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Biomedical subjects

B Vollmar

Publications and source records attributed to B Vollmar.

At least 109 records · Page 6Linked to original sources
PubMed1998

In vivo analysis of antithrombotic effectiveness of recombinant hirudin on microvascular thrombus formation and recanalization.

PURPOSE: This study was undertaken to evaluate in vivo the effect of recombinant hirudin (r-hirudin [HBW 023]), a potent thrombin inhibitor, on the process of microvascular thrombus formation and recanalization. METHODS: Thrombosis was induced photochemically in distinct arterioles (n = 25) and venules (n = 30) of the ear of 16 hairless hr/hr mice (8 to 10 weeks old, 25 to 30 g of body weight). r-Hirudin (1 mg/kg of body weight) was administered intravenously directly before thrombus induction; saline-treated animals served as controls. Thrombus formation (i.e., first platelet deposition at the endothelial lining [FPD]; inner luminal diameter reduction to 50% [D/2]; complete vessel occlusion [CVO]), vessel recanalization, microcirculatory parameters, and leukocyte-endothelial cell interaction were analyzed by means of intravital fluorescence microscopy. RESULTS: Hirudin significantly delayed the process of thrombus formation compared with saline-treated controls in both arterioles (FPD: 381 +/- 80 vs 137 +/- 25 seconds, P < 0.05; D/2: 627 +/- 49 vs 501 +/- 71 seconds; CVO: 925 +/- 78 vs 854 +/- 60 seconds) and venules (FPD: 173 +/- 11 vs 59 +/- 4 seconds; D/2: 342 +/- 54 vs 228 +/- 27 seconds; CVO: 541 +/- 85 vs 344 +/- 43 seconds; P < 0.05). In addition, r-hirudin-treated animals showed an increased rate of vessel recanalization at 24 hours after thrombus induction (arterioles: 54% [7 of 13] vs 0% [0 of 12], P < 0.05; venules: 77% [10 of 13] vs 53% [9 of 17]), whereas microcirculatory parameters and leukocyte-endothelial cell interaction were not affected. CONCLUSION: Our data indicate that r-hirudin not only counteracts the process of thrombus formation but also promotes vessel recanalization, thus supporting its use in clinical microvascular surgery.

Animals↗
PubMed1998

Effects of local cooling on microvascular hemodynamics and leukocyte adhesion in the striated muscle of hamsters.

OBJECTIVES: Cellular metabolism is dependent on the local temperature in tissues. Induced hypothermia has been shown to be protective in a number of conditions, especially traumatic, ischemic, burn, and neurological injury. However, the protective mechanisms of cold therapy remain controversial and the hemodynamic changes in the microcirculation of striated muscles in response to hypothermia have not been studied in detail previously. METHODS: In this study, we investigated the microvascular response of local cooling and rewarming in the striated muscle of hamsters by use of the dorsal skinfold preparation and in vivo fluorescence microscopy. RESULTS: We found that reduction of the surface temperature to 8 degrees C for 30 minutes caused arteriolar vasoconstriction with a decrease in diameters by 43+/-7% while the venular and capillary diameters remained unchanged. The cooling procedure also markedly reduced the functional capillary density and the blood flow velocity and diameters in all vessel types, i.e., arterioles, venules, and capillaries. Moreover, the percentage of capillaries with no flow increased from 0.4+/-0.5% to 44+/-14% after 10 minutes of cold therapy. However, these hemodynamic changes induced by local hypothermia were completely reversed to the precooling values after termination of cooling and 30 min of rewarming. Strikingly, we found no increase in the number of adherent leukocytes and vascular permeability after the cooling and rewarming period, while, in contrast, additional experiments with warm ischemia (30 minutes) and reperfusion (30 minutes), i.e., reduced microvascular perfusion and reperfusion at normothermia, caused a sustained decrease in local perfusion and a nine-fold increase in venular leukocyte adhesion. CONCLUSIONS: Taken together, our functional data demonstrate that hypothermia markedly reduces microvascular perfusion, which is completely restored upon rewarming. The reduced microvascular perfusion during hypothermia did not provoke an inflammatory response, whereas leukocyte recruitment was prominent after reduced perfusion at normothermia, indicating that transient hypothermia has no adverse effects on microvascular parameters in the striated muscle in vivo.

Animals↗
PubMed1998

Striated muscle microvascular response to zymosan-induced generalized inflammation in awake hamsters.

