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Biomedical subjects

M D Menger

Publications and source records attributed to M D Menger.

At least 109 records · Page 6Linked to original sources
PubMed1999

Do vitamin E supplements in diets for laboratory animals jeopardize findings in animal models of disease?

Vitamin E has been supplemented to the diets of farm animals to improve fertility, health, growth rates and quality of animal products. Because of the positive experience obtained in farm animals, vitamin E has been added in increasing amounts to the diets of laboratory animals. Today, vitamin E levels in standard rodent maintenance diets range from 30 mg/kg (France, United States), 90-120 mg/kg (Netherlands, United Kingdom) to as much as 200 mg/kg (Germany). While increasing fertility and health of laboratory animals, these vitamin E supplements affect diverse pathophysiological conditions and thus the outcome of animal models of disease. Because of the large variability of vitamin E levels between laboratories within and between different countries, results obtained in established animal models may no longer be comparable and/or reproducible. Researchers should be aware of these vitamin E supplements and carefully control for potential effects in their respective animal models that involve--or may involve--the generation of reactive oxygen species.

Animals↗
PubMed1999

Inhibition of tumor growth, angiogenesis, and microcirculation by the novel Flk-1 inhibitor SU5416 as assessed by intravital multi-fluorescence videomicroscopy.

Vascular endothelial growth factor (VEGF) plays a fundamental role in mediating tumor angiogenesis and tumor growth. Here we investigate the direct effect of a novel small molecule inhibitor of the Flk-1-mediated signal transduction pathway of VEGF, SU5416, on tumor angiogenesis and microhemodynamics of an experimental glioblastoma by using intravital multifluorescence videomicroscopy. SU5416 treatment significantly suppressed tumor growth. In parallel, SU5416 demonstrated a potent antiangiogenic activity, resulting in a significant reduction of both the total and functional vascular density of the tumor microvasculature, which indicates an impaired vascularization as well as significant perfusion failure in treated tumors. This malperfusion was not compensated for by changes in vessel diameter or recruitment of nonperfused vessels. Analyses of the tumor microcirculation revealed significant microhemodynamic changes after angiogenesis blockage such as a higher red blood cell velocity and blood flow in remnant tumor vessels when compared with controls. Our results demonstrate that the novel antiangiogenic concept of targeting the tyrosine kinase of Flk-1/KDR by means of a small molecule inhibitor represents an efficient strategy to control growth and progression of angiogenesis-dependent tumors. This study provides insight into microvascular consequences of Flk-1/KDR targeting in vivo and may have important implications for the future treatment of angiogenesis-dependent neoplasms.

Animals↗
PubMed1999

Secondary ischaemia in experimental free flaps--treatment by long acting prostacyclin analogues.

Secondary postoperative ischaemia due to venous occlusion is the most detrimental insult to free microvascular flaps. In an experimental rat free flap model the efficacy of long acting prostacyclin analogues iloprost (Ilomedin) and cicaprost in venous occlusion induced postoperative ischaemia was studied. Free, microvascular groin flaps were transplanted to the neck and the draining veins were temporarily occluded on the first postoperative day for a total of 20 min. In the untreated control group, haemorrhagic flap necrosis occurred. Intravital microscopy after secondary ischaemia revealed flap areas without reperfusion. The functional vessel density was significantly reduced. Reperfused capillaries were tortuous and significantly dilated. After reperfusion the interstitial leakage of macromolecular dextran increased, indicating loss of microvascular endothelial integrity. Intraarterial and intravenous applications of iloprost were able to diminish the ischaemic effects, giving a flap survival rate of 83%. Similar results were obtained by intravenous and enteral administration of cicaprost. Transcutaneous oxygen partial pressure measurements confirmed the viability of the surviving flaps. We conclude that both iloprost and cicaprost are effective in preventing venous occlusion induced failure of free microvascular groin flaps.

Animals↗
PubMed1999

In vivo analysis of the microcirculation of osteomyocutaneous flaps using fluorescence microscopy.

