New biological solutions for hemodialysis access.

Since Scribner described the first prosthetic chronic dialysis shunt in 1961, the surgical techniques and strategies to maintain vascular access have improved dramatically. Today, hundreds of thousands of patients worldwide are treated with some combination of native vein fistula, synthetic vascular graft, or synthetic semipermanent catheter. Despite significantly lower efficacy compared with autologous fistulae, the basic materials used for synthetic shunts and catheters have evolved surprisingly slowly. The disparity between efficacy rates and concomitant maintenance costs has driven a strong campaign to decrease the use of synthetic grafts and catheters in favor of native fistulae. Whether arguing the benefits of Fistula First or "Catheter Last," the fact that clinicians are in need of an alternative to expanded polytetrafluoroethylene (ePTFE) is irrefutable. The poor performance of synthetic materials has a significant economic impact as well. End-stage renal disease (ESRD) accounts for approximately 6% of Medicare's overall budget, despite a prevalence of about 0.17%. Of that, 15%-25% is spent on access maintenance, making hemodialysis access a critical priority for Medicare. This clinical and economic situation has spawned an aggressive effort to improve clinical care strategies to reduce overall cost and complications. While the bulk of this effort has historically focused on developing new synthetic biomaterials, more recently, investigators have developed a variety of cell-based strategies to create tissue-engineered vascular grafts. In this article, we review the evolution of the field of cardiovascular tissue engineering. We also present an update on the Lifeline™ vascular graft, an autologous, biological, and tissue-engineered vascular graft, which was the first tissue-engineered graft to be used clinically in dialysis patients.

Bone marrow-derived B cells preserve ventricular function after acute myocardial infarction.

OBJECTIVES: In view of evidence that mature cells play a role in modulating the stem cell niche and thereby stem cell potential and proliferation, we hypothesized that a mature bone marrow (BM) mononuclear cell (MNC) infusion subfraction may have particular potency in promoting hematopoietic or resident stem cell-induced cardiac repair post-infarction. BACKGROUND: Treatment of acute myocardial infarction (MI) with BM MNC infusion has shown promise for improving patient outcomes. However, clinical data are conflicting, and demonstrate modest improvements. BM MNCs consist of different subpopulations including stem cells, progenitors, and differentiated leukocytes. METHODS: Stem cells (c-kit+) and subsets of mature cells including myeloid lineage, B and T-cells were isolated from bone marrow harvested from isogeneic donor rats. Recipient rats had baseline echocardiography then coronary artery ligation; 1 x 10(6) cells (enriched subpopulations or combinations of subpopulations of BM MNC) or saline was injected into ischemic and ischemic border zones. Cell subpopulations were either injected fresh or after overnight culture. After 2 weeks, animals underwent follow-up echocardiography. Cardiac tissue was assayed for cardiomyocyte proliferation and apoptosis. RESULTS: Fractional ventricular diameter shortening was significantly improved compared with saline (38 +/- 3.2%) when B cells alone were injected fresh (44 +/- 3.0%, p = 0.035), or after overnight culture (51 +/- 2.9%, p < 0.001), or after culture with c-kit+ cells (44 +/- 2.4%, p = 0.062). B cells reduced apoptosis at 48 h after injection compared with control cells (5.7 +/- 1.2% vs. 12.6 +/- 2.0%, p = 0.005). CONCLUSIONS: Intramyocardial injection of B cells into early post-ischemic myocardium preserved cardiac function by cardiomyocyte salvage. Other BM MNC subtypes were either ineffective or suppressed cardioprotection conferred by an enriched B cell population.

Endothelium-dependent vasomotor dysfunction in pig coronary arteries with Paclitaxel-eluting stents is associated with inflammation and oxidative stress.

