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W W Bakker

Publications and source records attributed to W W Bakker.

At least 19 recordsLinked to original sources
PubMed1995

Glomerular inflammation in pregnant rats after infusion of low dose endotoxin. An immunohistological study in experimental pre-eclampsia.

Increased endotoxin sensitivity during pregnancy occurs in many animals, including rats. The mechanism of this phenomenon is not understood. In the present study it was investigated whether this increased sensitivity is reflected by an altered inflammatory pattern. Inflammatory cell influx, the O2(-)-producing potential of these cells, and expression of adhesion molecules was studied in the glomeruli of pregnant and cyclic rats at various intervals after low dose endotoxin infusion. Kidney sections were stained for monocytes and adhesion molecules (ICAM-1, VCAM-1, LFA-1, and VLA-4) using monoclonals, while potentially O2(-)-producing neutrophils (ie, activated neutrophils) were quantified using immunohistochemical methods. The results show early glomerular influx of activated neutrophils, maximally 4 hours after endotoxin. Both absolute neutrophil counts and relative numbers of activated neutrophils were significantly increased in pregnant versus cyclic rats. In contrast to cyclic rats, showing transient monocyte influx, in pregnant endotoxin-treated rats monocyte influx reaches a maximum at t = 168 hours. These cell kinetics were paralleled by expression of the various adhesion molecules. It was concluded that pregnancy profoundly influences not only the inflammation kinetics after endotoxin, but also the violence of the reaction, reflected by activated neutrophils. This altered glomerular inflammatory pattern may help to explain why low dose endotoxin infusion induces pre-eclamptic-like symptoms (such as an intraglomerular prothrombotic microenvironment and proteinuria) exclusively in the pregnant rat.

Animals↗
PubMed1994

A new animal model for human preeclampsia: ultra-low-dose endotoxin infusion in pregnant rats.

OBJECTIVE: An animal model for preeclampsia was developed by means of an ultra-low-dose endotoxin infusion protocol in conscious pregnant rats. STUDY DESIGN: Rats received a permanent jugular vein cannula on day 0 of pregnancy, through which endotoxin (1.0 micrograms/kg body weight) (n = 10) or saline solution (n = 6) was infused during 1 hour on day 14 of pregnancy. Blood pressure, albuminuria, and platelet counts were measured, and histopathologic studies was performed in these rats. RESULTS: A significant increase of blood pressure (p < 0.05) and of urinary albumin excretion (p < 0.05) was observed in endotoxin-treated pregnant animals, in contrast to control pregnant rats receiving saline solution. Platelet coagulopathy was found and glomerular fibrinogen deposits could be detected only in the endotoxin-treated pregnant rats. In addition, the activity of the glomerular antithrombotic enzyme adenosine diphosphatase was decreased in endotoxin-treated pregnant rats compared with saline solution-treated pregnant rats. CONCLUSION: Because histopathologic and clinical events in this model mimic predominant features of human preeclampsia, this model may enable further study into the pathophysiologic mechanisms of this complication of pregnancy.

Albuminuria↗
PubMed1994

Upregulation of antithrombotic ectonucleotidases by aspirin in human endothelial cells in-vitro.

Ecto ATP-diphosphohydrolase (apyrase) activity of human endothelial cells following aspirin treatment has been studied in-vitro. It was shown by HPLC analysis of supernatant samples that pre-incubation of the cultures with aspirin resulted in a significantly increased turnover of supplemented ATP into its degradation products (ADP and AMP). Enhanced expression of ectoenzyme after aspirin treatment could be observed as demonstrated by immunofluorescence-staining with monoclonal anti-apyrase antibodies. This suggests enhancement of endothelial ATP-diphosphohydrolase activity induced by aspirin. The present data obtained in human vascular cells in-vitro are in line with results from previous animal studies in-vivo, suggesting a novel cyclooxygenase-independent antithrombotic activity of aspirin.

