bluuebunny/crossref_metadata_2025 huggingface dataset:
Exposure and effects assessment of resident mink (Mustela vison) exposed to polychlorinated dibenzofurans and other dioxin-like compounds in the Tittabawassee River basin, Midland, Michigan, USA
Authors: Zwiernik Matthew J , Kay Denise P , Moore Jeremy , Beckett Kerrie J , Khim Jong Seong , Newsted John L , Roark Shaun A , Giesy John P
Published: April 2008

Historically, sediments and floodplain soils of the Tittabawassee River (TR; MI, USA) have been contaminated with polychlorinated dibenzofurans (PCDFs), polychlorinated dibenzo-p-dioxins (PCDDs), and polychlorinatedbiphenyls (PCBs). Median concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEQs) based on 2006 World Health Organization tetrachloro-dibenzo-p-dioxin toxic equivalency factors (TEFs) in the diet of mink (Mustela vison) ranged from 6.8 × 10−1 ng TEQ/kg wet weight upstream of the primary source of PCDF to 3.1 × 101 ng TEQ/kg wet weight downstream. Estimates of toxicity reference values (TRVs) derived from laboratory studies with individual PCDDs/PCDFs and PCB congeners or mixtures of those congeners, as well as application of TEFs, were compared to site-specific measures of mink exposure. Hazard quotients based on exposures expressed as concentrations of TEQs in the 95th percentile of the mink diet or liver and the no-observable-adverse-effect TRVs were determined to be 1.7 and 8.6, respectively. The resident mink survey, however, including number of mink present, morphological measures, sex ratios, population age structure, and gross and histological tissue examination, indicated no observable adverse effects. This resulted for multiple reasons: First, the exposure estimate was conservative, and second, the predominantly PCDF congener mixture present in the TR appeared to be less potent than predicted from TEQs based on dose–response comparisons. Given this, there appears to be great uncertainty in comparing the measured concentrations of TEQs at this site to TRVs derived from different congeners or congener mixtures. Based on the lack of negative outcomes for any measurement endpoints examined, including jaw lesions, a sentinel indicator of possible adverse effects, and direct measures of effects on individual mink and their population, it was concluded that current concentrations of PCDDs/PCDFs were not causing adverse effects on resident mink of the TR.
Oxidative stress and growth inhibition in the freshwater fish Carassius auratus induced by chronic exposure to sublethal fullerene aggregates
Authors: Zhu Xiaoshan , Zhu Lin , Lang Yupeng , Chen Yongsheng
Published: April 2008

The rapid growth of nanotechnology is stimulating research concerning the potential environmental impacts of manufactured nanomaterials. The present study summarizes, to our knowledge, the first examination regarding the potential effects of chronic exposure (32 d) of aquatic organisms (juvenile carp [Carassius auratus]) to sublethal concentrations (0.04–1.0 mg/L) of fullerene aggregates (nC60/aq; i.e., C60 suspended in water after long-term stirring) with average diameters of approximately 349 and/or 1,394 nm. The results demonstrated that the antioxidant enzymes superoxide dismutase and catalase were induced significantly in the gills and liver of C. auratus exposed to nC60/aq for 32 d, whereas a nonenzymatic antioxidant, glutathione, decreased in all tested tissues. In addition, lipid peroxidation (LPO) levels decreased in most cases, especially in the gills and brain, but exposure to 1.0 mg/L of nC60/aq led to a significant (p < 0.01) increase in the LPO level in the liver. This increase in LPO level in combination with the observed oxidative stress suggested that the liver might be the target of or most susceptible organ to nC60/ aq exposure. Furthermore, the body weight and total length of juvenile carp exposed to 1.0 mg/L of nC60/aq for 32 d decreased significantly (p < 0.05), indicating that nC60 /aq had an inhibitory effect on fish growth. The present findings imply that the oxidative stress induced by long-term exposure could be the main mechanism of the toxicity of nC60/aq to juvenile carp. This important work contributes to a better understanding of the potential health effects of exposure to manufactured nanomaterials on species in aquatic ecosystems.
Accuracy of chronic aquatic toxicity estimates determined from acute toxicity data and two time–response models
Authors: Barron Mace G , Raimondo Sandy , Russom Christine , Vivian Deborah N , Yee Susan H
Published: April 2008

Traditionally, chronic toxicity in aquatic organisms and wildlife has been determined from either toxicity test data, acute to chronic ratios, or application of safety factors. A more recent alternative approach has been to estimate chronic toxicity by modeling the time course of mortality as determined in standard acute toxicity tests, but these approaches have received limited validation. The accuracy of chronic toxicity estimates from two time–response models, linear regression analysis (LRA) and accelerated life testing (ALT), was investigated using a dataset of more than 150 matched species pairs of standard acute toxicity test data and measured chronic no-observed-effect concentrations (NOECs). Chronic survival was more accurately modeled by both ALT (accuracy, 69%) and LRA (accuracy, 76%) than was reproduction, growth, or the most sensitive endpoint (accuracy, 50–60%). In general, LRA estimates of chronic toxicity were less conservative than ALT estimates, with 66 to 79% of LRA estimates being greater than the measured NOEC. Acute datasets with early mortality produced estimates of chronic survival that were more accurate (ALT, 92%; LRA, 89%) compared to all datasets but were less conservative (84% of ALT estimates were overestimated vs 93% of LRA estimates). Acute datasets with late mortality resulted in poor ALT and LRA estimates of chronic toxicity for all endpoints. Additional survival time measurements did not improve the accuracy of ALT or LRA estimates of chronic toxicity over the standard four acute measurement times (24, 48, 72, and 96 h). The time course of mortality should be considered when applying time–response models to estimate chronic aquatic toxicity, with greater accuracy likely for chronic survival than for growth or reproduction.
Cenozoic gravity tectonics in the northern Gulf of Mexico induced by crustal extension. A new interpretation of multichannel seismic data
Authors: Rangin Claude , Le Pichon Xavier , Flotté Nicolas , Husson Laurent
Published: April 2008