Previous studies have indicated that freely transferred osteomyocutaneous flaps may fail despite anastomotic patency. While microvascular dysfunction is thought to be one of the major causes for this type of flap failure, little is known of its underlying mechanisms, probably due to the lack of adequate experimental models allowing detailed intravital microcirculatory analysis. Herein we report quantitative analysis of the microcirculation of periosteum, muscle, subcutis and skin by intravital fluorescence microscopy using an osteomyocutaneous free flap model in the hindlimb of rats. The microcirculation of the different tissues was studied after microanastomotic transfer (free flap), and was compared to that after solely elevating the tissue, mimicking a pedicled osteomyocutaneous flap. Transferred flaps, which were exposed to 1 h of ischaemia during the anastomotic procedure, showed a slight but significant decrease (P< 0.05) of functional capillary density in muscle, subcutis and skin when compared with the microcirculation of pedicled flaps, while capillary diameters, red blood cell velocity and blood flow of perfused capillaries remained almost unaffected. The decrease of functional capillary density was associated by a significant (P< 0.05) inflammatory response, as indicated by the increased number of leukocytes adherent to the endothelial lining of postcapillary venules. While the functional capillary density of periosteum was not affected by the free transfer procedure, the inflammatory response was found similar when compared with that observed in muscle and subcutis. Thus, our study indicates that even after a short 1-h ischaemic time period, capillary perfusion failure and leukocyte-endothelial cell interaction are the main events, characterising microvascular dysfunction after free transfer of osteomyocutaneous flaps. Using the model described herein, intravital microscopic analysis of the microcirculation proved an appropriate tool to study the individual microvascular response after free tissue transfer, and may thus be used to evaluate the effectiveness of novel therapeutic regimens which aim at counteracting microcirculatory dysfunction in free osteomyocutaneous flaps.

Animals↗
PubMed1999

Cardiopulmonary dysfunction during minimally invasive thoraco-lumboendoscopic spine surgery.

UNLABELLED: The endoscopic retroperitoneal approach to thoracolumbar anterior spine fusion is associated with CO2 insufflation into the thoracic space. We studied the cardiopulmonary effects of this CO2 thoraco-retroperitoneal insufflation compared with the conventional open surgical procedure using thoraco-phreno-lumbotomy in 12 pigs under balanced anesthesia, paralysis, and mechanical ventilation. During open surgery of the thoracolumbar spine, animals exhibited unchanged systemic and pulmonary hemodynamics, as well as ventilation and oxygenation variables. Animals retroperitoneally insufflated with CO2 (12 mm Hg) exhibited a significant increase of PaCO2 and a moderate decrease of PaO2, SaO2, and pH, with insignificant changes of central venous filling pressures and systemic hemodynamics. Endoscopic phrenotomy with thoracic CO2 insufflation instantaneously and drastically affected hemodynamic status and pulmonary gas exchange with marked hypoxia, hypercapnia, systemic hypotension, tachycardia, and pulmonary hypertension within minutes. An increase of minute ventilation, inspiratory oxygen fraction, and positive end-expiratory pressure promptly reversed these cardiopulmonary effects. CO2 evacuation allowed the animals to completely recover and regain almost baseline cardiopulmonary status, except for a reduced arterial blood pressure. Appropriate monitoring and immediate CO2 desufflation may be beneficial in cases of therapy-resistant hemodynamic, oxygenation, and ventilation difficulties. IMPLICATIONS: For endoscopic thoraco-lumbar spine fusion, CO2 thoraco-retroperitoneum-induced cardiopulmonary dysfunction must be of concern, especially in patients with cardiopulmonary compromise. Appropriate monitoring and immediate CO2 desufflation may be beneficial in cases of therapy-resistant hemodynamic, oxygenation, and ventilation difficulties.

Animals↗
PubMed1999

Microvascular response to compartment syndrome-like external pressure elevation: an in vivo fluorescence microscopic study in the hamster striated muscle.

