mTOR inhibitors and calcineurin inhibitors do not affect adhesion molecule expression of human macro- and microvascular endothelial cells.

We examined the effect of cyclosporin A, tacrolimus, sirolimus and everolimus on the cell growth, viability, proliferation, expression of cellular adhesion molecules (CAM) and leukocyte (PBMC) binding of human macrovascular (coronary artery, saphenous vein) and microvascular endothelial cells (EC). Tacrolimus did not affect EC integrity, growth or expression of CAM. Exclusively, EC from the coronary arteries showed a reduced cellular growth (about 30%) under cyclosporin A and tacrolimus treatment. In contrast, treatment with mTOR inhibitors reduced EC proliferative activity by about 40%, independently of the EC origin. No induction of apoptosis (caspase-3/7 activity) or cytotoxicity (MTS test) was observed. Long-term treatment with high concentrations of sirolimus and everolimus did not enhance the expression of CAM. Stimulation with tumor necrosis factor significantly increased the expression of CAM, independently of the drugs used. None of the mTOR inhibitors influenced the tumor necrosis factor-induced expression of CAM, whereas adhesion of PBMC increased significantly, as described by other papers. In summary, neither calcineurin inhibitors nor mTOR inhibitors activate human micro- and macrovascular EC. Therefore, the investigated drugs are unlikely to contribute to EC activation during transplant-associated vasculopathy.

Advantages of human umbilical vein scaffolds derived from cesarean section vs. vaginal delivery for vascular tissue engineering.

The current study investigated whether the mode of delivery and the mode of sample collection affect the functional properties of umbilical veins as scaffolds for vascular tissue engineering purposes. Human umbilical vein (HUV) from planned cesarean-sections (PCS) showed a 1.7-fold higher maximum contraction with potassium chloride compared to spontaneous vaginal deliveries (VDs, p=0.029). The maximum contractions with histamine were 2.0- and 2.9-fold higher in the PCS and emergency c-section (ECS) groups, respectively, compared to the VD group (p=0.003). The dose-response curves of serotonin were shifted to the right approx. 6- and 5-fold in the VD group compared to PCS and ECS, respectively (p=0.009). There were no differences between the birth groups in terms of tetrazolium dye reduction, platelet adhesion, and the structural integrity. The release of the antithrombotic compound prostacyclin from vessels of the PCS and ECS groups was 6.6- and 3.5-fold higher, respectively, than in the VD group (p<0.001). There was no correlation between the duration of ischemia and any of the functional parameters. This study provides evidence that vessels obtained from PCS are to be preferred for tissue engineering purposes, as they can be harvested in a sterile fashion and show superior vasoconstrictor responses and antithrombotic properties. The data also support a once-per-day pickup schedule for umbilical cords without a deterioration of the functional properties.

Properties of the human umbilical vein as a living scaffold for a tissue-engineered vessel graft.

Umbilical cords are usually discarded after delivery, even though they contain a set of functional vessels. We investigated whether the human umbilical vein (HUV) is suitable as a storable scaffold for the tissue engineering of small-caliber vessel grafts. Isolated HUVs were cryopreserved by freezing or vitrification. The reaction of the vessels to vasoactive compounds and the mechanical properties were determined in an organ bath. Mitochondrial metabolism, release of antithrombotic compounds, and platelet adhesion were measured on the luminal vessel surface. Seeding with endothelial cells was tested on denuded HUVs. The vessels showed a weak response to norepinephrine but were readily contracted by serotonin and by the thromboxane A2 mimetic U46619. Endothelium-dependent vasorelaxation was weak, reaching significance only for histamine. However, the vessels relaxed to sodium nitroprusside, and to acetylcholine if sandwiched with human saphenous vein. Cryopreservation did not change the mechanical properties in the relevant tension range. Vasoconstriction to potassium chloride and serotonin were reduced after freezing (22.9+/-7.6%, 27.7+/-10.2%) and after vitrification (2.6+/-5.8%, 4.3+/-7.1%). The mitochondrial metabolism was also attenuated after freezing (57.9+/-25.9%) and after vitrification (21.7+/-6.7%). Prostacyclin release was elevated after both cryopreservation procedures (4.0-fold, 3.9-fold), whereas there was no significant change in the adhesion of platelets. Denuded HUVs could readily be seeded with isolated endothelial cells before and after freezing. We conclude that HUV is suitable as a storable living scaffold with antithrombogenic properties.

mTOR-inhibitors simultaneously inhibit proliferation and basal IL-6 synthesis of human coronary artery endothelial cells.

