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Biomedical subjects

S Bartos

Publications and source records attributed to S Bartos.

At least 19 recordsLinked to original sources
PubMed1998

Cellular and molecular mechanisms of radiation inhibition of restenosis. Part I: role of the macrophage and platelet-derived growth factor.

PURPOSE: The major radiobiological issue in determining the rationale for the use of radiation to inhibit vascular restenosis is the identification of the target cell(s) and/or cytokine(s) responsible for neointimal hyperplasia and vascular remodeling. The central hypothesis of this report is that the macrophage/monocyte and PDGF are key elements in the process of neointimal hyperplasia seen following angioplasty, similar to their role in lesion formation and progression found in atherosclerotic thickening. Specific immunohistochemical and cytochemical stains were applied to a rat carotid model in a temporal series after balloon angioplasty to determine macrophage activity vs. smooth muscle cell proliferation, the latter being classically thought to be the cell responsible for restenosis. METHODS AND MATERIALS: Neointimal hyperplasia was created in an established rat carotid artery model by a balloon catheter technique. Immediately following injury, treatment groups received irradiation via high dose rate (HDR) brachytherapy, the 192Ir source being placed externally to the vessel. Radiation was delivered to a length of 2 cm of the injured vessel at doses of 5, 10, and 15 Gy, and the animals were sacrificed at various time points following treatment (24 h to 6 months). Serial sections of tissue were stained immunohistochemically with the primary antibodies CD11b, mac-1, anti-PDGF, and alpha-smooth muscle actin. RESULTS: Immediately (24 h) postinjury, there is an apparent migration of macrophages seen in the adventitia; after 1 week, proliferation and migration of macrophages could be seen clearly within all the vessel layers, especially in the intima; by 3 weeks, when there was evidence of neointimal hyperplasia, macrophages could still be seen, mainly in the intima scattered among the smooth muscle cells and myofibroblasts, and to a lesser degree at 6 months. There was corresponding expression of PDGF, whenever and wherever there were zones of activation/neointimal hyperplasia. Alpha-smooth muscle actin staining identified the smooth muscle cells distinct from the macrophages, and these SMCs exhibited activation in the neointimal hyperplasia zones at all later time points. Furthermore, we showed that radiation significantly reduced the macrophage population, while the onset of neointimal hyperplasia was accompanied by a return of the macrophage population. CONCLUSION: Our results suggest that the activated adventitial macrophage/monocyte are the key cells responsible for initiating the arterial neointimal hyperplasia and vascular remodeling developing postangioplasty as they are in the initiation and perpetuation of atheromatous thickening. Irradiation delivered immediately postinjury is, therefore, highly effective, because the macrophage population is exquisitely radiosensitive.

Animals↗
PubMed1998

Multiple nitric oxide sources in neurogenic plasma extravasation in rat hindpaw skin.

The contribution of nitric oxide (NO) to capsaicin-evoked plasma extravasation was studied in rat hindpaw skin. Two inhibitors of NO synthase were used: 7-nitroindazole, with a selectivity for nerve-derived NO, and the L-arginine derivative, N(omega)-nitro-L-arginine (L-NOARG), which is a non-selective inhibitor. Plasma extravasation was induced by intraplantar injection of 5 microg/50 microl capsaicin and measured by the Evans blue leakage technique. Both acute and chronic administration of 7-nitroindazole significantly reduced capsaicin-evoked plasma extravasation in rat hind-paw skin, whereas L-NOARG enhanced it. This enhancement was abolished non-stereospecifically by either L- or D-arginine. Our results suggest that NO production from different sources yields a complex action in maintaining the endothelial integrity in neurogenic plasma extravasation.

Animals↗
PubMed1997

Fate of the proximal aortic cuff: implications for endovascular aneurysm repair.

