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Biomedical subjects

G B Ryan

Publications and source records attributed to G B Ryan.

At least 91 records · Page 5Linked to original sources
PubMed1976

Distribution of endogenous albumin in the rat glomerulus: role of hemodynamic factors in glomerular barrier function.

Using an ultrastructural immunoperoxidase technique, the distribution of endogenous albumin in the rat glomerulus was delineated under normal and abnormal hemodynamic conditions. Superficial glomeruli in anesthetized Munich-Wistar rats were rapidly fixed in situ by applying glutaraldehyde to the renal surface. Fixed tissue slices were treated with anti-rat albumin Fab fragments conjugated to horseradish peroxidase (HRP), and were then subjected to the Graham-Karnovsky ultrastructural peroxidase localization procedure. During normal blood flow, dense reaction product specific for albumin was largely confined to the glomerular capillary lumen and endothelial fenestrae, with only small amounts detectable in the lamina rara interna, and none deeper in the basement membrane (GBM) or in the urinary space. If cortical tissue was subjected to routine immersion fixation, or if fixation was performed in situ after ligation of the renal artery, reaction product was detected throughout the GBM and in the urinary space. If fixation was performed in situ after ligation of the renal artery and vein (or artery, vein and ureter), reaction product was found in the GBM and, in very large amounts, in the urinary space. If blood flow was restored for ten minutes after five minutes of renal pedicle (artery and vein) occlusion, the distribution of albumin returned to normal. Thus, glomerular barrier function depends upon the maintenance of normal blood flow conditions.

Animals↗
PubMed1976

Glomerular permeability to proteins. Effects of hemodynamic factors on the distribution of endogenous immunoglobulin G and exogenous catalase in the rat glomerulus.

The distribution of endogenous immunoglobulin G (IgG) and exogenous catalase was delineated in the rat glomerulus under normal and abnormal hemodynamic conditions. IgG was identified by an ultrastructural immunoperoxidase technique using antirat IgG Fab fragments conjugated to horseradish peroxidase; catalase was identified by a cytochemical reaction. When superficial glomeruli in anesthetized Munich-Wistar rats were rapidly fixed in situ by dripping glutaraldehyde onto the renal surface, IgG and catalase were largely confined to the glomerular capillary lumen, with only small amounts in the lamina rara interna immediately beneath the endothelial fenestrae, and none deeper in the basement membrane (GBM) or in the urinary space. If cortical tissue was subjected to routine immersion fixation, or if fixation was performed in situ after ligation of the renal artery, IgG and catalase were found throughout the GBM but not in the urinary space. If fixation was performed in situ after ligation of the renal artery and vein (or artery, vein, and ureter), IgG and catalase were found in the GBM and in the urinary space. If blood flow was restored for 10 minutes after 5 minutes of occlusion of the renal artery and vein, the distribution of IgG and catalase returned to that seen during good blood flow, i.e. neither showed significant penetration beyond the endothelial layer. Thus, as was found previously for albumin, glomerular barrier function for IgG and catalase depends upon the maintenance of normal blood flow conditions. We propose that such conditions impose functional restrictions may be mediated by molecular sieving phenomena during normal ultrafiltration across the GBM, perhaps in association with concentration-polarization or charge effects or both. The epithelial slit pores may significantly modulate solute flux across the GBM by controlling the over-all rate of hydrodynamic flow during ultrafiltration.

Animals↗
PubMed1976

Absence of enhanced intimal thickening in the response of the carotid arterial wall to endothelial injury in hypercholesterolemic rats.

Young male Sprague-Dawley rats fed a high cholesterol, thyroid-suppressive diet were subjected to drying injury of carotid artery endothelium; animals were sacrificed at various times up to 3 months after injury, and the vessels were examined by light, scanning, and transmission electron microscopy. The diet induced marked elevation of serum cholesterol mainly present in lipoproteins of density less than 1.063. The morphology and degree of intimal thickening in the injured carotids of such animals were compared with the changes found in control groups of normolipemic rats. In the control groups, endothelium was completely regenerated between 7 and 14 days; intimal thickening was present at 14 days and at later stages and contained smooth muscle cells without lipid. In the cholesterol-fed animals, endothelial regeneration and intimal thickening occurred as in the controls with the following additional features: in the zone of intimal thickening in the injured segment, lipid was present in smooth muscle cells and, at later stages, in the extracellular matrix; undifferentiated mononuclear cells were also noted in the thickened intima and, at 3 months, were found adhering to normal and regenerated endothelium. However, no differences were found between control and hypercholesterolemic rats with respect to the degree of intimal thickening within the injured segment; enhancement of the smooth muscle proliferative response was not evident in the hypercholesterolemic rats. Our findings suggest that this form of hypercholesterolemia and its associated hyperlipoproteinemia may not be directly responsible for rat smooth muscle proliferation following endothelial denudation. They also indicate that hyperlipemia does not necessarily cause persistence of myointimal hyperplasia in arteries.