Divergent results regarding the immunosuppressive effects of mammalian-target-of-rapamycin-(mTOR)-inhibitors on venous endothelial cells (ECs) have highlighted the importance of an accurate EC-model. The purpose of this study was to determine mTOR-inhibitor effects at a specific site of action -- the human coronary-artery-ECs (HCAECs) -- and to compare these data with results gained from cultures of human saphenous vein ECs (HSVECs). This EC-model could enable us to gain insight into site-specific pharmacodynamics and the immunosuppressive management of transplant vasculopathy. ECs were cultivated with rising concentrations of mTOR-inhibitors in the presence/absence of tumor necrosis factor (TNF). Cell counts, DNA-synthesis, cytotoxicity and concentrations of the cytokine IL-6 as well as the chemokines IL-8 and MCP-1 were measured. Half-maximal inhibitory effects on cell growth were reached after about 30 h incubation and both cell types showed equal responses regarding cell growth and DNA-synthesis after 48 h incubation time. mTOR-inhibitors failed to suppress basal/TNF-induced secretion of IL-8 and MCP-1, but IL-6 synthesis after TNF-induction was reduced to 35%. In contrast to human saphenous vein ECs (HSVECs), mTOR-inhibitors also reduced basal IL-6-secretion of HCAECs (to 55%) and cell proliferation was simultaneously inhibited within the same concentration range. Taking everything into account, we conclude that EC-proliferation is inhibited at concentrations needed to suppress TNF-stimulated IL-6 synthesis. Furthermore, the specific suppression of basal arterial IL-6-secretion and the delayed onset of the mTOR-inhibitor effect on HCAEC-proliferation (maximum reached after about 36 h) might be of relevance for the prevention of transplant vasculopathy at its initial stage, e.g. as a component of cardioplegic solutions.

Endothelial cell dysfunction after coronary artery bypass grafting with extracorporeal circulation in patients with type 2 diabetes mellitus.

OBJECTIVE: Type 2 diabetes mellitus is a well-known risk factor in patients with severe coronary artery disease undergoing coronary artery bypass grafting (CABG). The aim of the study was to analyze the endothelial dysfunction in these patients by evaluating postoperative soluble inflammatory cytokines. METHODS: Patients undergoing CABG without (n=15, group A) and with (n=14, group B) diabetes mellitus were analyzed for their release of E-selectin, interleukin-6 (IL-6), and tumor necrosis factor (TNF) up to 3 days postoperatively. A pharmacokinetic quantitative kinetic evaluation (Kinetica 2000) of maximum concentrations (c(max)), time to reach c(max) (t(max)), area under the curve (AUC(0-inf)), and terminal elimination half time (t(1/2)) was performed using a non-compartmental model. RESULTS: There was no difference in preoperative plasma concentrations of the cytokines and in the postoperative kinetic analyses of TNF when comparing both groups. However, the release of IL-6 was restricted with c(max) of 1055+/-543 pg/ml for group B versus 2112+/-1532 pg/ml for group A (p< or =0.05), paralleled by a decrease in the absolute amount (AUC(0-inf)) of IL-6. The t(1/2) remained unaffected (13.9+/-6.6h and 12.7+/-4.6h, respectively). The AUC(0-inf) of E-selectin decreased by a factor of 1.7 (p< or =0.05) with unchanged c(max) but reduced t(1/2) (12.9+/-10h for group B vs 33.1+/-20.4h for group A; p< or =0.01) referring to an augmented endothelial uptake and degradation of E-selectin. CONCLUSIONS: CABG with extracorporeal circulation could be used to verify a specific endothelial dysfunction in diabetic patients characterized by an impaired release of IL-6 and an increased turnover of E-selectin.

Identification and reduction of cryoinjury in endothelial cells: a first step toward establishing a cell bank for vascular tissue engineering.

