Ultrastructural changes in the microcirculatory bed and filtration-reabsorption barrier of the kidney during temporary ischemia after unilateral nephrectomy

Ultrastructure of cellular elements of the microcirculatory bed and filtration-reabsorption barrier has been studied in 150 mature white rats, in which vascular fasciculus of the left kidney has been compressed for 30 min, 1-2 h with a subsequent restoration of the blood stream in the organ undergone ischemia on the 3rd, 7th, 14th, 30th, 60th, 180th, 360th days under conditions of the preliminarily right kidney nephrectomy. On the 3rd day after ischemia of the remained kidney for 30 min, structural components of the walls of the glomerular arterioles and those of the filtration-reabsorption barrier undergo certain ultrastructural changes, that with time elapsed (7, 14 days) gradually pass away, and amount of cells with hypertrophic processes increases. Ischemia for 1 h in the remained kidney with subsequent restoration of the blood stream on the 3rd, 7th days produces in the structures mentioned more pronounced destructive changes. During subsequent compensatory hypertrophy (the 30th, 60th days) of the remained kidney after its ischemia, in the microcirculatory bed elements and in the convoluted canal epitheliocytes intracellular regenerative and hyperplastic processes develop. However, ischemia for 2 h in the remained kidney produces severe destructive-necrotic phenomena in ultrastructure of the microcirculatory bed and of the filtration-reabsorption barrier.     

Assembly of the glomerular filtration surface. Differentiation of anionic sites in glomerular capillaries of newborn rat kidney

Glomerular development was studied in the newborn rat kidney by electron microscopy and cytochemistry. Glomerular structure at different developmental stages was related to the permeability properties of its components and to the differentiation of anionic sites in the glomerular basement membrane (GBM) and on endothelial and epithelia cell surfaces. Cationic probes (cationized ferritin, ruthenium red, colloidal iron) were used to determine the time of appearance and distribution of anionic sites, and digestion with specific enzymes (neuraminidase, heparinase, chondroitinases, hyaluronidases) was used to determine their nature. Native (anionic) ferritin was used to investigate glomerular permeability. The main findings were: (a) The first endothelial fenestrae (which appear before the GBM is fully assembled) possess transient, negatively charged diaphragms that bind cationized ferritin and are impermeable to native ferritin. (b). Two types of glycosaminoglycan particles can be identified by staining with ruthenium red. Large (30-nm) granules are seen only in the cleft of the S-shaped body at the time of mesenchymal migration into the renal vesicle. They consist of hyaluronic acid and possibly also chondroitin sulfate. Smaller (10-15-nm) particles are seen in the earliest endothelial and epithelial basement membranes (S-shaped body stage), become concentrated in the laminae rarae after fusion of these two membranes to form the GBM, and contain heparan sulfate. They are assumed to be precursors of the heparan sulfate-rich granules present in the mature GBM. (c) Distinctive sialic acid-rich, and sialic acid-poor plasmalemmal domains have been delineated on both the epithelial and endothelial cell surfaces. (d) The appearance of sialoglycoproteins on the epithelial cell surface concides with the development of foot processes and filtration slits. (e) Initially the GBM is loosely organized and quite permeable to native ferritin ;it becomes increasinly impermeable to ferritin as the lamina densa becomes more compact. (f) The number of endothelial fenestrae and open epithelial slits increases as the GBM matures and becomes organized into an effective barrier to the passage of native ferritin.     

Ultrastructural changes in the gallbladder mucous membrane during temporary experimental ischemia]

Temporary ischemia of the gall bladder was induced in rabbits by ligation of the gall bladder artery with silk. Histological examination revealed vascular disorders, such as hyperemia, blood stasis and focal hemorrhages. Electron microscopic studies showed the presence of increased number dark epithelial cells, expansion of intercellular area, loosening of the basal membrane and defects in it with invagination of the epithelial cells into the submucous layer. The most striking changes were discovered after a thrice-repeated 30-minute occlusion of the gall bladder artery. The degree of destructive changes proved to depend on the number of stimulated spasms (occlusions) and not on the duration of ischemia. This gives grounds to believe that multiple circulatory disorders participated in the complicated pathogenesis of cholecystitis.     

