Perfusion--fixation of human kidneys for ultrastructural analysis

Morphology of ischemic acute renal failure, normal function, and cyclosporine toxicity in cyclosporine-treated renal allograft recipients

To characterize morphologic changes in the early post-transplant period in cyclosporine-treated renal allograft recipients, we examined biopsies from three groups of cyclosporine-treated patients: normal function (N = 9), ischemic acute renal failure or "acute tubular necrosis" (N = 12), and cyclosporine toxicity (N = 7). Groups were compared with each other and with previously studied groups of azathioprine-treated patients and native kidney patients. The interstitial infiltrate commonly observed in normally functioning azathioprine-treated grafts was not observed in normally functioning cyclosporine-treated grafts, but two of nine such grafts had a significant venulitis, a change also seen in three of the patients with cyclosporine nephrotoxicity. "Acute tubular necrosis" (ATN) in cyclosporine-treated graft recipients was characterized by focal necrosis of complete tubular cross sections, a finding normally rare in other types of ATN, and by shedding into the tubular lumen of tubular cells with non-pyknotic nuclei, a finding supporting our previous observation of detachment of viable tubular cells in ATN but not in the normal kidney. Hyaline arteriolar thickening was the only morphologic finding on biopsy which distinguished patients with cyclosporine nephrotoxicity from other groups. In summary, the morphologic changes observed in cyclosporine-treated renal allograft recipients with ATN or normal function are quite different from those observed in azathioprine-treated patients. Cyclosporine appears to enhance the tubular injury observed in ATN. Hyaline arteriolar thickening is the main distinguishing feature of cyclosporine nephrotoxicity.

The case for perfusion fixation of large tissue samples for ultrastructural pathology

We present the case for the perfusion fixation of large, freshly isolated tissue samples of liver and lung from dog, rat, and mouse. Individual lobes of liver and lung were fixed by vascular perfusion using a technique that is simple and quick to perform and results in a reproducibly high standard of ultrastructural preservation compared to immersion fixation. A major advantage to the use of this technique lies in the ability to provide tissue samples for diagnostic ultrastructural pathology and toxicological pathology while avoiding the need for whole-organ or whole-body perfusion fixation. This advantage therefore permits the use of fresh tissue from the same organ for other investigative purposes (e.g., drug metabolism studies and pharmacokinetics), thereby allowing correlation of structure and function. The advantages of perfusion fixation compared to immersion fixation are discussed, and potential applications for tissue preparation of postmortem specimens and also for scanning electron microscopy are indicated.

Ultrastructural investigation of renal biopsies: a discussion of artifacts and special methodology

The aim of this presentation is to draw attention to the problems inherent in evaluating the ultrastructure of percutaneous renal biopsies and to discuss some of the special techniques which are useful in this area. It is important to realize that the ultrastructure as it appears in this kind of material does not necessarily reflect conditions in vivo. Comparison with suitable reference material may, however, permit reliable conclusions in terms of pathological diagnosis and pathogenesis. It is advocated that purely qualitative methods, which until now have predominated in ultrastructure work with renal biopsies, be replaced by morphometry and semiquantitative methods when it is possible and practical to do so in any research situation.

Ultrastructure of renal adenoma

Renal adenomas, defined as minute cortical foci of proliferating epithelium, are frequently occurring lesions reported to be present in 15%-22% of all adult human kidneys. They can often be found in kidneys with renal cell carcinoma. Their light microscopic structure makes it improbable that they should represent intrarenal metastases. The concept does not include clear cell foci. Ultrastructure of these cortical foci in human kidneys is not well known. A series of 10 intrarenal adenomas in carcinoma-bearing kidneys has been studied using tissue fixed rapidly after nephrectomy by perfusion with 2% glutaraldehyde. The results confirm their tubular origin. Ultrastructural markers of different segments of the nephron were demonstrated. Several of these markers might be present in each single case. The interpretation is that their ultrastructural characteristics do not indicate an origin from a special segment of the nephron. They may reflect an abnormal gene expression associated with the neoplastic change of the cell clone. Some changes are similar to those seen in cells from renal cell carcinoma, although not as prominent as in malignant cells.