OBJECTIVES: We sought to evaluate coronary epicardial and intramyocardial resistance, arterial vasomotor function, local inflammatory reaction, and superoxide anion (O(2)(.-)) production after overlapping paclitaxel-eluting stent (PES) implantation in a porcine model. BACKGROUND: PES implantation has been shown to elicit coronary vasomotor dysfunction. However, underlying mechanisms remain largely unknown. METHODS: Nine pigs received overlapping PES and bare-metal stents (BMS) in the coronary arteries, and 3 sham animals were naïve. At 1 month, inflammatory response at the overlapped region was assessed by histopathology and scanning electron microscopy. Endothelial vasomotor function and O(2)(*-) at nonstented coronary reference segments were measured by angiography and organ chamber tensiometry, and lucigenin luminometry; vasomotor function of distal resistance arteries was measured by myography. RESULTS: Paclitaxel-eluting stents showed reduced late lumen loss, but inflammation and luminal inflammatory cell adherence were higher than for BMS (p < 0.001) at overlapped segments. Endothelium-dependent relaxation to substance P was significantly impaired in PES at nonstented coronary reference segments (>or=15 mm proximally and distally) and perfusion bed resistance arteries (p < 0.05). In contrast, endothelium-independent relaxation to nitroglycerin and sodium-nitroprusside was similar between groups. Local O(2)(*-) production at both proximal and distal nonstented coronary reference segments was elevated for PES when compared with O(2)(*-) production in BMS and naïve arteries (p < 0.001). CONCLUSIONS: Abnormal endothelium-dependent relaxation at both coronary conduit and resistance arteries was demonstrated after overlapping PES implantation. Profound localized inflammatory reaction, as well as enhanced local oxidative stress, may contribute to vasomotor dysfunction.

Clinical and angiographic features of small vessel stenting in the drug-eluting stent era.

HYPOTHESIS: This study was designed to investigate the clinical and angiographic features and procedural outcomes of small-vessel stenting in a real-world experience during the transition era between drug-eluting stents (DES) and bare-metal stents (BMS). METHODS: Using one of the largest single-institutional cohorts, this study evaluated all patients who underwent percutaneous coronary intervention (PCI) from 2002 through 2005. Analysis was restricted to patients receiving a single stent or undergoing balloon-only angioplasty in a single anatomic site. Small-vessel stents (SVS) were defined as 2.00 to 2.75 mm and large-vessel stents (LVS) as 3.00 to 4.00 mm in diameter. RESULTS: A total of 19,580 stents were placed in 10,396 patients. Of 6208 patients fulfilling inclusion criteria, 1630 (26.3%) received SVS, and 4578 (73.7%) received LVS. The SVS group had more female (35.5% vs 26.3%, P < .001) and diabetic patients (27.9% vs 24.2%, P < .003) than the LVS group. Compared with LVS, SVS lesions were shorter (14.5 +/- 5.8 mm vs 15.7 +/- 6.4 mm, P < .0001) and more complex (66% vs 53% class B2/C lesions, P = .041). Indicators of procedural difficulty, including greater contrast volume, number of devices, total inflation time, and fluoroscopy time, were more commonly observed in the SVS group. After adjustment for confounding factors, the incidence of small treatment vessel diameter was significantly higher among the DES vs the BMS group (odds ratio [OR]: = 1.94, 95% confidence interval [CI]: 1.56-2.36). CONCLUSIONS: In addition to identifying distinct patient, lesion, and procedural performance characteristics, our study, one of the largest single-center experiences in small-vessel PCI, suggests that the availability of DES substantially increased the use of SVS, as opposed to balloon-only angioplasty, in this anatomically challenging setting.

Drug-eluting stents in preclinical studies: updated consensus recommendations for preclinical evaluation.