Morphological changes in the filtration-reabsorption barrier of the remaining kidney after its denervation and disordered lymph outflow

An electron microscopical investigation on combined effect of denervation and disturbance of lymphatic outflow to structural elements of the FRB in the preserved kidney after contralateral nephrectomy has been performed on 20 mature white rats in 3, 30, 180, 360 days. In 3 days in the cellular components of the FRB cytoplasmic structures are at the state of functional strain and overstrain. Hemostasis is observed in glomeruli and in peritubular capillaries, as well as edema of the interstitial connective tissue. In 30 days certain signs of hyperplasia and hypertrophy of intracellular structures appear in the components of the FRB. However, later (in 180, 360 days) certain tendency to predominance of processes of functional strain in the intracellular structures with their certain destruction and reaction of the connective stroma is observed.     

Molecular make-up of the glomerular filtration barrier

The glomerular filtration barrier is composed of glomerular endothelial cells, the glomerulus basement membrane and the podocyte cell layer. The filtration barrier is a target of injury in several systemic and renal diseases, and this often leads to progressive renal disease and kidney failure. Therefore, it is essential to understand the molecular biology of the glomerulus. During the last two decades, a lot of new information about molecular components of the glomerulus filtration barrier has been generated. Many of the key discoveries have been obtained through studies on the genetic background of inherited glomerular diseases. These studies have emphasized the role of podocytes in the filtration barrier function. During the last decade, the use of knockout mouse technology has become more available and given important new insights into the functional significance of glomerular components. Large-scale approaches, such as microarray profiling, have also given data about molecules involved in the biology and pathology of the glomerulus. In the coming decade, the use of global expression profiling platforms, transgenic mouse lines, and other in vivo gene delivery methods will rapidly expand our understanding of biology and pathology of the glomerular filtration barrier, and hopefully expose novel target molecules for therapy in progressive renal diseases.     

Electron microscopic study of glomerular filtration barrier in the rat kidney embedded in polymerized glutaraldehyde-urea.

Embedding kidney in polymerized glutaraldehyde-urea favors the retention of glycoprotein matrix of the cell coat and the basement membrane of the glomeruli. The basement membrane appears as a single layer with uniform amorphous matrix. Thick glycoprotein coat covers the whole surface of prodocytes and their foot processes. In areas other than the slits and the portion of the foot processes which touch on the basement membrane, the coat is a continuous layer with an average thickness of 490 A. In the slits between the foot processes of podocytes there is an actual fusion of glycoprotein coats; the average width of the slit is 415 A. The glycoprotein 'plugs' in the slit may be a significant portion of the glomerular filtration barrier against macromolecules, together with the basement membrane and the slit diaphragms.     

Ultrastructural changes in the brain capillaries after hypoxia

The authors describe ultrastructural changes in and around rat brain capillaries after hypoxia. The experimental animals breathed a mixture of 5% oxygen and 95% nitrogen for two or for three hours; a third group, which spent three hours in this atmosphere, was treated 24 h later. Cytoplasm processes and vesicles were observed on the luminal side in the endothelial cells, while the cytoplasm contained vacuoles and altered mitochondria. The basement membrane of the brain capillaries was uneven and longitudinal clear zones were formed in it. Altered mitochondria were present in the pericytes and astrocytes. The most pronounced changes were found in the astrocyte processes, which were light and hydrated and contained destroyed mitochondria and lamellar bodies resembling myelin. After 24 h, morphological changes still persisted, especially in the astrocyte processes.     