Animals↗
PubMed1976

Isolation of phagocytic cells from the rat renal glomerulus.

A method is described for the dissociation of rat glomerular cells in vitro. Isolated endothelial cells were characterized by the persistence of fenestrae. Mesangial cells showed a variety of morphologic appearances; if dissociation was performed after an intravenous injection of ferritin, such cells were identified by the presence of large ferritin-filled vacuoles. Intact epithelial cells were rarely seen, presumably because they did not survive the separation procedure. In culture, a high proportion of cells adhered to glass surfaces, were phagocytic, and had labeled heavily in vivo with ferritin; they were, thus, considered to be mesangial in origin. Receptors for immunoglobulin (Fc) and complement (c3) were also detected in such cells after 24 hours in culture, but not immediately after dissociation. Our findings suggest that a population of isolated glomerular cells, probably comprising mainly mesengial cells, is highly phagocytic and has the potential to develop Fc and C3 receptors. We propose that this technique offers a useful approach for the delineation of glomerular cell properties and functions.

Animals↗
PubMed1975

An ultrastructural study of the mechanisms of proteinuria in aminonucleoside nephrosis.

Sprague-Dawley rats injected i.v. with a single dose of puromycin aminonucleoside (PAN) developed massive proteinuria five days later. Electron microscopic studies of perfusion-fixed glomeruli showed that loss of epithelial foot processes and their replacement by flattened expanses of epithelial cytoplasm began at two days and was extensive by four days after the injection of PAN. At and after five days (correlating with the onset and persistence of massive proteinuria), areas of focal loss of the epithelial covering on the outside of the glomerular basement membrane (GBM) were observed in 30% of glomeruli. Intravenously administered ferritin was distributed normally in most sections of the GBM of nephrotic animals, but abnormally deep penetration of particles was observed in GBM segments that lacked an external covering of epithelium. The same changes were found following in situ fixation of superficially placed glomeruli of Munich-Wistar rats with PAN nephrosis. We propose that the massive, early proteinuria in PAN nephrosis may be primarily due to a glomerular epithelial lesion, leading to scattered focal defects in the external covering of the GBM. Increased bulk flow of glomerular filtrate across the GBM in such areas may explain the highly selective proteinuria found in this form of the nephrotic syndrome.

Animals↗
PubMed1975

Substructure of the glomerular slit diaphragm in freeze-fractured normal rat kidney.

In the renal glomerulus, the narrow slits between adjacent epithelial podocytes are bridged by a diaphragm (2, 8, 11). In rat and mouse kidneys fixed by perfusion with tannic acid and glutaraldehyde (TAG), it has recently been discovered that this diaphragm has a highly ordered, isoporous substructure (9). It consists of a regular array of alternating cross bridges extending from the podocyte plasma membranes to a centrally running filament. This zipperlike pattern results in two rows of rectangular pores, approximately 40 X 140 A in cross section, dimensions consistent with the proposed role of the diaphragm as an important filtration barrier to plasma proteins (6). In the present study, we found in freeze-cleaved and in freeze-etched normal rat glomeruli that the surface of the slit diaphragm has an appearance conforming to the pattern found in sectioned material.

Animals↗
PubMed1975

Endothelial regeneration in the rat carotid artery and the significance of endothelial denudation in the pathogenesis of myointimal thickening.

A new model was developed to study endothelial regeneration and the effects of endothelial denudation in large arteries. Complete endothelial loss was produced in a sharply defined, unbranched segment of the rat common carotid artery by brief drying with a gentle stream of air along the lumen of the vessel. Platelets became attached to the denuded surface, but no polymorphonuclear or mononuclear leukocytic adherence or infiltration was observed. Regeneration occurred by the ingrowth, from each end of the denuded segment, of sheets of rapidly dividing endothelial cells. Endothelial replacement was complete by 7 to 10 days after drying. It was also noted that, by 14 days after drying, a striking myointimal thickening developed in the central region of the denuded segment. This central region was the last area to be covered with new endothelium; while still denuded, the region showed edema and signs of cellular proliferation in the innermost medial layer. The myointimal thickening consisted of smooth muscle-like cells in a fibroelastic stroma in the deeper zones, and a layer of rounded, relatively undifferentiated cells in the superficial zones. Progressive regression and condensation of the thickening was observed between 14 days and 3 months. In this model, the clear demarcation and completeness of endothelial denudation in the arterial segment allow study of the over-all process of endothelial replacement, avoiding the confusion imposed by islands of residual endothelium or contributions from branch vessels. The results suggest that the new endothelium in this situation is derived from each end of the segment. In addition, because the method of inducing denudation does not cause significant damage to the underlying media (as shown by the absence of inflammatory cell attachment or infiltration), the model offers a unique opportunity to study the relationship between endothelial loss and changes in the vessel wall. The correlation between the duration of endothelial denudation and the extent of myointimal thickening suggests that sustained insudation of certain, as yet undefined, factors from the lumen may provoke cellular proliferation in the arterial wall. Further investigation of this model should provide information relevant to the pathogenesis of the fibromuscular thickenings of human atherosclerosis.

