Endothelium-dependent responses in long-term human coronary artery bypass grafts

Relaxant and antiadrenergic effects of ranolazine in human saphenous vein

OBJECTIVES

Ranolazine improves vascular function in animal models. We evaluate the effects of ranolazine on vascular function and adrenergic response in human saphenous vein.

METHODS

Rings from 53 patients undergoing coronary artery bypass grafting were mounted in organ baths. Concentration-response curves to ranolazine were constructed in rings precontracted with phenylephrine, endothelin-1, vasopressin, KCl and the thromboxane A2 analogue U-46619. In rings precontracted with phenylephrine, relaxation to ranolazine was tested in the absence and presence of endothelial factors inhibitors, K+ channel blockers and verapamil. The effects of ranolazine on frequency-response and concentration-response curves to phenylephrine were performed in the absence and presence of endothelial factors inhibitors and K+ channel blockers. Endothelial nitric oxide synthase, α1 adrenergic receptor and large conductance Ca2+-activated K+ channel protein expressions were measured by Western blotting.

RESULTS

Ranolazine (10-9-10-4 M) produced a concentration-dependent relaxation only in rings precontracted with phenylephrine that was reduced by endothelial denudation, NG-nitro-l-arginine methyl ester (10-4 M), charybdotoxin (10-7 M) and verapamil (10-6 M). Ranolazine diminished adrenergic contractions induced by electrical field stimulation (2-4 Hz) and phenylephrine (10-9-10-5 M) that were prevented by tetraethylammonium (10-3 M) and charybdotoxin (10-7 M). Ranolazine significantly decreased α1 adrenergic receptor and increased large conductance Ca2+-activated K+ channel protein expression in the saphenous vein.

CONCLUSIONS

Ranolazine diminishes the adrenergic vasoconstriction, acting as α1 antagonist, and by increasing large conductance Ca2+-activated K+ channel involvement. The relaxant effects of ranolazine are partially mediated by endothelial nitric oxide, large conductance Ca2+-activated K+ channels and the blockade of voltage-dependent Ca2+ channels.

Adaptive changes in autogenous vein grafts for arterial reconstruction: clinical implications

For patients with the most severe manifestations of lower extremity arterial occlusive disease, bypass surgery using autogenous vein has been the most durable reconstruction. However, the incidence of bypass graft stenosis and graft failure remains substantial and wholesale improvements in patency are lacking. One potential explanation is that stenosis arises not only from over exuberant intimal hyperplasia, but also due to insufficient adaptation or remodeling of the vein to the arterial environment. Although in vivo human studies are difficult to conduct, recent advances in imaging technology have made possible a more comprehensive structural examination of vein bypass maturation. This review summarizes recent translational efforts to understand the structural and functional properties of human vein grafts and places it within the context of the rich existing literature of vein graft failure.

In vivo human lower extremity saphenous vein bypass grafts manifest flow mediated vasodilation

OBJECTIVE

As in arteries, venous endothelium modulates vessel homeostasis and tone. The effect of an arterialized environment on venous endothelial function remains poorly understood. In particular, regulation of saphenous vein graft (SVG) blood flow and lumen caliber remains undefined. We hypothesized that mature SVGs would exhibit endothelium-dependent, flow-mediated vasodilation (FMD). We further hypothesized that endothelium-derived nitric oxide (NO) was an important mediator.

METHODS

Patients with femoral to popliteal artery SVGs that had maintained primary patency and were at least 1 year from surgery were enrolled. High-resolution, B-mode ultrasound scans were used to measure vein graft diameter before and 1 minute after reactive hyperemia (RH) to determine FMD. RH was created through application of 220 mm Hg to the calf for 5 minutes with a sphygmomanometric cuff. After a 10-minute recovery period, nitroglycerin-mediated, endothelium-independent vasodilation was measured 3 minutes after administration of nitroglycerin 0.4 mg sublingually. Brachial artery FMD was determined by validated techniques. L-N(G)monomethyl arginine (L-NMMA; 1 mg/kg infusion over 10 minutes) was used in a subset of patients (n = 6) to competitively inhibit endothelial NO synthase.

RESULTS

Nineteen subjects were enrolled. The median age of the SVGs was 34.6 (21.0-49.7) months. SVG flow-mediated, endothelium-dependent vasodilation was measured at 5.28% +/- 3.1% mean change in lumen diameter (range, 1.99%-9.36%; P < .0001 for diameter change). Nitroglycerin-mediated vasodilation was 3.7% +/- 1.0%, (range, 16%-10.04%; P < .005). Intravenous administration of L-NMMA abolished SVG FMD (5.7 +/- 1.4% before L-NMMA vs 0.01 +/- 0.01% during L-NMMA infusion; P = .0088) and attenuated brachial artery FMD (7.54% +/- 1.0% vs 5.7 +/- 1.4; P = .05).

CONCLUSION

SVGs manifest flow-mediated, endothelium-dependent, and nitroglycerin-mediated endothelium-independent vasodilation. Vein graft endothelium-dependent FMD is likely mediated by NO. Further investigation will be required to determine the role of endothelial function in vein graft patency.

Gene transfer of COX-1 improves lumen size and blood flow in carotid bypass grafts

BACKGROUND

In autologous saphenous vein grafts, prostacyclin (PGI(1)), a vasoprotective molecule produced by normal endothelial cells, is down-regulated compared with ungrafted saphenous veins and normal carotid arteries. Reduced PGI(2) synthesis may contribute to local platelet deposition, vascular smooth muscle cell (VSMC) accumulation, atherosclerosis, and ultimately failure of venous bypass grafts. We have examined whether gene transfer-mediated overexpression of COX-1 in grafted veins (1) increases PGI(2) and cyclic AMP (cAMP) production, (2) leads to vasodilation and improved local blood flow in the presence of hypercholesterolemia, and (3) reduces neointima formation.

MATERIALS AND METHODS

Jugular veins from New Zealand-White rabbits were incubated for 30 min ex vivo with 1 x 10(10) PFU/mL of an adenoviral vector encoding COX-1 (AdCOX-1; n = 10) or empty control (n = 10) and grafted to the carotid arteries. The rabbits were placed on a high-cholesterol diet for 4 w, and blood flow and histomorphometry of the grafts were assessed.

RESULTS

In the AdCOX-1 group, blood flow was significantly increased (16.0 +/- 3.3 versus 12.5 +/- 3.3 mL/min; P < 0.05) compared with controls, and luminal area (8.9 +/- 1.4 versus 5.3 +/- 1.2 mm(2); P < 0.01) and outer circumference were larger. In six identically treated rabbits, graft PGI(2) and cAMP synthesis was increased at 72 h in AdCOX-1 compared with controls.

