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Biomedical subjects

M D Menger

Publications and source records attributed to M D Menger.

At least 163 records · Page 9Linked to original sources
PubMed1997

Immunomodulatory action of G-CSF in a rat model of endotoxin-induced liver injury: an intravital microscopic analysis of Kupffer cell and leukocyte response.

In contrast to the anticipation that in sepsis granulocyte colony-stimulating factor (G-CSF) would overactivate the nonspecific immune system by recruiting and priming leukocytes with consequent aggravation of inflammatory tissue lesions, recombinant (r) G-CSF pretreatment was protective in various experimental non-neutropenic models of inflammation. The mechanisms of protection, however, are not fully understood. Using intravital fluorescence microscopy, we show that rG-CSF enhances leukocyte endothelial cell interaction within the microvasculature of normal rat livers, whereas rG-CSF pretreatment of animals exposed to lipopolysaccharide (LPS) attenuates the LPS-induced leukocytic response, including stasis in sinusoids as well as rolling and adherence in postsinusoidal venules with subsequent tissue infiltration. Moreover, rG-CSF, which did not affect Kupffer cell activity in normal rat livers, reduced the immediate activation of Kupffer cells on LPS exposure, as indicated in vivo by the delayed adherence/phagocytosis of intra-arterially administered latex particles associated with attenuation of proinflammatory cytokine release (tumor necrosis factor alpha and interleukin-6). Finally, rG-CSF reduced LPS-induced nutritive perfusion failure and hepatocellular excretory dysfunction. This study provides evidence for a distinct, possibly tumor necrosis factor alpha-dependent modulation of LPS-induced cellular response within the liver by rG-CSF, thereby achieving protection against microcirculatory perfusion failure and hepatic dysfunction.

Adjuvants, Immunologic↗
PubMed1997

High-resolution microscopic determination of hepatic NADH fluorescence for in vivo monitoring of tissue oxygenation during hemorrhagic shock and resuscitation.

Impaired microvascular oxygen supply reduces oxidative phosphorylation and causes an increase in cellular NADH, which was monitored densitometrically in vivo by high-resolution fluorescence microscopy (330-390/ > 430 nm excitation/emission wavelengths) in rat livers (n = 8) subjected to hemorrhagic shock and resuscitation. At each time point, NADH fluorescence was recorded from 10 different observation fields of the left liver lobe. Withdrawal of a total of 4.5 ml arterial blood for induction of volume-controlled hemorrhagic shock resulted in an increase in NADH fluorescence by approximately 31% from 45.1 +/- 3.9 to 59.2 +/- 4.2 aU, which was associated with a fall of arterial blood pressure from 110 +/- 3 to 51 +/- 8 mmHg, a decrease in hepatic tissue oxygenation (flexible polarographic surface electrode) from 18 +/- 2 to 2 +/- 1 mmHg, and a restriction of hepatic bile flow from 1.7 +/- 0.1 to 0.5 +/- 0.2 microliter/min x g. Normovolemic resuscitation with 10% hydroxyethylstarch failed to completely restore the metabolic state of liver tissue (NADH fluorescence 49.9 +/- 3.1 aU), arterial blood pressure (83 +/- 8 mmHg), hepatic tissue oxygenation (7.4 +/- 1.5 mmHg), and hepatocellular excretory function (1.3 +/- 0.1 microliters/min x g). During both shock and resuscitation, the ratio between pericentral and periportal NADH fluorescence intensities slightly increased, but calculation of coefficients of variance of interlobular NADH fluorescence did not reveal an increase in heterogeneity of tissue metabolic state. Significant correlations were found between NADH fluorescence and both hepatic tissue oxygenation (r2 = 0.78, P < 0.01) and hepatic bile flow (r2 = 0.85, P < 0.01), indicating that high-resolution intravital microscopic assessment of NADH fluorescence reflects appropriately the relation between local oxygen supply and demand in hepatic tissue in vivo.