The Gulf of Mexico margin in Texas is one of the most impressive examples of starved passive margin gravity collapse systems. Growth faults developed upslope and are compensated down slope by toe folding and thrusting. On the basis of new multi-channel seismic data with high penetration (down to 11 s-twtt) we present evidences for deep crustal extension and rifting that have enhanced superficial sliding. This hypothesis is supported by a significant heat flow anomaly and crustal thinning independently deduced from gravity data. This Cenozoic rifting episode is tectonically linked to left lateral motion along the Rio Bravo fault, a reactivated branch of the Texas lineament.
Thermal regime of the NW shelf of the Gulf of Mexico. Part A: Thermal and pressure fields
Authors: Husson Laurent , Henry Pierre , Le Pichon Xavier
Published: April 2008

The thermal field of the Gulf of Mexico (GoM) is analyzed from a comprehensive temperature-depth database of about 8500 bottom hole temperatures and reservoir temperatures. Our stochastic analysis reveals a widespread, systematic sharp thermal gradient increase between 2500 and 4000 m. The analysis of the pressure regime indicates a systematic correlation between the pressure and temperature fields.
Thermal regime of the NW shelf of the Gulf of Mexico Part B : Heat flow
Authors: Husson Laurent , Le Pichon Xavier , Henry Pierre , Flotte Nicolas , Rangin Claude
Published: April 2008

We restore the steady state heat flow of the NW shelf of the GoM by removing the transient effects of sedimentation, erosion and compaction. We estimate sedimentation and erosion rates for the NW margin of the GoM from stratigraphic data and vitrinite reflectance data, respectively, and show that they both affect significantly the thermal field. We perform a thermal modeling for 166 wells within the Texan shelf. We conclude that there is a general southeastward increase in the heat flow. This increase also correlates with major tectonic features of the NW shelf of the GoM. We propose that the main zones of extension, of fast recent sedimentation, and crustal thinning are due to geologically recent lithospheric thinning responsible for the higher heat flow.
The Rio Bravo fault, a major late Oligocene left-lateral shear zone
Authors: Flotte Nicolas , Martinez-Reyes Juventino , Rangin Claude , Le Pichon Xavier , Husson Laurent , Tardy Marc
Published: April 2008

It has generally been assumed that the last major compressive deformation in the Sierra Madre Oriental (Mexico) took place during the Laramide orogenesis (Upper Cretaceous – Early Eocene). We have studied the N120° Rio Bravo fault zone probably inherited from the Jurassic opening of the gulf of Mexico. This fault zone is located along the international boundary between United States and Mexico. We demonstrate that it was active mainly during the Oligocene. In the Ojinaga area (Chihuahua), the Sierra Madre Occidental, Oligocene volcanic sequences overlying conformably the sedimentary Upper Cretaceous sequence, are both tightly folded before 30 Ma. We think this folding is associated with motion of a major left-lateral fault, the Rio Bravo left lateral fault. These left-lateral fault system affects also the Sabinas fold-belt and extends below the Burgos bassin. This deformation is also imaged by gravimetric data and the offsets the Palaeocene-Eocene oil fields that are displaced left laterally. We propose that during the Oligocene, this ~1000 km long left-lateral shear zone that might be called the Rio Bravo fault was active during the Oligocene with a total offset of 40–60 km.
Open-Surface Digital Microfluidics
Authors: Yoon Jeong-Yeol
Published: April 2008

Open-surface digital microfluidics refers to droplet manipulations in an open surface. Different chemical/
biological reaction protocols can easily be demonstrated in the same device by reprogramming the order of droplet
manipulations. While continuous-flow or liquid-plug microfluidics within microchannels have inherently limited programmability,
there is no limit of reprogrammability in open-surface digital microfluidics. Three different mechanisms for
droplet manipulations are addressed in this mini-review: electrowetting-on-dielectric, magnetofluidics and wire-guide
manipulations. Brief theories of surface tension and work of adhesion are addressed. Potential applications are addressed
as well as their complications.
Experimental and Theoretical Steady State Maximum Temperature Localization along an Exothermic Tubular Chemical Reactor
Authors: Vernières-Hassimi L. , Abdelghani-Idrissi M.A. , Seguin D.
Published: April 2008