The effect of zymosan-induced generalized inflammation on the microcirculation of distant striated skin muscle was studied for a 12 day period in awake Syrian golden hamsters (n = 18) using the dorsal skinfold chamber model and intravital fluorescence microscopy. Intraperitoneal zymosan exposure (125 mg/100 g body weight) induced significant nutritive perfusion failure in the distant striated muscle tissue at Day 1 without complete recovery over the 12 day observation period, as indicated by the marked reduction of functional capillary density when compared with both baseline values and values of sham-treated control animals. Moreover, intraperitoneal zymosan exposure induced endothelial disintegration, as demonstrated by the continuous increase of macromolecular leakage throughout the 12 days of observation. Strikingly, zymosan did not induce significant leukocyte adherence to the endothelial lining of postcapillary and collecting venules of the striated muscle tissue. Thus, we conclude that in this model of generalized inflammation nutritive perfusion failure and loss of endothelial integrity in distant striated muscle is not mediated by activated leukocytes, but must rather be attributed to direct toxic effects of mediators, elicited by the local (intraperitoneal) zymosan challenge and systemically released.

Animals↗
PubMed1998

Experimental intracoronary stenting: comprehensive experience in a porcine model.

Appropriate animal models for intracoronary stenting are most important for improving understanding of the pathophysiology of acute occlusion and long-term re-stenosis, which currently limits the safety and efficacy of percutaneous transluminal coronary angioplasty in humans. Since the anatomy and physiology of swine coronary arteries closely resemble those of humans, the procine model should be ideal for testing of stents. This is a comprehensive report on an experimental set-up in pigs, communicating in detail the necessary techniques as well as some modifications facilitating safe intracoronary stent placement and successful follow-up studies for weeks or months. Stent procedure is performed in mechanically ventilated and haemodynamically monitored animals under balanced anaesthesia. Intracoronary application of flow wires allows the assessment of local flow conditions, flow properties and coronary flow reserve. Real-time intravascular ultrasonography (IVUS) provides detailed information on coronary morphology and enables the appropriate sizing of the coronary lumen. From our own experience, we like to propose that the use of the porcine model has the potential to gain new insights into the pathophysiology of intracoronary stent placement-associated complications and allows for the study of modifications in techniques and materials, and the development of novel pharmacological therapeutic strategies.

Angioplasty, Balloon, Coronary↗
PubMed1998

[Differential effect of preservative solutions (UW vs HTK) on mitochondrial redux status and energy metabolism during liver ischemia with oxygen persufflation].

Venous-systemic oxygen persufflation (VSOP) was performed in rat livers stored at 4 degrees C in either UW or HTK preservation solution. Since tissue anoxia is associated with a transformation of cellular NAD+ to NADH and the latter fluoresces upon UV-epiillumination, homogeneity and intensity of liver oxygenation could be analysed by intravital microscopic detection of NADH fluorescence. VSOP resulted in a significant decrease of the NADH signal, documenting effective tissue oxygenation in both UW and HTK. This effect was quite homogeneous (spatial variance < 15%). After 48 h of cold storage tissue levels of ATP (mumol/g dry weight) were increased upon VSOP in UW to 17.3 +/- 4.8 but only to 2.9 +/- 0.6 in HTK, while ATP amounted to less than 0.4 without VSOP in either of the groups. It is concluded that VSOP is an appropriate tool to prevent alterations of the hepatic redox status during ischemic preservation in UW and HTK. Metabolic preservation of energy-rich adenine nucleotides seems to be largely improved in combination with UW compared with HTK.

Adenosine↗
PubMed1998

[Differential modulation of CINC, NOSII and ICAM- gene expression in parenchyma and non-parenchyma cells of the liver by G-CSF--possible protective mechanisms of endotoxin-associated hepatotoxicity].

In endotoxin-exposed rat livers, G-CSF caused a reduction of CINC gene transcripts in the nonparenchymal cell fraction, which might be the mechanism for attenuation of microvascular leukocyte adherence and leukocyte-dependent tissue injury, as observed upon G-CSF application in a model of endotoxin-induced hepatotoxicity.

Animals↗
PubMed1998

In vivo analysis of hepatic NADH fluorescence. Methodological approach to exclude Ito-cell vitamin A-derived autofluorescence.