Animals↗
PubMed1997

Dietary vitamin E does not protect from endotoxin-induced hepatic microvascular dysfunction.

Starting from the concept that lipopolysaccharide (LPS)-associated hepatotoxicity involves the action of reactive oxygen species, the present study was conducted to test whether vitamin E, a lipophilic antioxidant, prevents LPS-induced hepatic microvascular dysfunction and liver injury. Fifty-two rats were divided into three groups and fed diets containing 0 (n = 16), 75 (n = 18) or 8000 mg (n = 18) alpha-tocopherol acetate/kg food for four weeks. At 1 h and 6 h after intravenous LPS-exposure (10 mg/kg E. coli LPS) hepatic microvascular response and liver injury were assessed by the analysis of Kupffer cell phagocytic activity, leukocyte-endothelial cell interaction and nutritive sinusoidal perfusion (intravital fluorescence epi- illumination technique) as well as bile flow, serum liver enzyme activities and tissue histomorphology. In animals fed with 75 mg vitamin E/kg (standard diet), LPS caused hepatic Kupffer cell activation (increased phagocytic activity) and hepatic microvascular leukocyte activation, with stasis in sinusoids and adherence in postsinusoidal venules (1 h) followed by leukocytic infiltration into tissue (6 h) and progredient sinusoidal perfusion failure (6 h). Hepatic microvascular injury was accompanied by reduced bile flow and enhanced liver enzyme release. Vitamin E-enriched diet (8000 mg/kg) and even vitamin E-deficient diet did not significantly affect LPS-induced hepatic microvascular cell activation and perfusion failure. Thus, we conclude, that vitamin E is not effective to protect from endotoxin-induced hepatic microvascular dysfunction.

Animals↗
PubMed1997

Improved islet isolation by 10% albumin does not influence graft angiogenesis and vascularization.

Addition of 10% albumin to the digestion medium has been suggested to enhance yield and integrity of harvested islets by inhibition of proteolytic activities and to improve endocrine function early after transplantation. The aim of this study was to evaluate in vivo by means of intravital fluorescence microscopy whether this rapid reversal of hyperglycemia after transplantation is due to improved graft vascularization. Pancreatic islets were isolated from Syrian golden hamsters by collagenase digestion using either solely Hank's balanced salt solution (HBSS) or HBSS supplemented with 10% human serum albumin. Islets were then transplanted into the dorsal skinfold chamber of syngeneic animals (control: N = 8 animals, n = 50 islets; albumin: N = 7, n = 41). The grafts' microvasculature was analysed on days 6, 10, and 14 after transplantation. Immunohistochemical staining for insulin was performed at the end of the microscopic observation period. Islet isolation with albumin supplementation did not increase islet yield. However, photomicroscopic analysis suggested a beneficial effect on the isolation process with improved islet integrity and prevention of outer margin irregularities, in particular in large islets. Analysis of revascularization 6 days after transplantation revealed in the control group a functional capillary density (FCD) of 477 +/- 47 cm-1. On day 10 FCD increased to 680 +/- 42 cm-1 with no further changes on day 14, indicating complete revascularization. Islets in the albumin group demonstrated a comparable FCD of 598 +/- 49 cm-1 on day 10 and complete revascularization on day 14 (655 +/- 45 cm-1). The angio-architecture of the islets was found similar in both groups, presenting with a glomerulum-like capillary network, comparable to that of pancreatic islets in situ. We conclude that the addition of 10% serum albumin to the collagenase digestion medium improves the preservation of the structural integrity of isolated pancreatic islets, however, does not influence the process of graft vascularization. Thus, improved early graft function may rather be due to superior preservation of islet cell integrity and function.

Animals↗
PubMed1997

Liver ischemia/reperfusion induces an increase of microvascular leukocyte flux, but not heterogeneity of leukocyte trafficking.

