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B W Zweifach

Publications and source records attributed to B W Zweifach.

At least 19 recordsLinked to original sources
PubMed1999

Protective role of adrenal glucocorticoids for gastric mucosa in spontaneously hypertensive rats.

BACKGROUND: Spontaneously hypertensive rats (SHR) are a representative animal model for disturbance of the pituitary-adrenal axis, as well as disturbance of the autonomic nervous system. METHODS AND RESULTS: In this study, we showed that adrenalectomy in SHR-induced spontaneous gastric ulcer formation. We further investigated how abnormal adrenal secretion is related to the attenuation of gastric ulcerogenesis, in terms of leucocyte infiltration and nitric oxide (NO) formation. Bilateral adrenalectomy, as well as a sham-operation, were carried out at 12 weeks in hypertensive SHR and Wistar-Kyoto rats (WKY) and observations were made three weeks later. The number of myeloperoxidase (MPO) positive cells, NADPH diaphorase histochemistry and NO synthase (NOS) activity were determined in gastric specimens. Only in adrenalectomized, but not sham-operated SHR, WKY and adrenalectomized WKY, could gastric ulcers be observed. Although the number of cells positive for MPO was significantly lower in hypertensive SHR than those in WKY, such cells were increased after adrenalectomy in SHR. In contrast, adrenalectomized WKY developed no increase in MPO-positive numbers. The number of NADPH diaphorase-positive cells increased after adrenalectomy in both strains, the extent of which was much greater in SHR than in WKY. Although NOS activity in SHR was lower than that in WKY, it was significantly increased after adrenalectomy. CONCLUSIONS: Our data show that the development of a significant gastric ulceration may be associated with entrapment of activated leucocytes in the gastric mucosa, as well as with an excessive production of NO in adrenalectomized SHR. An enhanced adrenal glucocorticoid may be a key factor for protecting the gastric mucosa in SHR.

Adrenal Cortex↗
PubMed1999

Mast cell degranulation and parenchymal cell injury in the rat mesentery.

OBJECTIVE: The objective of this study was to explore the degree of parenchymal cell injury after mast cell degranulation by application of compound 48/80 (CMP 48/80) in the absence of adherent leukocytes in the rat mesentery. METHODS: Rats were rendered leukopenic by injection of an antibody against leukocytes, and the mesentery was superfused with CMP 48/80 during intravital microscopy. The extent of cell injury was determined using a fluorescent cell-viability indicator, propidium iodide (PI). In an additional group, mast cell degranulation with CMP 48/80 was prevented by using the mast cell stabilizer Ketotifen. RESULTS: After a reduction in the number of circulating leukocytes, mast cell degranulation produced a mild increase in parenchymal cell injury. The injury levels significantly increased when individual regions of the mesentery were compared. Stabilization of the mast cells with Ketotifen reduced the injury to below baseline values. CONCLUSIONS: In the absence of leukocyte adhesion to the endothelium, mast cell degranulation contributes to parenchymal cell injury in the mesentery.

Animals↗
PubMed1998

Xanthine oxidase activity associated with arterial blood pressure in spontaneously hypertensive rats.

Recent evidence in vivo indicates that spontaneously hypertensive rats (SHR) exhibit an increase in oxyradical production in and around microvascular endothelium. This study is aimed to examine whether xanthine oxidase plays a role in overproduction of oxidants and thereby may contribute to hypertensive states as a consequence of the increasing microvascular tone. The xanthine oxidase activity in SHR was inhibited by dietary supplement of tungsten (0.7 g/kg) that depletes molybdenum as a cofactor for the enzyme activity as well as by administration of (-)BOF4272 [(-)-8-(3-methoxy-4-phenylsulfinylphenyl)pyrazolo(1,5-alpha)-1,3, 5-triazine-4-monohydrate], a synthetic inhibitor of the enzyme. The characteristic elevation of mean arterial pressure in SHR was normalized by the tungsten diet, whereas Wistar Koto (WKY) rats displayed no significant alteration in the pressure. Multifunctional intravital videomicroscopy in mesentery microvessels with hydroethidine, an oxidant-sensitive fluoroprobe, showed that SHR endothelium exhibited overproduction of oxyradicals that coincided with the elevated arteriolar tone as compared with WKY rats. The tungsten diet significantly repressed these changes toward the levels observed in WKY rats. The activity of oxyradical-producing form of xanthine oxidase in the mesenteric tissue of SHR was approximately 3-fold greater than that of WKY rats, and pretreatment with the tungsten diet eliminated detectable levels of the enzyme activity. The inhibitory effects of the tungsten diet on the increasing blood pressure and arteriolar tone in SHR were also reproducible by administration of (-)BOF4272. These results suggest that xanthine oxidase accounts for a putative source of oxyradical generation that is associated with an increasing arteriolar tone in this form of hypertension.