Adenosine Diphosphate↗
PubMed1993

Reproductive condition, glomerular adenosine diphosphatase activity, and platelet aggregation in the rat: effect of endotoxin.

In experiment A, the activity of the glomerular antithrombotic enzyme adenosine diphosphatase (ADPase) and the sensitivity of this enzyme for endotoxin (1.0 microgram/kg BW) in various reproductive conditions of female rats were studied through use of enzyme histochemical methods. In experiment B, the effect of this dose of endotoxin on the thrombotic tendency of the glomeruli in pregnant (Pr) and pseudopregnant (PSP) rats was studied by means of ex vivo alternate perfusion of the kidneys with human platelets and adenosine diphosphate (ADP). In experiment A, cyclic (C), ovariectomized (OVX), Pr, and PSP rats were infused with endotoxin or saline. Three days later (for Pr and PSP rats, Day 8), animals were killed. In intact rats (C, Pr, PSP), the activity of glomerular ADPase was the same; however, the activity decreased after OVX. Endotoxin decreased the activity of glomerular ADPase in Pr rats only. In endotoxin-treated Pr rats, spontaneously formed platelet microaggregates were present in a few glomeruli; in glomeruli of the other groups, microaggregates were not observed. Platelet microaggregates were also present in the venous microvasculature of endotoxin-treated Pr rats and, to a lesser extent, in that of other groups, while saline-treated OVX rats were negative in this respect. In experiment B, Pr and PSP rats were treated as in experiment A; ex vivo kidney perfusion was performed on Day 8. Immediately after perfusion, rats were killed. Only Pr endotoxin-treated rats exhibited significantly increased intraglomerular platelet aggregation.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Diphosphate↗
PubMed1993

A modified cerium-based histochemical method for detection of experimentally-induced ATPase impairment in glomeruli of the rat kidney.

We studied glomerular ATPase activity, as detectable at the light microscopic (LM) level in cryostat sections of the rat kidney, after unilateral local X-irradiation. The biochemically detectable reduction in glomerular ATPase activity after X-irradiation could be demonstrated at the LM level by application of a modified cerium-based technique. Results show a clear reduction of reaction product in glomeruli in X-irradiated kidneys as compared with the contralateral control kidney. Technical parameters (i.e., tissue fixation, second thickness, cerium concentration of the incubation mixture, and percentage H2O2 added for the amplification step) were established for optimal reproducibility of the staining results. We show that this modified staining protocol allows detection of differences of ATPase activity in contrast to conventional histochemical methods. Inhibition studies with various phosphatase inhibitors and competitive substrate inhibition experiments revealed that the enzyme is specific for nucleoside di- and triphosphatases. Since reduced glomerular adenine nucleotidase activity has recently been recognized as an early event in (experimental) glomerulonephritis, we feel that the new staining protocol presented here may be highly relevant for routine tissue section screening in nephropathological research.

Adenosine Triphosphatases↗
PubMed1993

Attenuation of anti-Thy1 glomerulonephritis in the rat by anti-inflammatory platelet-inhibiting agents.

Although both ecto-ADPase and prostacyclin (PGI2) inhibit platelets and neutrophils, their action in acute glomerulonephritis is unknown. We tested the PGI2 analog Iloprost and 2chloroadenosine (2Cl-ADO), an analog of adenosine, the end product of nucleotidase activities, during anti-Thy1 nephritis. Rats received anti-Thy1 immunoglobulin G (5 mg/kg body weight, intravenously) and subsequently one subcutaneous injection of either 2Cl-ADO (10 mg/kg body weight; (n = 6) or Iloprost (1 mg/kg body weight; n = 6). Control rats received anti-Thy1 immunoglobulin G with saline (n = 6) or saline alone (n = 6). After 24 hours, kidneys were processed for light-microscopical evaluation. Proteinuria was studied in additional rats. Results showed that both drugs inhibited intraglomerular platelet activation (P < 0.005). 2Cl-ADO also reduced intraglomerular O2- production of neutrophils (P < 0.05), in contrast to Iloprost. Intraglomerular immunoglobulin G deposition, complement activation, neutrophil influx, and myeloperoxidase release were not affected by 2Cl-ADO or Iloprost. However, proteinuria was completely prevented by both drugs. It is concluded that PGI2 and nucleotidases are potentially able to attenuate this form of nephritis by inhibiting platelet activity, whereas nucleotidases also inhibit neutrophil activity in vivo.