We analyzed a cryopreservation protocol which improves long-term storage of endothelial cells (EC) for tissue engineering purposes. Human umbilical vein EC were frozen in a high-potassium solution containing 10% dimethyl sulfoxide using 3 different cooling rates. After a storage time in liquid nitrogen of 1, 4, or 12 months, samples were thawed and compared to fresh cells in terms of growth rates, anti-inflammatory, and anticoagulant functions. Independent of cooling rate and storage time, the retrieval after cryopreservation ranged between 60% and 80%. However, viability of the cells cryopreserved at 10 degrees C/min decreased significantly from 78 +/- 5% to 64 +/-3% with storage. Storage time of 4 months resulted in a decreased cell multiplication factor over 4 and 12 days in culture. The lag phases returned to normal in the next passage. Thawed cells showed increased metabolic activity, reduced expression of thrombomodulin, and unchanged basal expression of adhesion molecules. However, the tumor necrosis factor-induced expression of adhesion molecules was significantly increased after long-term storage. This effect was partially compensated after expansion of the cells, whereas the prostacyclin release increased. Expansion of cryopreserved/thawed EC resulted in highly proliferative cells with antithrombotic properties and a capacity for inflammatory reactions, which makes them suitable for vascular tissue engineering.

Endothelial apoptosis and circulating endothelial cells after bypass grafting with and without cardiopulmonary bypass.

OBJECTIVE: We compared profiles of the numbers of circulating endothelial cells (CEC) and the apoptosis-inducing capacity of serum samples on human endothelial cells (hEC) in on-pump and off-pump coronary artery bypass grafting (CABG) patients. METHODS: Blood samples from 30 patients undergoing CABG (randomly assigned to two groups: 15 patients off-pump and 15 on-pump (cardiopulmonary bypass, CPB)) were collected after induction of anesthesia (preoperatively), at weaning from CPB/end of bypass grafting (0 h), and 1, 6, 12, 24, and 48 h afterwards. CEC were isolated with immunomagnetic anti-CD146-coated Dynabeads, and counted in a Nageotte chamber. The apoptosis-inducing activity of serum samples on hEC was examined by a tissue culture assay system. Apoptotic and normal cells were identified using phase contrast/fluorescence microscopy after DNA dye staining. RESULTS: CEC numbers and proportions of apoptotic hEC were significantly elevated during and after surgery in both groups (p<0.01). Compared with the on-pump group, CEC and proportions of apoptotic hEC were significantly lower (p=0.04 and p=0.03, respectively) in patients having CABG performed off-pump. Starting at comparable baseline levels, the mean CEC-number was highest at 6h postoperatively with 81.9 ml(-1) (range, 44-141) for on-pump patients and 63.3 ml(-1) (range, 48-105) for off-pump patients. hEC apoptosis peaked also at T4: 16.5+/-2.8% versus 11.3+/-2.2%. In both groups, CEC numbers and proportions of endothelial apoptosis were still elevated at 48 h after surgery. CONCLUSION: The number of circulating endothelial cells and apoptotic endothelial cell death are markers of endothelial activation and damage during CABG. This study provides evidence that CABG with the use of CPB in comparison to OPCAB surgery is associated with a significantly more pronounced endothelial response in the immediate postoperative period.

Anterior mitral leaflet mobility is limited by the basal stay chords.

BACKGROUND: We hypothesize that 2 tendon-like anterior basal stay chords, which remain taut during the entire cardiac cycle, limit the motion of the anterior mitral leaflet. METHODS AND RESULTS: Sonomicrometric crystals were implanted in 6 sheep at the insertion of stay chords at anterior mitral leaflet (S1 and S2), papillary muscle tips, fibrous trigones, mitral annulus, and the tip of the anterior leaflet (AL). Distances between crystals were recorded before and after section of stay chords. During the cardiac cycle, the angle alpha between mitral annulus and AL changed by +54.2+/-12.4 degrees; the angles between mitral annulus and S1 (beta1) changed by +25.7+/-14.6 degrees, and between mitral annulus and S2 (beta2) by +20.4+/-7.8 degrees. During diastole, AL twice crossed the virtual plane formed by the stay chords: during E-wave by a maximum of 6.5 mm (mean, 2.5+/-2.2 mm) and during A-wave by a maximum of 3.2 mm (mean, 1.7+/-0.9 mm). After section of both stay chords, total anterior mitral leaflet motion increased as follows: AL, +6.9+/-3.4 degrees; S1, +13.1+/-4.4 degrees; and S2, +30.9+/-11.7 degrees (P<0.05). CONCLUSIONS: Although the lateral movement of anterior mitral leaflet is limited by stay chords, the midportion moves unimpaired toward the septum, like a sail, between the 2 stay chords during diastole. A diastolic left ventricular-inflow and systolic left ventricular-outflow funnel mechanism is created. Stay chord section increased lateral anterior mitral leaflet movement.