CONCLUSION

Our data suggest a 30-min ex vivo exposure of vein grafts to AdCOX-1 increased local synthesis of PGI(2) and cAMP after graft surgery and resulted in better graft lumen and blood flow at 4 w.

Engineering blood vessels by gene and cell therapy

Cardiovascular-related syndromes are the leading cause of morbidity and mortality worldwide. Arterial narrowing and blockage due to atherosclerosis cause reduced blood flow to the brain, heart and legs. Bypass surgery to improve blood flow to the heart and legs in these patients is performed in hundreds of thousands of patients every year. Autologous grafts, such as the internal thoracic artery and saphenous vein, are used in most patients, but in a significant number of patients such grafts are not available and synthetic grafts are used. Synthetic grafts have higher failure rates than autologous grafts due to thrombosis and scar formation within graft lumen. Cell and gene therapy combined with tissue engineering hold a great promise to provide grafts that will be biocompatible and durable. This review describes the field of vascular grafts in the context of tissue engineering using cell and gene therapies.

On the biology of saphenous vein grafts fitted with external synthetic sheaths and stents

Autologous saphenous vein is used as a conduit to bypass atherosclerotic lesions in both the coronary artery (coronary artery bypass graft surgery [CABG]) and in femoral arteries (infrainguinal bypass graft surgery [IIBS]). Despite the undoubted success and benefits of the procedures, graft failure occurs in 50% of cases within 10 years after surgery. A principal cause of late vein graft failure is intimal and medial hyperplasia and superimposed atherogenesis. Apart from lipid lowering therapy, no intervention has hitherto proved clinically effective in preventing late vein graft failure which clearly constitutes a major clinical and economic problem that needs to be urgently resolved. However, we have studied the effect of external synthetic stents and sheaths in pig models of vein into artery interposition grafting and found them to have a profound effect on vein graft remodelling and thickening. In this review, therefore, we will summarise the mechanisms underlying vein graft failure and how these stents influence these processes and the possible mechanisms involved as well as the application of these devices in preventing vein graft failure clinically.

Inhibitory effects of NFkappaB decoy oligodeoxynucleotides on neointimal hyperplasia in a rabbit vein graft model

Autologous vein remains the commonly used conduit for bypass grafts; however, neointimal hyperplasia is known to be one of the major disease processes in vein graft failure. In this study, we focused on the important role of NFkappaB which controls the expression of numerous genes for various cytokines and adhesion molecules in the mechanism of graft failure. Thus, we investigated the inhibitory effect of NFkappaB decoy oligodeoxynucleotides (ODN) on vein graft failure in a rabbit hypercholesterolemic model. Jugular vein to carotid artery interposition grafts in rabbits were transfected intraoperatively with NFkappaB decoy ODN (40 micromol/l) by ex-vivo pressure-mediated transfection (300 mm Hg, 10 min). Treatment with NFkappaB decoy ODN significantly suppressed intimal hyperplasia 4 weeks after vein implantation as compared to scrambled decoy ODN, and increased medial thickness, leading to a significant reduction in intima-to-media ratio. Treatment with NFkappaB decoy ODN significantly inhibited the recruitment of macrophages and the proliferation of vascular smooth muscle cells (VSMC), while apoptosis in VSMC was significantly increased by NFkappaB decoy ODN. In addition, a study of vascular reactivity demonstrated that transfection of grafts with NFkappaB decoy ODN significantly improved endothelium-mediated vasorelaxation as compared to scrambled decoy ODN. Here, we demonstrated that inhibition of NFkappaB activation using decoy ODN inhibited the development of neointimal hyperplasia, followed by suppression of inflammatory changes and accumulation of VSMC in the neointima of rabbit vein grafts. The present study raises the possibility of a novel strategy for prevention of graft failure.

Minimally Invasive Saphenous Vein Harvesting Using a Laryngoscope: Procedural, Functional, and Morphologic Evaluation

BACKGROUND

Because commercial minimally invasive harvesting equipments significantly increase operation costs, they are not always available in all clinics worldwide. The aim of this study was to investigate whether minimally invasive saphenous vein harvesting using a laryngoscope can be applied efficiently and successfully.

METHODS

Thirty patients were prospectively randomized into two groups. One group underwent a minimally invasive technique using a laryngoscope; the other, open saphenous vein harvest. A modified bridging technique, in which tissue retraction and illumination is achieved with a sterilized laryngoscope, was used for minimally invasive harvesting. Smooth muscle contractile and endothelial functions were tested in vitro using an organ chamber. Morphology was examined with light microscopy.

RESULTS

There was no statistically significant difference in harvest times or length of the vein harvested by either of the above mentioned techniques. Total length of the incision in the minimally invasive group was significantly shorter than that in the open group. In follow-ups, no significant complications occurred in either group. Pain and leg edema were significantly less in the minimally invasive group compared to those of the open group. There was no significant difference in response to acetylcholine and 80 mM KCl between veins taken with the laryngoscope compared to veins taken with the traditional open technique. Similarly, histological data was unable to show any significant damage to the vessel wall.

CONCLUSIONS

Because the laryngoscopic saphenectomy does not harm the harvested graft, it can be applied, instead of other minimally invasive saphenous vein harvesting systems, with a zero cost, efficiently, successfully, and with satisfactory speed and significant reduction of postoperative leg pain and wound complications.

Novel Strategies for the Prevention of Bypass Graft Failure

Bypass vein graft disease remains a significant limitation to the care of millions of patients with ischemic disease of the heart and lower extremities. The pathogenesis of this rapid, aggressive, occlusive disease lies in the remodeling response of the grafts themselves to the new arterial environment. As such, the molecular and cellular biology of neointimal hyperplasia provides a unique opportunity for cardiovascular researchers to more closely model a human clinical entity from its inception to the development of advanced disease. Recent years have therefore seen a broad new array of possible interventions for vein graft disease based on a sophisticated translation of genetic and molecular science. One of these applications, E2F decoys, has already progressed to phase III clinical studies, and many others will likely follow as the tools for therapeutic translation continue to improve. These include both gene transfer and gene blockade strategies.

