Vein Grafts In Dogs Research Articles

Isotopic study of the effects of platelets on development of intimal thickening in autologous vein grafts in dogs

The effects of platelets on the development of intimal thickening of arterially transplanted autologous vein grafts was investigated using canine poor run-off models. A new apparatus consisting of a shielding lead block to measure in vivo platelet adherence only on the intima of the vein graft was developed. In 23 dogs, 51Cr-labelled platelets (20 microCi/kg) were injected and isotope emission over the grafts was counted. Platelet adherence was expressed as the thrombocyte accumulation index (TAI), i.e. the ratio of counts over the graft under an abnormal flow condition in the poor run-off model to those over the graft under normal flow conditions of the contralateral leg. The TAI of the total graft (TTAI) was significantly high immediately and on the first and third days after implantation. The TAIs of the proximal (PTAI) and distal (DTAI) portions of the vein graft were also high at these same times. At 7, 10, 14 and 21 days, the TAI was almost equal to 1.0, a time at which endothelial regeneration was complete as confirmed by scanning electron microscopy. Thus, the prominent intimal thickening of arterially transplanted autologous vein grafts in dogs, induced under an abnormal flow condition, correlates well with the enhanced platelet adherence on the intima of the vein grafts in an early period after implantation.

Hemagglutinating virus of Japan-liposome–mediated gene transfer of endothelial cell nitric oxide synthase inhibits intimal hyperplasia of canine vein grafts under conditions of poor runoff

Purpose: Late graft failure is a critical problem, particularly in the presence of poor runoff vessels. Intimal hyperplasia is considered to be the main cause of graft failure. We have already reported that intimal thickening of experimental vein grafts in dogs with poor runoff vessels is more pronounced than that in dogs with normal vessels. We and others also have reported that production of nitric oxide (NO) in the endothelium of canine vein grafts is impaired. In the present study, we asked whether in vivo gene transfer of endothelial cell NO synthase (ecNOS) would inhibit intimal hyperplasia of autogenous vein grafts implanted in limbs with poor distal runoff in dogs. Methods: After exposing femoral veins, the nuclear-targeted lac Z gene, bovine ecNOS cDNA, or control vector plasmid encapsulated in the hemagglutinating virus of Japan-liposomes was infused intraluminally, followed by incubation for 10 minutes at room temperature under a distending pressure of 100 mm Hg. Twenty reversed vein grafts were implanted under normal runoff conditions, and 4 days later these were used to confirm gene transfer to the vein grafts. Twelve reversed vein grafts were implanted under conditions of poor runoff, and 4 weeks after the operation intimal thickening was evident. Results: In vein grafts under normal runoff conditions, lac Z gene transfer exhibited diffuse and frequent X-Gal-positive signals in both medial and adventitial layers 4 days after implantation (n = 3). In case of the ecNOS gene–transferred vein grafts, bovine ecNOS protein was mainly detected in medial smooth muscle cells and adventitial cells 4 days after implantation, determined using immunohistochemical techniques and bovine ecNOS specific antibody (n = 3). In addition, ecNOS-transferred vessels showed intense purple signals by reduced nicotinamide adenine dinucleotide phosphate diaphorase and nitroblue tetrazolium reaction, in both medial and adventitial layers, whereas weak NOS activity was recognized at the adventitial vasa vasorum of the untreated veins or control vector transferred veins (n = 3, respectively). In vein grafts under poor runoff conditions, the intimal thickness at 4 weeks after implantation was significantly reduced by ecNOS gene transfer (n = 4; 90.0 ± 7.6 μm and 1.18 ± 0.07 mm 2) in comparison with buffer-treated vessels (n = 4; 195.8 ± 25.7 μm and 2.62 ± 0.48 mm 2) or vector vehicle–treated vessels (n = 4; 193.0 ± 15.8 μm and 2.65 ± 0.22 mm 2). Conclusions: Our findings show that gene transfer of ecNOS inhibited intimal hyperplasia of canine vein grafts caused by poor runoff conditions, as a result of an increased local production of NO. Thus ecNOS gene transfer warrants further study as a possible approach to prevent late graft failure. (J Vasc Surg 1998;27:135-44.)

