Ultrastructural observations on the pars descendens of the proximal tubule in the kidney of the male rat

Kidney injury molecule-1 identifies antemortem injury in postmortem adult and fetal kidney

There is currently no technique to unambiguously diagnose antemortem kidney injury on postmortem examination since postmortem tissue damage and autolysis are common. We assessed the ability to detect kidney injury molecule-1 (KIM-1) expression in adult and fetal kidneys examined at autopsy. In adult kidneys ( n = 52 subjects), we found that the intensity of KIM-1 staining significantly correlated with the antemortem level of serum creatinine, and this was independent of the extent of tissue autolysis. In addition, kidneys from a total of 52 fetal/neonatal subjects, 30 stillborns and 22 liveborns, were assessed for KIM-1 staining. Given that serum creatinine is unreliable and often unavailable in fetuses and newborns, we assessed preterminal hypoxia in fetuses by the presence of squames in pulmonary alveoli and by required intubation. KIM-1 expression correlated with these clinical indexes of hypoxia. The expression of KIM-1 was seen in a majority of the fetal and neonatal autopsy kidneys (77%, 40/52) as early as 16 wk of gestation, even in the presence of autolysis. Thus KIM-1 is a specific and stable marker of antemortem tubular injury in kidneys of adults and fetuses despite postmortem autolysis.

Uriniferous tubule: structural and functional organization

The uriniferous tubule is divided into the proximal tubule, the intermediate (thin) tubule, the distal tubule and the collecting duct. The present chapter is based on the chapters by Maunsbach and Christensen on the proximal tubule, and by Kaissling and Kriz on the distal tubule and collecting duct in the 1992 edition of the Handbook of Physiology, Renal Physiology. It describes the fine structure (light and electron microscopy) of the entire mammalian uriniferous tubule, mainly in rats, mice, and rabbits. The structural data are complemented by recent data on the location of the major transport- and transport-regulating proteins, revealed by morphological means(immunohistochemistry, immunofluorescence, and/or mRNA in situ hybridization). The structural differences along the uriniferous tubule strictly coincide with the distribution of the major luminal and basolateral transport proteins and receptors and both together provide the basis for the subdivision of the uriniferous tubule into functional subunits. Data on structural adaptation to defined functional changes in vivo and to genetical alterations of specified proteins involved in transepithelial transport importantly deepen our comprehension of the correlation of structure and function in the kidney, of the role of each segment or cell type in the overall renal function,and our understanding of renal pathophysiology.

Transmission and scanning electron microscopy of the kidney: Part II

The minipig has a multilobar kidney with a wide cortex and short papilla. The vascular bundles are of a simple type. Although short and long looped nephrons are both present, the short looped kind predominates. The minipig has many morphological similarities to dog and human kidneys. One particularly unique feature of the minipig papillary collecting duct cells, however, is the presence of electron-dense granules in the basal cytoplasm which appear to be secreted into the lateral intercellular spaces, perhaps forming a water-tight seal in a manner analogous to membrane-coating granules found in the epidermis of skin.

Sequential morphologic analysis of the nephrotoxicity produced in rats by single doses of chlorozotocin

Chlorozotocin is a chloroethylnitrosourea antitumor agent that is in clinical trial for a variety of human tumors. Renal failure has been a reported side effect of treatment with several of the chloroethylnitrosoureas, including chlorozotocin. To better understand the pathogenesis of this target organ toxicity, we have studied the nephrotoxicity of a single high, intermediate, or low dose of chlorozotocin in male F344 rats. We report here the sequence of histopathologic changes seen over a 1-10-day (high dose) or 1-28-day (intermediate or low dose) period. The single high dose (40 mg/kg, s.c.) produced an acute cortical necrosis involving the proximal tubules, followed by later necrotic changes in the collecting ducts in the inner medulla. Karyomegaly was noted at 10 days in occasional cells of the papillary collecting ducts and urinary epithelium lining the papilla. A single intermediate dose (25 mg/kg, s.c.) caused a similar but less severe injury of later onset. Proximal tubule injury was less severe and more limited. Necrosis of papillary collecting ducts was not seen; however, karyomegaly was pronounced in cells of the collecting ducts in the inner stripe of the outer medulla and inner medulla, and in the urinary epithelium covering the papilla. No discernible histopathology was present following the low dose (12.5 mg/kg, s.c.) of chlorozotocin. The histopathology was correlated with biochemical parameters. Our findings have possible implications for monitoring the severity of nephrotoxic side effects in patients, as well as provide preliminary evidence that this antineoplastic agent may itself cause preneoplastic changes, a finding with important long term implications.