OBJECTIVE: To quantitatively assess the nature and the magnitude of the microvascular response of striated muscle tissue upon elevation of external pressure, as in compartment syndrome. METHODS: Using the skinfold chamber model in Syrian golden hamsters and intravital fluorescence microscopy, we studied the individual response of the different segments of the microcirculation, i.e., the arterioles, capillaries, and postcapillary venules, in terms of vasomotor control (change of vessel diameter) and cessation of blood flow upon defined changes in external tissue pressure. RESULTS: The unique findings of our study are that (1) arteriolar flow ceased at mean external pressures of 25.6+/-2.4, 28.3+/-2.8, 34.5+/-4.6, and 44.4+/-6.8 mm Hg in vessels with diameters of less than 20, 20 to 40, 40 to 60, and greater than 60 microm, respectively, without signs of spasm or collapse even at a pressure maximum of 70 mm Hg, whereas (2) in venules the increase of external pressure was associated with a diameter reduction ranging from 5 to 25% with cessation of blood flow at mean external pressures between 27 and 33 mm Hg. Blood flow ceased in 50% of the muscle capillaries already at an external pressure of 12 mm Hg. Thus, at distinct external pressure levels venous and capillary blood flow ceased, but arterioles were still capable of carrying flow, which was directed along arteriolo-arteriolar "thoroughfare" channels. To restart blood flow, external pressure had to be decreased by 9, 11, 15, and 17 mm Hg in arterioles with diameters of less than 20, 20 to 40, 40 to 60, and greater than 60 microm, and by approximately 9 mm Hg in venules regardless of vessel diameter. Capillary blood flow was found to be restored at a mean reduction of external tissue pressure of approximately 4 mm Hg. CONCLUSION: Our study disproves the critical closing theory but complies-in particular because of the supposed constriction-induced increase of venular resistance-with the hypothesis of reduced arteriovenous pressure gradients as the cause of flow cessation in compartment syndrome. The necessity of a substantially increased perfusion pressure gradient to restart blood flow in arterioles, capillaries, and venules confirms the existence of yield stress in these microvessels. The high susceptibility of capillaries to elevated external pressure indicates the necessity of early fasciotomy to restore impaired nutritive circulation in cases of compartment syndrome.

Animals↗
PubMed1999

A chronic model for intravital microscopic study of microcirculatory disorders and leukocyte/endothelial cell interaction during normotensive endotoxemia.

Sepsis-induced microvascular leukocyte/endothelial cell interaction may result in a deterioration of capillary perfusion that finally leads to septic organ dysfunction. The aim of the present study was to characterize a novel, sublethal, two-hit model of chronic systemic sepsis that allows the repeated analysis of microcirculation by intravital microscopy. In Syrian golden hamsters the effect of a single i.v. endotoxin (LPS, 2 mg/kg, E. coli) injection (SH-LPS group, n = 5 animals) vs. a double LPS injection (DH-LPS group, n = 6 animals) was analyzed. After monitoring baseline parameters (t1), measurements were performed at 30 min (t2), 3 h (t3), 8 h (t4), 24 h (t5), 48 h (t6), 56 h (t7) and 72 h (t8) (both groups) after initial LPS exposure. In DH-LPS animals, a second LPS injection (2 mg/kg) was given at t6 (48 h). Intravital fluorescence microscopy was performed in a dorsal skin fold chamber preparation and allowed determination of leukocyte-endothelial cell interaction (leukocyte rolling and sticking), and measurement of functional capillary density (FCD), which served as a measure of capillary perfusion. The first LPS injection comparably altered leukocyte/endothelial cell interaction and capillary perfusion in both groups (t1-t6, P > 0.05, MANOVA). Between t6 and t8 leukocyte adherence decreased in SH-LPS animals, whereas in DH-LPS animals adherence remained constantly elevated (SH-LPS: -53.0 +/- 6.2% between t6 and t8 vs. DH-LPS: -3 +/- 5; P < 0.05). The ongoing inflammatory response in DH-LPS animals was associated with a progressive deterioration of FCD, whereas FCD remained constant in SH-LPS animals (DH-LPS: -71.5 +/- 17% between t6 and t8 vs. SH-LPS: 3.0 +/- 13%; P < 0.05). In parallel, coagulatory parameters were found significantly altered only in DH-LPS animals but not in SH-LPS animals. We conclude that "double hit" LPS exposure is an appropriate model (i) to analyze repeatedly over time microcirculatory disorders under conditions of persistent endotoxemia-induced inflammatory response, and (ii) to prove the effectiveness of novel anti-inflammatory strategies.

