Time course and extent of recovery of endothelium-dependent contractions and relaxations after direct arterial injury

Effects of Catheterization on Artery Function and Health: When Should Patients Start Exercising Following Their Coronary Intervention?

Coronary artery disease (CAD) is a leading cause of death worldwide, and percutaneous transluminal coronary angiography (PTCA) and/or percutaneous coronary intervention (PCI; angioplasty) are commonly used to diagnose and/or treat the obstructed coronaries. Exercise-based rehabilitation is recommended for all CAD patients; however, most guidelines do not specify when exercise training should commence following PTCA and/or PCI. Catheterization can result in arterial dysfunction and acute injury, and given the fact that exercise, particularly at higher intensities, is associated with elevated inflammatory and oxidative stress, endothelial dysfunction and a pro-thrombotic milieu, performing exercise post-PTCA/PCI may transiently elevate the risk of cardiac events. This review aims to summarize extant literature relating to the impacts of coronary interventions on arterial function, including the time-course of recovery and the potential deleterious and/or beneficial impacts of acute versus long-term exercise. The current literature suggests that arterial dysfunction induced by catheterization recovers 4-12 weeks following catheterization. This review proposes that a period of relative arterial vulnerability may exist and exercise during this period may contribute to elevated event susceptibility. We therefore suggest that CAD patients start an exercise training programme between 2 and 4 weeks post-PCI, recognizing that the literature suggest there is a 'grey area' for functional recovery between 2 and 12 weeks post-catheterization. The timing of exercise onset should take into consideration the individual characteristics of patients (age, severity of disease, comorbidities) and the intensity, frequency and duration of the exercise prescription.

Post-catheterisation arterial thrombosis in children--pathophysiology, prevention, and treatment

Lower limb ischaemia is the most frequent complication of cardiac catheterisation in children. It is often overlooked, but it can cause significant disability and may limit arterial access sites to repeat diagnostic or interventional catheterisations. A narrative review of the literature on arterial access site thrombosis in children was carried out with a special focus on current evidence that supports preventive and treatment strategies. Anticoagulation, thrombolysis, and thrombectomy have been used successfully to treat arterial access site thrombosis. However, it is not completely established which is the role of each treatment modality and what is the most appropriate timing to deliver it. Therefore, diagnostic and therapeutic strategies have to be prospectively investigated, particularly for clarifying the role of new pharmacologic interventions and of percutaneous and surgical thrombectomy in the current era.

Cyclosporin effect on noradrenaline release from the sympathetic nervous endings of rat aorta

Arterial hypertension is one of the main side effects of cyclosporin treatment and seems to be due to activation of the sympathetic nervous system. Some authors hypothesized that cyclosporin may act on the sympathetic nervous endings increasing catecholamine release, in agreement with our previous works which demonstrated an increase in rat plasma catecholamine levels after 30 mg/kg per day cyclosporin treatment for 7 weeks. Therefore, the aim of this work was to study the cyclosporin mechanism responsible for that increase in plasma catecholamines. Male Wistar rats were used. Noradrenaline release was performed in vitro experiments after loading rat aorta abdominal segments with 3H-noradrenaline (3H-NA). The release of 3H-NA was measured after electrical stimulation in the presence of 10(-6)M cyclosporin. In another set of experiments electrical stimulation was replaced by a pulse addition of cyclosporin (10(-6)M). Another group of rats was treated with 30 mg/kg per day cyclosporin for 7 weeks and catecholamine contents in aorta abdominal segments and adrenals were measured by high performance liquid chromatography system with electrochemical detection (HPLC-ECD). An increase in the 3H-NA release was observed in both types of in vitro experiments. Since cocaine abolished these cyclosporin effects, the obtained results suggest that cyclosporin may act on the catecholamine transporter across the membrane. In addition, after the 7 weeks of cyclosporin treatment, a significant decrease in catecholamine aorta contents was verified but in adrenals there was no difference regarding to controls. However, the dopamine synthesis/degradation ratio measured by the DA/DOPAC ratio suggests an increase in dopamine synthesis. These facts are in agreement with the enhanced plasma catecholamine levels and with the hypothesis of tissue catecholamine depletion. However, they do not explain the increase in plasma adrenaline levels, since adrenaline is a reflex of adrenal activity. The synthesized dopamine in adrenals seems to be unable to reach vesicles and to be metabolized in adrenaline. The observed decrease in HVA adrenal levels may be a consequence of extraneuronal uptake inhibition or inhibition by cyclosporin of the direct o-methylation of DOPAC. In conclusion, our results suggest that cyclosporin increases catecholamine release from the sympathetic nervous endings by a tyramine-like effect, i.e. by acting directly on the catecholamine transporter of the membrane.