Transcription factor decoys for the prevention of vein bypass graft failure

Failure of vein bypass grafts, performed for either coronary or lower extremity arterial occlusions, is a common clinical problem that incurs significant morbidity and mortality. Vein grafts provide a unique opportunity for genetic interventions, since the target tissue is available for manipulation ex vivo prior to implantation, and prior to the onset of the pathophysiologic events that lead to graft disease. Smooth muscle cell proliferation is a hallmark of neointimal hyperplasia in vein grafts and arteries, and is an attractive target for molecular therapy. Gene blockade strategies can be accomplished by delivery of small oligodeoxynucleotides (ODN) that target specific mRNAs ('antisense') or that competitively inhibit transcription factors ('decoys'). Transcription factors are attractive targets for molecular therapy since they influence the expression of a large number of genes involved in a coordinated cellular program. An ODN decoy approach has been developed targeting the transcription factor E2F, which is critically involved in cell cycle progression. Brief (10 minute) incubation of the ODN in solution, using non-distending pressure, results in efficient delivery of the ODN to >80% of cells in the vein wall. Preclinical studies in a rabbit model of vein grafting and hypercholesterolemia demonstrated a marked reduction in neointima formation, as well as prolonged resistance to graft atherosclerosis. Phase I/II studies conducted in lower extremity and coronary bypass patients have demonstrated safety and feasibility, and have also suggested possible efficacy. Large, randomized multicenter, phase III trials are currently under way to evaluate the efficacy of E2F decoy treatment on preventing vein bypass failure in both peripheral and coronary grafting procedures. These studies herald the arrival of a new class of molecular agents into the armamentarium of cardiovascular therapies.

Minimally invasive saphenous vein harvesting: effects on endothelial and smooth muscle function

BACKGROUND

The long saphenous vein remains the commonest conduit used in coronary artery bypass grafting procedures. Surgical trauma during vein harvesting can cause endothelial and smooth muscle injury that has important implications for vein graft longevity. Minimally invasive vein harvesting is advocated to reduce wound morbidity. However, the functional consequences of increased handling and traction, with potentially detrimental effects, remain unknown.

METHODS

Forty patients were prospectively randomized into either a minimally invasive (minimal) or traditional (open) saphenous vein harvest group. Smooth muscle contractile function was assessed by responses to potassium chloride and phenylephrine. Endothelial cell function was assessed by responses to serial escalations in concentration of acetylcholine, bradykinin, calcium ionophore, sodium nitroprusside, and N-nitro-L-arginine using isometric tension studies.

RESULTS

Harvest times were similar for both groups. The total incision length in the minimal group was significantly shorter than in the open group. There were no differences in smooth muscle contractions to either receptor-independent or receptor-mediated agonists between the two groups. Similarly, vasorelaxation in response to both endothelium-dependent and endothelium-independent agonists were similar in both groups.

CONCLUSIONS

Minimally invasive saphenous vein harvesting is associated with similar medial smooth muscle and endothelial function as open harvesting. These findings suggest that minimally invasive harvesting techniques can be used without major detrimental effects on vascular integrity.

Effects of dietary L-arginine on structure and function of flow-restricted vein grafts

PURPOSE

Experiments were designed to determine effects of dietary supplementation with L -arginine on structure and function of flow-restricted vein grafts.

METHODS

Saphenous veins were placed as bilateral interposition grafts in femoral arteries of two groups of adult male mongrel dogs; one group was maintained on a normal diet (control), the other group supplemented with L -arginine (200 mg/kg per day) beginning 1 week before surgery. In each dog, flow was reduced by 50% in one graft by placing an adjustable clamp on the artery distal to the distal anastomosis. Plasma amino acids and oxidized products of nitric oxide (NO(x )) were measured before and after L -arginine feeding. At postoperative week 4, grafts were removed and prepared for organ chamber studies to determine functions of the endothelium or smooth muscle and for histology.

RESULTS

Plasma L -arginine increased within 3 hours after feeding and increased from 141 +/- 8 nmol/mL to 169 +/- 11 nmol/mL (n = 6) after 5 weeks of supplementation. Plasma ornithine and citrulline paralleled arginine, whereas circulating NO(x ) was unchanged. Maximal contractions to 60 mmol/L KCl were reduced in grafts from L -arginine-fed dogs. Endothelium-dependent relaxations to the calcium ionophore A23187 and relaxations of the smooth muscle NO were reduced in grafts from L -arginine-fed dogs. Neointimal hyperplasia was increased in grafts with reduced flow and not affected by arginine feeding.

CONCLUSIONS

Dietary supplementation with L -arginine did not increase plasma NO in dogs with peripheral vein grafts or increase endothelium-dependent relaxations in control or flow-restricted grafts. Therefore, dietary supplementation with L -arginine may not improve long-term functions of flow-restricted peripheral bypass grafts.

Direct measurement of nitric oxide release from saphenous vein: abolishment by surgical preparation

BACKGROUND

Surgical preparation (distension) of the saphenous vein (SV) is applied routinely during harvesting in coronary artery bypass grafting (CABG). However, mechanical distension may impair the endothelium, which plays an important role in long-term patency. The present study investigated the effect of surgical preparation of the SV on nitric oxide (NO) release from the endothelium by direct measurement of NO.

METHODS

Saphenous vein segments taken from CABG patients were cut open longitudinally and placed in an organ chamber. An NO-sensitive electrode and NO meter were used to directly measure NO release induced by acetylcholine (ACh) and bradykinin (BK) from the surgically prepared veins (PV) compared with the control (nondistended) veins.

RESULTS

The basal release of NO in the PV group was significantly lower than that in the control group (3.4 +/- 1.4 nM, n = 9 versus 9.9 +/- 2.8 nM, n = 13, p = 0.002). The maximum concentrations of NO release induced by ACh and BK in the PV group were also significantly lower than those in the control veins (for ACh 10(-6) mol/L: 9.6 +/- 3.1 nM, n = 8 versus 41.9 +/- 11.2 nM, n = 12, p = 0.005; for BK 10(-8) mol/L: 8.3 +/- 3.7 nM, n = 7 versus 37.9 +/- 6.1 nM, n = 9, p = 0.003). Further, the duration of NO release in the PV group was significantly shorter than that in control veins (1.5 +/- 1.3 minutes, n = 8 versus 8.1 +/- 1.9 minutes, n = 8, p < 0.001).

CONCLUSIONS

Surgical preparation almost abolishes NO release by the SV and this may significantly contribute to the low long-term patency rate of the vein graft.

