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M D Menger

Publications and source records attributed to M D Menger.

At least 253 records · Page 14Linked to original sources
PubMed1992

Cryopreservation of islets of Langerhans does not affect angiogenesis and revascularization after free transplantation.

Cryopreservation of isolated islets of Langerhans will be a necessary procedure if pancreatic islet transplantation crosses the threshold for clinical treatment of diabetes mellitus. Although successful cryopreservation of rodent, canine, porcine and human islets has been documented in the past few years, little is known about the influence of the freeze-thaw procedure on the islet's potential to induce angiogenesis and revascularization, a process which is of crucial importance after free transplantation. We have analyzed the process of revascularization of 1- and 10-week-cryopreserved hamster islet isografts using intravital fluorescence microscopy. First signs of angiogenesis of cryopreserved islet grafts were observed on day 2 after transplantation, characterized by the protrusion of capillary sprouts. During the following days these sprouts formed a microvascular network, and revascularization was completed on day 10 after transplantation. Quantitative analysis of functional capillary density, capillary red blood cell velocity, capillary diameter and flow of individual capillaries did neither show differences between 1- and 10-week-cryopreserved islets, nor differences between cryopreserved islets and islets transplanted without cryopreservation were observed. From these results we conclude that cryopreservation of isolated pancreatic islet grafts is an adequate technique for long-term storage prior to transplantation.

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PubMed1992

Influence of experimental hyperglycemia on microvascular blood perfusion of pancreatic islet isografts.

The influence of hyperglycemia on the microvascular blood perfusion of pancreatic islet isografts of Syrian golden hamsters was analyzed by direct visualization of the islet's microvasculature by means of in vivo fluorescence microscopy. The experiments were performed using the hamster dorsal skinfold preparation, which allows for quantitative analysis of the microcirculation of islets grafted on the striated skin muscle. Islets were isolated from inbred hamsters by collagenase digestion and subsequently transplanted in normoglycemic (controls; n = 8) and hyperglycemic (65 mg/kg streptozotocin intravenously; n = 10) recipients. In both groups, revascularization of the islet grafts was completed on day 10 after transplantation. Quantitative analysis of capillary blood perfusion on days 6, 10, and 14 revealed no differences in functional capillary density and capillary red blood cell velocity of islets grafted into normoglycemic as compared to hyperglycemic animals. However, islet capillaries were significantly wider in hyperglycemic recipients (11.9 +/- 1.3 microns, P < 0.01) as compared to normoglycemic controls (8.9 +/- 0.4 microns). The increase of capillary diameters resulted in a significant rise (P < 0.01) of mean capillary blood perfusion from 1.76 +/- 0.39 nl/min in controls to 2.88 +/- 0.63 nl/min in hyperglycemic recipients, indicating an increase in microvascular blood perfusion due to hyperglycemia. From these results it is concluded that hyperglycemia is associated with higher capillary blood perfusion in revascularized islet isografts, similarly as known for pancreatic islets in situ.

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PubMed1992

Pancreatic islet transplantation: isolation, separation, and microvascularization.

Twenty years ago Ballinger and Lacy were the first to report cure of experimental diabetes in rats after free transplantation of isolated pancreatic islets. In a remarkable number of experimental studies on transplantation of isolated islets of Langerhans reversal of diabetes and restoration of normal glucose metabolism has been achieved in rodents. However, studies in larger animals and clinical attempts have been less successful. Beside graft rejection, the isolation and purification of a sufficient mass of islets have been identified as major obstacles. In addition, insufficient revascularization is thought to be, in part, responsible for early graft failure. Recent developments allow for consistently high yields of isolated islets using an automated method, in particular for isolation of human pancreatic islets. Furthermore, a variety of techniques have been implemented during the past years improving purification, including gradient separation, fluorescence-activated sorting, magnetic microsphere extraction and cryopreservation. Revascularization of the islet grafts may be enhanced by selection of adequate sites for transplantation and/or by supportive application of angiogenic peptides. Progress achieved during the past years allow for new hope for successful clinical islet transplantation.

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PubMed1992

[Delay phenomenon of the jejunum. Studies of nutritional blood supply and oxygen supply of the jejunum of the rabbit].