Leukocytic response plays a major role in the manifestation of hepatic ischemia/reperfusion (I/R) injury. To clarify whether post-ischemic hepatic leukocyte accumulation is based on increased leukocyte flux to the hepatic tissue due to systemic inflammation or chemoattractant activities or whether it represents solely a local tissue response without changing overall leukocyte flux and trafficking characteristics through the microvasculature, we studied acinar and sinusoidal leukocyte flux and distribution in rat livers in vivo both under normal (sham, n = 8) and post-ischemic (60' ischemia/75' reperfusion) conditions (I/R, n = 8), using fluorescence epi-illumination microscopy (rhodamine-6G). Hepatic ischemia/reperfusion significantly (p < 0.05) increased acinar leukocyte flux (58.4 +/- 20.9 cells/min vs 36.4 +/- 12.8 cells/min in sham controls); however, it did not exhibit increased heterogeneity of acinar leukocyte distribution, as indicated by the unchanged coefficient of variance (CV) of 0.36 +/- 0.16 (sham controls: 0.31 +/- 0.14). In parallel, analysis of individual sinusoidal leukocyte flux demonstrated significantly (p < 0.05) higher values (8.9 +/- 3.7 cells/min) after ischemia/reperfusion when compared with sham controls (5.7 +/- 1.9 cells/min), which, however, was not associated with increased heterogeneity of sinusoidal leukocyte trafficking (CV: 0.85 +/- 0.15 vs 0.85 +/- 0.16 in sham controls) and manifestation of preferential pathways. Analysis of blood cell count did not demonstrate an overall increase of total blood leukocyte count; however, an increased (p < 0.01) fraction of polymorphonuclear leukocytes (65.2 +/- 11.2%) and stab cells (9.5 +/- 7.9%) during post-ischemic reperfusion when compared with sham controls (8.8 +/- 3.5% and 0.2 +/- 0.4%) was demonstrated. Thus, the increase of hepatic leukocyte flux after ischemia/reperfusion may be the result of both the manifestation of a systemic inflammatory response and the increase of local chemoattractant activities, such as the production and release of the cytokine-induced neutrophil chemoattractant of the IL-8 family.

Animals↗
PubMed1997

Long-term function of experimental substitutes of the ileocecal valve.

The bacteriological barrier function of the ileocecal valve (ICV) can be replaced according to the principle of the nipple-valve anastomosis. Since late complications due to technical measures for stabilizing the ileal nipple have been hitherto unknown, 12 adult beagle dogs were operated on by three technical modifications of a nipple-valve anastomosis and were followed up for 1 year: In three cases the ileal nipple was stabilized by longitudinal staples (NVA), in three cases an intestinal neosphincter (INS) was produced by healing of the muscular layers between the ileal nipple and colon, and in six cases an oral zone of stabilization, preserving an aboral valve zone (S-NVA) was constructed. Measures for valve function at the end of the study period were the weight course of the animals and the intestinal bacterial profile, considering morphological complications of the substituted valves. As reference the respective bacterial counts in ICV and end-to-end anastomosis (EEA) were used, which had been determined in the same animals in earlier experiments. Following an initial increase in weight the 3 animals with NVA and the three animals with INS continuously lost weight from the 4th postoperative month onward. The 6 animals with S-NVA, however, showed from the 4th postoperative month onward a significantly higher weight level (p < 0.05), which remained constant up to the end of the 1-year observation period. Because of a morphologically intact structure of the substituted valve a significantly (p < 0.05) better bacteriological clearance of the ileum was confirmed in these animals after 12 months when compared with the EEA group. In contrast, in the NVA and INS animals a severe bacterial overgrowth of the entire small intestine was observed. This was caused by an intestinal stagnation due to partial prolapse of the nipple in NVA and due to fibrotic stenosis in INS. The results of our study suggest that technical measures to relieve the tendency to devaginate are only successful, if they do not lead to obstruction of the orthograde intestinal passage in the long term. Thus, only the clinical introduction of the S-NVA model may be justified.