Evidence that Alzheimer's disease is a microvascular disorder: the role of constitutive nitric oxide

Evidence is fast accumulating which indicates that Alzheimer's disease is a vascular disorder with neurodegenerative consequences rather than a neurodegenerative disorder with vascular consequences. It is proposed that two factors need to be present for AD to develop: (1) advanced ageing, (2) presence of a condition that lowers cerebral perfusion, such as a vascular-risk factor. The first factor introduces a normal but potentially insidious process that lowers cerebral blood flow in inverse relation to increased ageing; the second factor adds a crucial burden which further lowers brain perfusion and places vulnerable neurons in a state of high energy compromise leading to a cascade of neuronal metabolic turmoil. Convergence of the two factors above will culminate in a critically attained threshold of cerebral hypoperfusion (CATCH). CATCH is a hemodynamic microcirculatory insufficiency that will destabilize neurons, synapses, neurotransmission and cognitive function, creating in its wake a neurodegenerative state characterized by the formation of senile plaques, neurofibrillary tangles, amyloid angiopathy and in some cases, Lewy bodies. Since any of a considerable number of vascular-related conditions must be present in the ageing individual for cognition to be disturbed, CATCH identifies an important aspect of the heterogeneic disease profile assumed to be present in the AD syndrome. It is proposed that CATCH initiates AD by distorting regional brain capillary structure involving endothelial cell shape changes and impairment of nitric oxide (NO) release which affect signaling between the immune, cardiovascular and nervous systems. Evidence is presented that in many tissues there is a basal level of NO being produced and that the actions of several signaling molecules may initiate increases in basal NO levels. Moreover, these temporary increases in basal NO levels exert inhibitory cellular actions, via cellular conformational changes. Findings indicate that (a) constitutive NO is responsible for a basal or 'tonal' level of NO; (b) this NO keeps particular types of cells in a state of inhibition and (c) activation of these cells occurs through disinhibition. Consequently, tissues not maintaining a basal NO level are more prone to excitatory, immune, vascular and neural influences. Under such circumstances, these tissues cannot be down-regulated to normal basal levels, thus prolonging their excitatory state. Thus, the clinical convergence of advanced ageing in the presence of a chronic, pre-morbid vascular risk factor, can, in time, contribute to an endotheliopathy involving basal NO deficit, to the degree where regional metabolic dysfunction leads to cognitive meltdown and to progressive neurodegeneration characteristic of Alzheimer's disease.

Effects of transdermal nicotine treatment on structure and function of coronary artery bypass grafts

Smoking is a major risk factor for failure of coronary artery bypass grafts (CABG). Experiments were designed to determine effects of transdermal nicotine, independent of smoking, on structure and function of CABG. Saphenous veins were placed as CABG in untreated dogs (control) or in dogs treated with transdermal nicotine (one 11-mg or two 22-mg patches/day) for 5 wk. Serum nicotine and plasma nitric oxide were measured. Grafts were removed and prepared for organ chamber studies and histology. Serum nicotine averaged 12.1 and 118.7 ng/ml in the 11 mg/day and 44 mg/day groups, respectively. Plasma nitric oxide was higher in dogs treated with 11 mg/day doses compared with controls. In organ chamber studies, endothelium-dependent relaxations to thrombin and A-23187 and endothelium-independent relaxations to nitric oxide were greatest in grafts from dogs treated with 11 mg/day doses. Intimal thickness of the grafts were similar among groups. However, staining for bone sialoprotein was increased in the media of grafts from the 11 mg/day treatment group. These data suggest that transdermal nicotine in doses comparable and double to those used for conventional smoking cessation treatment in humans does not adversely affect early patency of canine CABG up to 4 wk postoperatively. Transdermal nicotine, however, may increase production of and response to nitric oxide in bypass grafts.

Intimal growth and neovascularization in human stenotic vein grafts

BACKGROUND

Myointimal thickening and microvessel ingrowth are commonly observed in vein graft stenosis, which complicates a third of infrainguinal bypass procedures. But a direct correlation between these two features has not been established. Our purpose was to analyze the relationship between neovascularity and intimal thickness in human vein grafts.

STUDY DESIGN

Twenty-two explant stenotic vein grafts (STVG), 8 nonstenotic arterialized vein grafts (AVG), and 20 age-matched control greater saphenous veins (CGSV) were analyzed histologically and compared morphologically by light microscopy. Digitized computer image analysis was used to measure intimal thickness and quantitate microvessel ingrowth. Immunolocalization of endothelial cells around the lumen and in microvessels was determined using antibodies to factor VIII and to endothelial nitric oxide synthase (eNOS), respectively.

RESULTS

Focal areas of endothelial disruption and thrombus deposition were present in 23% (5 of 22) of stenotic vein grafts. The neointima of STVG grafts was two- and fourfold thicker than that of AVG and CGSV, respectively (p < 0.0001). Microvessels were most frequently observed in the adventitia and media of STVG and increased in number with increasing intimal thickness (p < 0.001 by ANOVA).

CONCLUSIONS

A fourfold increased neointimal thickness in critically stenotic vein grafts is associated with increased medial and adventitial neovascularization. Remodeling alone with doubling of the intimal thickness in nonstenotic arterialized vein grafts does not appear to be associated with enhancement of the graft microvasculature. More specific observations using an experimental model may allow us to further define the role of angiogenesis in vein graft stenosis and to determine the therapeutic implications of such observations.

Human aortocoronary grafts and nitric oxide release: relationship to pulsatile pressure

BACKGROUND

Short and long-term failure of saphenous vein grafts continues to be a significant problem for cardiac surgeons. The purpose of this study was to elucidate the early adaptive changes of human artery and vein conduits with respect to nitric oxide (NO) production under various pressure and pulsatile distention conditions.

METHODS

Real-time amperometric NO determinations were made in an in vitro model using human saphenous vein segments (n = 12) and internal thoracic artery segments (n = 8) between 70 and 170 mm Hg, under static conditions recorded with a pressure transducer. Exposing the tissue to morphine (10(-6) M) also stimulated NO release. Under conditions in which the conduits were exposed to the respective pressures for 1 hour, they were then examined for their granulocyte-adhering potential using computer-assisted imaging techniques.

RESULTS

A pressure-dependent decrease of NO release was found after 32 minutes of pulsatile pressure (170 mm Hg) in artery and vein, the latter of which appeared to be affected more negatively (p < 0.05; because many more observation points differed significantly after 32 minutes compared to 110 mm Hg values). In vessels maintained for 1 hour at these different pressures and then exposed to morphine (1 microM), stimulated NO release significantly diminished in the veins (artery 37.4 nM NO versus vein 18.1 nM NO; p < 0.05). Increased pressures also correlated with an increase in granulocyte adhesion to veins that could not be reduced following morphine exposure.

CONCLUSIONS

Increased pressure and cyclic distention lead to loss of NO release and increased immunocyte adhesion, which are significantly more pronounced in saphenous vein than in internal thoracic artery, suggesting that in the long term this may contribute to the failure of saphenous vein conduits in coronary revascularization.

Gene therapy for vein grafts

Bypass vein graft failure represents the greatest limitation to the current surgical therapy of myocardial and lower extremity ischemia. Elucidation of the molecular and cellular biology of neointimal hyperplasia and subsequent vein graft atherosclerosis has formed a basis for the design and implementation of gene-based therapies to prevent vein graft disease. Manipulation of the genetic regulation of vascular cell cycle progression has been shown to effectively redirect vein graft biology away from neointimal disease and toward medial hypertrophy as a more adaptive form of remodeling in response to stresses of the arterial circulation, and has prevented experimental graft atherosclerosis. Early clinical experience suggests that this approach may provide an early avenue for translation of such a gene-based therapy in humans. Other experimental gene transfer strategies have also been explored in animal models of vein grafts, which may be particularly well suited to the application of genetic manipulation given the direct access to the tissue at the time of disease initiation.