This article deals with the experimental and theoretical localization of steady state maximum temperature along
an exothermic tubular reactor in counter current flow configuration; which represents a key parameter for safety in the
chemical engineering processes. The fluid flowing in the inner tube is a mixture of sodium thiosulfate solution in reaction
with hydrogen peroxide. To control the reactive fluid temperature, the inner tube is cooled with a refrigerant fluid flowing
through the annular space. The steady state is obtained from the resolution of the nonlinear partial differential equations
with the McCormack numerical method. The steady state temperature of the reactive fluid along the tubular reactor presents
a maximum value due to the exothermic chemical reaction. The maximum temperature value which represents the
critical point of the reactor is investigated. In particular its localization is studied for the first time according to various parameters
such as flow rates, reactant concentrations and inlet temperatures.
Testing Tinto: How Do Retention Theories Work for First-Generation, Working-Class Students?
Authors: Longwell-Grice Rob , Longwell-Grice Hope
Published: April 2008

This article presents results of a multiple case study involving four first-generation, working-class, white male college freshmen who discuss their perceptions of faculty support. These perceptions are analyzed using Tinto's theories of student retention, specifically as they relate to faculty-student interaction. The study found that first-generation, working-class students are intimidated by the idea of seeking out faculty for support, resulting in a lack of support from their faculty. Since Tinto's theories find a strong link between faculty support and student retention, this study suggests that colleges need to be more strategic and systematic in finding ways to develop faculty-student interactions for first-generation, working-class college students.
Early Childhood Experience in Nepal: A Study of Sickness, Treatment and Mortality
Authors: Carlaw Raymond W. , Pande Badri Raj , Vaidya Kokila , Nakermi Basundhara
Published: April 2008

This article reports on a longitudinal study of almost 7,000 children under six years in selected villages in Nepal, giving their morbidity and mortality history, treatments given and costs involved. The study suggests that about two children out of three are defined as sick by their mothers in any given year and that treatment is sought for about 40 percent of sickness in small children. Three of four children treated are treated by scientific medicine, that is by physicians, nurses or pharmacists. The principal causes of death are fevers and diarrhea. Education of mothers in spacing of births, hygiene, nutrition and rehydration therapy would appear to be the most important primary health care service, along with increased access to potable water and to medical clinics.
Multiple Methods for Workshop Evaluation
Authors: Saarlas Kristin Nicholson , Paluku Kalenga M. , Roungou Jean-Baptiste , Bryce Jennifer W. , Naimoli Joseph F. , Benzerroug El Hadi
Published: April 2008

Evaluation is a necessary component of all training, including workshops. Evaluation can provide information about the teaching and learning that occur during a workshop and document the extent to which long-term objectives were achieved after a workshop. Multiple methods for evaluating the process and outcomes of a regional workshop on Program Planning and Management for Malaria Control were developed and implemented by an evaluation team composed of African program managers and technical assistance partners, all of whom served as workshop trainers. Among the five methods used to assess the process of workshop implementation and participant satisfaction, a questionnaire administered at the close of the two-week workshop was found least useful in improving the training. Much more useful were the results of daily trainers' meetings and of two qualitative evaluation methods: large group feedback sessions and focused group discussions. Among the three methods used to evaluate the workshop outcomes, a review of the quality of the pre- and post-workshop national malaria control program plans by a panel of experts was found to be the most useful in providing information about the extent to which learning objectives were achieved. The involvement of trainers in evaluation activities permitted immediate action based on results. Our experience suggests that during brief workshops, evaluation should not compete with training activities for time and resources but must be considered an essential part of the curriculum. Effective and efficient workshop evaluation will require advance planning by trainers, support and training in evaluation methods for all members of the evaluation team, and advance consideration of how evaluation results will be summarized and translated into action.
Graphics and Ethos in Biomedical Journals
Authors: Hutto David
Published: April 2008

This article describes a study that examined the tables and figures in articles from a basic research journal, The Journal of Cell Biology, and compared them to tables and figures from an applied medical journal, The New England Journal of Medicine. Comparison of graphics between the two journals shows sharp differences in terms of range of graphics types, visual consistency within and between articles, or use of color. As the articles take into account what is needed by different audiences, the graphics help to build the credibility of the journal. The study also addresses the question of how scientific visuals contribute to the persuasiveness of a writer, looking at how the graphics within an article affect the credibility or ethos of the writer.
Toward a Critical Perspective of Culture: Contrast or Compare Rhetorics
Authors: Wang Junhua
Published: April 2008

Kaplan's framework of contrastive rhetoric has been widely accepted in the field of cross-cultural technical communication. However, in the last four decades, contextual factors such as economic globalization trend and the advances of communication technologies are changing our ways of interacting with others. As a result our understanding of culture and cultural differences need to be adjusted. In this research, I start by recommending a workable definition of culture in the present context—culture as a process, which establishes a foundation for cross-cultural rhetorical research in the new era when communication across cultures transcends national boundaries. Based on the critical perspective of culture, I continue to point out the limitations of contrastive rhetoric and argue that contrastive rhetoric's view of culture and its research purpose and methodology need to be modified to overcome its constraints and better meet the needs of the present social context.
Diversity, Group Identity, and Citizenship Education in a Global Age
Authors: Banks James A.
Published: April 2008

Worldwide immigration and quests for rights by minority groups have caused social scientists and educators to raise serious questions about liberal assimilationist conceptions of citizenship that historically have dominated citizenship education in nation-states. The author of this article challenges liberal assimilationist conceptions of citizenship and citizenship education. He argues that citizenship education should be reformed so that it reflects the home cultures and languages of students from diverse groups, and he contends that group rights can help individuals to attain structural equality. In the final part of the article, he discusses the implications of his analysis for transforming citizenship education.
Hypoxia Increases Superoxide Anion Production from Bovine Coronary Microvessels, But Not Cardiac Myocytes, via Increased Xanthine Oxidase
Authors: KAMINSKI P. M. , WOLIN M. S.
Published: April 2008

Objective: To determine if 30 min of hypoxia (Po2 8–10 Torr) affects basal, mitochondrial, or xanthine oxidase‐derived lucigenin‐detectable superoxide anion (O2.‐) production by intact isolated bovine coronary microvessels and myocytes.

