The effect of vascular endothelial growth factor on angiogenesis: an experimental study.

OBJECTIVE: to evaluate the effects of exogenous vascular endothelial growth factor (VEGF) on angiogenesis in a rabbit model of persistent hind limb ischaemia. MATERIALS AND METHODS: ischaemia was induced in the hind limbs of 42 New Zealand white rabbits divided into six groups, each of 7 animals. Group 1a and 1b received intramuscular injections of 1 and 2 mg VEGF/day, respectively, into the ischaemic hind limb for 10 days beginning on postoperative 11th day, and group 1c received IM injections of saline only. Group 2a and 2b received similar regimen of VEGF, but administered intra-arterially. Group 2c served as controls. Perfusion of the ischaemic limb was evaluated by thigh blood pressure and thigh circumference at 10, 25 and 40 days following limb ischaemia in all animals and by digital subtraction angiography, perfusion scans, histological examination of capillary density in 2 animals from each group. RESULTS: thigh pressure index and thigh circumference improved significantly in the VEGF treated animals (Groups 1a,b and 2a,b). Collateral formation, as assessed by angiography, scintigraphy and by histological examination, indicated marked formation of collaterals in the VEGF treated animals as compared with the controls. This was most pronounced in groups receiving the highest dose of VEGF. CONCLUSION: these data suggest that VEGF promotes angiogenesis, that the route of administration is unimportant, but that a dose-response relationship is present in this experimental ischaemic hind limb model.     

The effect of a thromboxane receptor antagonist on acute ePTFE arterial graft thrombogenicity--an experimental study in sheep.

ePTFE interposition grafts in the common carotid arteries of 16 adult sheep were used to study the effect of a thromboxane receptor antagonist. Vapiprost (GR 32191, Glaxo research group, London, UK). After insertion of the grafts the sheep were randomised to treatment (n = 8) or control (n = 8). Treatment was given as an intravenous injection with GR 32191 of 1 mg/kg body weight. The flow in one of the two inserted grafts was restricted from normal (190 ml/min) to 25 ml/min. Autologous 111-In labelled platelets and human 125-I labelled fibrinogen were injected intravenously. The radioactivity over each graft was measured for 4 h at two separate points with a gamma scintillation technique. Due to technical complications immediately before the start of the measurements one sheep in each group was excluded from the study. In the treated group three out of seven grafts with restricted flow occluded compared to all seven grafts with a flow reduction in the control group (p less than 0.05). The grafts with unrestricted flow occluded in two of seven in both groups. In the open grafts with unrestricted flow the fibrinogen activity was significantly reduced in the treated group compared to the control group. The platelet activity was not significantly reduced. It is concluded that GR 32191 significantly reduced the fibrinogen uptake as well as graft occlusions of ePTFE grafts in a low flow situation.     

The effect of contact Nd:YAG laser on arterial wall and atherosclerotic plaques. Considerations for angioplasty. An experimental study

The predictability and reproducibility of the laser effect in regard to depth of penetration and atheroablation are important considerations for clinical laser angioplasty. This study was designed to investigate those effects experimentally. A continuous wave contact laser system (SLT CL60R with an SLT MTR 1.5 sapphire tip) was used to produce a total of 592 lesions on 14 portions of atherosclerotic human aorta and 46 portions of intact pig aorta. Different power (1 to 40W) and time (0.1 to 10 sec.) were used. These tissue specimens were analyzed by an independent pathologist. Penetration and extent of thermal damage were recorded. The measurements were analyzed statistically. Analysis shows that the effect of the laser is reasonably well predictable horizontally (correlations .755 and .699) but not at all in depth (correlation .006).     