Changes in the glomerular filtration barrier during aging in rats

In this work, we analysed histochemical, biochemical and functional modifications of the glomerular basement membrane (GBM), occurring for aging, in the Rat. The results suggest an increase of collagenous components and a decrease of sulfated glucosaminoglycans as a function of age. In other respects, fixed anionic sites of the GBM, disclosed by colloidal iron, are almost exclusively restricted to the laminae rarae in one month-old rats, whereas the marker appears randomly scattered among the lamina densa in 12 month-old animals. These changes could be the cause of increased permeability of the GBM during aging.     

Transmembrane collagen XVII is a novel component of the glomerular filtration barrier

The kidney filtration barrier consists of the capillary endothelium, the glomerular basement membrane and the slit diaphragm localized between foot processes of neighbouring podocytes. We report that collagen XVII, a transmembrane molecule known to be required for epithelial adhesion, is expressed in podocytes of normal human and mouse kidneys and in endothelial cells of the glomerular filtration barrier. Immunoelectron microscopy has revealed that collagen XVII is localized in foot processes of podocytes and in the glomerular basement membrane. Its role in kidney has been analysed in knockout mice, which survive to birth but have high neonatal mortality and skin blistering and structural abnormalities in their glomeruli. Morphometric analysis has shown increases in glomerular volume fraction and surface densities of knockout kidneys, indicating an increased glomerular amount in the cortex. Collagen XVII deficiency causes effacement of podocyte foot processes; however, major slit diaphragm disruptions have not been detected. The glomerular basement membrane is split in areas in which glomerular and endothelial basement membranes meet. Differences in the expression of collagen IV, integrins α3 or β1, laminin α5 and nephrin have not been observed in mutant mice compared with controls. We propose that collagen XVII has a function in the attachment of podocyte foot processes to the glomerular basement membrane. It probably contributes to podocyte maturation and might have a role in glomerular filtration.     

Functional morphology of the glomerular filtration barrier of Gallus gallus

The anionic charge barrier and the endothelial and epithelial pore sizes on the glomerular filtration barrier (GFB) were examined in white leghorn chickens (Gallus gallus). Ruthenium red was used to stain anionic charge sites on the GFB. The tissue was treated by normal dehydration and freeze substitution dehydration for transmission electron microscopy (TEM). In addition, the basal lamina was isolated for study. The results of our study indicate that G. gallus possess a thick, negatively charged glycocalyx surrounding the podocytes and slit diaphragm and on the endothelium. However, in all cases, little anionic charge is present in the basal lamina. The pores on the endothelium are elliptical and have mean dimensions of 148 × 110 nm. This is in contrast to mammals, which have smaller, round pores. The epithelial pores in G. gallus measure approximately 35 nm in length, approximately 4 times larger than those found in mammals. These results indicate that the avian glomerulus may allow the filtration of larger molecules from the plasma than occurs in mammals and that the charge on the molecule may not be as restrictive a filtration characteristic as in mammals. © 1996 Wiley-Liss, Inc.     

Ultrastructural transformation of blood capillaries following implantation of a DMBA pellet

CNS blood capillary wall in the area of DMBA pill implantation was studied by electron microscopy 1--270 days following the implantation. Blood capillaries were shown to take an active part in precancerous processes. It was noted, in particular, that DMBA induced very suggestive alterations in the endothelial cells in the form of lipid-like structures, previously reported by the authors in the so-called hairy cells, appearing in the cytoplasm 24 hr after the experiment initiation. The appearance of such structures is considered as possible secondary product of the inter-action of DMBA and lipoprotein complexes of the membrane with subsequent dissolution of the carcinogen in lipids. The basal layer of blood capillaries was found to undergo considerable alterations in the form of its progressive rarification, widening the homogenization. A possible role of the altered basal layer in the accumulation of DMBA metabolites is discussed.     

Ultrastructural changes in the renal filtration barrier during hibernation of the common dormouse (Eliomys quercinus L.)

