Autogenous vein grafts in hypertensive (SHRSR) rats have increased smooth muscle cell hyperplasia in the graft neo-intima, compared with grafts in normotensive rats

Increased intimal hyperplasia after carotid endarterectomy in spontaneously hypertensive rats

This study evaluated the effects of hypertension on postoperative intimal hyperplasia using a rat carotid endarterectomy (CEA) model with spontaneously hypertensive rats (SHR) and normotensive Sprague-Dawley rats (SD). SHR and SD rats underwent left carotid exposure and CEA via an arteriotomy, scoring and removal of the intima, followed by arteriotomy closure. The rats were then sacrificed two weeks postoperatively. The left carotid artery was harvested and underwent elastin and double immunohistochemical staining. The percent of lumenal stenosis was calculated using morphometric measurements, and stained cells within the intimal hyperplasia were counted. The means and standard deviation of the means were calculated, and the two groups were compared using a 2-sample t test. The systolic blood pressure was 228 +/-35 mm Hg in the SHR group and 108 +/-8 mm Hg in the SD group (p<0.00001). The percent of lumenal stenosis was 82.6 +/-17.1% in the SHR group and 21.2 +/-13.7% in the SD rats (p value <0.0001). The percentage of cells staining for a-SM actin was equal in the SHR group and the SD group (> 91%) but the percentage of these cells staining for BrdU was 38.2 +/-8.4% in the SHR group and 10.7 +/-5.8% in the SD group (p< 0.00001). Hypertension in the SHR rats was associated with an increased lumenal stenosis due to increased intimal hyperplasia. The increased intimal hyperplasia was due to enhanced and accelerated replication of smooth muscle cells. Hypertension may be associated with increased restenosis rates after CEA.

Effect of external stenting and systemic hypertension on intimal hyperplasia in rat vein grafts

OBJECTIVE

Overdistention of vein grafts in arterial circulation and systemic hypertension are thought to be influential risk factors contributing to vein graft failures. This study tested the effects of external stenting in preventing systemic hypertension and overdistention of the rat vein graft in the long term.

METHODS

Jugular vein grafts were interposed into the carotid artery of normotensive (n = 39) and two-kidney, one-clip hypertensive (n = 30) rats. Jugular vein grafts wrapped with 1.5-mm-diameter polyester stents were used in normotensive (n = 26) and hypertensive (n = 25) rats. The vein grafts were harvested at 1, 2, 4, 8, 12, and 24 weeks after the grafting procedure. The neointimal area and wall thickness were measured by computerized planimetry, and Ki-67 immunohistochemistry was used to detect replicative smooth muscle cells in the graft wall.

RESULTS

In each group, intimal hyperplasia was apparent at 1 week and increased gradually to 24 weeks. The number of Ki-67-positive cells was most increased at 2 weeks after the grafting procedure and gradually decreased thereafter. The numbers of Ki-67-positive cells and the extent of intimal hyperplasia were not significantly different between normotensive and hypertensive rats. Both neointima formation and cell proliferation in the graft wall were significantly reduced by external stenting as compared with the results with unstented grafts.

CONCLUSION

Systemic hypertension by itself is not a risk factor for intimal hyperplasia and experimental vein graft failure in the long term. External stenting is effective against intimal hyperplasia, and it is possible to reduce the subsequent atherosclerotic change of the vein graft wall and improve the long-term patency of the vein graft with external stenting.

Autogenous artery grafts in hypertensive (SHR) rats do not have increased smooth muscle cell hyperplasia in the graft neointima, compared with grafts in normotensive rats

Vein-to-artery graft surgery is used widely to by-pass arterial stenoses, but such grafts can fail over a prolonged period as a result of excessive neointimal hyperplasia causing thrombosis and graft occlusion. It has been suggested that neointimal hyperplasia, in vein grafts, is a result of the vessel wall adapting to the higher intraluminal pressure of the arterial circulation, compared with the venous circulation. Autologous artery grafts have been used to bypass arterial stenoses. Initially it was assumed that donor artery segments would not develop neointimal hyperplasia as they are already adapted to the arterial circulation but this is not so. In this study we postulated that surgical or postsurgical trauma was the cause of neointimal hyperplasia in autologous artery-to-artery grafts. In addition, as artery grafts are pre-adapted to the arterial circulation, autologous artery-to-artery grafts in hypertensive rats should develop similar levels of neointimal hyperplasia as seen in normotensive rats. Artery-to-artery grafts were placed in a series of 20 spontaneously hypertensive rats (SHR). In a separate series of sham grafting experiments the effects of anoxia and clamp trauma were assessed in SHR and WKy normotensive control rats. Finally, clamping, anoxia and anastomosis trauma were assessed in a similar series of rats. In the artery-to-artery graft series there was no difference in neointimal thickness between the SHR and that previously reported for normotensive rats. Minimal neointimal hyperplasia was demonstrated in the sham grafted series of rats and only slightly more in the single anastomosis series. It was only in the full grafting procedure that considerable neointimal hyperplasia developed. These data demonstrate that neointimal hyperplasia in artery-to-artery grafts is not exacerbated by the hypertension. In addition, trauma appears to be the initiator of neointimal hyperplasia and the extent of trauma correlates with the degree of neointimal hyperplasia.

Vascular tissue adaptations in end-to-end autologous arterial grafts in rats: a morphometric analysis

Autologous vein grafts are employed extensively to bypass stenoses in the arterial circulation. More recently arterial segments have been used for such bypass surgery. In this study the adaptation of regenerating vascular tissues in experimental autologous artery grafts (4 mm long and 1 mm in diameter) in 20 adult male Wistar rats was analysed. At 1, 2, 4, 8 and 16 wk after insertion, 4 grafts per time interval were removed, processed for high resolution light microscopy and the thicknesses of the media and neointima, as well as the area fractions of smooth muscle cells, were analysed morphometrically. All grafts were reendothelialised by 2 wk. Neointimal hyperplasia (a subendothelial layer of smooth muscle cells) developed in all grafts and reached its maximal thickness (40.4 +/- 4.7 microns) at 2 wk. The area fraction of smooth muscle cells in the neointima of the artery grafts did not change significantly at any time from 2 to 16 wk. The media underlying the neointima of the artery grafts remained relatively constant throughout the 16 wk duration of the experiment. Whilst the total wall thickness of the grafts reduced significantly between 2 and 4 wk after insertion, at all times the grafts were thicker than the host artery.