Methods: O2.‐ was quantitated by lucigenin‐elicited chemiluminescence. Antimycin A (10 μM) and hypoxanthine (0.1 mM) were employed to increase O2.‐ from mitochondria and xanthine oxidase, respectively.

Results: Chemiluminescence from microvessels and myocytes was enhanced (∼ twofold, P < 0.05, n = 8–10) by inhibition of Cu,Zn‐SOD via pretreatment with diethyldithiocarbamate (10 mM, 30 min) and was decreased (P < 0.05, n = 8–10) by an intracellular scavenger of O2.‐ (10 mM Tiron), but not by added SOD (3 μM, n = 8–10). In the presence of SOD inhibition, hypoxia produced a hypoxanthine‐dependent (n = 8–10) twofold increase in chemiluminescence (P < 0.05, n = 10) in microvessels but not in myocytes. Other combinations of hypoxia, antimycin, or hypoxanthine did not significantly alter chemiluminescence.

Conclusions: Lucigenin appears to detect a basal intracellular source of O2.‐ in both microvessels and myocytes that is not derived from mitochondria or xanthine oxidase. Exposure to hypoxia does not appreciably increase basal O2.‐ in vessels or myocytes, but if exogenous hypoxanthine is supplied, microvessels show an increase in O2.‐ production presumably derived from xanthine oxidase.
Quantitative Laser Scanning Confocal Microscopy on Single Capillaries: Permeability Measurement
Authors: ADAMSON R. H. , LENZ J. F. , CURRY F. E.
Published: April 2008

Objective: We tested the hypothesis that there is significant solute loss to the superfusate during microvessel solute permeability measurement in frog mesentery which leads to underestimation of permeability coefficient. This is the first application of laser‐scanning confocal microscopy to measure microvessel permeability.

Methods: Microvessel permeability to sodium fluorescein (0.5 mg/ml, MW 376) was measured in the presence of bovine serum albumin (10 mg/ml) in Ringer's solution. Every 11–12 s an optical section transverse to the vessel axis (x‐z section) was collected. The images were corrected for fluorescence attenuation in the z direction and nonuniformity of light collection (shading) in the x direction by comparison to a fluorescent standard. Extravascular fluorescence, which increased linearly with time, and the step increase in fluorescence intensity of the vessel lumen were used to calculate an apparent permeability. Measurements were made first with the tissue superfused with Ringer and second after changing the superfusate to mineral oil in order to retain solute potentially lost to Ringer superfusate.

Results: The permeability to fluorescein measured with Ringer superfusate (5.0 ± SD 2.6 × 10−5 cm/s; n = 3) was not different from that measured with mineral oil covering the upper mesothelial surface (4.5 ± 1.9).

Conclusions: Therefore, the loss of sodium fluorescein through the upper mesothelium does not significantly alter permeability under these conditions. These techniques enable detailed analysis of solute concentration gradients surrounding microvessels.
Specific 125I Neuropeptide Y Binding to Intact Cultured Bovine Adrenal Medulla Capillary Endothelial Cells
Authors: SANABRIA P. , SILVA W. I.
Published: April 2008

Objective: This study involved the pharmacological detection and characterization of binding sites for the neuromodulator neuropeptide Y (NPY) in an in vitro preparation of capillary endothelial cells derived from bovine adrenal medulla.

Methods: Equilibrium binding assays were conducted on intact cells with 125I Bolton‐Hunter labeled NPY (125I‐BH‐NPY). The specificity of the high‐affinity binding site was evaluated in competition experiments with cold NPY, (Leu31, Pro34)NPY (a Y1 receptor ligand, Y1RL), NPY13–36 (a Y2 receptor ligand, Y2RL), and two other members of the pancreatic polypeptide‐fold (PP‐fold) family: peptide YY (PYY) and avian pancreatic polypeptide (APP). Forskolin‐stimulated adenylate cyclase activity was assessed to detect the participation of this second messenger pathway in the neuromodulator action at the studied cell preparation.

Results: Nonlinear regression analysis of the binding data indicated the existence of high‐affinity binding sites with an equilibrium dissociation constant (Kd) value of 39.00 ± 12.84 nM and a maximal binding (Bmax) of 489.89 ± 155.49 fmol/106 cells (mean ± SE, n = 6). NPY, Y1RL, and PYY displayed a concentration that inhibits the specific binding by 50% IC50 (nM) values of 4.06 ± 1.66 (n = 4), 2.94 ± 0.75 (n = 5), and 18.36 ± 10.36 (n = 3), respectively. APP and Y2RL were unable to compete with 125I‐NPY in the concentration range 0.001–1 μM. Further evaluation of second messenger pathways suggested that NPY binding sites in this model are coupled to the inhibition of adenylate cyclase. NPY significantly inhibited the forskolin‐stimulated adenosine cyclic 3′,5′‐(hydrogen phosphate) (cAMP) accumulation with a maximal effect of 37.03 ± 6.28%, n = 5 and an IC50 of 5.96 ± 1.87 nM. The Y1RL produced a comparable response (IC50 = 5.35 ± 1.39 nM, n = 4; maximal inhibition of 61.05 ± 13.03%) and Y2LR had no detectable effect at a similar concentration range.