Hexachloro-1:3-butadiene-induced renal tubular necrosis in the mouse

Administration of hexachloro-1:3-butadiene (HCBD) intraperitoneally at a dose of 50 mg/kg body weight caused necrosis of the proximal tubule of the mouse kidney. The earliest morphological changes detectable by light microscopy were observed after 4 h, and by 16 extensive proximal tubular necrosis was seen throughout the cortex. Active tubular regeneration was apparent by day 5 and by day 14 substantial recovery of morphology had occurred. In the electron microscope mitochondrial swelling was seen 1 and 2 h after dosing in the S1 and S2 segments of the proximal tubule, whereas by 4 and 8 h the major pathological changes were confined to the lower S2 and S3 segments and consisted of mitochondrial swelling and cellular necrosis. The extent of renal injury and regeneration correlated well with measurement of renal function. In conclusion, HCBD produces necrosis of the S2 and S3 segments of the proximal tubule in the mouse, this pattern of injury is different from that seen in the rat where HCBD produces selective necrosis of the S3 segment.

Histochemical evaluation of mouse and rat kidneys with lectin-horseradish peroxidase conjugates

Paraffin sections of mouse and rat kidney were stained with a battery of ten lectin-horseradish peroxidase conjugates and lectin binding was correlated with the ultrastructural distribution of periodate-reactive sugar residues as determined by the periodic acid-thiocarbohydrazide-silver proteinate technique. Various segments of the uriniferous tubule in both species showed differential affinity for labelled lectins. Significant differences were also evident between comparable tubular segments in mouse and rat kidneys. Neutral glycoconjugates containing terminal beta-galactose and terminal alpha-N-acetylgalactosamine were prevalent on the luminal surface of the proximal convoluted tubule in the rat, but alpha-N-acetylgalactosamine was absent in this site in the mouse. In both species, terminal N-acetylglucosamine was abundant in the brush border of proximal straight tubules but absent in proximal convolutions. Fucose was demonstrated in both proximal and distal segments of mouse kidney tubules but only in the distal nephron and collecting ducts in the rat. Lectin staining revealed striking heterogeneity in the structure and distribution of cellular glycoconjugates. Such cellular heterogeneity was previously unrecognizable with earlier histochemical methods. The marked cellular heterogeneity observed with several lectin-conjugates in distal convoluted tubules and collecting ducts of both species raises a prospect that lectins can provide specific markers for intercalated and principal cells in the mammalian kidney. Glycoconjugates containing terminal sialic acid and penultimate beta-galactose were present on vascular endothelium in both rodent kidneys, as were terminal alpha-galactose residues; but both species lacked reactivity for Ulex europeus I lectin in contrast to human vascular endothelial cells. The constant binding pattern of lectin conjugates allows convenient and precise differentiation of renal tubular segments and should prove valuable in the study of changes in kidney morphology promoted by experimental manipulation or pathologic changes.