Coronary drug-eluting stents are commonplace in clinical practice with acceptable safety and efficacy. Preclinical evaluation of novel drug-eluting stent technologies has great importance for understanding safety and possibly efficacy of these technologies, and well-defined preclinical testing methods clearly benefit multiple communities within the developmental, testing, and clinical evaluation chain. An earlier consensus publication enjoyed widespread adoption but is in need of updating. This publication is an update, presenting an integrated view for testing drug-eluting technologies in preclinical models, including novel devices such as bioabsorbable coatings, totally bioabsorbable stents, bifurcation stents, and stent-free balloon-based drug delivery. This consensus document was produced by preclinical and translational scientists and investigators engaged in interventional technology community. The United States Food and Drug Administration (USFDA) recently issued a Draft Guidance for Industry Document for Drug-Eluting Stents. This expert consensus document is consistent with the Food and Drug Administration guidance. The dynamic nature of this field mandates future modifications and additions that will be added over time.

Scanning electron microscopic analysis of defects in polymer coatings of three commercially available stents: comparison of BiodivYsio, Taxus and Cypher stents.

BACKGROUND: Although the use of polymer-based drug-eluting stents appears to markedly reduce the risk of in-stent restenosis, there are concerns about their safety including polymer layer integrity. OBJECTIVES: The objective of this study was to investigate the morphology of the polymer layer of 3 commercially available polymercoated stents, including the effects of balloon catheter expansion, by scanning electron microscopy (SEM). METHODS: We assessed discontinuities and other irregularities in the polymer layer of BiodivYsio, Taxus and Cypher stents by SEM after balloon expansion in saline solution at 37 degrees C. RESULTS: Distinctive polymer layer morphologies were found among the 3 stent types, including responses to balloon expansion and withdrawal. The BiodivYsio stent showed no waving or other irregularities on the outer surface, but excess polymer was present on stent edges and polymer was peeled off from the inner surface. The Taxus stent showed no irregularities on the outer surface, but there were polymer bridgings across strut loops and linear cracking of the bridges, as well as inner surface polymer defects with bare-metal exposure. The Cypher stent showed a rough surface with irregularities and waving on the outer surface. There also appeared to be polymer defects with bare-metal exposure in the loop region and peeling of the top-coated polymer layer in the loop. CONCLUSIONS: We found several types of defects in the polymer layers on commercially available polymer-coated stents. Some of these indicate potential risks of thrombosis, coronary microembolism of polymer layer pieces and late inflammatory or neointimal reactions.

Human tissue-engineered blood vessels for adult arterial revascularization.

There is a crucial need for alternatives to native vein or artery for vascular surgery. The clinical efficacy of synthetic, allogeneic or xenogeneic vessels has been limited by thrombosis, rejection, chronic inflammation and poor mechanical properties. Using adult human fibroblasts extracted from skin biopsies harvested from individuals with advanced cardiovascular disease, we constructed tissue-engineered blood vessels (TEBVs) that serve as arterial bypass grafts in long-term animal models. These TEBVs have mechanical properties similar to human blood vessels, without relying upon synthetic or exogenous scaffolding. The TEBVs are antithrombogenic and mechanically stable for 8 months in vivo. Histological analysis showed complete tissue integration and formation of vasa vasorum. The endothelium was confluent and positive for von Willebrand factor. A smooth muscle-specific alpha-actin-positive cell population developed within the TEBV, suggesting regeneration of a vascular media. Electron microscopy showed an endothelial basement membrane, elastogenesis and a complex collagen network. These results indicate that a completely biological and clinically relevant TEBV can be assembled exclusively from an individual's own cells.

A clinically relevant large-animal model for evaluation of tissue-engineered cardiac surgical patch materials.