Animals↗
PubMed1998

Mechanisms of cell injury in rat mesentery and cremaster muscle.

The events responsible for cell injury after a tissue stimulation are only incompletely understood. The purpose of this study was to examine mechanisms of cell injury in two tissues, rat mesentery and cremaster muscle, after tissue stimulation with N-formylmethionyl-leucyl-phenylalanine (FMLP) and platelet-activating factor (PAF). The response was studied in the same animal in random order using normal and leukopenic rats. The tissues were exteriorized after pentobarbital anesthesia. Five to six vascularized areas were chosen in each tissue, and cell injury and hydroperoxide production were assessed visually by continuous superfusion with 1 microM propidium iodide and 5 microM dichlorofluorescin diacetate (DCFH), respectively. FMLP (1 x 10(-8) M) and then PAF (1 x 10(-8) M) were added to the superfusate, and measurements were made at several time points. The second tissue was then examined using the same protocol. In the cremaster, there was little hydroperoxide production, and the tissue injury was eliminated after leukopenia. Leukopenia had no effect on tissue injury in the mesentery. Although hydroperoxide production was observed, there was no correlation between it and the tissue injury. The level of preactivation showed no correlation with either tissue injury or hydroperoxide production. In light of these results, mast cell degranulation may be an important mechanism of tissue injury in the mesentery.

Abdomen↗
PubMed1997

The leukocyte response to fluid stress.

Leukocyte migration from a hemopoietic pool across marrow endothelium requires active pseudopod formation and adhesion. Leukocytes rarely show pseudopod formation while in circulation. At question then is the mechanism that serves to minimize leukocyte pseudopod formation in the circulation. We tested the hypothesis that fluid shear stress acts to prevent pseudopod formation. When individual human leukocytes (neutrophils, monocytes) spreading on glass surfaces in vitro were subjected to fluid shear stress ( approximately 1 dyn/cm2), an instantaneous retraction of pseudopods was observed. Removal of the fluid shear stress in turn led to the return of pseudopod projection and cell spreading. When steady shear stress was prolonged over several minutes, leukocyte swelling occurs together with an enhanced random motion of cytoplasmic granules and a reduction of cytoplasmic stiffness. The response to shear stress could be suppressed by K+ channel blockers and chelation of external Ca2+. In rat mesentery microvessels after occlusion, circulating leukocytes project pseudopods in free suspension or when attached to the endothelium, even though immediately after occlusion only few pseudopods were present. When flow was restored, pseudopods on adhering leukocytes were retracted and then the cells began to roll and detach from the endothelium. In conclusion, plasma shear stress in the circulation serves to reduce pseudopod projection and adhesion of circulating leukocytes and vice versa reduction of shear stress leads to pseudopod projection and spreading of leukocytes on the endothelium.

Amiloride↗
PubMed1997

Leukocyte contribution to parenchymal cell death in an experimental model of inflammation.

The relationship between leukocyte migration and parenchymal cell death in vivo remains poorly documented. Accordingly, cell killing in the rat mesentery, as recorded by propidium iodide staining, was investigated with an intravital approach. Superfusion of platelet-activating factor (PAF, 10(-8) M) or N-formyl-methionyl-leucyl-phenylalanine (fMLP, 10(-8) M) led to extensive leukocyte extravasation but no significant cell death. In contrast, pretreatment with 10(-8) M PAF or fMLP for 1 h, followed by superfusion of PAF in combination with fMLP (both at 10(-8) M) led to an increase in cell death. Mesenteric parenchymal cells but no endothelial cells were killed. Some of the dead cells were identified as granulocytes/monocytes that were already in the tissue at the start of the experiment. The incidence of cell death was lower but not eliminated when leukocyte migration was blocked with a monoclonal antibody against CD18. A xanthine oxidase inhibitor, BOF-4272, failed to diminish cell death, whereas a hydroxyl radical scavenger, dimethylthiourea, attenuated cell killing without an effect on the number of adhering and migrating leukocytes. These observations demonstrate that leukocytes serve as a factor in the killing of extravascular cells only after the development of a level of stimulation that differs from that required to induce a migratory stimulus into the extravascular space.