Quantitative ultrastructure of human proximal tubules and cortical interstitium in chronic renal disease (hydronephrosis)

Surgically removed perfusion-fixed human kidneys with chronic renal disease (hydronephrosis) were studied by electron microscopy in order to determine whether there is a quantitative relationship between ultrastructural changes in proximal tubules in atrophy and changes in the surrounding cortical interstitium. Morphometric techniques were applied to montages of electron micrographs each covering several tubular profiles in the cortical labyrinth and to montages representing cross-sections of individual proximal convoluted tubules at a higher magnification. In order to enable a quantification of the spatial relations between individual tubular cross-sections and adjacent peritubular capillaries a tubulo-capillary index (TCI) was defined. This index was based on the mean distances between individual tubular cross-sections and adjacent peritubular capillaries and on the fraction of tubular circumference facing capillaries. Normal tissue from similarly fixed human nephrectomy specimens, which had been removed mainly because of neoplastic disorders, served as control material. In the hydronephrotic kidneys the relative volume of cortical interstitium (excluding capillaries) covered a range from 19.2-70.3%. Inverse correlations were demonstrated between the relative volume of cortical interstitium and various structural variables of proximal convoluted tubules, including tubular wall volume, the volume of mitochondria and the surface area of basolateral membranes. The TCI showed positive correlations with these tubular variables. No significant correlation was found between the volume fractions of cortical interstitium and capillaries. Finally, it was found that an increase in the volume fraction of the cortical interstitium from 16.2% in controls to 24.7% in cortical areas of hydronephrotic kidneys was associated with a 40-50% reduction in the volume of mitochondria and in the surface area of basolateral membranes in proximal tubules. The results are consistent with a pathogenic interrelationship between tubular and interstitial changes. An important factor in this relationship might be disturbed topographic associations between tubules and blood capillaries caused by the increase in cortical interstitium. The results further show that even slight increases in the cortical interstitial volume are associated with significant quantitative changes in tubular fine structure suggesting impaired tubular functions.

Tubular ultrastructure in acute renal failure: alterations of cellular surfaces (brush-border and basolateral infoldings)

Using a blind, semiquantitative technique, the degree of reduction of proximal tubular brush border (BB) and proximal and distal basolateral infoldings (BI) were measured in 25 renal biopsies from patients with acute renal failure (ARF) of ischaemic type. For comparison 12 biopsies from patients without ARF were studied, 6 were normal controls, six were from patients with minor change disease and slight glomerulonephritis. The mean scores for reduction of BB as well as proximal and distal BI were strongly increased in ARF compared to controls and the differences were highly significant. Some of the biopsies were taken during recovery and there was a significant negative correlation between the individual scores for reduction of BB and BI and simultaneous renal function. The disappearance of BB microvilli was correlated to tubular dilatation, but it could not be explained exclusively by "stretching" of the luminal surface due to dilatation. There was no correlation between reduction of BI and tubular dilatation. The data indicate a disturbance of cell membrane turnover in the active phase of ARF, possibly due to decreased synthesis, and they are consistent with a pathogenetic hypothesis implicating a decreased proximal Na+ resorption and consequently a pre-glomerular vasoconstriction.

Renal morphology in experimental vesico-ureteral reflux in pigs

As part of a study of experimental vesicoureteric reflux 20 pigs were allocated into five groups according to the presence of reflux, infravesical obstruction and urinary tract infection. The pigs were followed for 20 weeks and thereafter the pathology of the kidneys were studied. It was confirmed that reflux and urinary tract infection produce reflux nephropathy and that the most severe lesions were found in case of dilatation of the upper urinary tract due to infravesical obstruction. It was also substantiated that sterile reflux in case of infravesical obstruction with pronounced dilatation of the upper urinary tract can produce reflux nephropathy.

Ultrastructural analysis of human proximal tubules and cortical interstitium in chronic renal disease (hydronephrosis)

A systematic ultrastructural analysis of proximal tubule atrophy and cortical interstitial changes was carried out in human chronic nephropathy. The investigation was based on human hydronephrotic kidneys, which had been surgically removed and subsequently perfusion-fixed for light and electron microscopy. Normal kidney tissue, which was derived from nephrectomy specimens with pathological changes confined to part of the kidney or to the renal pelvis, was used for control material. A slight degree of proximal tubule atrophy was characterized by reduction of mitochondria and basolateral membranes, enlargement of large endocytic vacuoles and increased numbers of lysosomes containing lamellar material. In moderate atrophy these changes were further accentuated, and in addition there was an increasing loss of microvilli and a reduction of endocytic invaginations and small endocytic vacuoles. In severe atrophy all types of organelles were sparse and the architecture of the tubule cells greatly simplified. A distinctive feature of atrophic tubules was the presence in the tubule cells of large bundles of actin-like filaments, which were often associated with outpouchings of basal cell parts and basement membrane. The reduction of mitochondria and basolateral cell membranes and the changes of endocytic vacuoles and lysosomes indicate that proximal tubule atrophy also in early stages may be associated with impairment of tubular transport processes. Comparisons with previous observations in various types of experimentally induced tubule cell degeneration and with the ultrastructure of regenerating proximal tubule cells provide some evidence that degenerative changes as well as imperfect regeneration of tubule cells may contribute to the alterations of ultrastructure in tubular atrophy. It is suggested that changes of the cortical interstitium may be of pathogenic importance for the progression of tubular atrophy by altering the spatial relationships between tubules and capillaries.