Conclusions: The results demonstrate the existence of a Y1 receptor in the adrenal medulla capillary endothelial cells, which may be relevant to the postjunctional effect of NPY on this gland.
Mechanisms of Lactoferrin‐induced Leukocyte‐Endothelial Cell Adhesion in Postcapillary Venules
Authors: Asako Hiroshi , Kurose Iwao , Wolf Robert E. , Granger D. Neil
Published: April 2008

Objective: The objective is to determine the contributions of electrostatic charge, endothelial cell adhesion glycoproteins (P‐ and E‐selectins), and histamine to lactoferrin‐induced leukocyte adhesion in postcapillary venules.

Methods: Rat mesentery was prepared for intravital microscopic observation. Erythrocyte velocity, vessel diameter, leukocyte rolling velocity, number of adherent and emigrated leukocytes, and velocity, flux, and number of rolling leukocytes were monitored in mesenteric venules (25–35 μm initial diameter). After control measurements were obtained for all parameters, lactoferrin, other cationic proteins (histone or α‐chymotrypsinogen A), or transferrin (an anionic iron‐binding protein) were infused into the superior mesenteric artery, with repeat measurements taken 20 min into the infusion period. In other lactoferrin experiments, animals were treated with either a monoclonal antibody (MAb) directed against P‐ or E‐selectin, an H1‐ or H2‐histamine receptor antagonist, or diamine oxidase (histaminase).

Results: Increased numbers of rolling and adherent leukocytes were observed during infusion of lactoferrin, histone, or α‐chymotrypsinogen A but not with transferrin. The leukocyte‐endothelial cell adhesion (LECA) elicited by lactoferrin was substantially greater than that induced by histone and α‐chymotrypsinogen A. The P‐selectin MAb completely prevented lactoferrin‐induced LECA, whereas the E‐selectin MAb had no effect. Diamine oxidase and the H1− (but not the H2−) receptor antagonist were also effective in attenuating lactoferrin‐induced LECA.

Conclusions: These results indicate that lactoferrin‐induced LECA results from histamine‐mediated expression of P‐selectin on venular endothelial cells. The cationic nature of lactoferrin accounts for only a small part of its proadhesive actions.
Upregulation of Na+‐dependent Alanine Transport in Vascular Endothelial Cells by Serum: Role of Intracellular Ca2+
Authors: Escobales Nelson , Martinez Jose , Gonzalez Orlando
Published: April 2008

Objective: Amino acid transport and its regulation in vascular endothelial cells remains a largely unexplored area. In this study, we evaluated alanine transport in bovine aortic endothelial cells to assess possible mechanisms of regulation.

Methods: Alanine transport into confluent monolayers of endothelial cells was measured using 100 μM [3H]alanine in the presence and absence of external Na+, in cells deprived of serum for 24 hr (SD), and in SD cells exposed to 10% serum (S) for 3 hr (SD + S cells).

Results: Our results indicate that although SD did not significantly affect the Na+‐independent transport of alanine when compared to normal cells, serum addition to serum‐deprived cells markedly stimulated the Na+‐dependent uptake of this amino acid through system A. The stimulation of alanine transport pathway(s) by serum was totally abolished by pretreatment of endothelial cells with 10 μM. cycloheximide, suggesting a role of protein synthesis. Serum also induced a marked increase in calcium recycling at the cell membrane, suggesting that calcium is a key element of the serum signaling pathway. Indeed, both BAPTA (20 μM), a cellular calcium chelator, and thapsigargin (1 μM), an agent that depletes intracellular calcium stores, prevented the stimulation of alanine uptake by serum. Finally, pertussis toxin (400 ng/ml), an agent known to inactivate certain G‐protein‐dependent pathways, significantly reduced the serum‐dependent 45Ca uptake and [3H]alanine entry. However, the protein kinase C activator PMA (100 nM), significantly reduced the stimulation of alanine uptake by serum but did not affect the stimulation of calcium uptake.

Conclusions: Altogether these findings suggest that cell calcium is involved in the regulation of system A by serum in vascular endothelial cells.
Fiber Matrix Descriptors from Permeability Data Without Requiring Membrane Thickness: Theory, Results, and Optimization
Authors: Katz Murray A. , Lamarche Margaret
Published: April 2008

Objective: Permeability of basement membrane and all other barriers contains a term for membrane thickness (Δx). This naturally leads to development of methods for measuring Δx that are imprecise, inaccurate, expensive, subject to preparation artifact, and inattentive to variability. Although height and shape of permeability (P) vs. probe radius (α) curves are sensitive to Δx, ln(P) or ln(P/free diffusivity or Do) curves have shapes independent of Δx. It should, thus, be possible using such characteristics to determine fiber radius (rf) and void volume ratio (ε) without Δx. We developed such a method to derive membrane structure by the standard model of Ogston and present its experimental evaluation.