Acutely sodded expanded polytetrafluoroethylene grafts produce only prostacyclin: a qualitative difference from saphenous veins

Select subsets of patients require prosthetic graft material for revascularization. Although arterial prosthetic grafts of large caliber perform acceptably, grafts of <6 mm exhibit a high attrition rate. Microvessel endothelial sodding, a method resulting in the lining of prosthetic grafts with autologous endothelium, improves graft patency; however, aggressive antiplatelet therapy is still required, because terminating an antiplatelet regimen accelerates graft attrition. The present investigation was designed to address the acute production of vasoactive substances in microvessel endothelial cell sodded expanded polytetrafluoroethylene (ePTFE) grafts in an attempt to delineate a possible mechanism behind the continued requirement for antiplatelet therapy. Equal lengths of acutely sodded ePTFE grafts (canine falciform ligament source) and saphenous veins (SV) (canine source) were evaluated by superfusion bioassay. Basal secretion from ePTFE grafts relaxed the biodetector ring 1 +/- 3%, whereas SV relaxed the ring 10 +/- 3% (p < 0.05, ePTFE vs. SV). Relaxation with acetylcholine stimulation was 49 +/- 7% in grafts and 50 +/- 10% in veins (p = NS). Calcium ionophore stimulation produced relaxation of 37 +/- 9% from ePTFE grafts and 100 +/- 23% from SV (p < 0.05). Indomethacin added to perfusate reduced relaxations from sodded ePTFE grafts to 20.2 +/- 9.2% with acetylcholine stimulation and 12.5 +/- 4.3% with calcium ionophore (p < 0.05 vs. control); addition of N(G)-monomethyl-L-arginine (L-NMMA) had no effect on the release of vasoactive substances from ePTFE grafts. In contrast, relaxations of effluent from SV stimulated by acetylcholine and calcium ionophore were significantly attenuated with indomethacin and L-NMMA (p < 0.05 vs. control). Scanning electron microscopy demonstrated confluent endothelium in SV and a nonconfluent endothelial cell layer in grafts. Acutely sodded ePTFE grafts produce vasoactive substances that quantitatively and qualitatively differ from those produced by canine SV. The ePTFE grafts produce mainly prostanoids, whereas SV produce both nitric oxide and prostanoids. The endothelial cell isolation procedure and absence of immediate graft luminal confluence may contribute to the observed differences.

Nonpenetrating stapling: a valuable alternative for coronary anastomoses?

BACKGROUND

The safe development of minimally invasive coronary artery bypass operations might require alternatives to conventional suture-based anastomotic techniques. In this setting, nonpenetrating stapling is an attractive option because of its simplicity of use and potential for improved endothelial preservation.

METHODS AND RESULTS

In the experimental part of this study, porcine internal mammary arteries were anastomosed to left anterior descending coronary arteries using either an 8-0 polypropylene running suture or nonpenetrating microclips (7 anastomoses in each group). The endothelium-dependent relaxations to bradykinin of the arterial rings bearing the anastomosis and of noninstrumented rings were compared in organ chamber experiments. There were no significant differences in maximal relaxations (mean +/- SEM) between the microclipped and sutured anastomoses (81%+/-7% versus 74%+/-10%), which were both significantly lower than those of control coronary rings (98%+/-2%, p = 0.001 versus the two anastomosed groups). Histologic examination showed a comparable preservation of the coronary and graft endothelium with both techniques. The clinical part of the study comprised 7 patients in whom the left internal mammary artery was conventionally sutured to the left anterior descending whereas 13 saphenous vein grafts were anastomosed to their target vessels by nonpenetrating staples. There were no clip-related complications. An angiographic assessment of the venous grafts was performed within 10 days postoperatively in all patients. One graft is presumably occluded. The 12 remaining conduits were patent with stapled anastomoses featuring a widely open "shark-mouth" configuration.

CONCLUSIONS

These preliminary data suggest that non-penetrating stapling is an easy-to-use technique that competes well with conventional suturing, at least in terms of immediate results. Further studies are warranted to better define its potential place within the armamentarium of minimally invasive coronary artery bypass techniques.

Effects of cardioplegic solutions on the vasoreactivity of the internal mammary artery

BACKGROUND

During free internal mammary artery grafting, cardioplegia administration can be performed through the internal mammary artery. The present study examined whether cardioplegic solutions produce arterial graft constriction and functional endothelial damage.

METHODS

Forty internal mammary artery segments from 10 patients were incubated in Krebs solution (n=10), University of Wisconsin solution (n=10), Broussais Hospital solution (n=10), or blood cardioplegia (n=10).

RESULTS

There was a significant difference in sensitivity to norepinephrine between segments in Krebs solution and those in University of Wisconsin solution or Broussais Hospital solution but not segments in blood cardioplegia. There was a significant difference in relaxation to acetylcholine between segments in Krebs solution and those in the three other cardioplegic solutions and between those in blood cardioplegia and segments in University of Wisconsin solution or Broussais Hospital solution. There was no significant difference in relaxation to sodium nitroprusside between segments in any of the solutions.