Necrosis of the pars recta (S3 segment) of the rat kidney produced by hexachloro 1:3 butadiene

Administration of hexachloro 1:3 butadiene (HCBD) intraperitoneally at a dose of 200 mg/kg body weight caused necrosis of the parts recta of the proximal tubules situated in the outer stripe of the outer medulla of the rat kidney. The earliest morphological changes detectable by light microscopy were observed after eight hours, with several proximal tubules showing necrosis. By sixteen hours a distinct band of tubular necrosis was seen in the outer stripe of the outer medulla. One and two days after dosing proximal tubular necrosis was still evident whereas distal tubules were unaffected. By three days, vacuolation was observed in the pars convoluta of some proximal tubules. Active tubular regeneration was apparent by day five, which was accompanied by a marked increase in renal water and nonprotein sulphydryl content (NP-SH). By day fourteen substantial recovery had occurred. Ultrastructural changes were seen as early as one hour after HCBD (300 mg/kg, ip) although necrosis was not marked until 8 hr. Mitochondrial swelling was seen 1-4 hr after dosing in the S1 and S2 segments of the proximal tubule. By 8 hr the major pathological changes were largely confined to the S2 segment and consisted of loss of brush border, mitochondrial swelling and cellular necrosis. In conclusion HCBD produces a site-specific nephrotoxic effect on the proximal tubule in the rat. The pattern of injury was similar to that associated with some other nephrotoxic and ischaemic models of acute renal failure.

Ultrastructural changes in the kidneys of rabbits treated with lead acetate

Electron microscopical studies were carried out on the kidneys of rabbits given s.c. injections of 0 (control), 0.25 or 0.50 mg lead acetate/kg b.w. 3 times a week during 14 weeks. At the end of the experimental period the animals had lead blood levels of 60, 500 and 600 micrograms/l whole blood respectively. Treatment-related renal changes were found in the proximal tubules; they consisted of a dose-related increase in the amount of lysosomes in epithelial cells of the convoluted part, and of severely damaged cells and loss of brush border in the straight part. There was also an increase in lysosomal tubular inclusions, which are considered characteristic of lysosomes of the proximal tubular cells of the rabbit kidney. The significance of these findings for assessing the risk of occupational exposure to lead is briefly discussed.

Immunofluorescence of NADPH-cytochrome c (P-450) reductase in rat and minipig tissues injected with phenobarbital

The enzyme NADPH-cytochrome c (P-450) reductase was identified by indirect immunofluorescence in hepatocytes, bronchioles, and proximal tubules of liver, lung, and kidney, respectively, of rats and minipigs that had been injected with phenobarbital or saline. The distribution of this component of the cytochrome P-450-mediated microsomal system may be relevant to sites of drug toxicity and carcinogenesis.

Histochemical, autoradiographic and electron microscopic investigations of the renal proximal tubule of male and female rats after castration

After castration of 90-day-old male and female rats, changes appear in the renal proximal tubule. A distinction can be made between early changes (up to 10th postoperative day) and later changes (20th-30th postoperative day). Between the 3rd and 5th day after castration the kidney of the females shows an increase in free estrogen receptors (biochemical studies) which are localized in the pars contorta of the proximal tubule (autoradiographic studies), while the male kidney shows a marked increase in urinary protein excretion up to the 10th day after castration. Proximal tubule changes detectable histochemically and electron microscopically do not appear until day 20 or 30 after castration. The results of castration are similar in segments S1 and S2. By days 20 and 30 after castration there is a decrease in the activity of lysosomal enzymes (acid phosphatase, acid beta-galactosidase). Electron microscopy shows a conspicuous decrease in the number of giant lysosomes (mainly in females) and apical vacuoles (mainly in males). A marked increase in the number of lysosomes is found in the S3 segment; females always have more lysosomes than males. The number of peroxisomes is also greatly increased; they appear circular in the females but can assume bizarre shapes in the males. Lipid droplets appear in the basal region of the tubule cell of segments S2 and S3 in the males. The sex differences are preserved in all segments even after castration and become even more pronounced in the S3 segment.