The Acute and Chronic Effects of G-Lasing on Femoral Vein Grafts in Dogs

Each year, 5% of all coronary artery bypass operations are repeat procedures, and 15%-30% of coronary artery vein grafts occlude within the first eighteen months postoperatively. To evaluate the macroscopic and histologic effects of G-lasing on vein grafts and their patency, femoral veins were used to bypass bilaterally induced stenoses of femoral arteries in 10 dogs. The left vein grafts were G-lased with a 1.5 mm, hot-tipped argon laser at 5 watts for ninety seconds, while the right grafts were used as the controls. Acutely, each vein graft demonstrated no evidence of charring or perforation. The percentage of endothelium present in the G-lased vein grafts was consistently less than 5%, whereas the control vein grafts had an average of 70%. After ten weeks, the animals were sacrificed, and the vein grafts were evaluated for histologic changes and patency. There were no significant microscopic differences between the G-lased and control vein grafts. A statistically significant difference in graft patency was not achieved between G-Lased and control vein grafts at 10 weeks, but only a small number of grafts were studied. Further studies will be needed to evaluate the effects of G-lasing on the long-term patency of vein grafts.

Significance of the endothelial lining in prevention of intimal thickening of autogenous vein grafts in dogs

To better comprehend the role of the endothelial lining in occurrence and development of intimal thickening in arterially implanted autogenous vein grafts, two models of canine femoral arteries were prepared. In the Group I model, the implanted autogenous vein graft was kept under a normal flow condition for 2 to 4 weeks after implantation, then was exposed to an abnormal flow (poor run-off). In case of a 3- to 4-week normal flow, intimal thickening was practically nil. Scanning electron microscopic studies showed that this 3- to 4-week period corresponded to that of re-endothelialization of the autogenous vein grafts. Immunohistochemical studies of fibrinogen distribution in the autogenous vein graft wall in the Group II model revealed that the permeation of fibrinogen was enhanced in case of an abnormal flow condition for about 2 weeks after the implantation. We interpret these observations to mean that intimal thickening was induced by an accelerated permeability in the presence of abnormal flow conditions until full re-endothelialization after the implantation.

Effect of selective thromboxane synthetase inhibitor on vein grafts.

We evaluated the effect of a selective thromboxane synthetase inhibitor (TSI) on the patency of autogenous vein grafts in dogs. Treatment involved oral dosing (10 mg/kg bid) of TSI or placebo, combined with local treatment of the graft with TSI or placebo (papavarine) at the time of implantation. At harvest, two animals, one from each oral dosing group, had an occluded graft; both grafts had been locally treated with papavarine. We found no significant histopathologic difference between graft treatment groups. Attempts to estimate the effect of TSI dosing on the prostacyclin/thromboxane balance through radioimmunoassay analysis of graft perfusates were unsuccessful. As measured by in vitro platelet aggregation, oral TSI was found to alter platelet function, though not in a dose-dependent fashion, and the animals rebounded toward normal at 12 hours.

Development and regression of intimal thickening of arterially transplanted autologous vein grafts in dogs

To investigate the influence of hemodynamic conditions on intimal thickening of arterially transplanted autologous vein grafts, two experimental models of canine femoral arteries were prepared. In group I, in which an autologous vein graft was transplanted under abnormal flow conditions (distal poor runoff), intimal thickening gradually developed and reached 358 ± 33 μm at 8 months, whereas no thickening was observed under normal flow conditions at any time throughout the observation period. In group II the thickened intima, which developed under abnormal flow conditions for 1 month, was reimplanted into the contralateral leg under normal flow conditions. The thickness of the intima markedly regressed to about 66% at 1 month, 50% at 3 months, and 25% at 8 months, respectively, whereas no regression of the thickened intima was observed under continued abnormal flow conditions. Electron microscopic studies revealed that the thickened intima in group I was composed of proliferation of transformed smooth muscle cells with a marked increase in the mitochondria, the rough endoplasmic reticulum, and an abundant fibrous matrix, whereas with the regressed thickness of the intima of group II, the smooth muscle cells were spindle-shaped with distinct myofibrillae. These results provide pertinent data on the process involved in the intimal thickening in cases of graft placement.

Velocity distribution and intimal proliferation in autologous vein grafts in dogs.

Velocity distribution and intimal proliferation in autologous vein grafts in dogs.