CONCLUSIONS

These experiments suggest that storage in the different cardioplegic solutions studied does not preserve the initial vasoreactivity of the internal mammary artery. However, blood cardioplegia appears to be less deleterious in regard to endothelial and myogenic vascular function.

Loss of arterial dilation in the reendothelialized area of the flow-loaded rat common carotid artery

We have investigated regenerated endothelial cells and their possible contribution to arterial dilation in response to increased blood flow in rat common carotid artery (CCA). After endothelial denudation using a balloon catheter in the left CCA, an arteriovenous shunt was constructed between the left CCA and the left external jugular vein at 20 mm distal from the orifice in the denuded group. Animals that were given the arteriovenous shunt without denudation were used to form the nondenuded group. The blood flow rate in the left CCA was increased by sixfold after operation in the denuded group. We observed that endothelial cells were gradually regenerated from the orifice to the distal area and that the reendothelialized area after 4 to 8 weeks was approximately one third of the left CCA (5.31 +/- 1.49 mm at 4 weeks, 5.47 +/- 1.56 mm at 8 weeks). In the reendothelialized area of the left CCA after 4 to 8 weeks, the lumen diameter was significantly smaller than that of the nondenuded group and showed no significant difference from age-matched nonsurgical animals. The intimal and medial thickening, which would result in arterial stenosis in the reendothelialized area, was not observed in the denuded group, although the denuded control showed significant intimal thickening. From these results, we conclude that regenerated endothelial cells reduce intimal thickening but do not respond to increased blood flow to dilate the artery.

Continuous antegrade warm blood cardioplegia attenuates augmented coronary endothelium-dependent contraction after cardiac global ischemia and reperfusion

BACKGROUND

Experiments were designed to evaluate the effect of warm blood cardioplegia on endothelium-dependent contraction of the coronary endothelium after cardiac global ischemia and reperfusion.

METHOD

Dogs (n = 12 in each group) were exposed to extracorporeal circulation with the body temperature at 37 degrees C (group 1) or 28 degrees C (groups 2 and 3). The ascending aorta was crossclamped for 120 minutes while continuous infusion of warm blood cardioplegec solution (group 1) or intermittent infusion of cold (4 degrees C) crystalloid cardioplegic solution (group 2) was performed via the coronary arteries through the aortic root. Cardioplegic solution was not used in group 3 animals. The heart was then allowed to function for 60 minutes of reperfusion. Reperfused (groups 1, 2, and 3) and control (group 4) coronary arteries were then harvested for study.

RESULTS

Perfusate hypoxia caused endothelium-dependent contraction in the arteries of all four groups that could be attenuated by NG-monomethyl-L-arginine (L-NMMA) or L-NMMA plus D-arginine, but not by L-NMMA plus L-arginine or endothelin receptor A and B antagonist PD 145065. The endothelium-dependent contraction results in groups 2 and 3 (75% +/- 4% and 80% +/- 5%, respectively) were significantly greater than those in groups 1 and 4 (15% +/- 3% and 18% +/- 5%, respectively). Scanning electron microscope studies showed that platelet adhesion and aggregation, areas of microthrombi, disruption of endothelial cells, and separation of the intercellular junction could be found in coronary segments from groups 2 and 3, but not in vessels from groups 1 and 4.

CONCLUSION

These experiments suggest that global ischemia and reperfusion enhances hypoxia-mediated endothelium-dependent contraction of the coronary endothelium and damages the ultrastructure. These kinds of changes can be prevented by continuous antegrade infusion of warm blood cardioplegic solution during global ischemia.

Endothelial effects of hemostatic devices for continuous cardioplegia or minimally invasive operations

BACKGROUND

Improvements in myocardial protection may include the continuous delivery of normothermic blood cardioplegia. Technical aids are required for optimal visualization of the operative field during the performance of coronary anastomoses if cardioplegia is to be given continuously or during minimally invasive operations. However, the effects of the different hemostatic devices on coronary endothelial function are unknown.

METHODS

We compared the effects on endothelial function of two commonly used hemostatic techniques, coronary clamping and gas jet insufflation, with those of a technique using extravascular balloon occlusion to mimic systolic luminal closure by the surrounding myocardium. The three techniques were applied for 15 minutes on porcine epicardial coronary arteries from explanted hearts. For coronary clamping, standard bulldog clamps were used. Gas jet insufflation was applied by blowing oxygen (12 L/min) tangentially at a 45-degree angle 1 cm away from a 3-mm arteriotomy. Extravascular balloon occlusion was achieved with a needle-tipped silicone loop, the midportion of which, once positioned beneath the coronary artery, was inflated to push a myocardial "cushion" against the back of the vessel until its occlusion. Control rings were taken from the same coronary artery. The endothelial function of control and instrumented arterial rings was then studied in organ chambers filled with modified Krebs-Ringer bicarbonate solution.