The effect of prolonged aspirin therapy on experimental balloon-catheter arterial wall injury

Indications for aspirin following percutaneous transluminal angioplasty are not well defined. Although aspirin's early antithrombotic effect is believed to be beneficial, the long-term influence of aspirin on myointimal proliferative response following balloon-catheter angioplasty is still being investigated. This study quantitates arterial wall thickening, including intimal hyperplasia, at 4 months following balloon-catheter aortic injury in New Zealand white rabbits (n = 12), comparing aspirin treatment (30 mg/kg) with controls. Aspirin was administered daily for 1 month prior and 4 months following aortic injury. Myointimal proliferation was noted in both groups. The mean area of the intima and media as well as the maximum thickness of the intima were similar (p greater than .05) in both the aspirin treatment and control groups. Cellular hyperplasia was evaluated by media smooth muscle cell counts using an ocular reticle. There was a trend toward higher cell counts with aspirin treatment, although there was no significant difference between the two groups. Prolonged aspirin therapy did not alter the degree of myointimal hyperplasia at 4 months postinjury in our model.     

Aortic endothelial and smooth muscle cell co-culture: an in vitro model of the arterial wall.

Interactions between vascular endothelial (EC) and smooth muscle cells (SMC) contribute both to the normal function of the vascular wall and to the pathogenesis of lesions such as atherosclerosis and fibrointimal hyperplasia. However, study of these interactions has been hampered by the difficulty in growing these two cell types in simultaneous culture. Methods using conditioned media, shared media, and bilayer culture have been described, but none is well suited to the study of vascular cell interactions. We report a method for EC-SMC co-culture that preserves bilayer morphology, allows independent study of the cells and their matrices after intervention, remains stable over long periods in culture, and permits study of changes in cell-cell interaction with growth of the cells to confluence. This simple bilayer co-culture system simulates the in vivo situation and may enhance our understanding of EC-SMC interactions.     

Acute intraoperative arterial elongation: an experimental study.

OBJECTIVES: small arterial defects resulting from either trauma or resection of an aneurysm often present difficult problems to the vascular surgeon. DESIGN: to demonstrate that certain arterial gaps as a result of traumatic injury or aneurysm resection could be closed with acute intraoperative arterial elongation. Materials: fifteen mongrel dogs underwent acute intraoperative arterial elongation of the right superficial femoral artery, with the left side used for a control vessel. METHODS: arterial defects created surgically (median 50 (range 25 to 60 mm) mm). Appropriate length of artery was then undermined. A Foley catheter was placed proximally and distally directly beneath this undermined portion of vessel. The vessel is lengthened following 3 expansion/relaxation cycle of Foley catheter. Arterial gaps were closed by end to end anastomosis. Arterial pressure study was performed in all vessels. RESULTS: acutely, arterial pressure differences proximal and distal to the anastomosis were seen only when arterial gaps were exceeded 55 mm. There was no occlusion either acutely or after 4 weeks follow-up period. Light microscopic examination of arterial specimens revealed partial disruption of internal elastic lamina. At the end of the follow-up period, formation of neointima with regeneration of the internal elastic lamina was demonstrated. Scanning electron microscopy revealed minimal endothelial denudation. CONCLUSIONS: we believe that, acute intraoperative elongation can be used as an alternative technique to vein grafting for the repair of small traumatic arterial defects in selected cases.     

The arterial wall response to intimal injury in an experimental model

Repair of occult arterial injuries is advocated to prevent thrombosis, arteriovenous fistula, and pseudoaneurysm formation. However, recent clinical series describe the healing of arterial intimal injuries and recommend nonoperative therapy. To investigate the arterial wall response to intimal injury, we created intimal flaps in 46 canine femoral arteries. The intimal flaps were imaged by arteriography, angioscopy, and intravascular ultrasound acutely, and at one and three weeks and five months post-injury. Lumen area was measured using caliper techniques (arteriography) and computerized video planimetry (angioscopy, intravascular ultrasound). Intimal and medial thickness were measured by intravascular ultrasound prior to harvest for histologic evaluation by light microscopy. Analysis of 32 patent arteries was performed after exclusion of 14 thrombosed arteries. Residual lumen area (mm²) correlated closely among the imaging modalities at one week (8.7±1.1, 7.3±2.0, 6.9±1.8), three weeks (4.2±0.9, 2.9±1.0, 2.7±0.8), and five months (5.3±0.9, 5.0±0.5, 5.0±0.9). Maximal intimal and medial thickness occurred three weeks post-injury, coincident with the maximal reduction in lumen area. Although intimal injuries can cause acute and delayed arterial thromboses, observation may be appropriate in selected cases. The evaluation of those patients chosen for nonoperative therapy should extend beyond three weeks, as this is the time of maximal arterial wall response with a continued potential for adverse clinical events.Presented at the 16th Annual Meeting of the Peripheral Vascular Surgery Society, June 2, 1991, Boston, Massachusetts.     

