일측성 신혈류 차단 및 혈류재기에 의한 신피질의 형태학적 변화

Abstract

[한글]

Sequential Morphologic Changes Following Unilateral Renal Artery Ligation and Its

Removal

Chong Hoon Suh, M. D.

Department of Medical Science The Graduate School, Yonsei University

(Directed by Professors: Dong Sik Kim, M. D. and Yoo Bock Lee, M.D.)

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 nam 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 at al. (1970).

Experimental groups

Group Ⅰ: ligation for 15 minutes (18 animals)

Group Ⅱ: ligation for 30 minutes (18 anima)s)

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 glads knife in 400 to 500 A

thickness and stained with uranyl acetate and lead hydroxide. Observations were

mode with Hitachi 11-E model electron microscope.

Results and Discussion

Degenerative add destructive changes of the renal cortical tubules due to

ischemia resulted from ligation of the left renal artery and vein. The main

findings were cloudy 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 group 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 locally 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 lefts

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 boons 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 diapedesis without significant destruction of the endotheliun 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.

[영문]

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 nam 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 at al. (1970).

Experimental groups

Group Ⅰ: ligation for 15 minutes (18 animals)

Group Ⅱ: ligation for 30 minutes (18 anima)s)

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 glads knife in 400 to 500 A thickness and stained with uranyl acetate and lead hydroxide. Observations were mode with Hitachi 11-E model electron microscope.

Results and Discussion

Degenerative add destructive changes of the renal cortical tubules due to ischemia resulted from ligation of the left renal artery and vein. The main findings were cloudy 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 group 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 locally 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 lefts 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 boons 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 diapedesis without significant destruction of the endotheliun 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.