Animals↗
PubMed1997

Prevention of pancreatic islet xenograft rejection by dietary vitamin E.

In pancreatic islet transplantation, the adhesion of activated leukocytes to endothelial cells and the loss of microvascular integrity represent the critical microcirculatory events, which promote loss of graft function due to rejection. With the view that oxygen radicals may contribute to graft rejection, we studied the effect of the antioxidant vitamin E on microvascular rejection of islet grafts. Islets were transplanted syngeneically and xenogeneically (rat) into dorsal skin-fold chambers of hamsters, which received a non-vitamin-E-supplemented laboratory chow. Treated animals with xenografts were fed with a diet supplemented with vitamin E in a low (150 mg/kg) and high (8000 mg/kg) concentration. Intravital fluorescence microscopy demonstrated complete vascularization of syngeneic grafts at day 10 after transplantation, intact islet microcirculation at day 20 with a functional capillary density of 653 +/- 6 cm-1, and only few leukocytes adherent to the endothelial lining of the islets' microvasculature (88 +/- 23 mm-2). Xenogeneic islets showed initial signs of rejection at day 6, including adhesion of leukocytes to the microvascular endothelium (610 +/- 110 mm-2) and loss of endothelial integrity. After 20 days, functional capillary density was significantly lower (173 +/- 68 cm-1) when compared with syngeneic grafts, indicating failure of graft acceptance. Supplementation of the diet with low and high concentrations of vitamin E resulted in a significant (P < 0.05) reduction of xenograft leukocyte-endothelium interaction (146 +/- 29 mm-2 and 109 +/- 42 mm-2) at day 6 after transplantation and and adequate development of functional capillary density at day 20 (478 +/- 36 cm-1 and 539 +/- 86 cm-1; P < 0.05), indicating prevention of microvascular rejection. We conclude that dietary supplementation of the lipophilic antioxidant vitamin E attenuates leukocyte-endothelial cell interactions, preserves microvascular integrity, and thus inhibits microvascular rejection in a dose-dependent fashion. Our study underscores the pivotal mediator role of reactive oxygen species in islet xenograft rejection and, furthermore, suggests that dietary vitamin E may act as an adjunct anti-rejection treatment in clinical islet transplantation.

Animals↗
PubMed1997

Lymph vessel expansion and function in the development of hepatic fibrosis and cirrhosis.

The process of lymph vessel expansion and function in the development of CCl4-induced hepatic fibrosis and cirrhosis was studied using intravital fluorescence microscopy of the rat liver. The unique aspect of our approach was the use of high molecular fluorescein-isothiocyanate-labeled dextran (MW, 150,000) as fluorescent marker, which allowed for simultaneous assessment of both 1) the macromolecular blood hepatocytic exchange from the sinusoidal microvasculature (extra-/intrasinusoidal gray level intensity at 1, 3, 5, and 10 minutes after intravenous injection) and 2) the hepatic lymph system. In animals exposed with CCl4 up to 4 weeks, macromolecular trans-sinusoidal exchange was found progressively delayed. This was strongly associated with lymph vessel expansion and function, as indicated by a continuous increase of lymph vessel density and area. Delay of macromolecular exchange and lymph vessel expansion was found not further enhanced at fibrotic and cirrhotic stages of 8- and 12-week CCl4-exposed livers. Linear regression analysis revealed a strong negative correlation between lymphatic network density development and macromolecular trans-sinusoidal exchange (r2 = 0.99; P < 0.01). Thus, our study provides for the first time direct evidence for the pivotal role of lymphatic function for macromolecular transport in case of deteriorated sinusoidal hepatocellular exchange capacity.

Animals↗
PubMed1997

Capillary dysfunction in striated muscle ischemia/reperfusion: on the mechanisms of capillary "no-reflow".