Methods: Basement membranes were self‐assembled using 1: 1 Matrigel: 0.01 M Tris/150 mM NaCl/1.0 mM CaCl2 buffer on 0.4‐μ polycarbonate supports with transport measured in diffusion chambers using FITC‐labeled hydroxyethyl starch probes from 25 to 102 Å in radius. Sampling was at 0.5 hr and then for each hour up to 5. Other membranes were measured 7 days after formation.

Results: The best fit of the new technique occurred at 3 hr with R2 = 0.949 ± 0.003 SEM, rf = 36.8 ± 2.4 Å, and ε = 0.87 ± 0.02. Membranes studied for 7 days showed more variability but essentially the same characteristics.

Conclusions: Membrane thickness is not necessary to reduce permeability of basement membrane to structure, and optimum sampling time is 3 hr.
Transglomerular Transport of DEAE Dextran in the Isolated Perfused Kidney
Authors: Adal Yalçin , Pratt Lynette , Comper Wayne D.
Published: April 2008

Objective: The renal fractional clearance of [3H]DEAE dextran has been widely used to substantiate the charge selective model for renal permselectively, although there has only been one reported study on this type of clearance. This study sets out to examine the fractional clearance and glomerular processing of DEAE dextran.

Methods: Fractional clearance studies were performed using isolated perfused rat kidneys. The glomerular processing of DEAE dextran was assessed by examining the kinetics of DEAE dextran uptake in glomerluli isolated post perfusion.

Results: The fractional clearance of DEAE dextran used in the concentration range of 15–150 μg/ml in the perfusate of the isolated perfused kidney did not produce the classical in vivo facilitated transport of DEAE dextran as compared to dextran as observed by Bohrer et al. The fractional clearance curve displays retarded clearance of low molecular weight (small radii) DEAE dextran, giving the appearance of a ‘flat curve’. Similar results were obtained when an oxygen free radical scavenger cocktail was included in the perfusate. These results may be due to the fact that DEAE dextran binds to the glomeruli (at an order of magnitude greater than dextran sulfate). Perfused kidneys with [3H]DEAE dextran for 1 h followed by a five minute perfusion with unlabelled DEAE dextran revealed no significant change in the glomerular levels of [3H]DEAE dextran (unlike dextran sulfate). Perfusion of rat kidneys with 15 μg/ml DEAE dextran produced no changes in the electron microscopical morphology of the glomerulus and no changes in the fractional clearance of dextran.

Conclusions: These results do not support the glomerular charge selectivity model that involves a non‐binding electrostatic interaction of the charged dextran with the fixed anion charges of the glomerular capillary wall.
Regional Changes in Capillary Supply in Skeletal Muscle of Interval‐Sprint and Low‐Intensity, Endurance‐Trained Rats
Authors: Gute Dean , Laughlin M. Harold , Amann John F.
Published: April 2008

Objective: Exercise training produces regional increases in blood flow capacity among muscle fibers that experience increased activity during exercise. We tested the hypothesis that this increase is partially due to capillary angiogenesis among muscle fibers with large increases in activity during exercise training bouts.

Methods: Two training programs were evaluated: a program consisting of 10–12 weeks of exposure to low‐intensity (30 m/min, 0 incline, 60 min/day) (LET) exercise bouts, 5 days/week, and a second program consisting of 8–10 weeks of exposure to repetitive bouts (6/day) of sprint (60 m/min, 15% incline) exercise, alternating running (2.5 min) and recovery (4.5 min), 5 days/week (IST). Cage‐confined rats were utilized (SED) as controls. After training was completed, rat hindquarters were perfusion‐fixed with modified Karnovsky's fixative. Transverse sections from soleus (Sol), and red (GR), mixed (GM), and white (GW) portions of gastrocnemius muscle were prepared to evaluate capillarization. Sections were analyzed using the Olympus Cue 2 Image Analyzer to determine capillary/muscle fiber ratio (C/F), number of capillary profiles per square millimeter of muscle area (CND), capillary surface area per volume of tissue, and capillary volume density.

Results: Average area per muscle fiber and sarcomere length did not differ among groups. LET did not affect capillarization of the GW, whereas increasing C/F in GM (2.3 ± 0.1 versus 2.1 ± 0.1 for SED) and GR (3.0 ± 0.1 versus 2.6 ± 0.1 for SED). IST increased C/F and CND in GW (1.6 ± 0.1 versus 1.3 ± 0.0 for SED and 657 ± 74 versus 418 ± 53 for SED, respectively) and increased C/F ratio in GM (2.3 ± 0.1 versus 2.1 ± 0.1 for SED). IST did not increase capillarization of the GR. The capillarization of the soleus muscle was not affected by either exercise training program.