Reduction of abdominal wall blood flow by clamping or carbon dioxide insufflation increases tumor growth in the abdominal wall: an experimental study in rats

Background We have previously demonstrated that there is a reduction of blood flow in the abdominal wall in rats insufflated with air concomitant with an increase in tumor growth. The present study was designed to examine whether a reduction of blood flow achieved by clamping or insufflation with carbon dioxide (CO₂) would increase tumor growth in the abdominal wall.Methods In the first part of the experiments, laser Doppler blood flow of both rectus muscles was measured in 16 Wistar Fu rats. The left rectus muscle was clamped to reduce blood flow, and 5 × 10⁴ adenocarcinoma cells were injected into both rectus muscles. Clamping was maintained for 45 min. In the second part, 22 rats had 5 × 10⁴ adenocarcinoma cells injected into the rectus muscle and blood flow was measured. The experimental group (n = 11) was insufflated with CO₂ at 10 mmHg for 45 min; the control group (n = 11) was not insufflated. After 9 days, tumor weight and volume were analyzed.Results Clamping caused a 69% reduction of blood flow (p < 0.001), whereas no reduction was registered on the nonclamped side. Tumor weight (p = 0.028) and volume (p = 0.030) were increased on the clamped side. The insufflation of CO₂ caused a 71% reduction of blood flow, whereas no reduction was registered in the control group. Tumor weight (p = 0.006) and volume (p = 0.006) were increased in the insufflated group.Conclusion Clamping, as well as CO₂ insufflation, causes a significant reduction of blood flow in the abdominal wall, which seems to increase tumor growth at the same site.     

The healing of contact Nd:YAG laser irradiated arterial wall. An experimental study in piglets

The healing of an arterial lesion created by continuous wave contact Nd:YAG laser was investigated. Normal arterial walls were irradiated. It is nearly impossible to irradiate atheromatous plaques without involving adjacent normal arterial wall as well. The purpose of this study was to evaluate the healing process using a standard thermal laser. Different power outputs were used with 1.0 sec exposure. A cw Nd:YAG laser with a wavelength of 1064 nm was used. Eighteen piglets underwent laparotomy. An 0.6 mm fibre with a rounded 2.2 mm sapphire probe was introduced into the aorta and iliac arteries. The irradiation was performed vertically to the vessel wall. The artery specimens were studied histologically and through electron scanning microscopy. Immediately after irradiation, adherence of platelets was observed. At two days the core centre was invaded with mononuclear blood cells and polymorphonuclear leukocytes. At five days there was still some denudation of endothelium, and the initial debris started to disappear. At two weeks medial smooth muscle cells were seen around the necrotic zone. The area was encapsulated by layers of smooth muscle and collagen. The healing process seems similar to that of mechanical injury of the aortic intima.     

Platelet damage by protamine and the protective effect of prostacyclin: an experimental study in dogs

Protamine is given after cardiopulmonary bypass to reverse the effect of heparin. However, the adverse effects of an overdose have not been fully evaluated. In this canine study, a standard dose of one bolus of heparin (300 IU per kilogram of body weight) was neutralized by an infusion of protamine hydrochloride in a 1:2 ratio. Platelet number and function were severely reduced by this overdose of protamine, and this finding correlated with a prolongation of the bleeding time. Giving a titrated dose of protamine hydrochloride to reverse heparin activity, measured by the activated clotting time, affected neither platelet number nor function. When prostacyclin (0.5 microgram/kg/min) was infused during administration of an overdose of protamine, platelets again were not affected by the excess of protamine.     