2-Chloroadenosine↗
PubMed1992

Modulation of anti-Thy1 nephritis in the rat by adenine nucleotides. Evidence for an anti-inflammatory role for nucleotidases.

Extracellular adenine nucleotides are considered mediators of inflammation because they modulate functions of neutrophils and platelets. Until now, this role for adenine nucleotides has not been studied in vivo. In particular in the rat kidney, where ATP- and ADPase activity is present in the glomerular basement membrane, studies about the role of nucleotides may increase our understanding of the dynamics of glomerulonephritis (GN). Therefore, we examined effects of adenine derivatives ATP gamma S, ADP beta S and 2chloro-adenosine (2chloro-ADO) in vitro and during anti-Thy1 GN. The in vitro results show that ADP beta S and ATP gamma S are not degraded by glomerular nucleotidases but, on the other hand do stimulate O2- production of peritoneal exudate cells (PEC). In contrast, 2chloro-ADO significantly inhibits O2- production of peritoneal exudate cells. For in vivo studies rats were rendered nephritic by intravenous injection of monoclonal anti-Thy1 IgG (5 mg/kg body weight). Subsequently, rats were treated with saline (group 1, N = 10), 2chloro-ADO (group 2, N = 10), ADP beta S (group 3, N = 10) or ATP gamma S (group 4, N = 10). All analogs (10 mg/kg body weight) were administered both at t = 0 and t = 12 hour. After 24 hours, rats were sacrificed and kidneys were examined histochemically. In an additional group of nephritic rats (N = 5) proteinuria was studied after 2-chloro-ADO treatment. Results show increased intraglomerular platelet aggregation in nephritic rats treated with ADP beta S, whereas 2chloro-ADO inhibits aggregation significantly as compared with nephritic rats receiving saline. The percentage of granulocytes producing O2- is significantly increased in glomeruli after treatment of nephritic rats with ATP gamma S, whereas cell influx itself is not changed. In contrast, 2chloro-ADO inhibits intraglomerular O2- production, which is associated with the complete inhibition of proteinuria in the early phase of anti-Thy1 GN. These data demonstrate significant pro-inflammatory activities of extracellular adenine nucleotides during anti-Thy1 GN suggesting an anti-inflammatory role for glomerular ATP/ADPase, which in concert with 5' nucleotidase converts ATP and ADP to antiinflammatory ADO.

2-Chloroadenosine↗
PubMed1991

Demonstration of antithrombotic activity of glomerular adenosine diphosphatase.

We have demonstrated that reduced glomerular adenosine diphosphatase (ADPase) activity within the rat kidney is associated with an increased thrombotic tendency. To establish a possible causal relationship between these intraglomerular events, experiments were conducted to inhibit adenosine diphosphate (ADP) degradation without influencing other glomerular prothrombotic or antithrombotic mechanisms. Concurrently, we studied intraglomerular platelet aggregation. Two ways of selective inhibition of glomerular ADPase activity were applied: (1) by competitive substrates (ie, uridine diphosphate [UDP]), and (2) by the nondegradable ADP analogue ADP-beta-S. Both strategies were used during ex vivo alternate perfusion of kidneys with platelets and ADP (to test intraglomerular thrombotic tendency). Each group (n = 6) received different substrates or a combination of substrates. A significant increase in platelet aggregation was observed in kidneys after perfusion with platelets and ADP together with the competitive substrate UDP as compared to perfusions with platelets and ADP alone (78.5% +/- 9.8% v 27.9% +/- 11.4% glomeruli staining positive for platelets, P less than .005). In contrast, UDP alone had no effect on platelet aggregation. Other nucleoside polyphosphates (guanosine diphosphate and inosine triphosphate) were also effective as competitive substrates in the ex vivo perfusion model (n = 4). None of these substrates was capable of increasing ADP-induced aggregation when studied in vitro. In addition, ADP- beta-S also increased platelet aggregation in the perfusion model as compared with native ADP (P less than .005). These results show that selective reduction of ADP degradation in intact kidneys strongly promotes the intraglomerular proaggregatory condition. It can be concluded that glomerular ADPase exerts potent antithrombotic activity within the normal rat kidney.