Extracellular matrix (ECM) scaffolds may be useful as a tissue engineering approach toward myocardial regeneration in the infarcted heart. An appropriate large-animal model for testing the utility of biologically derived ECM in this application is needed. The purpose of this study was to develop such a model for optimal procedural success during and after patch implantation surgery. Myocardial infarction (MI) was created by embolization of the diagonal artery (DA) branch of the left anterior descending coronary artery with collagen suspension. After 4 to 6 weeks, 14 pigs received patch implant (ECM or expanded polytetrafluoroethylene). Six pigs were infarcted in the first DA and seven pigs in the second DA. Electrophysiology study was performed within 3 days before surgery. During surgery, the size and location of the infarct were measured. Infarcted myocardium (1.5-cm diameter) was transmurally excised under partial cardiopulmonary bypass. Patches (3-cm diameter) were sutured to the endomyocardial defect. Four pigs died postoperatively. After 1 month, 10 pigs were euthanized and the locations of patches were examined. Success rate of patch implant in the second DA (85.7%) was higher than the first DA (50%) group. Infarct size in the second DA was smaller than in the first DA (4.6+/-1.2 vs. 10.8+/-2.4 cm(2), P<.05). The second DA was more anteriorly positioned, which enabled easier access from the midsternal thoracotomy. However, the first DA was more laterally located requiring more manipulation of the heart during surgery. Electrophysiology revealed no ventricular tachyarrhythmia in the second DA but 33.3% in the first DA group (P<.05). At necropsy, the endocardial position of the first DA-infarct patches was anteroapical, whereas the second DA-infarct patches were more basolateral and often involved the anterior papillary muscle. The success rate of patch implant was associated with infarction size and location, and may be related to arrhythmic substrate. Experimental MI created by the second DA embolization is a feasible model for investigation of tissue-engineered cardiac patch implantation. This large-animal model is also suitable for study of cell therapy via endocardial catheter-based approaches or open surgical methods.

Extracellular matrix scaffold for cardiac repair.

BACKGROUND: Heart failure remains a significant problem. Tissue-engineered cardiac patches offer potential to treat severe heart failure. We studied an extracellular matrix scaffold for repairing the infarcted left ventricle. METHODS AND RESULTS: Pigs (n=42) underwent left ventricular (LV) infarction. At 6 to 8 weeks, either 4-layer multilaminate urinary bladder-derived extracellular matrix or expanded polytetrafluoroethlyene (ePTFE) was implanted as full-thickness LV wall patch replacement. At 1-week, 1-month, or 3-month intervals, pigs were terminated. After macroscopic examination, samples of tissue were prepared for histology, immunocytochemistry, and analysis of cell proportions by flow cytometry. One-week and 1-month patches were intact with thrombus and inflammation; at 1 month, there was also tissue with spindle-shaped cells in proteoglycan-rich and collagenous matrix. More alpha-smooth muscle actin-positive cells were present in urinary bladder matrix (UBM) than in ePTFE (22.2+/-3.3% versus 8.4+/-2.7%; P=0.04). At 3 months, UBM was bioresorbed, and a collagen-rich vascularized tissue with numerous myofibroblasts was present. Isolated regions of alpha-sarcomeric actin-positive, intensely alpha-smooth muscle actin-immunopositive, and striated cells were observed. ePTFE at 3 months had foreign-body response with necrosis and calcification. Flow cytometry showed similarities of cells from UBM to normal myocardium, whereas ePTFE had limited cardiomyocyte markers. CONCLUSIONS: Appearance of a fibrocellular tissue that included contractile cells accompanied biodegradation of UBM when implanted as an LV-free wall infarction patch. UBM appears superior to synthetic material for cardiac patching and trends toward myocardial replacement at 3 months.

Distal endothelial function and vascular morphology after catheter-based radiation in pig coronary arteries.