RESULTS

Contractions to potassium chloride and prostaglandin F2 alpha and endothelium-independent relaxation to sin-1, a nitric oxide donor, were unaffected in all groups. Endothelium-dependent relaxation to serotonin was impaired after clamping and preserved after gas jet insufflation and extravascular balloon occlusion. Maximal endothelium-dependent relaxation to serotonin was as follows: for coronary clamping, 63% +/- 6% versus 87% +/- 3% in controls; for gas jet insufflation, 67% +/- 12% versus 88% +/- 7%; and for extraluminal balloon occlusion, 79% +/- 6% versus 85% +/- 5%.

CONCLUSIONS

Whereas commonly used hemostatic devices may impair endothelial function, extravascular balloon occlusion appears to achieve effective hemostasis while preserving endothelial integrity.

Perfadex is superior to Euro-Collins solution regarding 24-hour preservation of vascular function

BACKGROUND

The aim of this study was to compare Perfadex with Euro-Collins solution regarding 24-hour preservation of endothelium-dependent relaxation and vascular smooth muscle function.

METHODS

The infrarenal aorta of 72 isogenic rats was studied in organ baths as fresh controls, after 24 hours of cold (4 degrees C) storage, and after 24-hour storage followed by transplantation and examination after 7 or 30 days. The thromboxane A2 analogue U-46619 was used to test contractility. Acetylcholine chloride was used to elicit endothelium-dependent relaxation and papaverine hydrochloride, to elicit endothelium-independent relaxation.

RESULTS

With both solutions, all grafts were patent after 7 and 30 days. Vessels preserved in Euro-Collins solution for 24 hours lost 95% (p < 0.001) of their contractility compared with fresh controls; 7 days after transplantation, they had regained 40% of initial contractility, and after 30 days, there was no significant decrease in contractility. Vessels preserved in Perfadex manifested no significant decrease in contractility at any time. Endothelium-dependent relaxation could not be evaluated in vessels stored for 24 hours in Euro-Collins solution because they had lost almost all contractility; 7 days after transplantation, endothelium-dependent relaxation was reduced by 65% (p < 0.001), but at 30 days after transplantation, there was no significant decrease in endothelium-dependent relaxation. Vessels preserved in Perfadex for 24 hours lost 17% (p < 0.05) of endothelium-dependent relaxation, but 7 and 30 days after transplantation, there was no significant decrease in endothelium-dependent relaxation.

CONCLUSIONS

Perfadex, but not Euro-Collins solution, has the capacity to preserve vascular function after 24 hours of storage followed by in vivo reperfusion.

Extracellular and standard University of Wisconsin solutions provide equivalent preservation of myocardial function

The deleterious effect of hyperkalemic cardioplegic solutions on coronary endothelium has been documented and has also been demonstrated with University of Wisconsin solution. We evaluated a new extracellular University of Wisconsin formulation for efficacy in heart preservation. Six neonatal piglet hearts were arrested with and stored in the standard intracellular University of Wisconsin solution (group 1: K+ 125 mEq/L, Na+ 29 mEq/L). Six piglet hearts were preserved for 24 hours with an extracellular University of Wisconsin solution that differed only in the concentrations of potassium and sodium (group 2: K+ 25 mEq/L, Na+ 129 mEq/L). Hearts underwent modified reperfusion with leukocyte-depleted aspartate-glutamate enriched blood cardioplegic solution followed by conversion to a left-sided working mode on a Langendorff circuit with perfusion from a support pig. Stroke work index was calculated at left ventricular end-diastolic pressures of 3, 6, 9, and 12 mm Hg. Sixty minutes after reperfusion, there was no significant difference in stroke work index between group 1 (16.4 +/- 1.9 x 1000 erg/gm) and group 2 (15.3 +/- 2.7 x 1000 erg/gm). There was also no significant difference in high-energy phosphate stores or myocardial water content between the two groups. Extracellular University of Wisconsin solution provides myocardial preservation equivalent to standard University of Wisconsin solution while preventing exposure of coronary endothelium to high levels of potassium, which justifies its use in clinical heart transplantation.

Human mammary artery endothelial sparing with fibrous jaw clamping

BACKGROUND

Temporary clamping of the internal mammary artery pedicle is required for visualization during coronary artery bypass grafting. A nylon fibril jaw surface has been developed for these clamps that exerts pressure only at discrete sites on the pedicle surface. The effect of this new jaw surface on endothelial cell function and integrity after compression is investigated in this study.

METHODS

Internal mammary artery specimens from 10 patients each were divided into three separate rings, and two of these rings were clamped for 30 minutes with either a smooth or fibrous jaw clamp. Isometric tensions were measured in organ chambers after contraction by relaxing the rings with the endothelium-dependent agent acetylcholine followed by the endothelium-independent agent sodium nitroprusside. The intimal surfaces of similar rings were silver stained to assess the percentage of intact endothelium.

