-HT2 antagonists. Selective blockade of alpha 1,alpha 2,beta 1-beta 2 adrenoceptors and amine uptake blockade were ineffective. This study indicates that, in rat hind-legs, the collateralized vascular bed is superreactive to serotonin in comparison with the normal bed. This resetting of reactivity to serotonin is due to the specific vascular structure as well as to an increased 5-HT2 receptor-mediated sensitivity.

Impaired tissue perfusion after inhibition of endothelium-derived nitric oxide

The effects of a blockade of the action or synthesis of endothelium-derived nitric oxide (EDRF) on vascular resistance and reactivity, platelet cGMP and tissue oxygenation were studied. Experiments were performed in isolated perfused rabbit hearts as well as in rabbit hindlimbs in vivo. In isolated hearts, perfusion with hemoglobin (6 microM) or NG-nitro-L-arginine (30 microM) significantly increased vascular resistance. The cGMP level in platelets passing through the coronary bed was found to be more than 50% lower than with intact EDRF production. EDRF inhibition also resulted in a reduced peak reactive hyperemia, an enhanced reactive vasoconstriction after a rapid increase in perfusion pressure (myogenic response), and in abolition of flow-dependent dilation of coronary resistance vessels. In rabbit hindlimbs, local blockade of EDRF-mediated dilations by gossypol resulted also in an increased vascular resistance and abolition of the increase in platelet cGMP induced by intraarterial infusion of acetylcholine. In addition, the oxygen uptake of the hindlimb (-46%) and the skeletal muscle pO2 were significantly reduced. It is concluded that continuously released EDRF has a functional role in maintaining adequate tissue perfusion and oxygen supply. Furthermore, the adaption of the vascular bed to rapid changes in flow and pressure is impaired after inhibition of EDRF.

Endothelium-derived relaxing factor and coronary vasospasm

The endothelium releases the powerful vasodilator and antiaggregatory substance, EDRF, both under basal conditions and upon stimulation by a wide variety of agents. Endothelial injury or dysfunction may play an important role in the spasmogenicity of the coronary artery, although other possible alterations related to atherosclerosis should also be considered. Among the possible stimuli, aggregating platelets are important as a source of vasoconstrictor substances. The endothelium may also produce the vasoactive substances EDHF and EDCF(s). Their pathophysiologic significance remains to be determined.