The relationship between polymorphisms in the endothelial cell nitric oxide synthase gene and the platelet GPIIIa gene with myocardial infarction and venous thromboembolism in African Americans

STUDY OBJECTIVES

To determine whether the polymorphic dinucleotide repeats found in intron 4 of the endothelial cell nitric oxide synthase (ecNOS) gene and the platelet GPIIIa PLA(1)/A(2) polymorphism are associated with myocardial infarction (MI) and venous thromboembolism (VTE) in African Americans. Because these two genes may interact physiologically, the third objective was to determine if there was a relationship between the polymorphisms with respect to MI and VTE.

DESIGN

A hospital-based case-control study. After informed consent was obtained, blood used for DNA extraction was drawn from the subjects.

SETTING

The study was conducted in the Anticoagulant Clinic and the Cardiology Clinic at Grady Memorial Hospital in Atlanta Georgia.

PATIENTS

Subjects were recruited from African-American patients with a reported history of MI (n = 110) or VTE (n = 91). Control subjects (n = 185) without a history of cardiovascular or venous disease were recruited from an outpatient clinic.

MEASUREMENTS AND RESULTS

The 393 ecNOS allele was more common among MI cases (36%; p = 0.01) and VTE cases (35%; p = 0.04) than among control subjects (26%). There was no association between the GPIIIa genotypes and either MI or VTE. However, among the MI subjects, there was a strong association between the ecNOS 393/393 genotype and the Pl(A2) allele. It was also found that the frequency of the 393 allele was higher in African-American persons (0.26) compared with what has been reported for Australian Caucasians (0. 14) and Japanese (0.10).

CONCLUSIONS

The 393 allele but not the Pl(A2) allele was significantly associated with both MI and VTE in African Americans. Homozygosity for the 393 allele was significantly associated to the diagnosis of MI prior to the age of 45. The combination of the 393 allele and a Pl(A2) allele was also highly associated with MI. The frequency of the 393 allele was significantly higher in African Americans than what has been reported for other populations. This study furthers not only extends the association of the 393 allele to VTE but has demonstrated an interaction with the Pl(A2) allele with respect to MI.

How to standardize vasomotor tone in serial studies based on quantitation of coronary dimensions?

In patients with coronary artery disease including those after coronary bypass graft operation and heart transplantation intervention studies based on serial quantitative coronary angiography, in part combined with intravascular ultrasound, are of increasing relevance. Since vasomotor tone of epicardial coronary arteries is influenced by a variety of factors, angiographic follow-up studies require standardization of coronary tone by induction of maximal dilation. We reviewed the effects of the most potent coronary vasodilatory drug groups, calcium antagonists and nitrocompounds, on coronary diameters. Intravenous or intracoronary injections of verapamil, diltiazem, nifedipine, nicardipine, and nisoldipine can cause profound coronary dilation which has been shown to be maximal with verapamil and nisoldipine. Shortcomings of calcium antagonists include short or unknown duration of action after bolus administration, severe drop in blood pressure, and lack of commercial availability of solutions for injection of many substances. Isosorbide dinitrate induces profound coronary dilation; however, after sublingual administration marked blood pressure decrease can occur, and the duration of action and ideal dose of intracoronary isosorbide dinitrate has not been investigated yet. Injections of molsidomine and its active metabolite, SIN-1, cause longlasting, reproducible, maximal coronary dilation, although only after a waiting period of at least 10 minutes; unfortunately, SIN-1 is only commercially available in France. Nitroglycerin induces reproducible maximal coronary dilation and is easy to administer sublingually or as intracoronary bolus injection with rapid onset of action and no major side effects. The short duration of action may require repeated administrations. To date, repeated intracoronary bolus injections of 0.1 mg nitroglycerin every 10 minutes seem to be the optimal known regimen for standardization of coronary vasomotor tone in serial angiographic studies. Further investigations in this field with old and new vasodilatory drugs are recommendable.

Difference in acetylcholine-induced nitric oxide release of arterial and venous grafts in patients after coronary bypass operations

OBJECTIVES

In vivo investigation of nitric oxide release in coronary bypass grafts has not been reported. We studied acetylcholine-induced nitric oxide release in vivo of coronary bypass grafts and vasomotor responses to acetylcholine of grafted coronary arteries in patients after coronary bypass grafting.

METHODS

We examined 24 internal thoracic artery grafts and 16 saphenous vein grafts in 39 patients. The mean ages of the patients were 65 years for the arterial grafts and 68 years for the venous grafts. Nitric oxide was measured as the plasma nitrite level by the Griess reaction. Before and after intragraft acetylcholine infusion (5 microg), blood was sampled from the distal end of the graft, and angiograms were taken and analyzed by cine-densitometry.

RESULTS

The plasma nitrite concentration after stimulation with acetylcholine compared with the control value was 134%+/-52% at 4 minutes (p=0.05) and 184%+/-107% at 6 minutes (p=0.01) in the arterial grafts; in the venous grafts these values were 101%+/-24% at 4 minutes (p=0.96) and 108%+/-36% at 6 minutes (p=0.69). Low-dose acetylcholine dilated the coronary arteries supplied by arterial grafts by 6.3%+/-16.6% whereas coronary arteries supplied by venous grafts were reduced by 9.8%+/-11.8% in diameter and the vasoactive responses were different (p=0.01).

CONCLUSIONS

In vivo internal thoracic artery grafts had more endothelium-derived nitric oxide release in response to acetylcholine than did saphenous vein grafts after coronary bypass grafting.

Differential action of angiotensin II and activity of angiotensin-converting enzyme in human bypass grafts

OBJECTIVE

The activity of the renin-angiotensin system may be important in determining the performance of coronary artery bypass grafts. We have examined the activity of tissue angiotensin-converting enzyme and the effects of angiotensin II in vessels used as bypass grafts.

METHODS

Organ bath studies were used to determine the vasoactive effect of angiotensin II. The activity of the angiotensin-converting enzyme was assessed by metabolism of a specific synthetic substrate.

RESULTS

The saphenous vein produced greater maximum responses to angiotensin II than did the internal thoracic artery. This response was not modified by inhibition of nitric oxide synthase, cyclooxygenase, or by an endothelin receptor antagonist in either vessel. Losartan, an AT1 receptor antagonist, inhibited the vasoconstrictor response in both blood vessels. Homogenates of saphenous vein and internal thoracic artery displayed tissue angiotensin-converting enzyme activity, which was inhibited by captopril. Enzyme activity was threefold greater in the vein. Both the contractile response to angiotensin II and the enzyme activity were retained in venous grafts removed up to 20 years after coronary bypass surgery.