RESULTS

Endothelium-dependent relaxation was spared after fibrous jaw clamping (75% versus 89%) but significantly impaired after smooth jaw clamping (25% versus 89%; p < 0.001). Endothelium-independent relaxation was unaffected by either intervention. The percentage of remaining intact endothelium upon silver staining was significantly less after smooth than after fibrous jaw clamping (24% versus 48%; p < 0.01).

CONCLUSIONS

Foam silicone with nylon fibrils on the jaw surface of internal mammary artery clamps preserves endothelial cell function and integrity. The remaining undamaged cells also may facilitate the subsequent regeneration of a confluent endothelial cell layer.

Angioplasty reduces pharmacologically mediated vasoconstriction in rabbit carotid arteries with and without vasospasm

BACKGROUND AND PURPOSE

We tested the hypothesis that vasospastic arteries do not reconstrict after angioplasty because angioplasty decreases smooth muscle contractility.

METHODS

Twenty-four rabbits had carotid angiography and placement of silicone elastomer sheaths around both carotid arteries in the neck. Sheaths were empty (control groups) or filled with clotted blood (vasospasm groups). Angiography was repeated 2 days later, and one carotid artery was dilated with a balloon catheter. Animals were killed 1, 5, or 28 days after angioplasty, and the carotid arteries were studied pharmacologically under isometric tension.

RESULTS

Before angioplasty, there was significant vasospasm in the vasospasm groups but not in the control groups (P < .05, ANOVA). Angioplasty produced significant, long-lasting dilation of arteries in the vasospasm groups. One and 5 days after angioplasty, arteries from control and vasospasm groups that had angioplasty had significantly reduced contractions to serotonin, KCl, and caffeine compared with arteries not subjected to angioplasty. Twenty-eight days after angioplasty, contractions were reduced in arteries subjected to vasospasm compared with controls, but there were no differences between arteries with or without angioplasty. At all times after angioplasty, vasospasm significantly decreased acetylcholine-induced relaxations of arteries contracted with serotonin. Relaxations were further decreased by angioplasty in the vasospasm group 1 day after angioplasty. Arterial wall compliance was significantly decreased in the vasospasm and control groups at all times after angioplasty, although there were no significant differences between arteries with and without angioplasty.

CONCLUSIONS

These results suggest that arteries do not reconstrict after angioplasty because angioplasty decreases smooth muscle contractility. There was no evidence that angioplasty disrupted the arterial wall matrix, as judged by the lack of increase in arterial wall compliance after angioplasty.

Improved long-term preservation of the coronary vasculature with University of Wisconsin solution

Experiments were designed to investigate coronary vascular function after prolonged cold storage of isolated rat hearts, using University of Wisconsin (UW) solution. Hearts perfused with crystalloid cardioplegic solution (Plegisol) were used as controls. After perfusion with 10 ml at 4 degrees C, hearts were stored for 1 or 10 hours in the respective solutions at 4 degrees C. To evaluate coronary vascular function after perfusion and storage, endothelium-dependent vasodilation was induced with 5-hydroxytryptamine (5-HT) and smooth muscle-dependent dilation with nitroglycerin (GTN). After perfusion only, or perfusion plus 1-hour storage, there was no intergroup difference in response to 5-HT and GTN. After 10-hour storage the vasodilatory response to 5-HT was abolished in the Plegisol group and slight vaso-constriction was observed, whereas in the UW group the vasodilatory effect of 5-HT persisted. The findings suggest that UW solution may be more favorable for prolonged cardiac preservation, as the coronary vascular reactivity was less affected.

Endothelium-dependent contraction of canine coronary artery is enhanced by crystalloid cardioplegic solution

Experiments were designed to determine whether hyperkalemic crystalloid cardioplegic solution enhances endothelium-dependent contraction of coronary arteries. Segments of canine coronary arteries (n = 8 in each group) were preserved in cold (4 degrees C) crystalloid cardioplegic solution (group 1) and physiologic solution (group 2) for 60 minutes. Segments of preserved and control (group 3) coronary arteries with or without endothelium were suspended in organ chambers to measure isometric force. Perfusate hypoxia (oxygen tension 35 +/- 5 mm Hg) caused endothelium-dependent contraction in the arteries of all three groups. However, vascular segments with endothelium of group 1 exhibited hypoxic contraction (68.5% +/- 15.3% of the initial tension contracted by prostaglandin F2 alpha 2 x 10(-6) mol/L, p < 0.05) that was significantly greater than contraction of the group 2 and group 3 segments with endothelium (26.6% +/- 5.6% and 20.6 +/- 4.4%). The hypoxic contraction in arteries of group 1 could be attenuated by NG-monomethyl-L-arginine, the blocker of endothelial cell synthesis of the nitric oxide from L-arginine. The action of NG-monomethyl-L-arginine could be reversed by L-arginine but not D-arginine. Thus after preservation with cardioplegic solution, augmented endothelium-dependent contraction, occurs by L-arginine-dependent pathway, would favor coronary vasospasm after cardiac operation.