Survey of the morphology of the dog kidney

Dogs are frequent subjects in experimental studies of renal physiology and pathology in spite of the paucity of information on their normal renal morphology. In this study, gross morphology, light microscopy, and scanning and transmission electron microscopy were used to describe dog renal anatomy. The dog has a multilobed kidney with the medulla fused into an elongate crest and a renal pelvis of elaborate shape. The outer zone of the medulla lacks a definitive outer stripe. The proximal tubule consists of four distinct anatomical segments. Dark cells are abundant in the collecting duct of the inner medulla. The majority of the nephron segments demonstrate remarkable similarities to those of the human kidney and less to those of the kidney of the laboratory rat.

An ultrastructural investigation of nephrotoxicity in rats induced by feeding cultures of Penicillium verrucosum var. cyclopium

A renal tubular lesion was induced in male rats by giving them a culture homogenate or culture filtrate of Penicillium verrucosum var. cyclopium by gastric gavage for 20 days. The fungus was obtained from stored maize in an area of endemic nephropathy in Bulgaria. Changes in the proximal convoluted tubules were studied by light and electron microscopy. The lesion was confined to the pars recta in the outer stripe of the outer zone of the medulla. It consisted of degeneration and necrosis of epithelial cells, prominent karyomegaly, arrested mitotic divisions and production of binucleate and tetranucleate tubular cells. Two patterns of degeneration occurred with comparable frequency: a vesicular form with pyknotic nucleus and electron lucent degeneration. Nuclei of the epithelial cells in affected tubules contained segregated nucleoli. The necrotic cells were replaced by actively regenerating cells derived from adjacent viable epithelium. The similarity between the tubular lesions induced in rats and the changes found in patients with Balkan endemic nephropathy is discussed.

The effect of sex hormones on the proximal tubules in the rat kidney

The three segments (S1, S2, S3) of the proximal tubule of the rat kidney were investigated, with special reference to lysosomes, after castration, estradiol application, and at the end of pregnancy. Especially in S1 and S2 castration induces an increase of cellular autophagy. The nuclei become smaller; endoplasmic reticulum (ER), ribosomes, and Golgi apparatus are reduced; catabolism predominates. In S1 more giant lysosomes occur; the total number of lysosomes increases whereas acid phosphatase activity decreases at the same time. Sex differences which exist in untreated animals disappear. Substitution with estradiol causes an activation of the proximal tubule cells: Heterophagy predominates, and cellular autophagy is reduced. Nuclear size is unchanged; ER, ribosomes and Golgi apparatus show a clear increase. Giant lysosomes are absent in S1. On the whole lysosomes are larger, but less numerous than after castration. Acid phosphatase is highly active. All changes are most evident in S3. At the end of pregnancy the proximal tubule cells are "stressed" considerably: Pinocytotic activity increases, and large numbers of cell organelles and many lipid vacuoles can be observed. The basal lamina in S1 and S2 becomes thicker. Lysosomes enlarge and increase in number in all segments; giant lysosomes are absent in S1; acid phosphatase is extremely high. The results indicate that sex hormones directly influence the regulation of the proximal tubule cell; moreover, they are indirectly important for the functioning of the kidney via changes in the whole organism.

Ischemic damage and repair in the rat proximal tubule: differences among the S1, S2, and S3 segments