CONCLUSIONS

These data demonstrate that marked differences exist in angiotensin-converting enzyme activity and AT1 receptor responses in the saphenous vein compared with the internal thoracic artery. These findings may have important implications for the performance of the vein when used as a coronary artery bypass graft and may have clinical implications for the use of angiotensin-converting inhibitors and AT1 receptor antagonists in the prevention and treatment of vein graft disease.

Expression of vascular adhesion molecules in saphenous vein coronary bypass grafts

BACKGROUND

Adhesion of blood elements to the endothelium is an important step in the development of vein graft disease. This study examines the expression of vascular adhesion molecules on explanted saphenous vein bypass grafts.

METHODS

Immunocytochemical staining was performed using explanted saphenous vein grafts from 28 patients. Antibodies against the endothelial markers CD31, von Willebrand factor, intercellular adhesion molecule-1, vascular adhesion molecule-1, and E-selectin were used.

RESULTS

Staining for CD31 and von Willebrand factor demonstrated the presence of endothelial cells in the lumen and the vasa vasorum. Expression of intercellular adhesion molecule-1 was variable between grafts, whereas vascular adhesion molecule-1 and E-selectin were almost always absent on the luminal endothelium. In contrast, the endothelium of the vasa vasorum stained positively for intercellular adhesion molecule-1 and vascular adhesion molecule-1, and was also seen on nonendothelial cells within the vessel wall. Expression of these adhesion molecules did not vary with the severity of vein graft disease.

CONCLUSIONS

This study highlights the blood vessels in the adventitia as possible sites for the adhesion and migration of cells into the vessel wall.

Vein grafts: haemodynamic forces on the endothelium--a review

OBJECTIVE

To review the mechanisms believed to be important in the development of vein graft stenosis, with particular attention placed on the adaptation of saphenous vein endothelium to a new haemodynamic environment.

DESIGN AND METHODS

Discussion based on review of published research.

RESULTS

The aetiology of vein graft stenosis remains to be established and appears to be multi-factorial. The increasing evidence for an important role of haemodynamic forces is discussed, particularly via the interaction of these force with the endothelium.

CONCLUSION

Further understanding of the interaction between haemodynamic forces, blood constituents and the newly implanted vein graft is required. Use of in vitro models is contributing increasing knowledge to this area, but ultimately better non-invasive methods of assessing haemodynamic forces in vivo are required.

Dilatation of saphenous vein grafts by nitric oxide

OBJECTIVES

To investigate firstly whether flow-dependent vasodilation is maintained in vein grafts, and secondly whether nitric oxide donors dilate vein grafts to improve the flow through graft stenoses.

DESIGN, MATERIALS AND METHODS

The vasodilatation of mature patent vein grafts, in response to reactive hyperaemia and glyceryl trinitrate (GTN), was assessed by the change in external diameter using duplex ultrasonography. The severity (ratio of proximal systolic velocity, V1, to peak systolic velocity at the stenosis, V2, of vein graft stenoses was determined by duplex ultrasonography before and after 24 h of local application of GTN patches.

RESULTS

In post-occlusion hyperaemia the diameter of patent distal vein grafts (n = 7) increased to a maximum of 112 +/- 1.9% of resting diameter after 2 min, p = 0.026. The diameter increased further to 117 +/- 2.5% of the resting value 5 min after oral GTN (n = 5), p = 0.007. The velocity ratio, V2/V1, through graft stenoses (n = 6) decreased by 20 +/- 5% after application of GTN patches, principally as a result of reduction in V2, mean difference 0.8, p = 0.15. The changes in response to GTN were more evident for proximal than distal vein graft stenoses.

CONCLUSION

Flow-induced vasodilatation responses, which have been attributed to the endothelial release of nitric oxide, are maintained in patent vein grafts: the grafts dilate even further in response to GTN. The application of GTN patches close to a vein graft stenoses appears to reduce the velocity ratio through vein graft stenoses. GTN patches might be used to reduce the risk of graft occlusion when there is a delay between the detection and the treatment of haemodynamically significant graft stenoses.

Cell cycle inhibition preserves endothelial function in genetically engineered rabbit vein grafts

We have recently shown that ex vivo gene therapy of rabbit autologous vein grafts with antisense oligodeoxynucleotides (AS ODN) blocking cell cycle regulatory gene expression inhibits not only neointimal hyperplasia, but also diet-induced, accelerated graft atherosclerosis. We observed that these grafts remained free of macrophage invasion and foam cell deposition. Since endothelial dysfunction plays an important role in vascular disease, the current study examined the effect of this genetic engineering strategy on graft endothelial function and its potential relationship to the engineered vessels' resistance to atherosclerosis. Rabbit vein grafts transfected with AS ODN against proliferating cell nuclear antigen (PCNA) and cell division cycle 2 (cdc2) kinase elaborated significantly more nitric oxide and exhibited greater vasorelaxation to both calcium ionophore and acetylcholine than did untreated or control ODN-treated grafts. This preservation of endothelial function was associated with a reduction in superoxide radical generation, vascular cell adhesion molecule-1 (VCAM-1) expression, and monocyte binding activity in grafts in both normal and hypercholesterolemic rabbits. Our data demonstrate that AS ODN arrest of vascular cell cycle progression results in the preservation of normal endothelial phenotype and function, thereby influencing the biology of the vessel wall towards a reduction of its susceptibility to occlusive disease.

Effects of thoracic epidural anesthesia on changes in ischemic myocardial metabolism induced by intracoronary injection of endothelin in dogs

OBJECTIVE

Thoracic epidural anesthesia (TEA) has been reported to alleviate ischemic damage to the myocardium. Endothelin, an endothelium-derived peptide and a potent coronary vasoconstrictor, may contribute to poor cardiac perfusion and ischemia. The objective was to examine regional myocardial metabolism during ischemia caused by intracoronary injection of endothelin with and without TEA.

DESIGN

The three experimental groups and three treatments were randomized.

SETTING

All studies were conducted in a university research laboratory.

PARTICIPANTS

Thirty anesthetized dogs comprised the study groups.

INTERVENTIONS

Study animals were divided into three groups of 10 animals each identified as normal saline (NS); TEA; and TEA + blood pressure controlled (TEA + BPC). The NS group had 0.5 mL/kg of normal saline injected into the T4-5 epidural space. The TEA group had 0.5 mL/kg of saline containing 1% lidocaine injected into the T4-5 space. The TEA + BPC group had blood pressure and heart rate maintained at pre-epidural injection values by partially occluding the descending aorta and by atrial pacing. Endothelin (15 pmol/kg) was bolus injected into the left anterior descending (LAD) artery of each heart. Systolic and diastolic blood pressure, heart rate, and LAD coronary blood flow (CBF) were monitored. Three minutes after injection of endothelin, myocardial tissue was sampled from the distribution of the LAD artery and from the control, left circumflex (LCx) artery. ATP, ADP, AMP, lactate, and pyruvate were measured by enzymatic methods.