Assessment of hepatic surface NADH fluorescence is complicated by questions concerning the relative contribution of Ito cell-associated vitamin A autofluorescence, which cannot be distinguished from each other using ultraviolet epi-illuminated microfluorographs. However, as presented herein, vitamin A autofluorescence can easily be eliminated due to its rapid photobleaching property. In line with in vitro studies on liver perfusion reported by Suematsu and coworkers (1993b), we assessed NADH fluorescence in liver surface regions, which were epi-illuminated for elimination of vitamin A autofluorescence and were allowed to recover for 20 min prior to onset of the experiment. To assess whether this procedure is stringent for accurate estimation of NADH fluorescence, we studied NADH fluorescence in non prebleached surface regions after a 30 sec and 60 sec epi-illumination period. Epi-illumination of these hepatic surface regions for more than 20 sec guaranteed also complete elimination of vitamin A autofluorescence (Vollmar et al., 1996) and further allowed to calculate the subsequent loss of NADH fluorescence due to a potential photobleaching effect after 30 sec and 60 sec of continuous light exposure. Corresponding data of the present study reveal a constant loss of NADH fluorescence of approximately 20% due to its photobleaching property over the time period from 20-60 sec of epi-illumination. Linear regression analysis of the kinetics of NADH fluorescence upon continuous light exposure allowed the calculation of the initial NADH fluorescence, excluding the interference with the Ito cell vitamin A-derived autofluorescence. The concurrency of this mathematically assessed value for the initial (non-bleached) NADH fluorescence within normal hepatic livers with the recovered value of NADH fluorescence allows the conclusion that the procedure for elimination of vitamin A autofluorescence, including ultraviolet epi-illumination with a subsequent NADH recovery period of at least 20 min, is not a prerequisite for the reliable assessment of intraindividual changes of hepatic NADH fluorescence in vivo. Thus, valid assessment of hepatic NADH fluorescence in vivo can be performed by analyzing initial NADH fluorescence bleaching kinetics, and does not necessarily require the 20 min recovery period after bleaching of the Ito cell vitamin A-derived autofluorescence.

Animals↗
PubMed1997

Pentoxifylline reduces venular leukocyte adherence ("reflow paradox") but not microvascular "no reflow" in hepatic ischemia/reperfusion.

Postischemic reperfusion injury is caused by microcirculatory disturbances, including both nutritive perfusion failure (no reflow) and leukocyte activation (reflow paradox). Recent studies brought evidence that pentoxifylline (PTX) reduces tissue injury, decreases enzyme release, and improves survival after normothermic liver ischemia/reperfusion. The mechanisms of action, however, by which PTX protects postischemic tissue from injury have not been elucidated yet. With the use of fluorescence microscopy in a rat hepatic ischemia/reperfusion model, we studied in vivo the action of PTX on the manifestation of postischemic sinusoidal perfusion failure and microvascular leukocyte adherence. Microvascular reperfusion after 20 min portal triad cross-clamping was characterized by the cessation of blood flow within individual sinusoids (no reflow) and accumulation of leukocytes within the hepatic microvasculature, with stasis in sinusoids and rolling and firm adherence in postsinusoidal venules. PTX (20 mg/kg x hr i.v.) significantly (P < 0.05) attenuated microvascular leukocyte accumulation (44,600 +/- 1833 mm(-3) vs 67,684 +/- 2620 mm(-3) in saline-treated controls) and firm adherence of leukocytes in postsinusoidal venules (316.9 +/- 40.9 mm(-2) vs 522.9 +/- 95.0 mm(-2)); however, PTX did not influence manifestation of individual sinusoidal perfusion failure. Since reperfusion-induced parenchymal cell damage was found reduced in treated animals, we conclude that PTX attenuates postischemic injury in rat liver by reduction of leukocytic/inflammatory response but not by prevention of nutritive perfusion failure.

Animals↗
PubMed1997

Biophysical aspects of liver aeration by vascular persufflation with gaseous oxygen.

BACKGROUND: Venous systemic oxygen persufflation of the liver (i.e., gaseous insufflation of oxygen via the venous vascular system) has proven to be an effective tool for preventing anoxic tissue injury during extended time periods of ischemic preservation. It also allows for an improved recovery of the persufflated organ after orthotopic transplantation. METHODS: Biophysical aspects of the persufflation technique with regard to persufflation pressure (9 mmHg versus 18 mmHg) and oxygen concentration (pure oxygen versus air) in the persufflation gas were investigated in rat livers, using epi-illumination microscopic detection of autofluorescence of NADH, which accumulates in anoxic tissue. RESULTS: We demonstrated that a low-pressure persufflation (9 mmHg) is as sufficient as a higher pressure persufflation (18 mmHg) in oxygenating the ischemic organ. Moreover, oxygenation of the liver was found to be complete and rather homogeneous upon the pure oxygen persufflation, irrespective of the insufflation pressure used. In contrast, insufflation of air instead of pure oxygen resulted in insufficient aeration of the liver, even at the higher persufflation pressure of 18 mmHg. CONCLUSIONS: Our results indicate that the oxygen concentration of the persufflation gas rather than the persufflation pressure is a determinant of successful tissue oxygenation during cold storage.

Animals↗
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↗