PURPOSE: Long-term success of endoluminally placed grafts for exclusion of abdominal aortic aneurysms (AAAs) relies on secure fixation at the proximal and distal cuffs and, as such, assumes that the fixation sites will not dilate over time. Data regarding this issue, however, are not yet available. This study was performed to evaluate the region of the proximal anastomosis in patients many years after having undergone conventional AAA repair to determine the potential for late dilatation after placement of an endoluminal device. METHODS: Three hundred forty-six patients underwent repair of an infrarenal AAA at our institution between January 1985 and December 1990. Of 97 eligible living patients, 33 both had their original CT scans available and underwent repeat scanning at a mean of 88.6 +/- 23.8 months (mean +/- SD; range, 40 to 134 months) after repair. RESULTS: The overall 5-year survival rate was 73%. The mean preoperative infrarenal aortic cuff diameter by CT scan was 24.5 +/- 3.7 mm (range, 19 to 33 mm). At an average of 89 months after repair, the mean infrarenal aortic diameter increased 4.3 mm to 28.8 +/- 7.7 mm (range, 20 to 52 mm; p = 0.0004 by t test). The proximal cuff at this time measured 30 mm or more in 11 patients (33%), and as early as 6 years after operation three of the seven patients (43%) scanned within this time period had cuffs that were dilated to 30 mm or more. Late dilatation to 30 mm or more was rare (16%) in patients who had preoperative cuffs that measured 27 mm or less. The mean late iliac artery size was 16.9 +/- 8.9 mm (range, 10 to 52 mm), and 30% (10 of 33) measured 20 mm or more. CONCLUSIONS: One third of all patients who survive AAA repair experience significant dilatation of their proximal aortic cuff over time. Proximal dilatation is rare but not absent in patients who have smaller initial aortic cuff diameters. This dilatation rarely causes problems after conventional suture fixation, but the long-term implications of cuff dilatation after endoluminal repair are unclear. Our findings suggest that endovascular aortic prostheses that have the ability to continue to self-expand many years after implantation may be required and that endovascular prostheses may not be the best option for patients who have a long life expectancy or for those who have preoperative proximal cuffs greater than 27 mm.

Aorta, Abdominal↗
PubMed1997

Primary fibrinolysis during supraceliac aortic clamping.

PURPOSE: An increased incidence of bleeding complications has been observed after supraceliac aortic clamping (SCC). This study was performed to identify possible hemostatic abnormalities that contribute to this problem. METHODS: A prospective cohort study over a 3-month period was performed by comparing hemostatic parameters in 10 consecutive patients who required elective SCC with those of eight concurrent randomly selected control subjects who required infrarenal clamping (IRC) for abdominal aortic reconstruction. Measures of coagulation, fibrinolysis, platelet function, temperature, hemodilution, and hepatic function were performed at selected times before, during, and after operation. RESULTS: Aneurysm size, fibrinogen, D-dimers, prothrombin, partial thromboplastin time, platelet counts, bleeding times, hemodilution, and temperature were comparable in both groups. Patients in the SCC group, however, consistently developed a primary fibrinolytic state within 20 minutes after supraceliac clamping, reflected by significantly decreased euglobulin clot lysis times (ECLT; p < 0.0001), elevated tissue plasminogen activator (t-PA) levels (p < 0.0006), elevated t-PA-to-plasminogen activator inhibitor-1 ratios (p < 0.0001), and reduced alpha 2-antiplasmin levels (p < 0.002). SCC produced hepatocellular injury documented by elevations in both aspartate transaminase (p < 0.0001) and lactate dehydrogenase (p < 0.009). CONCLUSIONS: SCC rapidly induces a primary fibrinolytic state manifested by increased circulating t-PA, reduced alpha 2-antiplasmin, and increased fibrinolytic activator-to-inhibitor ratios. These effects may be a result of hepatic hypoperfusion caused by SCC leading to insufficient clearance of t-PA. Antifibrinolytic agents may be of benefit if bleeding develops after aortic procedures that require supraceliac clamping.

Aged↗
PubMed1991

Influence of redox potential on metabolism of glucose in mixed cultures of rumen microorganisms.

The rumen inocula taken from cows and sheep were incubated in pH controlled anaerobic batch cultures and the effect of the elevated redox potential (Eh) on metabolism of glucose was examined. In Eh regulated cultures (Eh = +100 mV) the VFA production and production of methane were decreased with a concomitant increase of production of lactate. In these cultures counts of lactilytic bacteria tended to be lower and counts of lactic acid bacteria higher than in cultures with a normal Eh. The elevated Eh also exerted an inhibitory effect on the rumen protozoa. The relevance of these changes to the rumen metabolism is discussed.

Animals↗
PubMed1989

The effect of monensin on in vitro utilization of lactate in the rumen contents.

The effect of monensin on the in vitro utilization of lactate in the rumen contents of a steer, cow and two wethers was investigated. The rate of the utilization of lactate in monensin-treated cultures was on average only two thirds of that found in cultures without monensin. Monensin tended to increase acetate and to decrease butyrate in cultures with lactate. After 11-week adaptation of a wether to monensin the inhibitory effect of ionophore persisted, being, however, less pronounced and without influence on the molar percentages of VFA. Effects of monensin reported here seem to be caused by its inhibiting action against rumen lactilytic protozoa. There were no significant differences between monensin from Elanco and the Czechoslovak analogue.

Animals↗
PubMed1989

Metabolism and some characteristics of ruminal strains of Megasphaera elsdenii.