PURPOSE: Endovascular irradiation inhibits neointimal hyperplasia in ballooned and stented arteries but impacts both diseased and adjacent normal tissue. Little is known about the effects of irradiation on downstream vasculature. In this study, we investigated vascular function and structure of pig coronary arteries distal to sites of endoluminal irradiation. MATERIALS AND METHODS: Vasomotor responses of distal arteries to contraction of KCl and PGF2alpha and endothelium-dependent (substance P and A23187) and -independent (sodium nitroprusside) relaxation were studied in naïve, sham-treated, irradiated, stented, and stented plus irradiated vessels. Light and scanning electron microscopy were used to assess vascular morphology. RESULTS: Relaxations to substance P and A23187 at 1 month post treatment were significantly decreased in the irradiated group, whereas contractile response to PGF2alpha was significantly increased. Hemorrhage, mural thrombus, and inflammation were present at the upstream-irradiated site; inflammatory cells were also present adherent to the endothelium in the distal segments. CONCLUSIONS: Distal vasomotor function reflects an influence from the nature of a proximal intervention. The effect of irradiation on downstream conduit arteries to increase the threshold of contractility and suppress endothelium-dependent relaxation may be related to the presence of inflammatory cells at both the upstream-instrumented site as well as the distal location.

Impact of intraaortic balloon counterpulsation on arterial blood flow in juvenile pigs with heart failure.

OBJECTIVES: To assess the impact of intraaortic balloon counterpulsation on coronary, renal and aortic blood flow in an animal heart failure model. BACKGROUND: Heart failure exacerbations are still often treated with inotropic medications despite a lack of evidence demonstrating any benefit with these drugs. Intraaortic balloon counterpulsation may be considered in certain cases a bridge to recovery. METHODS: Four juvenile pigs underwent pacemaker implantation to induce a rapid-pacing mediated dilated cardiomyopathy. After approximately 4 weeks of rapid pacing, the mean ejection fraction was reduced to 28.8+/-9.5% with a mean systolic blood pressure of 64/44 mmHg. The pigs then underwent surgical placement of flow probes around the circumflex coronary artery, renal artery and infrarenal aorta. A Millar catheter was used to calculate Dp/Dt and a Swan-Ganz to calculate cardiac output. Data were recorded at baseline and after 10 minutes of balloon pumping. The pigs were euthanized post-procedure. RESULTS: Coronary blood flow was increased 9.7% by balloon counterpulsation from 38.3 +/- 12.0 to 42.0+/-11.4 ml/s (p=NS). Renal blood flow was reduced 11.9% by counterpulsation from 130.0+/-88.6 ml/s to 114.5+/-76.6 ml/s (p=NS). Infrarenal aortic blood flow was not changed (mean of 900 ml/s with and without counterpulsation); blood pressure, cardiac output and Dp/Dt were not changed after 10 minutes of pumping. There was little impact observed by changing the position of the balloon closer to or farther away from the apex of the aortic arch. CONCLUSION: Intraaortic balloon counterpulsation did not significantly improve hemodynamics in the pig heart failure model. This may be attributed to the high compliance of the juvenile pig's aorta, thus attenuating the pressure wave generated by counterpulsation. A larger volume balloon would merit investigation for this application.

Vasomotor function of pig coronary arteries after chronic coronary occlusion.

Placement of an ameroid constrictor in large-conduit pig coronary arteries causes progressive stenosis and distal myocardial ischemia. Blood perfusion in the ischemic region is partly dependent on vasomotor responses to neural and humoral factors distal to the occlusion site. To ascertain the degree of impairment of vascular function in pigs, the authors induced myocardial ischemia by placing an ameroid constrictor in the left circumflex coronary artery and examined vascular reactivity and histopathology distal to the constriction site. The sensitivity of the distal left circumflex coronary and nonoccluded control left anterior descending arteries to PGF(2alpha) was similar. After nitric oxide blockade using Nw-nitro-l-arginine methylester (l-NAME), the sensitivity and maximal contraction to PGF(2alpha) were significantly increased in both the left circumflex coronary (EC50: 5.86 +/- 0.74 vs. 3.28 +/- 0.84 microM; C(max): 4.63 +/- 0.28 vs. 6.25 +/- 0.30 g, P < 0.01) and left anterior descending (EC50: 6.57 +/- 0.73 vs. 2.78 +/- 0.16 microM; C(max): 5.09 +/- 0.37 vs. 6.95 +/- 0.39 g, P < 0.01) arteries. Substance P-induced relaxation (100 pM) was blocked to a larger degree in the distal left circumflex coronary artery when compared with the left anterior descending artery (76.9 +/- 4.2% vs. 56.4 +/- 3.1%, P < 0.05). Endothelium-independent relaxation to sodium nitroprusside was similar in the left circumflex coronary and left anterior descending arteries before and after nitric oxide blockade. Histopathologic examination showed no major differences between distal left circumflex coronary artery segments and left anterior descending artery controls. However, scanning electron microscopy showed endothelial hypertrophy and activation in specimens from the left circumflex coronary arteries. In summary, as a result of the major hemodynamic changes induced by a chronic constriction and eventual occlusion of a large coronary artery, distal segments underwent adaptive compensatory changes. Such compensation may be related to an increased nitric oxide production by the hypertrophic endothelium in response to alterations in coronary hemodynamics.