We have studied kidney samples of 16 garden dormouses (Eliomys quercinus L.) divided into two groups, 8 hibernating and 8 non-hibernating. Hibernation produces structural modifications in the glomerular ultrafilter: (1) the endothelial pores decrease in number and size; (2) the podocytic food processes increase in number and the slit pores decrease in size; (3) in the basement membrane there are no structural morphological modifications. In short, we could say that the permeability of the glomerular ultrafilter decreases during hibernation. This fact helps to understand the decrease in the rate of urine formation that takes place in the presence of a low body temperature and a metabolic depression.     

Ultrastructural changes in the spermatogenic epithelium and in the basic components of the blood-testis barrier in adult rats following repeated administration of estradiol dipropionate]

Electron microscopic studies of the testes were conducted in intact adult Wistar rats and in rats given repeated injections of a 0.1% solution of estradiol-dipropionate-0.3 mg week for 10 weeks. Administration of the hormone caused focal inhibition of spermatogenesis (6 weeks) accompanied by development of destructive changes in the spermatogenic cells. These pathological changes were reversible and disappeared two months after the cessation of the hormone injection, and the spermatogenesis was restored. Development of the pathological changes in the spermatogenic epithelium was accompanied by disturbances of the fine structure of the main components of the blood-test is barrier (Sertoli cells, tunica propria of the seminiferous tubules).     

Development of glomerular capillaries of the definitive kidney in the prenatal ontogenesis of man

The morphology of development of the glomerular capillaries in the human definitive kidney has been studied during prenatal ontogenesis. They are laid down in two ways: in the renal corpuscule rudiment from the migrated angioblasts and by ingrowth of the capillaries from the precapillary branchings of afferent arterioles into the nondifferentiated aggregate of nephrogenic cells. Both types of glomerulogenesis are observed after the afferent arterioles reach the corpuscule rudiments.     

Scanning electron microscopy of the glomerular filtration membrane in the rat kidney

The rat kidney was perfused with saline and glutaraldehyde, treated with Murakami's tannin-osmium impregnation method, ethanol-freeze cracked and dried by the critical point method. Gold-palladium evaporated specimens were observed in a field-emission scanning electron microscope. The glomerular filtration membrane, fractured in different planes was observed with the following results: 1. Adjacent pedicles originate from different podocytes. No interpedicular bridges of apparent cytoplasmic nature could be found. 2. The basement membrane, in grazing fractures shows a horizontally layered architecture. 3. The attenuated endothelial sheet (lamina fenestrata) is divided into compartments, which we suggest should be called "areolae fenestratae", by cytoplasmic crests radiating from the nucleated portion of the endothelial cell. A crest also occurs along the cell margin, which contacts a similar crest at the margin of the adjacent cell. 4. The pores in the areolae fenestratae are variable in size (30-150 nm diameter). A knob-like projection from the apparently naked basement membrane is found in a portion of the pores. 5. Numerous microvilli may occur on the endothelium. Some of them anastomose and fuse with one another to form a net whose meshes appear identical with the endothelial pores. Domes and shelves formed of a fenestrated cytoplasmic sheet also occur above the ordinary level of the endothelial lining. A hypothesis implicating microvilli in the partial renewal of the endothelial sheet is proposed.     

Fat absorption following temporary ischemia of the small intestine

Ischemia of the rat small intestine lasting 40 min leads to pronounced structural disorders in lipid transport across the enterocytes, reduction in enzymatic activity of the cells and in absorption function, and to the loss of fat with feces. The normalization of the indicated parameters occurs at varying times and ends after 1 month. Fat transport abnormality is marked by an increase in lipid drops in the cavities of the smooth endoplasmic network, appearance of large and numerous matrix lipids, by a greater reduction, as compared to normal, in the membranes of the rough endoplasmic network and lamellar complex in the epithelium of the villi. Accumulation of lipids and retardation of their release from the cytoplasm are determined by incomplete differentiation of the epithelium, which is also combined with a decreased enzymatic activity.