Megasphaera elsdenii belongs to the group comprising the ruminal and intestinal lactate- and sugar-fermenting species. In the present study the fermentation characteristics, metabolism of glucose and lactate, and susceptibility to antimicrobial agents of four ruminal strains were investigated. Particular attention was given to the mixed-substrate fermentation pattern and resultant fermentation acid profile. Lactate was utilized more rapidly than glucose in media with both carbon sources. Interaction of the two substrates changed the composition of fermentation end products toward more valerate and less propionate in cultures with glucose and lactate. Contrary to the indications in Bergey's Manual of Systematic Bacteriology, butyrate, not caproate, was the main end product of glucose metabolism. The strains examined were rather insensitive to many antimicrobial compounds, especially to ionophores and other antimicrobial feed additives.

Animals↗
PubMed1987

Interactions between rumen amylolytic and lactate-utilizing bacteria in growth on starch.

The growth and metabolism of the rumen amylolytic bacteria Streptococcus bovis, Butyrivibrio fibrisolvens and Bacteroides ruminicola, growing in pure cultures and co-cultures with the rumen lactilytic bacteria Megasphaera elsdenii and Veillonella alcalescens were followed. The interaction of amylolytic bacteria with V. alcalescens represents a simple food chain. The interaction with M. elsdenii is more complex, since there is a simultaneous competition for products of the starch degradation.

Animals↗
PubMed1987

The redox potential, rH and pH values in the gastrointestinal tract of small ruminants.

Oxidation-reduction potentials (Eh), pH and rH in the gastrointestinal tract were measured in six goats and two sheep fed on ground barley and hay, with or without the addition of urea. Each ration was supplied for three weeks. The animals were slaughtered after morning feeding, the contents of relevant parts of the gastrointestinal tract were sampled, pH and Eh values were measured and rH values calculated. The range of the oxidation-reduction potential was rather extensive, from -300 to +186 mV. The variability of rH values was smaller, being between 4.6 and 12.9, except for three values. The following linear relationship holds for findings of Eh and pH: Eh (mV) = 292-69.9 pH with a correlation coefficient of r = 0.84. In those parts of the gastrointestinal tract, where the fermentation process occurs (the rumen, caecum and colon), the Eh and rH values are lower than those in the abomasum and duodenum. Urea addition has no effect on the oxidation-reduction equilibrium.

Animal Feed↗
PubMed1986

Stoichiometry of glucose and starch splitting by strains of amylolytic bacteria from the rumen and anaerobic digester.

The stoichiometry of glucose and starch splitting by the amylolytic bacteria Streptococcus bovis, Selenomonas ruminantium, Butyrivibrio fibrisolvens, Eubacterium ruminantium and Clostridium sp. was followed. There were many differences in the ratios of metabolites and in growth yields, as well as in the cell composition, between the growth on glucose and starch. The bacteria employ different nutritional strategies with respect to both energy sources.

Animals↗
PubMed1982

Dynamics of the redox potential and rh of the rumen fluid of goats.

The redox potential (Eh) of the rumen fluid of goats varied from -145 to -190 mV and the corresponding rH values from 6.3 to 8.6. The redox potential values of the rumen fluid were influenced by changes in pH. The most oxidizing Eh values --and at the same time the lowest rH and pH values--were observed after a feeding ration containing readily available carbohydrates. No relationship was found between the fermentation rate and the redox potential. The association between the oxidation reduction state and the metabolic activity is best expressed by the rH values. In in vitro experiments, a higher pH or the addition of cysteine or sodium sulphide moved the redox potential of the rumen fluid towards more reducing values. A shift towards more oxidizing values occurred after acidification of the medium, or after the action of heavy metal ions or atmospheric O2. Various other compounds, including bubbling of the rumen fluid with hydrogen, had little or no effect. SH-groups probably play an important role in the formation of the negative redox potential in rumen fluid.

Animals↗
PubMed1979

[An in-vitro method of ruminal juice cultivation, suitable for the comparison of various sources of nonprotein nitrogen for ruminants].

The method of cultivating rumen fluid in buffer with nutrient admixture under CO2 atmosphere is described. The method serves for the comparison and description of the properties of NPN sources for ruminants. Its applicability is demonstrated on the example of urea. During incubation, all parameters of the medium remain within an admissible range. Considering the analyses of the incubation medium, i. e. determination of the pH value, ammonia, urea, volatile fatty acids, total protein, and redox potential, it is recommended to monitor the course of fermentation for six hours and to take samples in the intervals of 0, 1, 2, 4 and 6 hours.

Animal Feed↗