Animals↗
PubMed1999

Role of TNF-alpha in local surgical trauma-induced microvascular dysfunction.

BACKGROUND/AIM: The aim of this study was to gain insight into the mechanisms of microvascular dysfunction after local surgical trauma. METHODS: The effect of anti-tumor necrosis factor (TNF)-alpha antibody (Ab) on microvascular function, including arteriolar diameter response, nutritive perfusion, leukocyte-endothelial cell interaction and endothelial integrity disruption, was studied in hamster skinfold chamber preparations using intravital fluorescence microscopy. RESULTS: Directly after the surgical procedure, arteriolar diameters were found to be markedly (p < 0.05) reduced, but recovered significantly at 8 h and reached plateau levels after 24 h. Surgical trauma further induced a strong inflammatory response characterized by a significant (p < 0.05) increase in leukocyte adherence to the endothelium of postcapillary venules. This inflammatory response was associated with an increase in microvascular permeability, indicating endothelial integrity disruption. Anti-TNF-alpha Ab had no significant effect on the surgical trauma-induced arteriolar vasomotor dysfunction; however, it effectively (p < 0.05) reduced venular leukocyte adherence and attenuated the increase in microvascular permeability. CONCLUSION: Our study indicates that arteriolar constriction, leukocyte-endothelial cell interaction and endothelial macromolecular leakage have to be considered as the characteristic microvascular response after local surgical trauma. It is conceivable that TNF-alpha plays a role in mediating the inflammatory response, but not the dysfunction of vasomotor control.

Animals↗
PubMed1999

Beta-adrenoceptor inhibition for induction of acute cardiac failure in pigs.

For the testing of heart assist devices most animal models of acute cardiac failure that are usually used show certain disadvantages. We therefore developed a new method using the beta-adrenoceptor antagonist carazolol. We administered a bolus injection of 1 mg/kg followed by a continuous infusion of 1 mg/kg/h in adult German 'Landrasse' pigs. Blood pressure, heart rate, cardiac output and maximum left ventricular pressure rise time showed a significant (P < 0.05) reduction of the control value varying between 40% and 59%. The method is suitable for the testing of surgical approaches in heart failure.

Acute Disease↗
PubMed1999

[Laparoscopic-transperitoneal and lumboscopic-retroperitoneal surgery of the spine. Developments from animal experiments for use in clinical practice].

With the use of an in vivo porcine training model we established the transperitoneal laparoscopic approach for the instrumentation of anterior lumbar spine fusion with Bagby-and-Kuslich (BAK) interbody implants as well as "Brantigan" cages. The transperitoneal laparoscopic approach caudally from the aortic bifurcation allows the spine fusion procedure of the caudal but not of the cranial part of the lumbar spine. Because ventral stabilization of the upper lumbar spine is frequently necessary, in particular in trauma patients with spine body fractures, an additional retroperitoneal minimal-invasive (lumboscopic) approach was established using again the in vivo porcine training model. We demonstrate that via this approach spine fusion can easily be performed including the Th12 segment after fenestration of the diaphragm. With the experience from the in vivo experiments, both techniques could safely and successfully be transferred to clinical practice with the advantage of markedly reducing the extent of operative trauma compared with the corresponding open approaches.

Animals↗
PubMed1999

Role of microcirculation in hepatic ischemia/reperfusion injury.

There is a large body of evidence that the liver microcirculation has to be considered as a major target in hepatic ischemia/reperfusion injury. The nature of microvascular injury, which precedes manifestation of hepatic parenchymal tissue damage, includes both hypoxia due to lack of microvascular perfusion (i.e. no-reflow), and a reperfusion-associated inflammatory response, which includes the activation and dysfunction of leukocytes and Kupffer cells (the reflow paradox). No-reflow in sinusoids is thought to be caused by endothelial cell swelling and intravascular hemoconcentration, and involves also a deterioration of the balance between ET and NO. The reflow paradox is associated with: (i) the release and action of proinflammatory cytokines (TNF-alpha, IL-1) and oxygen radicals; (ii) the up-regulation of endothelial and leukocytic adhesion molecules (selectins, beta-integrins, ICAM-1); and (iii) the interaction of leukocytes with the endothelial lining of the hepatic microvasculature.