The major dysfunction of capillaries after prolonged periods of ischemia is the lack of re-establishment of nutritive blood flow upon onset of reperfusion, i.e., capillary no-reflow. Several mechanisms have been proposed to cause capillary no-reflow, including intravascular hemoconcentration and thrombosis, leukocyte plugging, endothelial cell swelling, vasomotor dysfunction, and interstitial edema formation. Electron microscopic studies suggest that thrombus formation and intravascular clotting are not significant mechanisms. Moreover, intravital microscopic studies have demonstrated that plugging of capillaries by leukocytes is not a primary cause for the manifestation of no-reflow in postischemic striated muscle. In contrast, both in vivo studies and histological examinations support the concept that ischemia/reperfusion induces the disruption of the endothelial integrity with loss of fluid to endothelial cells and the interstitial space. As a consequence, these pathological sequelae are associated with intravascular hemoconcentration, endothelial cell swelling and interstitial edema formation, which contribute to capillary lumenal narrowing, increase of hydraulic resistance, and, thus, impairment of perfusion. Whether the postischemic diameter response with dilation of reperfused capillaries and lumenal narrowing of no-reflow capillaries involves endothelin/nitric oxide-triggered capillary pericyte function remains to be determined.

Animals↗
PubMed1997

A new model for quantitative in vivo microscopic analysis of thrombus formation and vascular recanalisation: the ear of the hairless (hr/hr) mouse.

The alteration of rheological blood properties as well as deterioration of vascular perfusion conditions and cell-cell interactions are major determinants of thrombus formation. Herein, we present an experimental model which allows for quantitative in vivo microscopic analysis of these determinants during both thrombus formation and vascular recanalisation. The model does not require surgical preparation procedures, and enables for repeated analysis of identical microvessels over time periods of days or months, respectively. After i.v. administration of FITC-dextran thrombus formation was induced photochemically by light exposure to individual arterioles and venules of the ear of ten anaesthetised hairless mice. In venules, epi-illumination induced rapid thrombus formation with first platelet deposition after 0.59 +/- 0.04 min and complete vessel occlusion within 7.48 +/- 1.31 min. After a 24-h time period, 75% of the thrombosed venules were found recanalised. Marked leukocyte-endothelial cell interaction in those venules indicated persistent endothelial cell activation and/or injury, even after an observation period of 7 days. In arterioles, epi-illumination provoked vasomotion, while thrombus formation was significantly (p <0.05) delayed with first platelet deposition after 2.32 +/- 0.22 min and complete vessel occlusion within 20.07 +/- 3.84 min. Strikingly, only one of the investigated arterioles was found recanalised after 24 h, which, however, did not show leukocyte-endothelial cell interaction. Heparin (300 U/kg, i.v.) effectively counteracted the process of thrombus formation in this model, including both first platelet deposition and vessel occlusion. We conclude that the model of the ear of the hairless mouse allows for distinct in vivo analysis of arteriolar and venular thrombus formation/recanalisation, and, thus, represents an interesting tool for the study of novel antithrombotic and thrombolytic strategies, respectively.

Animals↗
PubMed1996

Conditioning of liver grafts by donor bolus pretreatment with epoprostenol.