Superiority of voriconazole over amphotericin B in the treatment of invasive aspergillosis after heart transplantation.

Invasive aspergillosis in immuncompromised patients occurs frequently. Surgical therapy in combination with chemotherapy with amphotericin B and itraconazole is standard therapy. We describe a heart transplant recipient with invasive Aspergillus fumigatus infection in the lung, which was treated successfully with voriconazole after systemically high-dose intravenous therapy with amphotericin B failed.

Disseminated Cladophialophora bantiana infection in a heart transplant recipient.

Cerebral phaeohyphomycosis caused by Cladophialophora bantiana, a dematiaceous fungus, is a rare disease. The majority of cases have been reported among immunocompetent patients; only 4 cases have been published that describe transplantation patients. The overall prognosis is poor. Surgical therapy in combination with chemotherapy with itraconazole is recommended. We report the case of a heart transplant recipient with cutaneous, cerebral, and lung manifestation of Cladophialophora bantiana who died despite surgical and systemic, high-dosage itraconazole treatment.

Hybrid management of aortic rupture and lung failure: pumpless extracorporeal lung assist and endovascular stent-graft.

Acute traumatic aortic rupture represents a potentially life-threatening situation. Because of the extremely high early mortality, emergency surgical repair used to be the preferred method of treatment. This group of patients usually is seen with a wide variety of injuries and comorbid conditions, all of which have a major impact on surgical outcome. We present an alternative hybrid approach that combines on-site placement of pumpless extracorporeal lung assist, subsequent patient transfer, and endovascular stent-graft implantation. This procedure may be a potentially useful strategy to reduce the comorbidity and the mortality of both lesions.

Role of apoptosis in myocardial stunning after open heart surgery.

BACKGROUND: Myocardial preservation during open heart surgery is a subject of intense investigation. A prerequisite for further improvement is a better understanding of the underlying pathophysiologic mechanisms responsible for postoperative myocardial stunning. In this report, we analyzed the role of apoptosis in myocardial stunning. METHODS: Myocardial samples were obtained from 11 patients undergoing elective coronary artery bypass grafting before (control) and after cardioplegic arrest and reperfusion. Specimens were examined for apoptosis by electron microscopy, in situ end-labeling of DNA fragments, and biochemically for mitochondrial cytochrome c release. RESULTS: Electron microscopy revealed condensation and margination of nuclear chromatin after surgery, as well as swelling and membrane rupture in mitochondria of single myocytes surrounded by healthy cells. TUNEL-positive cells were also found. Cytochrome c release, an initial step in apoptosis, revealed a 3.4 +/- 0.4-fold increase during surgery (p < 0.0001). Furthermore, cytochrome c release from otherwise intact mitochondria showed a negative correlation with left ventricular function and a positive correlation with the duration of cardioplegic arrest and reperfusion (p < 0.05). CONCLUSIONS: Our data demonstrate that programmed cell death is evident early after open heart surgery and correlates with declining cardiac contractility. We conclude that apoptosis may be an important mechanism in postoperative myocardial stunning.

Stentless xenografts and homografts for right ventricular outflow tract reconstruction during the Ross operation.

BACKGROUND: Shortage of homografts prompted us to replace the transplanted pulmonary trunk with stentless xenografts during the Ross procedure. The 5-year follow-up in comparison with pulmonary homografts is presented. METHODS: From April 1997 to March 2002, of 51 patients undergoing a modified Ross procedure 15 patients (age range 55 to 65 years, mean 59 +/- 5) received a stentless xenograft, and 36 patients (15 to 56 years, mean 36 +/- 11) a pulmonary homograft for right ventricular outflow tract (RVOT) reconstruction. Follow-up was complete for a mean of 3.1 years (range 6 to 60). Regularly performed echocardiography included determination of valve annulus, peak instantaneous gradient, leaflet performance, location of obstruction, and degree of regurgitation. RESULTS: There was 1 late death and 1 reoperation for homograft stenosis. The homograft annulus diameter decreased by a mean of 10% (range 3 to 10 mm; p < 0.01), and peak Doppler gradient increased significantly (p < 0.001). All patients except 1 had gradients less than 25 mm Hg. Gradients in xenograft patients were stable at a low level (6.5 +/- 4.3 mm Hg to 8.8 +/- 7.4 mm Hg at the latest follow-up). Mild pulmonary regurgitation was noted in 46.6% (xenografts) and 19.5% (homografts). Leaflet quality and mobility were maintained in all patients. CONCLUSIONS: Pulmonary homografts underlie a process of annular reduction after the Ross procedure, which is usually not associated with graft stenosis. Mild pulmonary regurgitation is more common in xenografts than in homografts. RVOT reconstruction using stentless xenografts represents a satisfactory treatment modality for aged patients.