Adenosine Diphosphate↗
PubMed1991

Survey of the occurrence of adenosine polyphosphatase in extracellular matrix of rat tissues. A cytochemical investigation.

The extracellular presence of adenosine polyphosphatase was investigated in a number of rat tissues. The enzyme was demonstrated in basement membranes of epithelial cells of duodenum, urinary bladder, tongue, choroid plexus, submandibular salivary gland, lung and kidney, as well as in basement membranes of capillaries in these tissues. Furthermore adenosine polyphosphatase was demonstrated on collagen fibrils and in the cytoplasm of fibroblasts of all investigated tissues. It appears that the presence of adenosine polyphosphatase in basement membranes is a widespread phenomenon. Since extracellular ADP and ATP are known to promote respectively platelet aggregation and inflammation, the presence of extracellular ADP and ATP-hydrolyzing activity might contribute to inhibit these processes.

Adenosine Triphosphatases↗
PubMed1991

Reduced thrombogenicity of artificial materials by coating with ADPase.

A novel coating solution for the improvement of biocompatibility of polyurethane-based vascular prostheses was tested in rabbits and rats in vivo. Segments of coated and uncoated vascular prostheses were implanted into the peritoneal cavity of rats, followed by induction of experimental haemorrhage; otherwise whole vascular prostheses were implanted in the carotid artery of rabbits using microsurgical procedures. While in both rats and rabbits, the uncoated material showed abundant formation of fibrinoid thrombi, clear reduction of thrombus formation was seen in all ADPase coated materials following implantation in vivo.

Animals↗
PubMed1991

Intraglomerular thrombotic tendency and glomerular ADPase. Unilateral impairment of ADPase elicits a proaggregatory microenvironment in experimental glomerulonephritis.

It has been proposed, predominantly from ex vivo studies, that glomerular ADPase may function as an antithrombotic principle within the rat kidney. Therefore, intraglomerular platelet aggregation was studied in vivo in rats after impairment of glomerular ADPase activity using local X-irradiation (20 Gy). Biochemical assays in suspensions of glomeruli obtained from rats 24 hours after local X-irradiation (group I) demonstrated a significant reduction in ADPase activity as compared to sham treated rats (group II; p less than 0.01). Cytochemical observations at the ultrastructural level showed that this reduction in glomerular enzyme activity represents in particular ADPase activity detectable in the basement membrane. Following X-irradiation, intraglomerular platelet aggregation was quantitatively studied in two groups of rats. Both groups received X-irradiation of the left kidney (20 Gy). Twenty-four hours after X-irradiation, animals received an intravenous injection of either 0.5 ml of saline (group III; N = 6) or 0.5 ml of heterologous nephrotoxic serum (NTS; group IV; N = 6). Subsequently, 24 hours after this injection, platelet aggregation in left kidneys was compared with aggregation in contralateral non-X-irradiated kidneys. The results showed that while X-irradiation per se did not induce intraglomerular platelet aggregation as compared with the contralateral kidney (0.20 +/- 0.08% versus 0.17 +/- 0.06% platelet aggregation/glomerulus), a significant increase in platelet aggregation could be demonstrated in X-irradiated kidneys in the early phase of nephrotoxic serum nephritis as compared with the contralateral nephritic kidney (2.45 +/- 0.66% versus 1.37 +/- 0.35% platelet aggregation per glomerulus; p less than 0.005). A potential effect of altered influx of inflammatory cells after X-irradiation could be excluded since no difference in H2O2 producing cells was observed between left and right kidneys. Thus, while ADPase impairment by X-irradiation does not induce platelet aggregation per se, it is clear that in proaggregatory conditions, like in NTS nephritis, the thrombotic tendency, due to decreased glomerular ADPase, is enhanced. These results demonstrate the functional significance of glomerular ADPase activity as an antithrombotic principle following platelet activation in vivo.