MEASUREMENTS AND MAIN RESULTS

It was found that in each group endothelin consistently decreased LAD CBF, but the decrease was less in the TEA + BPC group. In the tissue distribution of the LAD, the levels of ATP and energy charge potential were lower, and the level of lactate was higher in the NS group than in the TEA or the TEA + BPC groups (p < 0.01).

CONCLUSIONS

These results confirm that (1) endothelin injected into the LAD artery decreases CBF and causes selective myocardial ischemia in a fashion similar to intravascular stenosis of the LAD rather than to mechanical occlusion and (2) TEA, with or without pressure support, lessens the degree of regional ischemia induced by injection of endothelin in the LAD.

Explanted vein grafts with an intact endothelium demonstrate reduced focal expression of endothelial nitric oxide synthase specific to atherosclerotic sites

The endothelial L-arginine:nitric oxide (NO) system is fundamental to vascular function. It is becoming evident that this system is compromised in aorto-coronary vein grafts, although it is not clear how it is affected. It was postulated that the development of intimal lesions in vein grafts may be associated with reduced expression or loss of endothelial NO synthase (eNOS). The immunocytochemical localization and quantitative expression of eNOS were therefore investigated in normal human saphenous veins (n = 6) and explanted vein grafts (n = 6). The vein grafts demonstrated marked morphological changes evident as fibro-intimal hyperplasia (FIH) and focal sites of atherosclerosis, often occurring along the same length of graft. Staining for eNOS was abundantly evident in the endothelium of normal veins but revealed a differential reduction in staining intensity in vein grafts. Staining intensity measurements revealed a significant reduction (P < 0.001) in the amount of eNOS present in areas of atherosclerosis as compared with normal veins and areas of vein graft with FIH changes alone. This reduction in the relative quantity of antigen was specific to eNOS, since the endothelial markers von Willebrand factor (vWf) and CD31 showed no such variations. These data support the view that vascular activity of NO is impaired in atherosclerosis and indicate that reduced expression of eNOS, and therefore by inference lower NO production, may make an important contribution to this phenomenon.

Effects of pulsatile perfusion on human saphenous vein vasoreactivity: a preliminary report

This study examined the effects of exposure to arterial blood pressure and flow on human saphenous vein catecholamine sensitivity. Unused portions of saphenous vein from eight patients undergoing peripheral bypass procedures were mounted parallel in a specially designed organ culture apparatus and perfused with tissue culture medium with 95% CO(2) at 37 degrees C. One segment was fixed between two cannulas while the medium was gently agitated (control) and the other was actively perfused via a pulsatile pump system at a rate of 60 beats/min, peak pressure of 100 mmHg and peak flow of 200 ml/min (pulsed; mean pressure 60 mmHg; mean flow 115 ml/min). After 48 h, vein segments were removed and tested for in vitro isometric contraction in response to KCI, norepinephrine and histamine, and relaxation in response to acetylcholine, calcium ionophore A23187, and sodium nitroprusside. There were no differences in mean(s.e.m.) maximal contraction in response to KCI (control 0.61(0.16) g versus pulsed 0.72(0.27)g; P = n.s.), norepinephrine (control 1.00(0.56) g versus pulsed 1.51(0.54) g; P= n.s.), or histamine (control 1.47(0.85) g versus pulsed 1.95(0.64) g; P= n.s.). However, pulsed veins exhibited increased sensitivity to both norepinephrine (control -logED50 6.20(0.23) versus pulsed mean(s.e.m.) 6.60(0.17); P< 0.05) and histamine (control -logED(50) 5.60(0.27) versus pulsed 6.24(0.20); P = 0.05). Pulsed veins exhibited slightly less acetylcholine-induced relaxation although the difference did not reach statistical significance (control mean(s.e.m.) relaxation at 1 x 10(6)M 9.2(14.0)% versus pulsed -13.3(6.4)%; P = n.s.). There were no differences in relaxation in response to either A23187 (control 1 x 10-(4)M 178(19)% versus pulsed 191(68)% or sodium nitroprusside (control 225(15)% versus pulsed 254(17)%; P = n.s.). The data presented herein indicate that exposure of human saphenous vein to the hemodynamics of the arterial environment for 48 h results in catecholamine supersensitivity while contractile and relaxant function are not affected.

Pathophysiology of vein graft failure: a review

Vein bypass grafting is an integral component of cardiovascular surgical practice for both arterial and venous diseases. However, many of these grafts will eventually fail due to either intrinsic or extrinsic causes. This review examines the current understanding and knowledge of venous histology, vein graft pathology and the associated endothelial and smooth muscle cell physiology and pharmacology. In addition, the status of research on the therapeutic control of vein graft intimal hyperplasia and accelerated atherosclerosis is assessed.

The expression and function of G-proteins in experimental intimal hyperplasia

G-proteins are membrane-bound signal transduction proteins which couple extracellular receptor signals to various effectors. This study examines the expression and the function of G-proteins (alpha i, alpha s, alpha q, and alpha o) in experimental intimal hyperplasia. Vein bypass grafts were placed in 30 New Zealand White rabbits and were harvested after 28 d. The contralateral jugular veins served as controls. Isometric tension studies were performed on rings from veins and vein grafts (n = 10), and Western blot and mRNA analyses were performed in another 20 vessels. There was a fivefold increase in alpha q, a 2.7-fold increase in the alpha i2, and a 3.3-fold increase in alpha s expressions in vein grafts compared with veins. Detectable expression of alpha i3 was observed in vein grafts but not in jugular veins. In addition, there was a 3.8-fold increase in beta subunits in the vein grafts compared with the veins. mRNA for alpha s, alpha i3, and alpha i2 were all elevated in the vein grafts. No detectable levels of the alpha i1 protein or its mRNA were present in either veins or vein grafts. Contractile responses in the veins were not inhibited by pertussis toxin. The contractile responses to norepinephrine were enhanced by twofold, and the responses to serotonin developed de novo in vein grafts compared with veins. The contractile responses to both norepinephrine and serotonin were only partially inhibited by pertussis toxin in the vein grafts even though there was 100% ADP ribosylation with pertussis toxin in both veins and vein grafts. These data suggest that intimal hyperplasia is associated with increased or novel expression of G-proteins in vivo which occur simultaneously with the development of pertussis toxin-sensitive contractile responses. Changes in G-proteins at a transcriptional level or at the level of RNA stability may be involved in the response of smooth muscle cells to injury and to intimal hyperplasia formation.