Expression of adhesion molecules and cytokines in vitro by endothelial cells seeded on various polymer surfaces coated with titaniumcarboxonitride.

Although endothelial cell (EC) seeding improves the patency of vascular prostheses, the detachment of adherent ECs after the restoration of circulation remains one of the major obstacles. Polymer surfaces for endothelialization can be optimized. In this study, polyethylene terephthalate (PET), polypropylene (PP), polytetrafluoroethylene (PTFE), polyurethane (PUR), and silicone were coated with a titaniumcarboxonitride (Ti(C,N,O)) layer by a plasma-assisted chemical vapor deposition process to verify the effect of titanium onto human saphenous vein ECs. Almost confluent EC monolayers were evaluated for 1) proliferation activity and 2) expression of adhesion molecules using cellular enzyme-linked immunosorbent assay and release of cytokines. The results showed that all titanium-coated polymers and uncoated PET have no toxic effect on human saphenous vein ECs excepting uncoated PTFE, PP, and silicone. Moreover, growing ECs showed an insignificant decrease in cytokine production and an unessential change in basal expression of adhesion molecules. Tumor necrosis factor-alpha-induced response depends on polymer surface: for example, intercellular adhesion molecule-1 expression decreased. E-selectin expression was unchanged for culturing ECs on coated PET, PP, and PTFE and reduced for polyurethane and silicone. Vascular cell adhesion molecule-1 expression was unchanged for coated PUR and silicone and reduced for PET, PP, and PTFE. In summary, titanium-coating layers promote adhesion of human ECs on polymer vascular grafts with no proinflammatory reaction of ECs.

Extracorporeal circulation in non-cardiac surgery.

Tradition and experience of cardiopulmonary bypass in the hand of cardiac surgeons Led to several spin-offs of this extracorporeal technique. Acute organ support is realized for situations of failing cardiac output, circulatory arrest respectively, of pulmonary failure and of drowning. Extracorporeal circulation is a promising adjunct to aim in better surgical technique and treatment in neurosurgery, thoracic aortic surgery, complex Lung resection, tumor surgery and procedures where safe organ perfusion must be ascertained. Chemotherapy and hyperthermia in limb carcinoma is highly successful if performed with the help of extracorporeal circulation. Progression in transcutaneous cannulation technique makes application of machinery easy and from operation facilities independent. Replacement of Long lasting periods of chest compression for heart massage is a future perspective if circulation is maintained by transcutaneously adapted miniaturized heart-lung-machine. Long lasting traumatizing mechanical ventilation of a severely diseased lung maybe replaced by extracorporeal lung assistance to give better chances for the lung to recover. Thoughts for these new interdisciplinary duties of cardio surgical units were discussed in the committee for the Symposium for the Future of Cardiac Surgery.

Tricuspid valve repair in a case with congenital absence of left thoracic pericardium.

We present a case of severe tricuspid valve insufficiency because of disruption of the anterior tricuspid leaflet with congenital absence of left thoracic pericardium. Findings suggest that tricuspid valve disruption was a result of distorted right ventricular geometry because of luxation of the heart into left thoracic cavity. Tricuspid valve could be repaired by reinsertion of anterior tricuspid leaflet and De-Vega annuloplasty. Normal hemodynamic was obtained and weaning from cardio pulmonary bypass was possible by lifting the heart in orthotopic position using increased positive end expiratory pressure. Postoperative course was uneventful.

Development of endothelium-denuded human umbilical veins as living scaffolds for tissue-engineered small-calibre vascular grafts.