Endothelium-dependent relaxation after short-term preservation of vascular grafts

As the integrity of graft endothelium seems to be essential to successful long-term patency in coronary operations, its preservation demands the utmost care. The aim of the present study was to investigate the effects of currently used solutions on endothelium-dependent relaxation after short-term storage of vessels at room temperature or at 4 degrees C. The infrarenal rat aorta was selected for study because its use enabled standardization of the investigation, which was performed in organ baths on 672 vessel segments from 112 Sprague-Dawley rats. Stable vasoconstriction was obtained with the thromboxane analogue U-46619. Acetylcholine was used to elicit endothelium-dependent relaxation. The results obtained for vessels preserved for 2 hours were compared with those for autologous vessels studied immediately after harvesting. Vessel contractility was unaffected by the preservation solutions, except in the Ringer's acetate group, where it was reduced by 50% (p < 0.05). Endothelium-independent relaxation, tested with papaverine, was unaffected in all groups. Ringer's lactate, Krebs solution, and Perfadex (a low-potassium-dextran-glucose solution) did not significantly affect endothelium-dependent relaxation either at room temperature or at 4 degrees C, although a tendency to impaired relaxation was seen in these three groups after cold storage. Standard Ringer's solution and fresh heparinized blood each significantly reduced endothelium-dependent relaxation in vessels stored at room temperature (p < 0.05), but not in those stored at 4 degrees C. Endothelium-dependent relaxation was significantly reduced after storage in normal saline solution (p < 0.05) and in Ringer's acetate (p < 0.01), both at room temperature and at 4 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute endothelial reperfusion injury after coronary artery bypass grafting

Coronary artery endothelium exhibits functional impairment after ischemia and reperfusion. Canine left anterior descending coronary arteries were exposed to ischemia (60 minutes) followed by reperfusion (60 minutes) through a left internal mammary artery graft. In organ chamber experiments, control (left circumflex coronary artery) and reperfused (left anterior descending coronary artery) arterial segments were contracted with prostaglandin F2 alpha and exposed to hypoxia (oxygen tension = 35 +/- 5 mm Hg). Reperfused coronary rings with endothelium exhibited contractions to hypoxia that were significantly greater than contractions in control rings with endothelium (+78% +/- 8% and +14% +/- 5%, respectively; p < 0.05). This phenomenon could be blocked by NG-monomethyl-L-arginine. Electron microscopic studies showed platelet adhesion and aggregation, denudation of the endothelium and disruption of the intercellular junctions, edematous subendothelial matrix, and vesiculation of the smooth muscle cells in reperfused LAD. Swelling, vacuole formation, and loss of neurofilament occurred in the nerve fibers accompanying the vessels. These phenomena were not observed in control vessels. This study demonstrates that early after coronary artery bypass grafting, hypoxia can induce coronary vasospasm mediated by an L-arginine-dependent metabolic pathway in the endothelium. The ultrastructural changes in the coronary endothelium include platelet adhesion, aggregation, and platelet-induced contraction of coronary smooth muscle. The endothelium-dependent hypoxic coronary vasospasm and ultrastructural changes in the coronary endothelium may play an important role in the pathogenesis of myocardial ischemia and infarction after coronary artery bypass grafting.

Chronic exposure to cyclosporine affects endothelial and smooth muscle reactivity in the rat aorta

Chronic exposure to cyclosporine affects vascular reactivity. Experiments were designed to characterize the endothelium-dependent and endothelium-independent vascular reactivity of rats exposed to oral cyclosporin A (CyA). Two subsets of rats (n = 6) were treated with CyA (20 mg/kg/day) and olive oil (cyclosporine vehicle), respectively, for a period of 8 weeks. Aortic rings (4-5 mm) were suspended for isometric force measurement in organ chambers containing Krebs Ringer solution (37 degrees C, 95% O2, 5% CO2). The maximal endothelium-dependent relaxation to cumulative doses of acetylcholine was significantly decreased in the CyA-treated aortic rings compared to olive oil-treated ones (data expressed as percent of initial contraction; CyA, 50% +/- 3% versus olive oil, 37% +/- 7%; p < 0.05). However, endothelium-dependent relaxations to histamine and adenosine diphosphate and endothelium-independent relaxation to sodium nitroprusside were not affected in both groups. An endothelium-dependent contraction to serotonin and aggregating platelets were observed in the CyA group, but not in the control group. The endothelium-independent contraction to norepinephrine was enhanced in the CyA group (CyA ED50, log -7.66 +/- 0.18 mol/L versus olive oil ED50, log -7.01 +/- 0.11 mol/L; p < 0.01). These experiments suggest that chronic exposure to cyclosporine A could contribute to augmenting vascular tone by (1) decreased release of endothelial relaxing factor mediated by muscarinic receptors, (2) increased production of endothelium-related constricting factor mediated by serotoninergic receptors, and (3) greater vascular smooth muscle sensitivity to circulating catecholamine.