Despite improved preservation methods, graft dysfunction after liver transplantation continues to contribute considerably to postoperative morbidity and mortality. In clinical and experimental studies prostaglandin (PG)I2 analogs proved effective in the treatment of liver damage of different origin. Using in vivo fluorescence microscopy in a rat liver transplantation model, we studied the effect of donor bolus pretreatment with the PGI2 analog epoprostenol on hepatic graft revascularization. After epoprostenol bolus pretreatment (group 1: liver transplantation/PGI2), perfusion of liver sinusoids after reperfusion was significantly improved as compared with untreated donor livers (group 2: liver transplantation (95.2+/-0.6% vs. 75.3+/-3.8%, mean +/- SEM; P=0.001) and epoprostenol was found almost in the range of that in normal nontransplanted livers (99.4+/-0.2%). In addition, leukocyte adherence in liver lobules (21.0+/-3.5 vs. 115+/-11.5 n/lobule; P=0.001) and postsinusoidal venules (23.0+/-3.8 vs. 113+/-11.3 n/mm2 endothelial surface; P=0.002) was significantly reduced in the pretreated grafts. Bile production in the recipient was significantly increased by epoprostenol pretreatment of the donor (1.88+/-0.4 vs. 0.63+/-0.13 g/100 g liver*1 hr; P=0.015), indicating restored liver function. These results suggest that the prostacyclin analog epoprostenol is effective in preconditioning the graft prior to transplantation, i.e., improving preservation and increasing graft resistance to ischemia/reperfusion injury. Thus, favorable effects on early graft function after clinical liver transplantation may be achieved by introducing epoprostenol pretreatment into the harvesting procedure.

Animals↗
PubMed1996

Adhesion molecules as determinants of disease: from molecular biology to surgical research.

Cellular adhesion is mediated by distinct cell surface receptors (adhesion molecules) and plays a pivotal role in the biological processes of morphogenesis, cell migration and cell-cell communication. During the past decade many adhesion molecules have been identified and structurally analysed. This has allowed an understanding of their role in the pathophysiology of disease, including inflammation and sepsis, ischaemia and reperfusion, transplant rejection, atherosclerosis and thrombosis, angiogenesis and wound healing, as well as carcinogenesis and tumour metastasis. Understanding of the molecular mechanisms of cellular communication is not only vital for advances in surgical pathophysiology, it also has the potential to widen the spectrum of diagnosis and therapy of disease. Analysis of expression of individual surface molecules may help in the diagnosis of transplant rejection and allow a prognostic determination of tumour progression and metastasis formation. Moreover, manipulation of adhesion molecule function by monoclonal antibodies, antisense oligonucleotides or single gene products may open the door for novel therapeutic regimens to prevent transplant rejection and ischaemia-, sepsis- and shock-induced tissue injury.

Cell Adhesion Molecules↗
PubMed1996

Role of microcirculatory derangements in manifestation of portal triad cross-clamping-induced hepatic reperfusion injury.

Postischemic liver dysfunction following portal triad cross-clamping (PTC) predisposes patients for the development of multiple system organ failure (MSOF) and is associated with increased mortality of MSOF. The deterioration of the hepatic microcirculation may play a pivotal role in the pathophysiologic sequelae of PTC-induced reperfusion injury. We quantitatively analyzed in vivo the role of microcirculatory derangements in the manifestation of hepatic reperfusion injury following ischemia by PTC. Sprague-Dawley rats were subjected to 20 min PTC followed by 60 min reperfusion (PTC, n = 18). Sham-operated animals without ischemia served as controls (sham, n = 15). Within 45-60 min of reperfusion, hepatic microcirculation (sinusoidal perfusion, leukocyte-endothelial cell interaction) was analyzed by means of intravital fluorescence microscopy; tissue oxygenation was assessed using a platinum multiwire surface electrode. Liver enzymes and bile flow were determined as indicators of hepatocellular integrity and liver function. In vivo analysis of postischemic hepatic microcirculation revealed the induction of leukocyte-endothelial cell interaction within sinusoids and postsinusoidal venules and concomitant sinusoidal perfusion deficits associated with tissue hypoxia. In addition, PTC resulted in increased serum levels of liver enzymes and a marked reduction of bile flow. Regression analyses demonstrated significant correlations between hepatocellular desintegration/liver dysfunction and PTC-induced microcirculatory disorders. These results underline the predominant role of microcirculatory disturbances in the development of PTC-induced hepatic reperfusion injury and support the concept that normalization of postischemic microcirculation may be a most effective therapeutic regimen to prevent hepatocellular damage and liver dysfunction.

Animals↗