External heating of stents by radio waves: pilot studies in rabbit aorta.

PURPOSE: This experiment was designed to assess the feasibility of radio frequency energy delivered by a prototype radio frequency generator inductive heating device (REVAX) positioned external to the body, for transient heating of stents after arterial implant. METHODS AND MATERIALS: Twenty-one New Zealand White rabbits underwent stenting of their infrarenal aorta. Nine rabbits were stented and immediately placed in the REVAX for external stent heating with internal temperature probes in place. Twelve rabbits were stented and 3 days later either heated or placed in the generator as a sham for 20 min. The animals were terminated 28 days later. RESULTS: The REVAX was able to heat the aortic stents in a controlled fashion; in Phase II experiments, the stent temperature was raised to 42 degrees C for 20 min. In Phase I mild necrosis was noted at the stent struts. In Phase II, necrosis and mineralization of the media was seen at the stent struts, and evidence of neointimal suppression was observed. CONCLUSION: This study demonstrated that external heating of stents in a blood vessel in a live animal via radio frequency energy is feasible. Further studies will be needed to assess whether any specific heating regimen might inhibit fibrocellular neointimal hyperplasia.

Mortality rates of interventional and surgical procedures performed in domestic juvenile farm pigs and Yucatan mini-pigs.

Perioperative and postoperative care are critical factors in cardiac catheterization and cardiothoracic surgical procedures. A retrospective analysis of mortality data in cardiovascular catheter and surgical studies performed in domestic juvenile swine (DJS) and Yucatan mini-swine (YMS) was conducted. A total of 529 animals in 35 studies were included in the analysis, which included six study categories: coronary stenting (Stent) and percutaneous transluminal coronary angioplasty (PTCA) alone; Stent and PTCA in combination with ionizing radiation (Stent/Rad, PTCA/Rad); myocardial ischemia (ISCH); and three non-ISCH surgical procedures grouped under "other surgeries" (Other Surg). Casualties were defined as animals that died spontaneously before the assigned termination date. The highest mortality rate occurred in the ISCH group (29.7% +/- 2.2%). Mortality of the Stent/Rad animals (26.1% +/- 6.3%) was significantly higher than those in the Stent and PTCA groups (12.1% +/- 3.1% and 7.9% +/- 3.2%; P< 0.05 for both). Similarly, mortality in the ISCH group was significantly higher than that in the Stent, PTCA, or Other Surg animals (29.7% +/- 2.2% versus 12.1% +/- 3.1%, 7.9% +/- 3.2%, and 3.0% +/- 3.0%, respectively; P< 0.05 for all comparisons). We did not observe differences between YMS and DJS. Most casualties in the ISCH group took place during weeks 1 (28.0% +/- 8.4%) and 4 (29.3% +/- 6.2%) after placement of the coronary ameroid constrictor. The majority of animals in the Stent/Rad and PTCA/Rad groups died within 1 week after the procedure (67.7% +/- 12.8% and 79.3% +/- 12.5%, respectively). We conclude that radiation therapy used in combination with stenting increases the mortality rate of this catheter-based procedure. Animals subjected to ISCH or a transcatheter procedure in combination with ionizing radiation should be monitored closely during the perioperative period to prevent unacceptably high mortality rates.