INTRODUCTION: Delay procedure has been shown to effectively improve microvascular perfusion in skin flaps. In analogy to skin, we have analyzed the effect of delay on regional blood flow and surface tissue PO2 of a proximal segment of the jejunum. METHODS: Under nembutal anesthesia (30 mg/kg BW) and mechanical ventilation a total of 15 rabbits were laparotomized. Regional blood flow of the jejunum was estimated using radioactive-labeled microspheres, and tissue PO2 was assessed by means of a platinum-multiwire surface electrode. In order to induce acute ischemia three consecutive jejunal arteries were ligated, and the proximal marginal vascular arch was temporarily occluded by a microvascular clip. Delay procedure was induced by 1) ligation of the jejunal arteries, 2) in situ-maintenance of the jejunal segment for two weeks followed by 3) relaparotomy and occlusion of the proximal marginal arch (n = 8). Regional blood flow of the jejunum and tissue PO2 were also assessed in sham-operated animals (n = 7). RESULTS: After acute ischemia regional blood flow (0.27 (0.05) ml x min-1 x g-1, mean (SEM)) and surface tissue PO2 (39 (3) mmHg) of the jejunal segment were found significantly (p < 0.05) reduced as compared to baseline (0.82 (0.12) ml x min-1 x g-1 and 66 (1) mmHg) and sham-operated animals (0.69 (0.12) ml x min-1 x g-1 and 62 (5) mmHg), respectively. In contrast, delay of the jejunal segment resulted in almost complete preservation of regional blood flow (0.56 (0.04) ml x min-1 x g-1) and surface tissue PO2 (65 (1) mmHg). CONCLUSION: We therefore like to propose that the jejunal delay phenomenon may be clinically used to reduce ischemic complications in jejunal transposition for esophagoplasty.

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PubMed1991

Role of oxygen radicals in the microcirculatory manifestations of postischemic injury.

Reperfusion after transient tissue ischemia constitutes an irrevocable need to preserve tissue viability. However, release of prolonged ischemia will either result in failure of the microcirculation to reperfusion (no-reflow) and thus the prolongation of hypoxia, or in restoration of blood flow resulting in reoxygenation of the inflicted tissue. While ischemia damages the tissue primarily through hypoxia-induced depletion of energy stores, reoxygenation paradoxically contributes to tissue damage through the formation of oxygen radicals, the release of chemoattractant mediators (TNF, IL-1, LTB4), and the activation of circulating polymorphonuclear leukocytes (PMNs). Through the action of chemoattractant mediators and the upregulation of leukocytic (CD11/CD18) and endothelial adhesion receptors (ICAM, GMP-140), activated PMNs adhere to the endothelium, release further chemoattractants and oxygen radicals and undertain a vicious circle, which will ultimately result in further tissue damage. Both the no-reflow phenomenon and the events initiated by reflow--termed herein as the reflow-paradox--contribute to the failure of the nutritive microvascular perfusion and loss of tissue viability following ischemia and reperfusion.

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PubMed1991

Microvascular phenomena during pancreatic islet graft rejection.

Transplantation of insulin secreting tissue as a free graft has the potential to become a safe and simple procedure to cure diabetes. However, clinical results, i.e. achievement of insulin independency, are poor, in spite of the use of immunosuppressive regimens, which are regularly successful in whole organ transplantation. In contrast to whole organ grafts, which are revascularized immediately after transplantation, free pancreatic islet grafts require the process of revascularization in order to establish a microvascular network, sufficient for the nutritional blood supply. We have demonstrated for the first time in vivo images of the process of revascularization of free islet xenografts including microvascular phenomena during graft rejection. Rat islet xenografts were isolated by collagenase digestion and transplanted into hamster dorsal skinfold chambers. After 6, 10 and 14 days the microvasculature of the islet grafts was analyzed by means of intravital fluorescence microscopy. Xenogeneic grafts were revascularized during the first 6 days similarly compared to syngeneic grafts; however, on day 10 after transplantation a reduction in size of the microvascular network as well as a decrease in functional capillary density and a reduction in capillary red blood cell velocity were observed, accompanied by microvascular rejection phenomena, such as an increase of microvascular permeability, edema formation, capillary widening and intravascular accumulation of white blood cells (WBCs) with concomitant WBC-endothelium interaction in post-capillary venules. Treatment with 2.5 mg/kg/d (+/-)-15-deoxyspergualin could not completely alleviate these microvascular rejection phenomena.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed1991

Hepatic microcirculatory disturbances due to portal vein clamping in the orthotopic rat liver transplantation model.