Animals↗
PubMed1997

Mechanisms for increased blood flow resistance due to leukocytes.

Despite the small number of leukocytes relative to erythrocytes in the circulation, leukocytes contribute significantly to organ blood flow resistance. The present study was designed to investigate whether interactions between leukocytes and erythrocytes affect the pressure-flow relationship in a hemodynamically isolated rat gracilis muscle. At constant arterial flow rate, arterial pressure was increased significantly when relatively few physiological counts of leukocytes were added to a suspension containing erythrocytes at physiological hematocrits. However, the arterial pressure after perfusion of similar numbers of isolated leukocytes without erythrocytes was only slightly increased. An increase in resistance was also observed when leukocytes were replaced with 6-micron microspheres. We propose a new mechanism for increasing the hemodynamic resistance that involves hydrodynamic interactions between leukocytes and erythrocytes. In the presence of larger and less deformable leukocytes, erythrocytes move through capillaries more slowly than without leukocytes. Therefore erythrocytes are displaced from their axial positions. Slowing and radial displacement of erythrocytes serve to increase the relative apparent viscosity attributable to erythrocytes, thereby causing a significant elevation of organ blood flow resistance.

Animals↗
PubMed1997

Fluid pressures in the rabbit popliteal afferent lymphatics during passive tissue motion.

The mechanisms of pressure and flow generation in the initial lymphatic network remain undefined in many details. Active pump mechanisms by lymph smooth muscle contraction have been demonstrated in collecting lymph ducts while passive mechanisms by periodic lymph compression in noncontractile initial lymphatics have received relative little attention. The aim of this study was to examine lymph flow before and during periodic passive tissue deformation under different lymph outflow pressures. Lymph flow rate and lymph outflow pressure were measured in rabbit popliteal prenodal lymphatics during whole leg rotations. The hind legs were rotated in a sagittal plane at selected frequencies. During constant leg rotation, lymph flow rates reached steady levels which depend on lymph outflow pressure. When lymph outflow was occluded, intralymphatic pressures increased progressively to levels which depend on leg rotation frequency. Both lymph flow rate and pressure showed higher values with foot edema than in the absence of foot edema. These results suggest that periodic tissue deformation, lymph outflow pressure, and interstitial free fluid volume are important determinants of the lymph flow rate.

Animals↗
PubMed1996

Glucocorticoid modulates vasodilator response of mesenteric arterioles in spontaneously hypertensive rats.

We previously reported that the response of the arterioles in spontaneously hypertensive rats (SHR) to histamine is blunted compared with that in normotensive control rats (Wistar-Kyoto rats [WKY]). The present study was designed to analyze the extent to which this blunted arteriolar response may be attributed in SHR to the concurrent elevation of circulating glucocorticoids through the use of adrenalectomy with and without dexamethasone supplementation. Mesenteric arterioles were observed by intravital microscopy under general anesthesia, and their lumen diameters were measured after histamine superfusion. The concentration-response curve with histamine was compared with that of an endothelium-independent vasodilator, sodium nitroprusside. At the end of each experiment, papaverine was applied topically to determine the maximal diameter for each vessel, from which a measure of arteriolar tone could be computed. The arteriolar tone in sham-operated SHR is set at a higher steady-state level than in sham-operated WKY. The concentration required for a 50% dilator response (EC50) of histamine in adrenalectomized SHR was restored to the level of WKY. Adrenalectomy did not significantly affect the EC50 of histamine in WKY. When adrenalectomized SHR received a supplement of dexamethasone, the arteriolar response was found to show the same refractory pattern to histamine as sham-operated SHR. In contrast, the EC50 of sodium nitroprusside in sham-operated and adrenalectomized SHR was similar to that in sham-operated WKY. Our results indicate that the impaired dilator response to histamine in SHR is related to an enhanced adrenal glucocorticoid secretion.