The effect of polymethylmethacrylate on bone: an experimental study

Summary In order to assess the response of bone to low-viscosity polymethylmethacrylate, CMW or Simplex acrylic cement was digitally packed while in a doughy state into drill holes in the proximal diaphysis in each of four long bones (humeri and tibiae) of mongrel dogs. Histological assessment was performed in areas of minimal load at the interface between the viscoelastic bone and the acrylic cement. Decalcified and undecalcified sections were evaluated and a remodeling or activity index calculated. Fluorescent labeling studies were performed in order to assess bone growth. Animals were killed at 2, 4, or 5 months. Histological analysis showed a thin connective-tissue membrane containing scattered giant cells and histiocytes at the bone-cement interface. Inflammation was not an important facet of this response. The marrow and trabecular bone were viable, except for scattered localized areas of marrow necrosis and fibrosis immediately adjacent to the cement. The bone adjacent to the cement showed a lower remodeling or activity index, fewer fluorescent bands, and smaller distances between successive bands, suggesting decreased bone formation and turnover. The etiology of these findings may include vascular disturbance secondary to disruption of the cortical and marrow circulation, temperature effects during cement polymerization, and/or chemical effects from the acrylic monomer.     

The effect of polymethylmethacrylate on bone: an experimental study

In order to assess the response of bone to low-viscosity polymethylmethacrylate, CMW or Simplex acrylic cement was digitally packed while in a doughy state into drill holes in the proximal diaphysis in each of four long bones (humeri and tibiae) of mongrel dogs. Histological assessment was performed in areas of minimal load at the interface between the viscoelastic bone and the acrylic cement. Decalcified and undecalcified sections were evaluated and a remodeling or activity index calculated. Fluorescent labeling studies were performed in order to assess bone growth. Animals were killed at 2, 4 or 5 months. Histological analysis showed a thin connective-tissue membrane containing scattered giant cells and histiocytes at the bone-cement interface. Inflammation was not an important facet of this response. The marrow and trabecular bone were viable, except for scattered localized areas of marrow necrosis and fibrosis immediately adjacent to the cement. The bone adjacent to the cement showed a lower remodeling or activity index, fewer fluorescent bands, and smaller distances between successive bands, suggesting decreased bone formation and turnover. The etiology of these findings may include a vascular disturbance secondary to disruption of the cortical and marrow circulation, temperature effects during cement polymerization, and/or chemical effects from the acrylic monomer.     

The mechanical influence of tissue engineering techniques on tracheal strength: an experimental study on sheep trachea.

Tissue engineering is an attractive concept for facilitating the transplantation of different tissue types with a low immunogeneity and a well-preserved tissue structure. We examined the influence of treatment with trypsin/ethylenediamine tetraacetic acid (EDTA) on the mechanical properties of tracheae. Fresh sheep tracheae were stored in a trypsin/EDTA solution for various periods of time (24, 46, and 72 h) and their breaking strength was subsequently examined. The results were compared with native trachea. The treatment with trypsin/EDTA results in a considerable reduction of the mechanical stability under load, in this case compared with the tensile strength, that does not correlate with the results obtained from light-optical microscopy. The results from this study reveal that tissue preparation with trypsin/EDTA does not seem to be a suitable method of preparatory treatment of tracheae intended for transplantation.     

The effect of a combined thromboxane receptor- and synthesis-antagonist on platelet, fibrinogen and leucocyte uptake in ePTFE grafts: an experimental study in sheep.