Magnetic resonance imaging of the iliofemoral arteries after balloon dilation angioplasty of aortic arch obstructions in children

BACKGROUND

We wished to determine the nature and incidence of changes in the iliofemoral arteries after balloon dilation angioplasty (BDA) for aortic arch obstruction in children and to determine the reliability of gradient magnetic resonance imaging (MRI) in their detection.

METHODS AND RESULTS

Sixty-three children, including 62 with and 1 without arch obstruction, underwent MRI of the iliofemoral vessels. Of these, 36 patients had undergone transfemoral BDA (7 after previous transfemoral diagnostic catheterization), 12 had undergone diagnostic transfemoral catheterization but not BDA, and 15 had no history of femoral arterial catheterization. The iliofemoral arteries were normal on MRI in all 15 children without catheterization. Among the 36 children who had undergone BDA, the ipsilateral iliofemoral artery was normal in 15, mildly narrowing in 7, and severely stenotic or occluded in 14 (39%), including 6 of 9 patients treated for acute femoral artery thrombosis and 8 with no history of femoral artery thrombosis. Two patients had documentation of progressive obstruction. Six patients had concordant conventional angiography. There was a significant correlation between the number of balloon catheters used for the angioplasty and severe occlusive changes. Nine of 19 patients who had undergone diagnostic transfemoral catheterization had severe obstructive changes on MRI; 8 of 9 weighed < 10 kg at catheterization.

CONCLUSIONS

Obstructive lesions of the iliofemoral arteries are common after transfemoral BDA of arch obstructions (58%) and can be reliably evaluated with gradient MRI. Catheter size and manipulation are the main contributing factors.

Mechanisms of coronary vasomotor dysfunction in the transplanted heart

The transplanted heart sustains both cold ischemic and reperfusion injuries. These can produce coronary vascular endothelial or smooth muscle injury or both, which, in turn, can produce coronary vasomotor dysfunction. Using a canine model of autologous heart transplantation, we examined the following coronary vasomotor control mechanisms in isolated coronary artery rings: (1) endothelial-dependent cyclic guanosine monophosphate (cGMP)-mediated vasorelaxation (response to acetylcholine); (2) endothelial-independent cGMP-mediated vasorelaxation (response to sodium nitroprusside); and (3) beta-adrenergic cyclic adenosine monophosphate (cAMP)-mediated vasorelaxation (response to isoproterenol hydrochloride). Further, these mechanisms were related to 3 hours of cold ischemia alone and to 3 hours of cold ischemia plus 1 hour of reperfusion. Autologous heart transplantation was performed in dogs, and isolated distal left anterior descending coronary artery rings were studied in individual organ chambers. Cold ischemia alone produced significant dysfunction of beta-adrenergic cAMP-mediated vasorelaxation, which was exacerbated after reperfusion. Neither endothelial-dependent nor endothelial-independent cGMP-mediated vasorelaxation was dysfunctional after cold ischemia alone, but both were significantly impaired after reperfusion. We conclude that cold ischemia and reperfusion each produce coronary vasomotor dysfunction in the transplanted heart. Cumulatively, such coronary vasomotor dysfunction can acutely impair coronary vasodilatation and potentially jeopardize myocardial blood flow in the transplanted heart.

Thromboxane A2: an endothelium-derived vasoconstrictor in human internal mammary arteries

The internal mammary artery (IMA) has become the conduct of choice for coronary artery bypass grafting. However, the IMA graft can exhibit vasoconstriction during the perioperative period. Experiments were designed to determine the role of cyclooxygenase products in human IMA during hypoxia. Rings of IMA, with and without endothelium, were suspended in organ baths containing physiologic salt solution. Rings were contracted with norepinephrine and then exposed to hypoxia for 15 minutes. In segments with endothelium, hypoxia induced a transient relaxation followed by contraction. This contraction was associated with a significantly increased production of thromboxane B2, the stable metabolite of thromboxane A2 (n = 10; from 120.7 +/- 3.5 pg/mg wet tissue before hypoxia to 175.8 +/- 5.2 pg/mg during hypoxia; p < 0.05). This hypoxic contraction could be attenuated by indomethacin. However, thromboxane B2 could not be detected in samples from organ baths containing IMA segments without endothelium before or during hypoxia. This study demonstrated that endothelium of human IMA grafts releases thromboxane A2 basally and that production is augmented by hypoxia, which acts to constrict the underlying vascular smooth muscle, increase vascular tone, and promote ischemic events such as vasospasm and thrombosis, particularly in hypoxemic patients.