Adrenalectomy↗
PubMed1996

Transvascular and interstitial migration of neutrophils in rat mesentery.

OBJECTIVE: The consequential implications of the leukocyte-endothelial cell adhesion reaction, as well as the subsequent migratory activity of the leukocytes within the interstitium proper, are currently known only in general phenomenological terms. Our objective was to carry out a detailed quantitative analysis of transendothelial and interstitial migration. METHOD: We incorporated several new features, such as the video recording of time-lapse photography in conjunction with the time history of individual leukocytes under the influence of representative stimulators and inhibitors. The mesentery was suffused with the chemical activator N-formyl-met-leu-phe (fMLP, 5 x 10(-8) M) and histamine (10(-6) M) for periods up to 3 h. This leads to an attachment of neutrophils preferentially to the walls of small postcapillary venules followed by migration into the adjacent interstitium. RESULTS: The time interval between the initial neutrophil adhesion to the luminal side of the venules and their first appearance on the abluminal side of the venule wall was about 25 min. The time interval for the actual physical migration across the endothelium was only about 1-2 min. There was an initial increase in the number of neutrophils migrating across the wall per unit time after the application of fMLP. However, this effect then gradually decreased over the course of 1 h. In the extravascular tissue, the neutrophils appeared to migrate along random pathways with an average trajectory away from the venular wall. When histamine (1 microM) was applied topically in conjunction with fMLP, the overall migratory flux across the venular wall increased, although the cells migrated comparatively short distances into the interstitium. After pretreatment with phalloidin (25 micrograms/kg), an actin cross-linking agent, neutrophil adhesion and migration in response to fMLP stimulation was reduced. The mast cell stimulator 48/80 (25 mg/ml) resulted in rapid degranulation, which was accompanied by an insignificant increase in neutrophil diapedesis. After fMLP stimulation there was reduced neutrophil emigration in the presence of mast cell inhibitors, such as lodoxamide (1 microgram/kg) and ketotifin (microgram/kg). CONCLUSIONS: Our results demonstrate that both the endothelial cells and interstitial mast cells are involved in the rate of transvascular migration of leukocytes across postcapillary venules and into the interstitium.

Animals↗
PubMed1995

Neutrophil activation, tumor necrosis factor, and survival after endotoxic and hemorrhagic shock.

Polymorphonuclear neutrophils (PMNs) may contribute to organ injury in both hemorrhagic and endotoxic shock. Both models of shock exhibit a "flight of the leukocytes," but the mechanisms for entrapment of leukocytes in the microcirculation differ. The objective of this study was to investigate lipopolysaccharide (LPS)-induced shock and hemorrhagic shock with similar survival rates, in terms of circulating PMNs, activated circulating PMNs, plasma tumor necrosis factor (TNF) activity, and PMN adhesion. In the LPS protocol, rats received 6.5 mg/kg E. coli LPS i.v., which resulted in 50% survival. In the hemorrhagic shock protocol, rats were maintained for 3 h at 40 mm Hg mean arterial pressure, and survival during a 24-h observation period was 40%. LPS injection and hemorrhage caused rapid neutropenia in survivors and nonsurvivors. Low circulating PMN counts persisted during hypotension in the hemorrhagic protocol and among nonsurvivors in the LPS protocol, but in both protocols a tendency toward significantly higher circulating PMN counts in survivors compared with nonsurvivors was found. In both protocols, survivors had significantly lower fractions of circulating activated PMNs and lower adhesion of circulating PMNs to nylon fibers. In the LPS protocol, higher plasma TNF activity was found in nonsurvivors than in survivors, but no TNF activity in plasma could be found throughout the hemorrhagic protocol. These results indicate that nonsurvivors in both shock models exhibit higher levels of PMN activation. No correlation was detected between PMN activation and plasma TNF activity to suggest that TNF serves as the primary mediator of circulating PMN activation.

Animals↗
PubMed1995

In vivo evidence for microvascular oxidative stress in spontaneously hypertensive rats. Hydroethidine microfluorography.