Most modifications and applications of the orthotopic rat liver transplantation (ORLT) model require clamping of the portal vein, thus leading to ischemia of the gut. The purpose of this study was to evaluate the effect of portal vein clamping during ORLT on hepatic microcirculation and leukocyte--endothelial interaction by intravital fluorescence microscopy. ORLT were performed following 1 hr of cold storage in EuroCollins solution without (standard group) and with insertion of a portojugular shunt (shunt group) to minimize intestinal ischemia. ORLT induced reduction of perfused sinusoids (83%) and velocity of leukocytes (311 +/- 4.5 microns/sec; mean +/- SEM) compared with nontransplanted controls (99% and 417 +/- 4.9 microns/sec). Portojugular shunt during ORLT improved hepatic microvascular perfusion (89% and 355 +/- 3.4 microns/sec; P less than 0.05). Furthermore, percentage of permanent and temporary adherent leukocytes decreased significantly when a portosystemic shunt was applied (from 33.5 +/- 1% to 22.1 +/- 1% and 19.7 +/- 1.2% to 14.0 +/- 0.9%; P less than 0.05). The results of the study reveal that intestinal congestion and reperfusion results in a rise in leukocyte adhesion to the sinusoidal wall and in disturbances of the hepatic microcirculation. It seems likely that increased endotoxin concentrations in the portal vein induce an activation of hepatic macrophages that subsequently cause release of chemoattractant mediators. In conclusion, side effects of intestinal ischemia during experimental liver transplantation surgery on liver function due to release of chemoattractant mediators should be considered when experimental data are transferred to clinical settings.

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PubMed1991

In vivo fluorescence microscopy for quantitative analysis of the hepatic microcirculation in hamsters and rats.

Using intravital fluorescence microscopy and epi-illumination, the hepatic microcirculatory system of Syrian golden hamsters was analyzed, and the morphology and microhemodynamics were compared to those of rats. After contrast enhancement with 1 mumol/kg acridine orange i.v., the epi-illumination technique allows for visualization of capillary sinusoids and postsinusoidal venules, which are running in parallel with the liver surface, while afferent microvessels could be visualized in only few of the liver lobules investigated. In rat livers, the capillary sinusoids showed morphology similar to that of hamsters, however, postsinusoidal venules could frequently not be observed when applying epi-illumination, since these microvessels are piercing perpendicularly into the depth of the liver tissue. Microhemodynamic analysis, including the sinusoidal perfusion rate, sinusoidal red blood cell velocity and diameters, microvascular white blood cell (WBC) count and the phenomenon of WBC-endothelium interaction, as well as the hepatocellular uptake of the fluorescent compound acridine orange were found to be similar in hamsters as compared to rats. Although transillumination for in vivo microscopy may have the potential to visualize the complete hepatic microcirculatory system due to an increased focus depth, the epi-illumination technique has the advantage for quantitative assessment not only of the morphology of the hepatic microcirculatory system and microvascular blood perfusion, but also allows for evaluation of cellular phenomena within the hepatic microvessels, such as WBC accumulation, WBC-endothelium interaction, phagocytotic activity of Kupffer cells, and hepatocellular transport of fluorescent compounds. Hepatic microcircular disturbances, including accumulation of WBCs and WBC-endothelium interaction are causative in the development of organ failure in conditions such as hemorrhagic and septic shock, and, in particular, postischemic reperfusion injury following liver surgery and liver transplantation. Since accumulation of WBCs and their interaction with the microvascular endothelium are primarily found in postsinusoidal venules, in vivo microscopy of the hamster liver represents a favorable model for studies on cellular phenomena within the hepatic microcirculation.

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PubMed1990

Quantitative analysis of neovascularization of different PTFE-implants.

