Pathobiology of intimal hyperplasia

Morphology and function of preserved microvascular arterial grafts: an experimental study in rats

The aim of this study is to examine the morphology and function and small-caliber, arterial grafts after preservation in the University of Wisconsin solution (UW). Rat carotid arteries were stored in UW (n = 10) or in phosphate-buffered saline (PBS) (n = 10) for 1, 3, 7, and 14 days and were examined with light microscopy (LM) and scanning electron microscopy (SEM). Rat aortic preparations were stored in UW or PBS for 1 hour, 24 hours, 72 hours, 7 days, and 14 days and assessed for functional responses (stimulated contraction and endothelium-dependent relaxation). Segments (5 mm) of rat carotid arteries were stored in UW or PBS for 3 days, 7 days, and 14 days and orthotopically implanted as autografts and allografts. No immunosuppressive or anticoagulant agents were used. After 28 days of implantation, the grafts were assessed for patency and excised for LM and SEM. In UW, the endothelial layer remained intact up to 9 days of storage. In PBS, the endothelial layer showed deterioration after 1 day and was completely lost after 3 days. Functional responses were demonstrated to exist for as long as 7 days storage in UW. In PBS, no responses could be evoked after 24 hours storage. Autografts preserved in UW for 3 days (n = 6), 7 days (n = 6), and 14 days (n = 6) showed patency rates of 83.3%, 66.6%, and 66.6%, respectively, whereas patency rates of allografts were 66.6%, 33.3%, and 33.3%, respectively. Autografts stored in PBS for 3 days (n = 6), 7 days (n = 6), and 14 days (n = 6) showed patency rates of 33.3%, 33.3%, and 50%, respectively, whereas patency rates of allografts were 16.7%, 0%, and 33.3%, respectively. The UW preserved autografts showed normal morphology. All other groups showed vessel wall degeneration which in the allograft groups, were accompanied by lymphocellular infiltration. In conclusion, the endothelial layer and vessel wall of arteries are adequately preserved in UW. Functional responses are retained up to 14 days storage in UW, but, are lost after 24 hours storage in PBS. Autograft implantation studies accordingly show good performance of arterial segments preserved in UW, whereas allografts are subject to degradation as a result of rejection.

Influence of perioperative storage solutions on long-term vein graft function and morphology

It has been shown that suboptimal preparation of a vein graft prior to its insertion results in immediate morphologic and functional damage to the endothelial cells but not to the underlying smooth muscle cells. However, little is known about whether such perioperative injury to the vein grafts influences the subsequent development of intimal hyperplasia and smooth muscle cell contractility. This study examines the influence of storage in saline solution or Ringer's lactate on the development of intimal hyperplasia and vasomotor function in experimental vein grafts. Twenty-six New Zealand white rabbits had a carotid vein bypass graft performed after the veins had been immersed (15 minutes) in either heparinized saline solution (Sal; n = 13) or Ringer's lactate (RL; n = 13), and each group was harvested after 28 days for either histologic (n = 8) or functional studies (n = 5; four 5 mm rings/graft). Saline storage of the vein graft resulted in a 38% increase in the thickness of the intimal hyperplasia (113 +/- 2 vs. 83 +/- 2 microns, Sal vs. RL; mean +/- SEM; p < 0.05) without a change in medial thickness (87 +/- 5 vs. 86 +/- 8 microns, Sal vs. RL; p > 0.05). The two sets of vein grafts showed no difference in sensitivity to norepinephrine, serotonin, and bradykinin.(ABSTRACT TRUNCATED AT 250 WORDS)

The integrity of experimental vein graft endothelium--implications on the etiology of early graft failure

INTRODUCTION

the vascular endothelium serves as a functional barrier between the circulating blood and the vessel wall. It is an essential element for the maintenance of vascular homeostasis and is implicated in the pathogenesis of vascular disease. Reversed vein bypass grafting is considered to be a devastating procedure for the endothelial cell layer of the graft during the first 7 days. At this time, smooth muscle cell proliferation, the forerunner of intimal hyperplasia, begins. Loss of endothelial cell integrity is cited as an important factor in this smooth muscle cell response. The integrity of the vein graft endothelial lining after grafting was examined in this study.

METHODS

reversed vein bypass grafting of the common carotid artery using external jugular vein was performed in 24 New Zealand white rabbits. All grafts were pressure fixed (80 mmHg) in situ, at 0 and 10 min, 6 h and 1, 3, 5, 7 and 14 days postoperatively. The endothelial cell layer was examined by light microscopy (LM), scanning (SEM) and transmission electron microscopy (TEM) and immunohistochemistry (Factor VIII) using standard histological procedures.

RESULTS

the endothelium was observed by SEM and confirmed by both LM, Factor VIII and TEM in all specimens. It covered almost the entire surface examined. At 0 and 10 min, endothelial cells were present and displayed minimal evidence of injury. At 6 h and 1 day, numerous red cells, polymorphonucleocytes (PMNs), platelets and fibrin were adherent to the luminal surface. Blood cells were also seen beneath the endothelium. At day 3, the adherent fibrin and cellular elements were reduced with most of the endothelial lining intact. Within 10 min, TEM demonstrated that these cells were stretched, very thin with few microvesicles and a blurred cytoplasm, which would indicate viability but a degree of cellular injury. By day 1, the endothelial cells were lifted from their underlying structures by subendothelial oedema and an infiltrate predominantly of PMNs. By day 5, the blood cells and fibrin which were adherent to the endothelium had been dispersed and the subendothelial infiltrate was to a large extent replaced by disintegrated PMNs. On days 7 and 14, a viable confluent endothelial cell layer was present and a degree of intimal hyperplasia was noted. The endothelial cells appeared to have enlarged nucleoli and cytoplasms filled with a considerable quantity of rough endoplasmic reticulum.

CONCLUSION

the endothelium of reversed vein grafts is preserved at the time of implantation and at all time intervals studied in this model. These findings do not support the assumption that endothelial denudation is a prerequisite for intimal hyperplasia. Endothelial cell dysfunction and morphological changes are maximal within the first 3 days after grafting but appear to recover by the 5th postoperative day. The gross preservation of the endothelial cell layer implies that therapeutic approaches, to mitigate endothelial cell injury and its consequences, should be focused on the preoperative period and the first 5 days following implantation.