The factors that predispose to the accelerated organ injury that accompanies the hypertensive syndrome have remained speculative and without a firm experimental basis. Indirect evidence has suggested that a key feature may be related to an enhanced oxygen radical production. The purpose of this study was to refine and use a technique to visualize evidence of spontaneous microvascular oxidative stress in vivo in the spontaneously hypertensive rat (SHR) compared with its normotensive control, the Wistar-Kyoto rat (WKY). We investigated the effects of adrenal glucocorticoids on the microvascular oxidative stress sequence. The mesentery was superfused with hydroethidine, a reduced, nonfluorescent precursor of ethidium bromide. In the presence of oxidative challenge, hydroethidine is transformed intracellularly into the fluorescent compound ethidium bromide, which binds to DNA and can be detected by virtue of its red fluorescence. The fluorescent light emission from freshly exteriorized and otherwise unstimulated mesentery microvessels was recorded by digital microscopy. The number of ethidium bromide-positive nuclei along the arteriolar and venular walls in SHR was found to be significantly increased above the level exhibited by WKY. The elevation in ethidium bromide fluorescence in SHR arterioles could be attenuated by a synthetic glucocorticoid inhibitor and in rats subjected to adrenalectomy. The administration of glucocorticoids after adrenalectomy by injection of dexamethasone restored the oxidative reaction in SHR arterioles. Treatment with dimethylthiourea and with a xanthine oxidase inhibitor attenuated the superoxide formation. Although a nitric oxide synthase inhibitor (NG-nitro-L-arginine methyl ester) enhanced the ethidium bromide staining in WKY, it did not affect that in SHR.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Vasodilator response of mesenteric arterioles to histamine in spontaneously hypertensive rats.

Recent evidence suggests that spontaneously hypertensive rats (SHR) exhibit an impaired response to inflammatory mediators. We designed this study to analyze the response of arterioles of SHR after stimulation with a proinflammatory agent, histamine, compared with the response of arterioles of normotensive Wistar-Kyoto (WKY) controls. We observed mesenteric arterioles by intravital microscopy in rats under general anesthesia and measured their lumen diameters after histamine superfusion. To compare the concentration-response curve with histamine, we also studied the effect of an endothelium-dependent vasodilator, acetylcholine, and an independent vasodilator, sodium nitroprusside. At the end of each experiment we applied papaverine topically to determine the maximal diameter for each vessel, from which we computed arteriolar tone. Arteriolar tone in SHR is set at a higher steady state level than in WKY. The concentration required for a 50% dilator response (EC50) of histamine in SHR was significantly higher than that in WKY. In SHR the arteriolar response showed the same refractory pattern to histamine as to acetylcholine. In contrast, the EC50 of sodium nitroprusside in SHR was similar to that in WKY. Our results indicate that SHR exhibit an impaired dilator response to histamine that is due to a blunted endothelium-dependent vasodilation.

Animals↗
PubMed1995

Circulating leukocyte counts, activation, and degranulation in Dahl hypertensive rats.

Previous evidence has shown that rats with spontaneous hypertension have on average about twice as many circulating leukocytes in comparison with their normotensive counterparts, the Wistar-Kyoto rats. Since such high levels of leukocytes may increase the risk for vascular complications for hypertensive animals, it is useful to ascertain whether a comparable derangement is present in other forms of hypertension. The present study deals with the properties of the circulating leukocytes in rats exhibiting another form of experimental hypertension; Dahl salt-sensitive (Dahl-S) hypertensive rats were compared with Dahl salt-resistant (Dahl-R) control rats. Measurements were performed to determine the following: circulating hematocrit levels, leukocyte counts, differential counts, number of activated leukocytes (by means of nitro blue tetrazolium [NBT] reduction), leukocyte adhesion in vitro and neutrophil CD-18 expression, alkaline phosphatase activity in individual neutrophils and in the plasma, and myeloperoxidase activity in neutrophils. The experimental cohort consisted of Dahl-S and Dahl-R rats maintained for a 6-week period on a 6% NaCl diet. The results show a highly significant elevation in the number of total leukocytes, neutrophil and monocyte counts, and NBT-positive neutrophils and monocytes in Dahl-S but not Dahl-R rats. There was a significant loss of alkaline phosphatase and myeloperoxidase activity in the neutrophils of the salt-treated Dahl-S rats but not in the neutrophils of the untreated Dahl-S or Dahl-R rats. No significant differences were found in neutrophil adhesion under in vitro test conditions between the two strains maintained on the salt diet.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Impairment of selectin-mediated leukocyte adhesion to venular endothelium in spontaneously hypertensive rats.