Conclusions: IST increased capillarization in muscle tissue composed of a high percentage of fast glycolytic fibers (GW and GM) and LET increased capillarization of muscle tissue composed of a high percentage of fast oxidative‐glycolytic fibers (GM and GR).
Influence of Microvascular Architecture on Oxygen Exchange in Skeletal Muscle
Authors: Pittman Roland N.
Published: April 2008

The normal function of skeletal muscle requires that a continuous supply of oxygen be provided by the cardiovascular system. This article reviews the development of our understanding of the role of microvascular architecture on the oxygen transport system, with emphasis on direct microcirculatory observations and mathematical modeling dating from the work of August Krogh to present studies. The contributions of the various elements of the vascular network (i.e., arterioles, capillaries, and venules) and microvascular hemodynamics to oxygen exchange are discussed. Oxygen moves through the microvascular network by convection, almost all of it being reversibly bound to the hemoglobin within red blood cells. Thus, the flow properties and distribution of the red cells within the network can play a significant role in oxygen transport. Because the walls of all the vessels in the microcirculation appear to be permeable to oxygen, it continuously diffuses between the blood and the interstitium, the direction depending on the oxygen partial pressure difference. Because of the high permeability of the vascular wall to oxygen, the complex spatial relationships among the various microvessels lead to correspondingly complex diffusive interactions among them. The proximity of capillaries, arterioles, and venules, along with the anastomotic connections and tortuosity of capillaries, provides the “complex spatial relationships” that lead to diffusive interactions between neighboring capillaries, between capillaries and nearby arterioles and venules, and between paired arterioles and venules. Although there are a number of outstanding problems regarding our understanding of oxygen transport at the microcirculatory level, the most interesting and significant of these has to do with the adjustments that are made in the transition from the resting state to that of sustained aerobic exercise.
Estimation of In Vivo Pulmonary Microvascular and Interstitial Geometry Using Digital Image Analysis
Authors: VENTUROLI DANIELE , CRISAFULLI BEATRICE , DEL FABBRO MASSIMO , NEGRINI DANIELA , MISEROCCHI GIUSEPPE
Published: April 2008

Objective: To determine microvascular diameter and perivascular interstitium thickness at the lung surface in the in situ, in vivo lung.

Methods: Microscopic images of the lung surface collected through a “pleural window” by a videocamera were digitized with a monochrome frame grabber (512 × 512 pixels, 8 bits per pixels) to be computer analyzed by image processing techniques.

Results: We found that the maxima in the distribution of the standard deviations of gray levels in adjacent neighbors 7 × 7 pixels wide identify the edges between the microvessel lumen and the surrounding perivascular interstitium. Furthermore, the maxima in the distribution of the standard deviation of the standard deviations of gray levels identify the edges between the perivascular interstitium and the lung tissue.

Conclusions: This technique can be applied to microvessels ranging in diameter from 30 μm to 200 μm and perivascular interstitial thickness of the order of 10–150 μm. Our approach allows for the definition of microvascular geometry even for noisy images and represents an improvement compared to other edge detection methods. The proposed analytical procedure may provide a useful tool to study lung fluid balance and microvascular reactivity in the in situ lung in the normal state and in response to a variety of functional conditions.
Renal Medullary Microcirculation: Architecture and Exchange
Authors: MICHEL C. C.
Published: April 2008

The architecture of the renal medullary microcirculation is highly specialized. Consistent with their role in countercurrent exchange, the vessels (the vasa recta and the intervening capillaries) have high permeabilities to fluid and small hydrophilic solutes. The urea permeability of the continuous endothelium of the descending vasa recta (DVR) in the outer medulla is greatly enhanced by a urea transporter. Aquaporin channels have also been identified in these vessels. In spite of the absence of lymphatics from the inner medulla, fluid uptake from the interstitial fluid (ISF) through the fenestrated endothelium of the ascending vasa recta (AVR) appears to be driven by differences in hydrostatic and oncotic pressure. Because the AVR have high Lp's [10−5 cm s−1 (cm H2O)−1] and are mechanically linked to surrounding structures, small increments of ISF pressures above the pressure within the AVR can drive significant volumes of fluid into AVR if ISF volume expands. The lower reflection coefficients to serum albumin of the AVR as compared with the DVR may be important in the clearance of interstitial plasma protein. Recent work on isolated DVR from the outer medulla has revealed that these vessels are capable of vasoconstriction and thus of regulating medullary blood flow.
Thromboxane Contributes to Submaximal Coronary Dilation During Myocardial Ischemia
Authors: ELLER BRIAN T. , BROOKS LEONARD A. , DELLSPERGER KEVIN C.
Published: April 2008

Objectives: Thromboxane has been shown to contribute to coronary constriction in conduit coronary arteries during platelet aggregation at the site of a critical stenosis. Previous studies from our laboratory suggest that following a critical coronary stenosis, persistent vasomotor tone occurs. We tested the hypothesis that thromboxane is responsible for that increased tone.

Methods: To test this hypothesis, 14 mongrel dogs of either sex were anesthetized and subjected to a critical coronary stenosis where distal coronary perfusion pressure was reduced to 36 ± 2 mm Hg. During the coronary stenosis, SQ 29,548 (thromboxane/endoperoxide receptor antagonist) was administered intravenously (0.2 mg/kg and 2.0 mg/kg). Coronary microvascular responses were observed by directly visualizing the epicardial microcirculation. Diameters were measured using intravital microscopy coupled to stroboscopic epi‐illumination and jet ventilation to compensate for cardiac and respiratory‐induced motion.