The role of serotonin blockers in cardiac anesthesia

In the complex setting of cardiac surgery and cardiopulmonary bypass, several potent mediators are released that by interacting may cause clinical syndromes like coronary ischemia, systemic hypertension, pulmonary hypertension, and renal failure. One of the mediators is serotonin, released from aggregating platelets, and causing vasoconstriction by activating S2-serotonergic receptors, particularly in patients with an impaired endothelial function, as in atherosclerosis. The most important available specific S2-serotonergic receptor antagonist is ketanserin. If administered during or after cardiac surgery, ketanserin lowers systemic and pulmonary blood pressure, and improves peripheral and pulmonary perfusion without causing reflex tachycardia or an increase in pulmonary shunt fraction.

Control of the structural and functional consequences of vein graft intimal hyperplasia with a 21-aminosteroid--U74389G

Following angioplasty and vein bypass grafting, there is endothelial cell injury, infiltration of leukocytes and smooth muscle cell (SMC) proliferation leading to intimal hyperplasia which may result in stenosis and can lead to eventual occlusion. This study examines the effect of the 21-aminosteroid U74389G (Upjohn Company), on the formation of vein graft intimal hyperplasia in vivo and on SMC DNA synthesis and proliferation in vitro. Twenty New Zealand White rabbits had a right carotid interposition bypass graft using the ipsilateral external jugular vein. Ten animals received chronic oral therapy with U74389G (25 mg/kg/day; begun 5 days before surgery and continued until harvest) and 10 control animals received vehicle only. All animals were sacrificed on the 28th postoperative day. Vein grafts were harvested either for histology/videomorphometry (n = 6 per group) or for in vitro isometric tension studies (n = 4; four 5 mm rings per graft). The incorporation of [3H]thymidine into the cellular DNA of serum-stimulated rabbit aortic SMC (passage 6th to 12th) was assessed in the presence of increasing concentrations of U74389G (10(-9) to 10(-4) M). The effect of U74389G on in vitro cell proliferation was also assessed. Treatment with U74389G produced a 44% decrease in overall mean intimal thickness from 82 +/- 1 microM (mean +/- S.E.M.) in the controls to 57 +/- 10 microM in the U74389G treated vein grafts (p = 0.003).(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term human vein graft contractility and morphology: a functional and histopathological study of retrieved coronary vein grafts

Vasoreactivity of 11 coronary artery vein bypass grafts and 13 human saphenous veins was examined. Isometric tension studies were performed in response to potassium chloride (110 mmol/l), noradrenaline (10(-9)-10(-4) mol/l), serotonin (10(-9)-10(-4) mol/l) and histamine (10(-8)-10(-2) mol/l). After precontraction with noradrenaline (10(-5) mol/l), the response to acetylcholine (10(-8)-10(-4) mol/l) and the calcium ionophore A23187 (10(-8)-10(-4) mol/l) was also assessed. Results are given as mean(s.e.m.). Compared with saphenous veins, vein grafts showed decreased sensitivity to noradrenaline (1.7(0.5) versus 0.4(0.1) mumol/l, P = 0.01), no change in sensitivity to serotonin (55(18) versus 37(15) mumol/l, P > 0.05) and supersensitivity to histamine (3.2(0.9) versus 30.1(13.2) mumol/l, P = 0.01). Vein grafts had a decreased maximal contraction to potassium chloride (1.1(0.3) versus 5.5(0.8) g, P = 0.0001), noradrenaline (1.2(0.3) versus 4.1(0.8) g, P = 0.005), histamine (1.2(0.3) versus 4.5(0.8) g, P = 0.003) and serotonin (0.7(0.2) versus 5.7(0.6) g, P = 0.0002) compared with saphenous vein. Precontracted vein grafts did not relax in response to acetylcholine; in contrast, saphenous vein relaxed in a dose-dependent manner to a maximal relaxation of 22(3) per cent. Both saphenous vein and vein graft relaxed in response to A23187. Vein graft intimal thickness was approximately fourfold greater than that of saphenous vein (540(110) versus 136(30) microns). Scanning electron microscopy of vein and vein graft revealed an intact endothelium. Coronary artery vein grafts are capable of responding to various contractile agonists; these response are notably different from those of saphenous vein and there is a loss of endothelium-dependent relaxation. Even at a late stage vein grafts are not inert but are functional conduits with an abnormally responsive endothelium and a less potent, but significantly altered, smooth muscle contractile profile.

Human saphenous vein grafts explanted from the arterial circulation demonstrate altered smooth-muscle and endothelial responses

PURPOSE

Animal models have been used to assess the function of vascular smooth muscle and endothelium of veins grafted into arterial circulation. The primary model consists of grafting the external jugular vein into the carotid artery of the rabbit. These studies suggest a selective increase in the responsiveness of the grafted veins to serotonin. However, in both human cardiac and peripheral vascular operations, the saphenous, not the jugular, is the vein most frequently used. Thus the propriety of the rabbit model is unknown.

METHODS

Human saphenous veins and vein grafts were obtained from patients undergoing leg vein bypass graft revisions (n = 8). The reversed vein grafts were placed into arterial circulation for periods ranging from 4 to 26 months before removal (mean 16 months). All vessels were immediately cut into rings and suspended in organ chambers for recording isometric contractions to norepinephrine and serotonin.

RESULTS

The maximal contractions elicited by both norepinephrine and serotonin were reduced in human vein grafts in comparison to the results in human saphenous vein (maximal response to norepinephrine 1.42 +/- 0.34 gm [vein graft] vs 4.59 +/- 1.13 gm [saphenous vein], p = 0.031; maximal response to serotonin 2.68 +/- 0.58 gm [vein graft] vs 4.72 +/- 1.11 gm [saphenous vein], p = 0.042). Human vein grafts were less responsive to norepinephrine than was saphenous vein (negative log of concentration that caused 50% of the maximal response -5.91 +/- 0.10 and -6.84 +/- 0.22, respectively; p < 0.009). After precontraction with norepinephrine (to 30% of the maximal response), saphenous vein, but not vein grafts, demonstrated endothelium-dependent relaxation to acetylcholine (maximum relaxation 27.4% +/- 6.8%; p = 0.001).

CONCLUSIONS

Human saphenous veins grafted into arterial circulation exhibit loss of endothelium-dependent relaxation to acetylcholine and diminished contractions to agonists (norepinephrine and serotonin). In contrast to rabbit data, serotonin elicits dose-dependent contractions in both human saphenous vein and human vein grafts. Since the vascular wall contractility varies widely across species, the relevance of rabbit vein graft data to human bypass grafts is uncertain.