Rats were subjected to 25 min of unilateral renal artery occlusion and were studied at 5, 15, and 30 min and at 1, 2, 4, 8, 16, 24, and 48 hr following ischemia. The patterns of epithelial injury and repair in proximal tubule (PT) segments S1, S2, and S3 were followed, and associated changes in renal function were determined. We found that S1 and S2 cells alike are only reversibly injured and recover completely to normalcy within 4 hr, whereas S3 cells selectively undergo progressive cell injury and death and are exfoliated into tubular lumina. The necrotic S3 cells are replaced by mitotic division of survivor cells 24 to 48 hr following the ischemic insult. In addition, there was selective damage within tubular cells. Wiithin 5 min of blood reflow following ischemia, the majority of brush border microvilli (MV) in all three PT segments underwent coalescence by membrane fusion and thus were interiorized into the cytoplasm of PT cells. A minority of MV fragmented and were shed into PT lumina, but nephron obstruction by shed membranes was only mild and transient, unlike in the 1-hr ischemia model. Loss of MV reached a maximum of 15 min. By 30 min, MV began to reappear; by 2 hr, large numbers of MV had been regenerated; and by 4 hr, S1 and S2 cells appeared normal. The regenerative process included the luminal repositioning of previously interiorized MV membrane. MV regeneration occurred in S3 segments also, but before the process was complete, the cells developed features of irreversible cellular injury. Glomerular filtration rate (GFR) was 22% of control at 30 min of reflow, rose progressively to 55% of normal by 7 to 8 hr, and was normal at 24 hr. Single nephron filtration rate (SNGFR) was not significantly different from normal throughout. Proximal tubular sodium reabsorption was depressed and urinary sodium excretion increased at 30 min and at 2 to 3 hr, i.e., at times when MV alterations were prominent, but both were normal by 7 to 8 hr when MV in S1 and S2 cells had been fully reconstituted. Our major conclusions are: 1) There is differential susceptibility by cell type to ischemic injury in rat PT. 2) A rapid brush border loss/regeneration cycle occurs after ischemic injury. 3) Intact brush border may be required for normal sodium reabsorption by PT. Reasons for the GFR/SNGFR discrepancy are unclear, but tubular malfunction may partly explain the phenomenon.

A freeze-fracture study of tight junctions in the pars convoluta and pars recta of the renal proximal tubule

The morphology of tight junctions of the renal proximal tubule was studied comparing the pars convoluta and pars recta of rat, golden hamster, rabbit, cat, dog and tupaia. Though some interspecies variations were observed, the convoluted portions of the proximal tubules revealed quite uniformly very leaky tight junctions with mainly 1-2 strands. Along the whole proximal tubule of the rabbit kidney including the pars recta only minor differences of the zonulae occludentes were found. By contrast, the tight junctions of the pars recta in other species were much more elaborate, especially in cat and tupaia, having up to 6 strands and an overall depth of more than 150 nm. The implications of these findings are discussed with special regard to the functional differences between the pars convoluta and pars recta of the proximal tubule.

Comparative morphometric study of the cells of the third proximal segment of the rat kidney under different conditions of fixation

The morphometric study of the P3 segment of rat proximal tubule has shown that neither the method of fixation, nor the fixative itself, significantly change the relative and absolute volumes of the cell compartments, provided that the fixation media are made approximately isotonic.

Effect of mannitol, dextran (macrodex), allopurinol, and methylprednisolone on the morphology of the proximal tubule of the rat kidney made ischemic in vivo

Rats were anesthetized and their lift kidneys were made ischemic for 1 h by clamping of the aorta just above the left renal artery. Mannitol (2.5 g/kg), Dextran 70 (0.6 g/kg), methylprednisolone (50 and 100 mg/kg), and allopurinol (100 mg/kg body weight) were administered before, during, or after the ischemia period in order to test the effect of each of these drugs upon this model of renal injury. At 24 h after the release of the aortic clamp the left kidneys of the drug treated animals wwere perfusion fixed and processed for light and electron microscopy. Dextran administration to animals with ischemic kidneys gave rise to a pronounced vacuolization ("osmotic nephrosis"), in the entire proximal tubule and especially in the pars recta. This was in contrast to dextran administration to rats with nonischemic kidenys, which showed no or very mild "osmotic nephrosis." This demonstrates that ischemia makes rat kidneys more susceptible to the development of "osmotic nephrosis." In controls (no drug treatment) one hour of renal ischemia gave partial necrosis of pars recta of the proximal tubule, while the pars convoluta tubule survived. Mannitol treatment significantly reduced the amount of necrosis of the pars recta, whereas dextran, methylprednisolone, and allopurinol had no or a negative effect on the survival of the cells of the pars recta segment. It is suggested that mannitol protects against the development of necrosis by increasing medullary blood flow in combination with a counteractive influence on the cellular swelling, which is known to occur in ischemia.