Animals↗
PubMed1999

Differential effect of anti-TNF-alpha antibody on proinflammatory cytokine release by Kupffer cells following liver ischemia and reperfusion.

To study the role of tumor necrosis factor-alpha (TNF-alpha) for induction of the proinflammatory cytokine cascade after liver ischemia and reperfusion (I/R), rats were injected intraperitoneally with anti-TNF-alpha monoclonal antibodies (mAb) or placebo (IgG1) 30 min prior to global hepatic ischemia. Blood levels of TNF-alpha, interleukin (IL)-1alpha and -6 were determined. In addition, Kupffer cells (KC) were harvested after 60 min of reperfusion and spontaneous cytokine release was measured. Sham-operated animals were used as controls. Levels of proinflammatory cytokines in serum and KC supernatants were detected using specific bioassays and ELISA. Liver I/R resulted in increased (p < .01) serum levels of TNF-alpha, IL-1alpha, and IL-6, which was associated with an enhanced (p < .05) release of these cytokines by KC. In vivo pretreatment with anti-TNF-alpha mAb led to complete neutralization of TNF-alpha serum levels and decreased (p < .01) IL-6 levels (-62%). Moreover, anti-TNF-alpha mAb markedly (p < .05) decreased the release of TNF-alpha (-69%) and IL-6 (-56%) by KC, while IL-1alpha was not affected. These data indicate that TNF-alpha produced early after liver I/R triggers both its own secretion as well as IL-6 release by KC during reperfusion while the release of IL-1alpha occurs independent from TNF-alpha.

Animals↗
PubMed1999

Intravital microscopy for the study of the microcirculation in various disease states.

The study of the microcirculation by intravital microscopy represents a sophisticated research tool to analyse complex biological interactions and disease mechanisms as well as to develop and test novel prophylactic and therapeutic approaches aimed at the prevention or attenuation of manifestation of disease-associated microvascular disorders and cellular dysfunction. This may include pathogenesis of atherosclerosis and thrombosis, fibrosis and cirrhosis as well as hypertension, diabetes and tumorogenesis. In addition, using the microscopic technique, circulatory and cellular disorders in surgical diseases and procedures, such as shock and resuscitation, ischaemia/reperfusion and transplantation, trauma, sepsis and inflammation, as well as burn injury and wound healing, may be analysed. With the background of the increasing knowledge of molecular and cellular mechanisms of disease evaluated in vitro, the technique of intravital microscopy ideally allows to bridge over from those in vitro observations to test their potential relevance in vivo.

Animals↗
PubMed1999

Surface cooling inhibits tumor necrosis factor-alpha-induced microvascular perfusion failure, leukocyte adhesion, and apoptosis in the striated muscle.

BACKGROUND: Surface cooling is frequently used in a number of conditions, especially traumatic, ischemic, burn, and neurologic injury to reduce the tissue damage. However, the protective mechanisms of cold therapy on traumatized tissues remain unclear. Tumor necrosis factor-alpha (TNF-alpha) is a fundamental mediator in inflammatory reactions and trauma-induced tissue injury. In the present study, we examined the microvascular response to TNF-alpha challenge and the effects of local cooling on the TNF-alpha-induced changes in the striated muscle of hamsters. METHODS: By the use of the dorsal skinfold chamber preparation and in vivo fluorescence microscopy in combination with computer-based image analysis, we determined TNF-alpha-induced leukocyte rolling and adhesion to microvascular endothelium, capillary perfusion, venular leakage, and cellular apoptosis with and without surface cooling. RESULTS: We found that topical administration of 2000 units TNF-alpha caused a progressive impairment of microvascular perfusion and increased leukocyte recruitment and vascular macromolecular leakage. Local cooling to 10 degrees C for 60 minutes markedly (P < .05) inhibited the TNF-alpha-induced capillary perfusion failure and leukocyte response and slightly attenuated the increase of microvascular permeability after 180 minutes of stimulation. Furthermore, it was observed that 24 hours of TNF-alpha stimulation increased the number of apoptotic cells (i.e., nuclear condensation and fragmentation) by 10-fold. This TNF-alpha-mediated effect was almost abolished by treatment with local hypothermia. CONCLUSION: These data suggest that the protective effect of surface cooling of traumatized tissue is due to its attenuation of the microvascular inflammatory response associated with the inhibition of the process of apoptosis.

