Studies of the human fetal kidney. II. Permeability characteristics of the developing glomerulus

Ontogenesis of glomerular basement membrane: structural and functional properties

Protein A-gold immunocytochemistry was applied in combination with morphometrical approaches to reveal the alpha 1(IV), alpha 2(IV), and alpha 3(IV) chains of type IV collagen as well as entactin on renal basement membranes, particularly on the glomerular one, during maturation. The results have indicated that a heterogeneity between renal basement membranes appears during the maturation process. In the glomerulus at the capillary loop stage, both the epithelial and endothelial cell basement membranes were labeled for the alpha 1(IV) and alpha 2(IV) chains of type IV collagen and entactin. After fusion, both proteins were present on the entire thickness of the typical glomerular basement membrane. At later stages, the labeling for alpha 1(IV) and alpha 2(IV) chains of type IV collagen decreased and drifted towards the endothelial side, whereas the labeling for the alpha 3(IV) chain increased and remained centrally located. Entactin remained on the entire thickness of the basement membrane during maturation and in adult stage. The distribution of endogenous serum albumin in the glomerular wall was studied during maturation, as a reference for the functional properties of the glomerular basement membrane. This distribution, dispersed through the entire thickness of the basement membrane at early stages, shifted towards the endothelial side of the lamina densa with maturation, demonstrating a progressive acquisition of the permselectivity. These results demonstrate that modifications in the content and organization of the different constituents of basement membranes occur with maturation and are required for the establishment of the filtration properties of the glomerular basement membrane.

Ontogenesis of angiotensin-I converting enzyme in human kidney

The kidney distribution of angiotensin-I converting enzyme (ACE) was studied in 14 fetuses (11 to 30 weeks old) and 7 children (2 days to 13 years old) by immunohistochemistry using specific antibodies to human kidney ACE. Immunohistochemical techniques included indirect immunofluorescence on cryostat sections of frozen tissue, immunoperoxidase and immunofluorescence of fixed tissue embedded in Paraplast, and immunoelectron microscopy. The ACE distribution in the fetal kidneys was independent of the age of the fetus. ACE was detected in two locations: 1) on the basolateral membranes and primary apical microvilli of epithelial cells from early differentiating proximal tubules; the labeling was intense in brush borders of fully developed proximal tubules; and 2) on glomerular endothelial cells; cells were lined by reaction product as soon as capillaries invaded the inferior cleft of the S-shaped body. Tubular ACE distribution was identical in the postnatal kidneys. The staining of the glomerular endothelium was extremely inconstant. The presence of ACE in proximal tubular cells and glomerular endothelial cells at the beginning of nephron differentiation may indicate that it is involved in the development of nephron function and renal hemodynamic.

Distribution of intravenously injected cationized ferritin within developing glomerular basement membranes of newborn rat kidneys

To label heparan sulfate proteoglycans and other strong anions within glomerular basement membranes (GBM) during assembly, cationized ferritin (CF), with a narrow isoelectric range of 7.7 to 8.2, was intravenously injected into newborn rats. Kidneys were then fixed and processed for electron microscopy at intervals ranging from 1 to 72 h after CF injection. One hour after injection, CF bound extensively to the lamina rara interna and externa of developing GBM and mesangial matrix and to tubular basement membranes (TBM). In double basement membranes of early stage glomeruli, large amounts of CF were also seen in central areas between the endothelial and epithelial basement membranes. In maturing-stage glomeruli, CF bound throughout interior regions of GBM outpockets projecting into the epithelial side of capillary walls as well as to the laminae rarae. Because in adult rats CF binds only to the laminae rarae, the abundant anionic sites seen here in newborns between double basement membranes and within GBM outpocket interiors may be subsequently neutralized or removed during the GBM assembly process. In addition to basement membranes, CF was also located intracellularly within endocytic vesicles and lysosomes of glomerular endothelial, mesangial, and epithelial cells 1 h postinjection. CF was also present in similar structures within the tubular epithelium. In contrast to these findings, CF was gradually lost from developing GBM 5, 15, and 24 h after injection and was essentially cleared from all GBM, mesangial matrices, and TBM after 48 h. Large CF aggregates were progressively accumulated within mesangial lysosomes, however. The transient binding of CF to GBM anionic sites seen here was most likely due to its endocytic removal by developing glomerular endothelial, mesangial, and epithelial cells. Anions in the circulation probably also competed effectively with the GBM and TBM for bound CF.

