Abstract

In acute renal failure, the glomeruli does not show any significant morphologic changes even with the electron microscopic studies (Dalgaard and Pedersen, 1959; Dalgaard, 1960; Holden et al., 1965), and the oliguric phase has been explained by glomerular filtrates being reabsorbed through the damaged tubular epithelium (Dunn et al., 1941). But Clarkson et al. (1970), who studied the oliguric phase in acute renal failure caused by hypovolemic shock mostly due to toxic effect of drugs such as barbiturates, found, electron microscopically, glomerular coagulation which had not hitherto been reported. The present study is to describe the sequential morphologic changes following renal ischemia and its removal, and to discuss on a morphologic basis the possible sources of the regenerated tubules and replacement of the infarcts and to assume the nature of oliguric phase in acute renal failure produced by ischemia. Materials and Methods ; Albino rats, weighing around 250gm and having been fed on the usual commercial diet containing fat of more than 15% and protein more than 30%, were used for the experiments. The rats were divided into 4 groups, according to the duration of clamping the left main renal vessels, and a control group in which only sham operations were Performed. The left main renal vessels were ligated with sterile silk and polyethylene tube, utilizing the method of Terry et al. (1970). Experimental groups; Group I: ligation for 15 minutes (18 animals). Group II: ligation for 30 minutes (18 animals). Group III: ligation for 60 minutes (18 animals). Group IV: ligation for 90 minutes (18 animals). Control group: sham operation (4 animals). Two rats from each experimental group were killed at the immediate, 1 hour, 12 hour, 24 hour, 2 day, 4 day, 7 day, 10 day and 15 day period after removal of the ligature. Both kidneys were examined grossly and a small piece was obtained for electron microscopic examination from each left kidney and the remainders including the right kidney were fixed with formalin for light microscopy. Specimens for light microscopy were processed by routine H & E method. PAS staining for mucopolysaccharide and Verhoeff elastic with van Gieson counter staining for connective tissue were also done. Samples for electron microscopy were fixed with 1% osmium tetraoxide in veronal buffer at pH 7.4, embedded in Epon 812 following dehydration with graded alcohol. Sections were made by glass knife in 400 to 500 Å thickness and stained with uranyl acetate and lead hydroxide. Observations were made with Hitachi 11-E model electron Microscope.
Results
and Discussion ; Degenerative and destructive changes of the renal cortical tubules due to ischemia resulted from ligation of the left renal artery and vein. The main findings were clouds swelling, sloughing of the pyknotic epithelial cells, patchy infarction and the appearance of strong PAS positive spherical bodies in the cytoplasm and tubular lumen. All these changes were observed approximately one hour after ligation of the vessels, but the infarction was not evident until after twelve hours. The epithelial sloughing was rather prominent in group III and IV. The spherical PAS positive bodies were considered to be cytoplasmic degradation products on electron microscopic study. Regenerative changes, including mitosis of the epithelial cells which usually were found between the tubular basement membrane and sloughed cells, and the appearance of the undifferentiated cells with clear-looking cytoplasm and large nuclei, were encountered in all four groups less than two days after removal of the ligature. The tubules were almost completely regenerated and replaced the infarct within 4 days in croup I and within 7 days in group II, but, although the mitotic activity was more prolonged, the tubular differentiation into proximal and distal segments was moderate to poor in group III and IV even by the 15th day. Furthermore interstitial tissue seemed to be prominent focally and its arrangement was irregular in these groups. The possible origin of the regenerated tubular epithelial cells is considered in three ways, namely, 1, the interstitial cells, 2. the epithelial cells of less damaged nephrons, and, 3 the less damaged epithelial cells of any nephron. The first possibility is initially negated because the interstitial tissue is mesenchymal. Secondly the destructive changes were always patchy in distribution but usually recovered by epithelial regeneration. If functionally reserved nephrons were present, they were resistant to the ischemia and could be the origin of tubular regeneration. But these regenerated cells could not escape from the original nephrons through the basement membrane. The third possibility is based upon the difference of oxygen consumption between the renal cortex and medulla (Thorburn et al.1961). The cortical zone requires much more oxygen than the medullary zone in the normal state and the medullary tubules are unequivocally more resistant to ischemia. And the regenerated tubules will be bound to the tubular basement membranes except for the parts where the basement membranes are even destroyed when more severe ischemia occurs. Eosinophilic necrosis of the media of the arcuate and interlobular arteries and massive RBC diapedesia without significant destruction of the endothelium or internal elastic membranes were the identifiable changes of blood vessels in all groups except in group I. Following necrosis, the vessel walls were thickened, evidently due to the mitosis of the medial smooth muscle cells, and consequently the luminae were narrowed. These sequential alterations of the blood vessels were parallel to the duration of the ligation. Light and electron microscopic examination of glomeruli revealed no visible alteration in the capillary endothelium, epithelium or basement membrane. In summary, unilateral ischemic lesion of the kidney produced by ligation of the main renal vessels is likely to recovered through active proliferation of the less damaged epithelial cells of any nephron, and the oliguric phase in acute renal failure following ischemia is considered not to be due to the morphologic changes of the glomerulus only.