The present study was designed to elucidate whether molecular mechanisms for leukocyte adhesion to microvascular endothelium may differ between spontaneously hypertensive rats and Wistar Kyoto rats. Leukocyte rolling and adhesion were investigated while monitoring venular wall shear rates in the mesenteric microcirculation stimulated with histamine or tert-butyl hydroperoxide in the two strains. In Wistar Kyoto rats, 10 microM histamine as well as 500 microM tertbutyl hydroperoxide promoted a significant reduction of venular leukocyte rolling velocity and subsequent adhesion. These changes in leukocyte behavior were blocked by monoclonal antibodies against P-selectin (PB 1.3) and against sialyl Lewis X-like carbohydrates (2H5). However, spontaneously hypertensive rats exhibited a blunted response of the stimulus-elicited leukocyte rolling, which was associated with impairment of venular P-selectin expression as well as a decrease in the expression of sialyl Lewis X-like carbohydrates on circulating neutrophils. No significant differences were detected between the two strains not only in the surface CD11b/CD18 expression but also in the CD18-mediated adhesivity of neutrophils to intracellular adhesion molecule-1 transfectants in vitro. These results suggest that impairment of selectin-mediated leukocyte adhesion is an event responsible for disorders of inflammatory responses in spontaneously hypertensive rats.

Animals↗
PubMed1995

Temporal correlation between maximum tetanic force and cell death in postischemic rat skeletal muscle.

To gain insight into the mechanisms responsible for muscle dysfunction after ischemia-reperfusion, a rat spinotrapezius muscle preparation was developed which enabled sequential measurements of in vivo maximum tetanic force production and cell death assessed using digital microfluorographic determination of propidium iodide (PI) staining. After 60 min of no-flow ischemia, maximum tetanic force fell significantly during 90 min of reperfusion compared with control, nonischemic muscles. The most striking fall was evident within 30 min of reperfusion and occurred concomitant with an explosive increase in PI-positive myocyte nuclei. Treatment with the oxygen radical scavenger, dimethylthiourea, attenuated both the fall in force and increased PI staining. Indeed, the rise in PI-positive nuclei correlated closely (r= 0.728) with the reduction of maximum tetanic force developed following ischemia and reperfusion under all conditions. Superoxide dismutase also attenuated the rise in PI-positive nuclei. Assessment of mitochondrial inner membrane potential (deltapsi) using Rhodamine 123 fluorescence revealed that myocytes with the lowest initial mitochondrial membrane potential were subject to the greatest injury after 90 min of reperfusion (r= 0.828). These results support the hypothesis that myocyte injury, as visualized by PI-staining, reflects an impaired contractile function in fibers with a low oxidative potential which is likely mediated by oxygen radicals.

Animals↗
PubMed1995

Microcirculatory homeostasis 1930-1990: insight into microcirculatory readjustments provided by studies on the peripheral circulatory insufficiency of the shock syndrome.

The present overview is intended to serve several purposes. It highlights efforts over the years to resolve the difficult key issues raised by August Krogh in the 1930s and by the urgent need created in the 1940s and 1950s by World War II to come to grips with the basic problems underlying the collapse of tissue perfusion in the syndrome of circulatory shock. The complex operational issues raised by circulatory insufficiency at the systemic, as well as the local tissue level, during the shock syndrome, are used as a framework to keep in perspective the impact of advances in methodology, ultrastructure, and in recent years in molecular biology on microvascular research. In view of the current continuing need to integrate the newly emerging body of in vitro information into specific aspects of the operation of the peripheral vascular tree, emphasis is placed on the advances in dealing with data provided by in vivo microscopy of selected tissues. This overall review had made it clear that a top priority remains the need to separate the effects of systemic and locally derived readjustments, and to identify the basis for the substantial differences in cellular behavior exhibited by the vascular and perivascular components of the various organs and tissues of the body that can serve as predisposing factors in regional pathophysiology.

Homeostasis↗