Renal functional maturation: renal handling of proteins by mature and immature newborns

Renal clearance of creatinine (Ccr), total protein excretion, urinary protein composition and renal clearance of albumin (Calb) were measured and calculated in male premature and mature infants of gestational age 29-41 weeks and in mature infants 1 and 3 months of age. Total protein excretion decreased slightly but not significantly during maturation. The urinary protein composition changed significantly as the fraction of low molecular weight proteins decreased from 48% at a gestational age of 29-33 weeks to 24% in mature infants aged 3 months, the albumin fraction increased from 39%-46% and the proportion of higher molecular weight proteins increased from 12%-29%, respectively. Calb decreased from 2.73-0.80 microliter/min/1.73 m2 in the presence of a rise in Ccr, resulting in a significant fall of the ratio Calb/Ccr from 0.0137 in the youngest prematures to 0.00147 in 3-month-old mature infants.

Effects of mesangial localization of polyvinyl alcohols on glomerular basement membrane thickness

We studied the effects of mesangial localization of polyvinyl alcohols (PVA) on glomerular basement membrane (GBM) thickness in inbred Lewis rats. To avoid possible influences of PVA redistribution after localization in liver, lung, and other organs, the kidneys of rats given PVA were transplanted into uninephrectomized normal rats. Normal kidneys transplanted into normal rats served as a control. GBM thickness at the time of transplantation was the same in PVA kidneys as in normal kidneys. However, by 18 weeks post-transplant GBM thickness was greater in PVA kidneys, and this increase was sustained at 30 weeks. Within the glomeruli of PVA kidneys, lobules with marked mesangial PVA accumulation had more marked GBM thickening than lobules with little or no PVA accumulation. It is concluded that changes within the mesangium can influence GBM thickness. Whether this represents a direct effect of mesangial architectural distortion, a consequence of local phlogistic activities such as the influx of macrophages into the mesangium of glomeruli with PVA localization, or the result of intraglomerular hemodynamic perturbations is unclear.

A study of scanning (SEM) and transmission (TEM) electron microscopy of the glomerular capillaries in developing rat kidney

Kidneys of 2 to 10 day-old rats of Wistar and Sprague-Dawley strains were fixed with glutaraldehyde by retrograde vascular perfusion and then prepared for observation in TEM and SEM. In addition methacrylate casts of differentiating glomerular capillaries were examined by SEM. Although the glomerular vascular pattern differs from one glomerulus to another, its differentiation proceeds according to the following general plan. First the glomerular capillary splits longitudinally, finally to form 3 to 5 lobules consisting of a capillary network, sustained centrally by the mesangium. In the present study the differentiation of glomerular capillaries is described in five successive arbitrarily selected stages. At Stage I a capilllary loop penetrates between the lower limb and the middle segment of the S-shaped body, the rudimentary nephron. At Stage II the capillary undergoes a first subdivision, establishing the primitive lobulation of the glomerulus. At Stage III the vascular and urinary poles differentiate. At Stage IV the glomerulus assumes the aspect of a spherical body, and the capillaries in each lobule undergo subdivision. In Stage V the glomerular vascular pattern approaches its adult appearance, although the maturation processes continue for an extended period of time. Hence in the 10 day-old rat the best-differentiated glomeruli are half the size of adult glomeruli, and their capillary loops are proportionally less well-developed. The capillaries of adjacent lobules may communicate with each other, but a direct vascular shunt between the afferent and efferent vessels cannot be demonstrated.

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.