Animals↗
PubMed1990

Intraglomerular platelet aggregation and experimental glomerulonephritis.

Oxygen free radical production inhibits ADPase-mediated antithrombotic action. Different forms of experimental glomerulonephritis (GN) are characterized by early glomerular influx of inflammatory cells and thrombus formation. The causal relationship of these inflammatory events is obscure. Previous studies have shown that glomerular ADPase in the rat kidney may function as a potent antithrombotic principle, whereas this enzyme is highly sensitive for oxygen free radicals. To study whether O2- producing inflammatory cells are able to induce intraglomerular thrombosis via impairment of ADPase, we investigated influx of inflammatory cells in relation to glomerular ADPase activity and platelet aggregation in three models of GN. In two of these models (anti-Thy1 and anti-GBM GN) influx of neutrophils and thrombus formation occurs, whereas in anti-FX1A nephritis this aspect of the inflammatory phase is not present. The results show a relationship between influx of oxygen free radical-producing cells, reduction of glomerular ADPase activity and increased platelet aggregation. Moreover, it is shown that impairment of glomerular ADPase and increased platelet aggregation in anti-Thy1 and anti-GBM GN could be reduced by treatment with superoxide dismutase and catalase. The demonstration that activated neutrophils perfused ex vivo in the rat kidney can directly affect glomerular ADPase and antithrombotic potential in an O2- dependent manner, further supports the proposed sequence of events; oxygen free radicals produced by activated neutrophils reduce glomerular ADPase activity, leading to facilitation of thrombus formation.

Animals↗
PubMed1989

Do circulating factors play a role in the pathogenesis of minimal change nephrotic syndrome?

This review examines the studies which have been undertaken to test the hypothesis that minimal change nephrotic syndrome of childhood (MCNS) is a primary immune disorder and that there is altered T-cell function which results in release of a circulating factor. This factor alters glomerular permeability, perhaps by modifying charge sites in the glomerular capillary bed, and results in selective proteinuria. The abnormalities in immune function observed in MCNS are summarized, as are the studies of circulating factors which have been identified. Although some agents have been shown to alter capillary permeability, the unequivocal demonstration of such a factor causing selective proteinuria in vivo, either directly or indirectly, is lacking. The question is raised whether intrarenal release or activation of mediators of altered permeability, rather than the systemic release of such factors, may be important in the pathogenesis of MCNS.

Blood Proteins↗
PubMed1989

Thymocytes reacting with heterologous antibodies against GP 330 in autologous immune complex glomerulopathy (AICG) in the rat. The relation between susceptibility for AICG and anti-GP 330-binding thymocytes.

Autologous immune complex glomerulopathy (AICG) is induced by immunizing rats with a crude brushborder fraction of rat kidney tubules (Fx1A) or with the purified GP 330 antigen. In these animals, anti-brushborder antibodies develop, leading to subepithelial immune complexes along the glomerular capillary wall. In rats with AICG, thymocytes sensitized against Fx1A as well as thymocytes recognizing anti-Fx1A are present. These latter cells might play a role in the specific tolerance against the pathogenetic antigen GP 330. To substantiate this notion, immunofluorescence studies were performed in which the number of anti-GP 330 binding cells was quantified in thymus cell suspensions of rats with AICG, in control rats and in naive rats with different genetic background. It is shown that increased numbers of anti-GP 330-binding thymocytes in rats with AICG are associated with a decline in the serum anti-brushborder titer. Furthermore, it appears that the number of anti-GP 330-binding thymocytes in naive rats of the non-responder Brown Norway strain is significantly higher as compared to the PVG/c and Lewis strains, which are susceptible for AICG. The correlation between the numbers of anti-GP 330-binding thymocytes and the susceptibility for AICG suggests a role for these cells in maintaining the tolerance against the Fx1A (GP 330) antigen.