The process of neovascularization was analyzed in vivo in different expanded polytetrafluoroethylene (e-PTFE) implants which are frequently used in cardio-thoracic and vascular surgery. We have used the model of the hamster dorsal skinfold chamber which allows quantitative analysis of the microcirculation by means of intravital fluorescence microscopy. Pieces of approximately 1 mm2 of the cardiovascular patch (CVP, fibril length: 30 microns; n = 21), surgical membrane (SM, fibril length: 1 micron; n = 16), and soft tissue patch (STP, fibril length: 22 microns; n = 12) were implanted into the skinfold chambers. On day 10 after implantation, the functional density of newly formed microvessels was significantly (P less than 0.05) higher in CVP (145.0 +/- 10.9 cm-1) as compared to SM (688 +/- 13.9 cm-1) and STP (86.9 +/- 21.2 cm-1). In addition, CVP revealed a larger zone of neovascularization (311.6 +/- 19.4 microns) and the tightest integration (dynamic breaking strength: 17.9 +/- 3.0 cN/mm2) into the perigraft tissue, while SM demonstrated only few microvessels and no integration (6.0 +/- 1.9 cN/mm2) into the perigraft. None of the three different PTFE-implants revealed transmural ingrowth of capillaries. The internodal distance of PTFE implants seems to be the most important factor for neovascularization. Surgical membrane used for the replacement of passive biological membranes demonstrated, as is its purpose, little neovascularization and no integration into the perigraft tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed1990

Neovascularization of prosthetic vascular grafts. Quantitative analysis of angiogenesis and microhemodynamics by means of intravital microscopy.

Neovascularization of prosthetic vascular grafts seems to play an important role in the prevention of early graft failure due to infection of thrombotic occlusion. The process of angiogenesis and neovascularization was analyzed for three different prosthetic vascular grafts (PTFE, Dacron double microvelour and gelatin-coated Dacron double microvelour) in vivo by means of fluorescence microscopy. Under Nembutal anesthesia (50 mg/kg BW) Syrian golden hamsters were fitted with a dorsal skinfold chamber, which contains the cutaneous skeletal muscle as well as subcutaneous tissue, and allows for quantitative analysis of the microcirculation for a prolonged period of time. In each chamber one piece (1mm2) of all three vascular grafts was implanted. Five days after implantation neovascularization was ascertained in 9/11 (coated) and 8/11 (non-coated) Dacron grafts, while only 4/11 PTFE implants revealed new microvessels. On day 10 the density of newly-formed microvessels was significantly higher (p less than 0.001) in Dacron grafts (234.3 +/- 31.2 cm-1 and 238.9 +/- 41.3 cm-1 respectively) as compared to PTFE implants (154.9 +/- 30.4 cm-1). In addition, Dacron grafts revealed a larger neovascularization zone extending into the perigraft tissue. 12 days after implantation non-coated Dacron grafts were most tightly integrated into the perigraft tissue. The better neovascularization of Dacron might be due to the high porosity of the graft compared to low porous PTFE, which revealed insufficient neovascularization.

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PubMed1990

Direct monitoring of capillary perfusion following normovolemic hemodilution in an experimental skin-flap model.

The effects of normovolemic hemodilution on skin flap survival are studied in a recently developed skin-flap model (homozygous hairless mouse ear) in which nutritional capillary flow is monitored directly by means of intravital microscopy from the time of flap creation throughout the establishment of necrosis. Two diluting agents (dextran 60 and hydroxyethyl starch 200) are utilized. Our quantitative findings demonstrate that the amount of nonperfused tissue following flap creation in both the dextran (n = 23) and starch (n = 13) groups was significantly decreased as compared with controls (n = 19). Our qualitative observations suggest that improved hemorrheologic properties at the microcirculatory level are responsible for the observed decreased necrosis. Various mechanisms by which hemodilution may act to prevent necrosis are discussed.

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PubMed1990

A specific fluorescent dye for ex situ staining of vital islets of Langerhans: neutral red.

We present a new technique for specific ex situ fluorescent staining of islets of Langerhans with neutral red. Depending on the concentration of neutral red (1 microgram/ml), this technique allows the differentiation between exocrine and endocrine pancreatic tissue, according to differences in fluorescence intensity. Pancreatic islets can be stained not only in situ, but in particular ex situ after pancreas digestion. Since intravital staining of the pancreas in situ with neutral red is not applicable in human transplantation, the staining procedure ex situ may be a useful tool for islet purification by particle sorting, using a fluorescent-light-activated system; thus, a sufficient mass of purified islets for free transplantation may be isolated.

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