The effect of blockade of the CD11/CD18 integrin receptor on infarct size in patients with acute myocardial infarction treated with direct angioplasty: the results of the HALT-MI study.

OBJECTIVE: The purpose of this study was to determine whether Hu23F2G (LeukoArrest), an antibody to the CD11/CD18 integrin receptors, would reduce infarct size in patients undergoing primary angioplasty for an acute myocardial infarction. BACKGROUND: Reperfusion injury in acute myocardial infarction has been shown experimentally to be related to neutrophil accumulation. Inhibitors of the CD11/CD18 or CD18 integrin receptors have been shown to reduce infarct size in experimental models. METHODS: Patients within 6 h of onset of chest pain with ST-segment elevation were randomized to receive either 0.3 mg/kg or 1.0 mg/kg of Hu23F2G or placebo just before angioplasty of occluded arteries (Thrombolysis in Myocardial Infarction TIMI flow grade 0 or 1). The primary end point was infarct size as measured by sestamibi single-photon emission computed tomography (SPECT) scan five to nine days later. RESULTS: Four-hundred and twenty patients were enrolled and received a placebo or the study drug. The groups did not differ in baseline or angiographic characteristics or angioplasty results. Infarct size was 16%, 17.2% and 16.6%, for placebo, 0.3 mg/kg and 1.0 mg/kg, respectively, of the left ventricle (p = NS). No differences were evident in those patients with anterior myocardial infarction or those presenting within 2 h of onset of chest pain. Corrected TIMI frame count was also not different between groups. Clinical events at 30 days were very low, with a mortality of 0.8%, 1.4% and 3.3%, respectively. The drug was well tolerated, with a slight increase in minor infections in the high dose group. CONCLUSIONS: The results of this multicenter, double-blind, placebo-controlled, randomized clinical trial demonstrated that an antibody to CD11/CD18 leukocyte integrin receptor did not reduce infarct size in patients who underwent primary angioplasty.

Endovascular irradiation impairs vascular functional responses in noninjured pig coronary arteries.

PURPOSE: To assess the effects of endovascular irradiation on vascular structure and function in pig coronary arteries in the absence of vascular injury. METHODS AND MATERIALS: Vasomotor responses to contractions of KCl and prostaglandin F2alpha (PGF2alpha), relaxations to endothelium-dependent (substance P, A23187) and -independent (sodium nitroprusside, SNP) agents; endothelial morphology and superoxide anion (02*-) production were investigated in control (naive), sham and irradiated (20 Gy, 32P) arteries 1 month after irradiation. RESULTS: Contractions to KCl and PGF2alpha in the presence of L-NAME were significantly decreased, relaxations to substance P and A23187 were abolished and SNP-induced relaxation was potentiated in irradiated arteries compared to naive and sham-treated vessels. Scanning electron microscopy (SEM) revealed enlarged endothelial cells (ECs) exhibiting surface microvilli. O2*- production was significantly increased in irradiated vessels (437.0 +/- 37.3 vs. 126.0 +/- 11.6 RLU/s/mg tissue, P < .01). CONCLUSIONS: One month after brachytherapy, normal pig coronary arteries showed abnormal vascular reactivity, altered endothelial morphology and increased production of O2*-. Lack of relaxation to substance P and A23187 reflects ionizing radiation-mediated damage to ECs, whereas potentiation of relaxation to SNP suggests additional deleterious effects on medial smooth muscle cells (SMCs). Increased O2*- production might have contributed to endothelial dysfunction by scavenging nitric oxide (NO).