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.

Effects of University of Wisconsin solution on endothelium-dependent coronary artery relaxation in the rat

University of Wisconsin (UW) solution has been reported to enhance myocardial preservation in heart transplantation. To evaluate the effects of UW solution on coronary artery endothelial function, we designed experiments to compare UW solution with a standard crystalloid hyperkalemic cardioplegic solution (CHCS). Isolated rat hearts were studied in a modified Langendorff apparatus for coronary endothelial function. Groups 1 and 2 were perfused with 4 degrees C CHCS (24 mmol/L of KCl) and UW solution, respectively, for 10 minutes at a pressure of 80 cm H2O, whereas group 3 underwent warm ischemia for 10 minutes. Groups 4 and 5 were perfused with and stored for 4 hours in cold (4 degrees C) CHCS and UW solution, respectively. Group 6 underwent 4 hours of topical cooling (4 degrees C) without any cardioplegic perfusion. All groups had 6 hearts each. Endothelium-dependent relaxation and endothelium-independent relaxation of the coronary arteries were tested by infusing 5-hydroxytryptamine (5HT) (10(-6) mol/L) and sodium nitroprusside (10(-5) mol/L), respectively, before and after perfusion with and storage in one of the two cardioplegic solutions. The coronary vasodilatation induced by 5HT and sodium nitroprusside was not altered in hearts perfused with (group 1) or perfused with and stored in CHCS (group 4). Coronary flow increase after 5HT infusion was significantly decreased in hearts perfused with (group 2) (before, 35% +/- 10%; after, 13% +/- 10%; p < 0.01) or perfused with and stored in UW solution (group 5) (before, 34% +/- 5%; after, -5% +/- 12%), indicating severe endothelial dysfunction.(ABSTRACT TRUNCATED AT 250 WORDS)

Crystalloid cardioplegia and hypothermia do not impair endothelium-dependent relaxation or damage vascular smooth muscle of epicardial coronary arteries

Canine hearts were arrested with crystalloid cardioplegic solution (45 minutes at 7 degrees C) to determine whether either cardioplegia or hypothermia impairs the production of endothelium-derived relaxing factor or damages the vascular smooth muscle of epicardial coronary arteries. In addition, isolated coronary artery segments were exposed to either cold (7 degrees C) or warm (37 degrees C) crystalloid cardioplegic solution and physiologic salt solution in vitro for 45 minutes. After cardiac arrest or incubation with the solutions, segments of epicardial coronary artery were prepared and studied in organ chambers. Cardioplegic arrest of the heart or exposure to cardioplegic solution in vitro (7 degrees or 37 degrees C) did not alter endothelium-dependent relaxation of epicardial coronary artery segments in response to adenosine diphosphate or acetylcholine (10(-9) to 10(-4) mol/L). Cardioplegic arrest did not alter G protein-mediated, endothelium-dependent relaxation in response to sodium fluoride. In addition, smooth muscle contraction in response to potassium ions (voltage-dependent) or prostaglandin F2 alpha (receptor-dependent) and relaxation in response to isoproterenol (cyclic adenosine monophosphate-mediated) or sodium nitroprusside (cyclic guanosine monophosphate-mediated) was unaltered after exposure to cardioplegic solution or hypothermia. These experiments demonstrate that hyperkalemic crystalloid cardioplegia does not irreversibly alter function of epicardial coronary arteries. We hypothesize that coronary artery endothelial cell dysfunction identified in previous studies of cardioplegia may have been due to the effects of barotrauma or shear stress on the vasculature and not the effect of cardioplegia per se.

Endothelial vasomotor regulation in health and disease

The purpose of this review is to provide the anaesthetists with a comprehensive update on the endothelial-cell control of local blood flow. This single cell layer was originally thought to represent only a passive barrier. It is now evident that it plays an active role in a broad variety of biological functions. Since the discovery of the endothelial-derived relaxing factor (EDRF), it has been the subject of a considerable amount of research. It is established that EDRF is secreted continuously at a basal state and that many physical stimuli as well as vasoactive substances can modulate its secretion. Evidence presented indicates that the endogenous vasodilatation produced by EDRF is similar to that of the exogenous nitrovasodilator nitroglycerin and nitroprusside (i.e., nitric oxide). Aside from EDRF, the endothelium produces other vasodilating as well as vasoconstricting factors. A review of the physiology of the endothelium regarding the local control of blood flow is provided along with its influence upon several pathophysiological states. Also included is an overview of the influence of anaesthetic agents on endothelial function. These findings linking vasomotor control to endothelial function will help to explain pathophysiological process and may lead to new therapeutic modalities.