Early vascular changes in the intestine of bilaterally nephrectomised rats

Ultrastructural changes in the arterioles of the intestinal submucosa were observed in rats 20 to 24 hr after bilateral nephrectomy. Sham-operated rats served as controls. The changes of arterial pressure after the nephrectomy or sham operation was measured directly through carotid artery cannulation, and analysed by the paired t-test. Ferritin was injected intravenously into two rats in each group 60 min. before fixation in order to trace plasma insudation into the arteriolar wall. Mean blood pressure was 102 +/- 9 and 112 +/- 6 mm Hg (mean +/- S.E.), before and after the nephrectomy, respectively. The latter was significantly higher than the former, though it remained in the normotensive range. It was also higher than that in control rats after sham operation. In sham-operated rats, there were neither vascular lesions nor evidence of increased leakage of ferritin into arteriolar walls. Arterioles from the nephrectomised rats, on the other hand, exhibited foci of smooth muscle cell necrosis characterised by cellular fragmentation and the deposition of fibrinoid and electron-dense granules. The fibrinoid was of two types of axial periodicity, i.e., 20--23 nm and 16--17 nm, respectively. Dense granules, 13--90 nm in diameter, were encountered mainly between the basement membrane and plasma membrane of smooth muscle cells. Though scanty fibroblasts were seen, there was no infiltration of mononuclear cells in the adventitia accompanying medial necrosis. Ferritin particles accumulated in the necrotic foci of the media in high concentration, and were seen in endothelial gaps, within the cytoplasm and in palsmalemmal vesicles of the endothelial cells. The main pathway of ferritin insudation into the media was considered to be by way of endothelial gaps.