Animals↗
PubMed1998

An intravital fluorescence microscopic study of hepatic microvascular and cellular derangements in developing cirrhosis in rats.

Quantitative data defining the relationship between the hepatic microcirculation and the development of liver pathological changes could provide a basis for a better understanding of fibrogenic processes, such as cirrhosis. Therefore, we established the technique of intravital fluorescence microscopy and computer-assisted microcirculation analysis systems in developing cirrhosis in rats with the aim of quantitatively assessing the association of hepatic microvascular morphology with its disordered acinar architecture, and nonparenchymal cell transformation with collagen deposition, parenchymal cell loss, and liver dysfunction. In animals chronically exposed to carbon tetrachloride (CCl4), the most significant microvascular changes progressively observed in vivo were the concomitant appearance of 1) sinusoid-free space around dilated postsinusoidal venules with 2) substituting occurrence of yellow-green autofluorescent collagen deposition, 3) reduction in sinusoidal density, but 4) increase of vascular lumen caused by the formation of shunting vessels bypassing the sinusoids. Present on-line analysis further indicated the local coincidence of changed spatial distribution of Ito cells (accumulation of vitamin A ultraviolet autofluorescence in zone 3) with fibrotic autofluorescent septa, causing significant collapse of parenchymal tissue (hepatocellular bis-benzamide fluorescence) and diminution of hepatocellular excretory function (bile flow). Regression analysis revealed strong correlations between loss of parenchymal tissue and both collagen deposition and sinusoidal rarefication, as well as between sinusoidal rarefication and collagen deposition. Thus, sequential in vivo analysis presented herein provides the new information on the concomitant onset of cellular, fibrotic, and microvascular changes in developing fibrosis/cirrhosis, excluding that distinct cellular or fibrotic alterations are a prerequisite for the manifestation of microcirculatory and vascular derangements or vice versa.

Animals↗
PubMed1998

Microscopic analysis of NADH fluorescence during aerobic and anaerobic liver preservation conditions: A noninvasive technique for assessment of hepatic metabolism.

Gaseous insufflation of oxygen via the venous vascular system is thought to be an useful tool for preventing anoxic tissue injury during extended time periods of ischemic preservation and for allowing for an improved recovery of organ function after transplantation. The present study aimed at the application of a noninvasive technique for monitoring effectiveness and homogeneity of gaseous areation by using an epiillumination microscopic technique for assessment of tissue nicotinamide adenine dinucleotide (NADH) fluorescence. Rat livers were flushed with and stored in University of Wisconsin solution at 4 degrees C for 48 h (n = 20). In half of the experiments (n = 10) gaseous oxygen was applied subsequent to organ harvest. Using ultraviolet-excitation high-resolution microscopy and computer-assisted image analysis liver surfaces were scanned for NADH intensity and spatial heterogeneity at 1, 24, and 48 h preservation time. Livers simply stored without aeration served as controls (n = 10). NADH intensity data were compared with corresponding data of tissue adenosine triphosphate (ATP) concentrations determined enzymatically. NADH fluorescence already differed at 1 h preservation between the two groups with significantly lower values in the aerobically stored livers. NADH fluorescence further decreased between 1 and 24 h preservation and remained low until 48 h, whereas in the anaerobically stored livers NADH fluorescence was found to be constantly high over the entire observation period. Aerobic storage resulted in rather homogeneous tissue oxygenation with an intrahepatic variation of NADH fluorescence <20%. In parallel, oxygen persufflation appropriately restored tissue ATP content within 1 to 24 h of preservation, while the simply stored livers exhibited pronounced depletion of ATP. We demonstrate for the first time that by means of retrograde gaseous oxygenation, ischemic livers can be readily and effectively oxygenated. Our study further indicates that the noninvasive microscopic analysis of tissue NADH fluorescence may be an useful tool for estimating efficiency of strategies in organ preservation.

Adenosine↗