Arterial expanded polytetrafluoroethylene (ePTFE) grafts were interpositioned in the common carotid arteries of 20 adult sheep. This model was used to study the effect of a combined thromboxane receptor- and synthesis-antagonist, Ridogrel (R 68070), on acute graft patency and platelet, fibrinogen and leucocyte uptake. The animals were randomised to treatment (n = 10) or control groups (n = 10). Treatment was given as an intravenous injection with Ridogrel of 8 mg kg body weight-1. The flow in one of the two inserted grafts was restricted to 25 ml min-1. Autologous 111In-labelled platelets, 125I-labelled fibrinogen and 99m-Tc-labelled leucocytes were injected intravenously and the radioactivity over the vessels measured before and after graft insertion using the gamma scintillation technique. After graft insertion the measurements continued for 4 h at two separate points over the proximal and distal anastomosis areas. In the treatment group six out of 10 grafts with restricted flow remained patent compared with nine out of 10 grafts with flow reduction in the control group (N.S.). The median thrombus weights did not differ significantly. There was no difference in the platelet and fibrinogen activities at the proximal anastomosis but distally the animals receiving treatment had a significant reduction during the first 2 h of the experiment. The leucocyte activity in the treatment group compared to the control group did not differ proximally but distally the activity was significantly higher during the last 3 h of the experiment. In the group with unrestricted flow all grafts in both groups remained patent. The thrombus weight was significantly lower in the treatment group compared with the control group.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of uraemia upon wound healing: an experimental study.

Acute uraemia was induced in rats by performing a 70 per cent nephrectomy. Uraemia was shown to delay the healing of intestinal anastomoses and abdominal wounds in rats as judged by bursting strength tests. Cellular proliferation was depressed at wound edges but there was no reduction in the total amount of hydroxyproline present in the wounds. Fibroblast growth in tissue culture was affected by the addition both of uraemic plasma and of urea solution to the culture medium. The possible causes of these effects are discussed.     

Duplex ultrasonography versus arteriography in the diagnosis of arterial injury: an experimental study.

Duplex ultrasonography (DUS) and arteriography (ART) were evaluated using an experimental model of arterial trauma in order to determine the accuracy of DUS compared with ART and to define the characteristic ultrasonographic features of arterial injuries. Occlusions (n = 19), blunt injuries (n = 24), lacerations (n = 25), arteriovenous fistulae (n = 13), or no injuries (sham, n = 19) were surgically created in the femoral and carotid arteries of 25 dogs. Following closure of the incisions, DUS was performed and interpreted by a staff vascular surgeon without knowledge of the presence or type of injury. Biplane selective ART was evaluated by an independent staff radiologist. Although DUS and ART were equally accurate in evaluating arterial injuries, DUS was more sensitive (90.1% +/- 3.3% versus 80.2% +/- 4.4%, p = 0.002) and better at identifying lacerated arteries (p = 0.01). However, ART had greater specificity (94.7% +/- 5.1% versus 68.4% +/- 10.7%, p = 0.04) and was more accurate for identifying normal arteries (p = 0.04). The validity of DUS increased in the latter half of the study, thus demonstrating a learning curve. Duplex ultrasonography was a more sensitive screening modality than ART for evaluating arterial injuries in our experimental model, thereby supporting its use in clinical trials to evaluate its accuracy, reliability, and cost effectiveness in the trauma setting. Furthermore, management decisions can be based on the specific type of injury, pathologic condition of the arterial wall, and hemodynamic factors identified by DUS. Clinically occult arterial injuries can be followed by repeat DUS to define the natural history of these injuries.     

Coronary artery stabilization causes endothelial damage: an electron microscopic study on dogs.

In recent years, to protect patients from adverse effects of cardiopulmonary bypass, off-pump coronary artery bypass operations are performed. In these operations, effective coronary artery immobilization is the standard for a fine anastomosis. This is usually maintained with the help of prolene immobilization sutures, bulldog occluders or mechanical epicardial devices. The aim of this study is to show whether these stabilization devices cause any damage to the coronary artery endothelium. Sixteen dogs are included in this study and are divided into four groups. The control group consisted of one dog (Group I) and different immobilization techniques are applied to the other groups, which were five dogs each (Groups II, III, and IV). Coronary artery biopsies are obtained, then the samples are studied under scanning electron microscope (SEM) for endothelial injury and all samples are scored. Among the techniques used, bulldog occluders caused less injury on the coronary endothelium than the prolene sutures.