The basement membrane of the atrophic kidney tubule. An electron microscopic study of changes in rats

In a light and electron microscopic study of the rat's kidney after obstruction of the renal vein or after subtotal nephrectomy the tubular basement membrane changes occurring during the ensuing atrophy of the tubules have been examined. Characteristically, they consist of diffuse widening, focal thickening with vesicular and granular inclusions, circumscribed dissolution, or reduplication of this structure. These observations have led to the conclusion that the tubular basement membrane is formed by both interstitial and tubular cells, although the interstitial cells contribute the greater share to its formation, maintenance and renewal. The thickening of the basement membrane taking place in tubular atrophy must, however, be attributed entirely to the interstitial cells.

Participation of monocytes in glomerulonephritis in acute serum sickness of rabbit

Acute serum sickness in the rabbit was studied with special reference to the role of monocytes in the inflammatory process in the glomerulus. It was revealed that macrophages were the major factor in producing glomerular hypercellularity in acute serum sickness. Proliferation of intrinsic glomerular cells or accumulation of polymorphonuclear leukocytes (PMNs) was minimal. Ultrastructural characteristics of these phagocytic cells were described. Macrophages engulfed various inflammatory products such as fibrin and cell debri in the glomerular capillary. Colloidal carbon administered at the active inflammatory stage was found to be mostly engulfed by macrophages, little by mesangial cells, and was not seen in endothelial or epithelial cells and PMNs. The selective ingestion of the carbon particles by these macrophages made it possible to differentiate them from glomerular cells. This in turn indicated that the macrophages were derived from neither endothelial nor menangial cells and that they were of blood monocytic origin. It was suggested that monocytic cells participated in glomerular inflammation but they, on the other hand, contributed to the repair of glomerular injuries through their active role for phagocytosis.

The glomerular mesangium: uptake and transport of intravenously injected colloidal carbon in rats

Collodial carbon, 70 mg/100 g, was injected into rats which were sacificed for histologic study of the kidneys at intervals of five minutes to seven weeks. Transient thrombocytopenia and albuminuria were observed. Uptake of carbon by the mesangium of glomeruli was maximal at 32 hr and gradually decreased thereafter. Semiquantitative analysis of the distribution of carbon particles within glomeruli revealed a predominately peripheral localization during early time periods, and increased relative concentration of particles within more central zones and in the lacis area at the vascular pole of the glomerulus at two to seven weeks, indicating that one of the mechanisms for clearance of materials from the mesangium was movement of particles in the direction of the lacis area. Sequential electron microscopic studies showed that carbon particles moved through fenestrae in the endothelium covering the mesangium into channels between mesangial cells. Observations at later intervals suggested that carbon eventually reached the vascular pole by being passed on from one mesangial cell to the next. Vasoactive amines or other substances derived from platelets may play an important role in initiating the process of mesangial uptake.

The glomerular mesangium. I. Kinetic studies of macromolecular uptake in normal and nephrotic rats

This study was designed to define quantitatively the function of the rat glomerular mesangium in the uptake and processing of intravenously administered protein macromolecules (radiolabeled aggregated human IgG, AHIgG-(125)I), to relate this function to that of the general reticuloendothelial system, and to examine the effects of increased glomerular permeability to protein on the mesangial cell system.Mesangial localization of human IgG as demonstrated by immunofluorescent microscopy showed good correlation with concentrations of AHIgG-(125)I in preparations of isolated glomeruli. In normal rats the concentrations of AHIgG-(125)I in glomeruli were similar to those of lung, liver, and spleen and demonstrated a rapid decrease with increasing time intervals after aggregate administration. In rats given aminonucleoside of puromycin a marked increase in mesangial uptake of aggregates was found while studies of nephrotic lungs, liver, spleen, and blood showed no such differences. Glomerular levels of AHIgG-(125)I in aminonucleoside animals could not be correlated with the quantity of proteinuria. Nephrotic and control animals given unaggregated human IgG showed little glomerular localization by immunofluorescent microscopy; no difference in the concentration of this protein in nephrotic as compared to control glomerular isolates was found.Thus, the mesangium in normal animals functions in a manner analogous to that of the general reticuloendothelial system. In nephrotic rats the mesangial uptake of macromolecules is makedly increased, a finding not observed in other tissues.