Tissue-engineered small-calibre vessel grafts may help to alleviate the lack of graft material for coronary and peripheral bypass grafting in an increasing number of patients. This study explored the use of endothelium-denuded human umbilical veins (HUVs) as scaffolds for vascular tissue engineering in a perfusion bioreactor. Vessel diameter (1.2 ± 0.4 mm), wall thickness (0.38 ± 0.09 mm), uniaxial ultimate failure stress (8029 ± 1714 kPa) and burst pressure (48.4 ± 20.2 kPa, range 28.4-83.9 kPa) were determined in native samples. The effects of endothelium removal from HUVs by enzymatic digestion, hypotonic lysis and dehydration were assessed. Dehydration did not significantly affect contractile function, tetrazolium dye reduction, mechanical strength and vessel structure, whereas the other methods failed in at least one of these parameters. Denudation by dehydration retained laminin, fibronectin, collagen and elastic fibres. Denuded HUVs were seeded in a perfusion bioreactor with either allogeneic HUVs endothelial cells or with saphenous vein endothelial cells harvested from patients with coronary artery disease. Seeding in a perfusion bioreactor resulted in a confluent monolayer of endothelial cells from both sources, as judged by histology and scanning electron microscopy. Seeded cells contained von Willebrand factor and CD31. In conclusion, denuded HUVs should be considered an alternative to decellularized blood vessels, as the process keeps the smooth muscle layer intact and functional, retains proteins relevant for biomechanic properties and for cell attachment and provides a suitable scaffold for seeding an autologous and flow-resistant endothelium.

Minimized extracorporeal circulation system in coronary artery bypass surgery: a 10-year single-center experience with 2243 patients.

OBJECTIVE: Coronary artery bypass grafting (CABG) is the gold standard for the surgical therapy of multivessel coronary artery disease. To reduce the side effects, associated with standard extracorporeal circulation (ECC), a concept of minimal extracorporeal circulation (MECC) was devised in our center. We report on our 10-year experience with the MECC for coronary revascularization. METHODS: From January 1998 to August 2009, 2243 patients underwent CABG with MECC in our center. In a retrospective observational study, we analyzed indication, preoperative patient co-morbidity, postoperative clinical course, and perioperative outcome of all patients operated on with MECC. Furthermore, the risk factors for mortality in the MECC group were assessed. RESULTS: Patients showed a mean logistic European System for Cardiac Operative Risk Evaluation (EuroSCORE) of 4.5±0.1%. The mean age of the patients was 66.8±9.1 years. The overall 30-day mortality after CABG with MECC was 2.3%, ranging from 1.1% for elective to 13.0% for emergent patients and was significantly better than standard ECC. Only 15.3% (n=344) of patients with MECC required intra-operative blood transfusion. Postoperative catecholamine support, red blood cell transfusion, need for hemodialysis, release of creatinine kinase, incidence of stroke, and postoperative delirium were low after MECC revascularization. Ejection fraction below 30% (odds ratio (OR): 5.1), emergent operation (OR: 9.4), and high-dose catecholamine therapy (OR: 2.6) were associated predictors for mortality. CONCLUSION: MECC until now is an established concept and has become an alternative for ECC in routine CABG in our center. The use of the MECC system is associated with low mortality and conversion rate. Excellent survival rates and low transfusion requirements in the perioperative course were achieved.

Effects of shear forces and pressure on blood vessel function and metabolism in a perfusion bioreactor.

Bovine saphenous veins (BSV) were incubated in a perfusion bioreactor to study vessel wall metabolism and wall structure under tissue engineering conditions. Group 1 vessels were perfused for 4 or 8 days. The viscosity of the medium was increased to that of blood in group 2. Group 3 vessels were additionally strained with luminal pressure. Groups 1-d through 3-d were similar except that BSV were endothelium-denuded before perfusion. Groups 1-a through 3-a used native vessels at elevated flow rates. Group 3 vessels responded significantly better to noradrenaline on day 4, whereas denuded vessels showed attenuated responses (p < 0.001). Tetrazolium dye reduction did not depend on perfusion conditions or time except for denuded vessels. pO2 gradients across the vessels were independent of time and significantly higher in group 2 (p < 0.001). BSV converted glucose stoichiometrically to lactate except vessels of groups 3, 1-d, and 3-d which released more lactate than glucose could supply (p < 0.001). Group 1 vessels as well as all vessels perfused with elevated flow rates showed a loss of endothelial cells after 4 days, whereas group 2 and 3 vessels retained most of the endothelium. These data suggest that vessel metabolism was not limited by oxygen supply. Shear forces did not affect glucose metabolism but increased oxygen consumption and endothelial cell survival. Luminal pressure caused the utilization of energy sources other than glucose, as long as the endothelium was intact. Therefore, vessel metabolism needs to be monitored during tissue engineering procedures which challenge the constructs with mechanical stimuli.