The cytochemical demonstration of catalase and D-amino acid oxidase in the microbodies of teleost kidney cells

The distribution of catalase and D-amino acid oxidase, marker enzymes for peroxisomes, was determined cytochemically in the kidney tubules of an euryhaline teleost, the three-spined stickleback. Catalase activity was localized with the diaminobenzidine technique. The presence of D-amino acid oxidase was determined using H2O2 generated by the enzyme, D-alanine as a substrate, and cerous ions for the formation of an electron-dense precipitate. Both enzymes appeared to be located in microbodies. The combined presence of these enzymes characterizes the microbodies as peroxisomes. Biochemically and cytochemically, no urate oxidase or glycolate-oxidizing L-alpha-hydroxy acid oxidase could be demonstrated. Stereological analysis of the epithelia lining the renal tubules showed that the fractional volume of the microbodies is 5 to 10 times higher in the cells of the second proximal tubules than in the other nephronic segments or the ureter. The fractional volume of the microbodies was similar in kidneys of freshwater and seawater fishes.

Biological effects of alkali-treated protein and lysinoalanine: an overview

The renal alterations induced by alkali-treated protein and lysinoalanine are reviewed and their biological implications discussed. Alkali-treated proteins and lysinoalanine, an unusual amino acid formed in proteins during alkali treatment, have been shown to produce a renal alteration characterized by nuclear and cytoplasmic enlargement, with alterations in DNA synthesis, mitotsis and nucleoprotein. These changes are localized in the straight portion of the proximal renal tubule and have been observed in rats but not in several other species. The nephrotoxic effect of synthetic lysinoalanine has been consistently demonstrated, but the ability of alkali-treated protein to induce renal alterations is apparently modified by factors other than lysinoalanine content. Factors which may influence the development of the kidney lesions in animals fed alkali-treatment protein are discussed, including nutritional factors, the chemical form of lysinoalanine in the protein, species differences, and metabolic fate. Other clinical and experimental conditions that result in similar renal alterations are presented for comparison with the lysinoalanine induced lesion, and possible functional consequences are considred.

Studies on the pathophysiology of acute renal failure. I. Correlation of ultrastructure and function in the proximal tubule of the rat following administration of mercuric chloride

Acute renal failure was induced in male rats by the subcutaneous injection of 4 mg HgC12 per kg body weight. Changes in the proximal tubule were studied by light and electron microscopy at six time intervals from 15 min to 24 h. Renal function was monitored at 6 and 24 h. Between 15 min and 3 h changes were similar in all regions of the proximal tubule (pars convoluta and pars recta). Dispersion of cytoplasmic polysome groups was widespread and mitochondrial matrices were condensed in some cells. No changes were noted in the brush border but increased endocytotic activity occurred in some convoluted tubules at 1 and 3 h. At 6 h severe changes had occurred in the pars recta in the medullary rays. Microvilli of the brush border were focally absent, the mitochondria were swollen and the endoplasmic reticulum was dilated. At this time only subtle changes occurred in the pars recta in the outer stripe of the outer medulla. However by 24 h necrosis was widespread throughout the pars recta, yet changes in the proximal convoluted portion were minimal. A significant azotemia, decreased GFR and increased FENa+ and FEK+ occurred at 6 and 24 h after HgC12 injection. Thus HgC12 at 4 mg per kg body weight produced reproducible renal failure and necrosis involving the pars recta of every nephron but necrosis did not begin in the pars recta until after 6 h while acute renal failure was probably initiated much earlier. The following hypothesis is presented. HgC12 initially interacts with the entire proximal tubule. Although injury is sublethal in the pars convoluta it is responsible for greatly diminished sodium reabsorption and is related to the pathogenesis of the renal failure through feedback mechanisms involving the macula densa and release of renin. This results in renal hemodynamic alterations, decreased GFR and other functional disturbances associated with renal failure. The development of necrosis in the pars recta appears to be a relatively late event, possibly due to further accumulation of Hg++ in this region. In any case, the necrosis appears pathogenetically dissociable from the mechanism of acute renal failure.