Animals↗
PubMed1974

Factors affecting the redistribution of surface-bound concanavalin A on human polymorphonuclear leukocytes.

Human neutrophil polymorphonuclear leukocytes (PMN) were studied to determine the influence of cellular locomotion upon the redistribution and capping of concanavalin A (Con A). Con A was detected by fluorescence (using Con A conjugated to fluorescein isothiocyanate [Con A-FITC]), or on shadow-cast replicas (using Busycon canaliculatum hemocyanin as a marker for Con A). After labeling with Con A 100 microg/ml at 4 degrees C and warming to 37 degrees C, locomotion occurred, and the Con A quickly aggregated into a cap at the trailing end of the cell. When locomotion was inhibited (with cytochalasin B, or by incubation in serum-free medium at 18 degrees C) Con A rapidly formed a cap over the central region of the cell. Iodoacetamide inhibited capping. PMN labeled with FITC, a monovalent ligand, developed caps at the tail only on motile cells; FITC remained dispersed on immobilized cells. PMN exposed to Con A 100 microg/ml at 37 degrees C bound more lectin than at 4 degrees C, became immobilized, and showed slow central capping. The Con A soon became internalized to form a perinuclear ring. Such treatment in the presence of cytochalasin B resulted in the quick formation of persistent central caps. Colchicine (or prior cooling) protected PMN from the immobilizing effect of Con A, and tail caps were found on 30-40% of cells. Immobilization of colchicine-treated cells caused Con A to remain in dispersed clusters. Thus, capping on PMN is a temperature- and energy-dependent process that proceeds independently of cellular locomotion, provided a colchicine-sensitive system is intact and the ligand is capable of cross linking receptors. On the other hand, if the cell does move, it appears that ligands may be swept into a cap at the tail whether cross-linking occurs or not.

Binding Sites, Antibody↗
PubMed1973

Mesothelial injury and recovery.

This paper describes the cytologic effects of drying or wetting of visceral peritoneum and the course of mesothelial regeneration. Using en face silver staining and electron microscopy, it was found that mesothelial cells disappeared from the surface after the cecum was either briefly dried or kept wet with isotonic saline for 30 minutes; the fibrin-slide technic showed that such injury caused a loss of the normal serosal fibrinolytic activity. In following the course of mesothelial regeneration using the same technics, it was apparent that free-floating peritoneal mononuclear cells settled on the denuded surface where they spread out, attached to one another, and developed features (eg, microvilli) typical of mature mesothelial cells; such new mesothelium showed a greatly enhanced fibrinolytic activity.

Animals↗
PubMed1973

Human smooth muscle autoantibody. Its identification as antiactin antibody and a study of its binding to "nonmuscular" cells.

When human serum containing smooth muscle autoantibodies (SMA) is incubated with extracts containing thrombosthenin (the contractile material of platelets) or thrombosthenin-A (the actin-like moiety of thrombosthenin), it loses its ability to bind to smooth muscle. Such binding is also diminished when SMA serum is incubated with lysed platelets; this effect is not seen if the SMA serum is incubated with intact platelets. The incubation of other autoantibodies (such as antimitochondrial or antinuclear antibodies) with thrombosthenin does not affect their binding to the specific antigens. It appears that SMA is directed against the actin fraction of thrombosthenin-ie, SMA is an antiactin antibody. Hence the name of antiactin autoantibody (AAA) seems more appropriate than smooth muscle autoantibody (SMA). A study of the distribution of antiactin autoantibody binding in rat, rabbit and man shows that several "nonmuscular" structures contain actin under normal conditions; these include megakaryocytes and platelets, normal rat hepatocytes, the brush borders of renal tubules, the periphery of epithelial cells of the intestine, polymorphs and lymphocytes in lymph nodes (but not thymic cortical lymphocytes). In addition, certain cell types (such as granulation tissue fibroblasts, cultivated fibroblasts, hepatocytes or regenerating liver and epidermal cells growing over a skin wound) can reversibly acquire a massive network of actin-containing microfilaments resembling those in smooth muscle.

Absorption↗