Animals↗
PubMed1989

Experimental endotoxemia in pregnancy: in situ glomerular microthrombus formation associated with impaired glomerular adenosine diphosphatase activity.

The mechanism of increased sensitivity for endotoxin in pregnancy as reflected by the formation of microthrombi in renal glomeruli is unknown. It has been shown that reduced glomerular diphosphatase (ADPase) activity in the rat kidney greatly increases the intraglomerular thrombotic tendency. We now studied experimental intraglomerular thrombosis ex vivo in association with glomerular ADPase activity in pregnant and nonpregnant control rats after infusion of either endotoxin or saline solution. Each animal (Wistar rat) was equipped with a permanent vena jugularis catheter and received either endotoxin (1.0 micrograms/kg body weight) (n = 6) or saline solution (n = 5) 7 days before being killed; nonpregnant rats were also treated with endotoxin (n = 5) or saline solution (n = 4). On day 21, before the animals were to be killed, they were anesthetized and their left kidneys were perfused with adenosine diphosphate solution (10 micrograms/ml) and platelet-rich plasma (1 x 10(9) cells/ml). Perfused kidneys were processed for light microscopy, electron microscopy, enzyme cytochemistry at the ultrastructural level, and immunohistology. The results showed decreased ADPase activity exclusively in the glomerular basement membrane of kidneys of pregnant rats treated with endotoxin in contrast to the findings in control rats. In addition, exclusively in the group of endotoxin-treated pregnant rats, significantly increased intraglomerular platelet aggregation could be detected after alternate perfusion ex vivo. We suggest that, in the present model, enhanced susceptibility of glomerular ADPase for endotoxin is due to pregnancy-associated factors that have yet to be identified. This increased susceptibility may promote in situ formation of intraglomerular microthrombi.

Animals↗
PubMed1988

The specificity of nephritogenic antibodies. V. Glomerular localization of anti-GP 330 and anti-GP 90 antibodies present in passive Heymann serum.

Administration in the rat of rabbit antibodies directed against rat tubular brushborder antigens (FXIA) leads to membranous glomerulopathy (HICN) associated with glomerular immune complexes (ICXS). These anti-FXIA antibodies (Abs) contain two major specificities, anti-GP 330 and anti-GP 90. The contribution of each specificity to the localization of anti-FXIA Abs was studied by direct immunofluorescence. Perfusion studies, under conditions which avoid ischaemia, confirmed that in this system glomerular localization of anti-FXIA Abs depends only on anti-GP 90 Abs, and the failure of anti-GP 330 Abs to localize after perfusion could not be attributed to ischaemia. In contrast, intravenous (i.v.) injection of anti-GP 330 Abs results in granular deposits of rabbit IgG, similar to those observed using anti-FXIA Abs. Injection i.v. of anti-GP 90 Abs results only in (faint) linear deposits. Using alternating and combined perfusion studies with these Abs, it is shown that anti-GP 90 Abs do not influence localization of anti-GP 330 Abs. In addition, systemic administration of anti-GP 90 Abs combined with perfusion of anti-GP 330 Abs does not facilitate localization of anti-GP 330 Abs. Although directly after i.v. injection of anti-FXIA Abs some anti-GP 90 Abs probably localize in the glomerular capillary wall, our results exclude a dominant or ancillary role for anti-GP 90 Abs in the formation of glomerular Icxs in HICN.

Animals↗