Studies on the pathophysiology of acute renal failure. II. A histochemical study of the proximal tubule of the rat following administration of mercuric chloride

Acute renal failure was induced in male rats by the subcutaneous injectioon of 4 mg HgC12 per kg body weight. Enzyme activities of the proximal tubule were studied histochemically at six time intervals from 15 min to 24 h. The enzyme studied were alkaline phosphatase, 5'-nucleotidase, acid phosphatase, alpha-glycerophosphate dehydrogenase (NAD-independent), malic dehydrogenase, succinic dehydrogenase, latic dehydrogenase, glucose-6-phosphate dehydrogenase and glucose-6-phosphatase. Decreases in activity were observed for alkaline phosphatase and 5'-nucleotidase after 15 min. Acid phosphatase was decreased after 30 min. These three enzymes returned to control levels after 3 h, but malic dehydrogenase and alpha-glycerophosphate dehydrogenase were decreased at this time interval. Succinic dehydrogenase was first decreased after 6 h. The earliest morphological changes detectable by light microscopy were observed in pars recta tubules in the medullary rays after 6 h, a time when all enzymes studied showed widespread decreased activity throughout the proximal tubule. After 24 h, the pars convoluta appeared morphologically normal but the pars recta was necrotic and exhibited calcification, whereas enzyme activity was decreased (absent in some cases) in both pars convoluta and pars recta. These results support the hypothesis that Hg++, when given in a sublethal dose, is associated with early histochemical changes in the brush border of the proximal tubule, which may be related to early changes in sodium reabsorption and to the subsequent development of acute renal failure. The observation that changes in plasma membrane-associated enzymes occur early and prior to alterations in enzymes of mitochondria and the endoplasmic reticulum suggests that Hg++ interacts initially with the plasma membrane.

A model to study cell injury: morphological changes of the proximal tubule of the rat kidney during ischemia and during recovery from ischemic injury in vivo

Studies on structural cell changes as a function of ischemia time and studies on the recovery process of ischemically injured cells have implications for our general understanding of the features of cellular reaction to injury. For this reason a model was worked out to follow the morphological changes taking place in the proximal tubule of the rat kidney during ischemia and during recovery from an ischemic episode. The pars convoluta and the pars recta of the proximal tubule were examined separately and compared with one another.

Microbodies of the rat renal proximal tubule: ultrastructural and cytochemical investigations

The present study was undertaken to provide a detailed morphological and cytochemical characterization of the microbodies of the rat renal proximal tubule following perfusion fixation. The following observations were made: 1) Two basic types of microbodies (Mb-I and Mb-II) can be identified. Mb-I have both circular and tubular profiles which are located peripherally within the granular matrix of these microbodies. Mb-II have marginal plates and crystalloid inclusion in addition to circular and tubular profiles. 2) Circular and tubular profiles, 100 nm in diameter, described by previous investigators as being infrequent in occurrence, are the most consistent morphological characteristic of rat renal microbodies after perfusion fixation. These profiles have a homogeneous center surrounded by a double or single ring of granules. The uniform size and spacing of these granules within profiles establish a basic 100 A periodicity found in both types of microbodies. 3) Evidence is presented which suggests that both "nucleoids" and "tubular protrusion rods" as described by other investigators of the rat renal microbodies may result from poor fixation and/or osmotic stress. 4) The density of the matrix of Mb-I is, in contrast to previous reports, greater than the density of adjacent mitochondria. 5) Marginal plates or crystalloid inclusions were demonstrated in some microbodies (Mb-II) of all the rats studied; periodicities of 100, 200, and 300 A were identified within these structures. 6) Both types of microbodies were positive for catalase activity, but were negative for acid phosphatase activity. On the basis of both morphological and cytochemical criteria, it seems plausible that these two populations of renal microbodies (Mb-I and Mb-II) represent a morphological and functional continuum.