Results: Coronary microvessels were divided into small (< 150 μm) and large (> 150 μm) arterioles. During SQ 29,548 administration, small coronary arterioles demonstrated no additional dilation during a critical coronary stenosis. In contrast, coronary microvessels > 150 μm demonstrated a dose‐dependent vasodilation to SQ 29,548 (0.2 mg/kg: 6 ± 2%; 2.0 mg/kg: 11 ± 4%; P < 0.05 vs. no change). A time control study in six additional animals demonstrated no significant coronary microvascular diameter changes following a critical stenosis over the time course of SQ 29,548 administration.

Conclusion: Endoperoxides contribute to poststenotic microvascular vasoconstriction in vessels 150–300 μm.
Nitric Oxide Affects Microvascular Permeability in the Intact and Inflamed Vasculature
Authors: Kubes Paul
Published: April 2008

There is a growing body of evidence that nitric oxide modulates the movement of fluid and protein out of the vasculature. However, the results obtained from whole organ, single vessel, and endothelial monolayer studies are often not consistent. In fact, there is much evidence that endogenous nitric oxide increases microvascular permeability and equally compelling evidence to suggest that endogenous nitric oxide decreases microvascular permeability. In this review we summarize and critically evaluate the data published to date regarding the role of nitric oxide as a modulator of microvascular permeability under both normal conditions and following exposure to various stimuli. The last section of the chapter discusses the importance of nitric oxide as a modulator of microvascular permeability in inflammatory conditions. Particular emphasis is placed on the stimuli used, the organ systems studied, and the measurements performed to investigate the effects of nitric oxide on microvascular permeability alterations.
Type II Collagen Is a Major Component of Bovine Retinal Microvessel Extracellular Matrix
Authors: SWINSCOE JOHN C. , CARLSON EDWARD C.
Published: April 2008

Objective: To determine which interstitial collagen types may be present in bovine retinal microvessel extracellular matrix (ECM).

Methods: Dissociated bovine microvessels were treated with detergents and the resultant purified ECM monitored by transmission electron microscopy (TEM). Pepsin‐extracted soluble ECM collagens were identified by Western blots. Collagens were further purified by neutral salt precipitation and carboxymethyl cellulose (CMC) chromatography before cyanogen bromide (CNBr) peptide mapping and two‐dimensional peptide mapping of CMC‐generated fractions. Interstitial collagens were localized by immunofluorescence on frozen sections.

Results: Transmission electron microscopy of detergent‐purified microvessel ECM demonstrated numerous 10–50‐nm collagen fibrils associated with basal laminae regardless of vessel diameter. Western blots showed that soluble ECM collagens were strongly positive for type II, moderate for type III, and weak for type I. CNBr peptide maps and two‐dimensional maps of neutral salt and CMC‐purified fractions confirmed the presence of type II collagen. Immunofluorescence localized type II collagen in large and small vessels of the retina.

Conclusions: Type II collagen is an unexpected major component of bovine microvessel ECM, whereas types I and III are present in minor amounts. Type V collagen is also a substantial ECM component. Accordingly, all four types may contribute to a heterogeneous population of collagenous fibrils identified by TEM in intact isolated retinal microvessel ECM.
Visualization of Endothelial Clefts and Nuclei in Living Microvessels with Combined Reflectance and Fluorescence Confocal Microscopy
Authors: He P. , Adamson R. H.
Published: April 2008

Objective: The cellular basis for spatial heterogeneity along postcapillary venules in their response to inflammatory mediators is not understood. To study permeability regulatory processes on an individual cell basis in intact microvessels, we developed methods to delineate individual endothelial cells within living, single perfused microvessels.

Methods: Individual postcapillary microvessels in the mesenteries of frogs and hamsters were perfused with chloride‐free Ringer's solutions containing AgNO3 (0.1 g per 100 ml) for 5–10 s. Vessels were immediately flushed with Ringer's solution containing serum albumin and some vessels subsequently perfused with the fluorescent nucleic acid stain YO‐PR0‐1 (1 μM) for 10–15 min. Vessels were imaged in situ using laser scanning confocal microscopy. A reflectance image from silver precipitate in the endothelial clefts and a fluorescence image of the nuclei were simultaneously recorded. Stacks of confocal images were merged and used to reconstruct the three‐dimensional orientation of endothelial cells. Hydraulic conductivity of some frog mesenteric venular vessels, measured before and after perfusion with AgNO3, was used to assess the integrity of the vessels.

Results: The endothelial cell clefts were delineated with a very fine, readily imaged precipitate of silver. Hydraulic conductivity measured after AgNO3 perfusion in frog mesenteric venular microvessels was not significantly different from control. Vessels showed a slight reduction in reactivity to inflammatory stimuli. The three‐dimensional pattern of endothelial cells in the living vessels was imaged.

Conclusions: Combining confocal microscopy with silver staining in single perfused microvessels was shown to be an effective means to delineate the three‐dimensional pattern of endothelial cells forming microvessel walls. It enables further study of the vascular structure and function relationships at the individual cell level in intact microvessels.
Putrescine: A Novel Inhibitor of Glycosylation‐Induced Cross‐Links in Laniinin
Authors: TSOPANOGLOU NICOS E. , ZIOUDROU CHRISTINE , TSILIBARY EFFIE C. , CHARONIS ARISTIDIS S.
Published: April 2008

Objective: To determine whether putrescine, a naturally occuring polyamine, is able to prevent nonenzymatic glycosylation‐induced cross‐linking of basement membrane components. Cross‐linking, leading to the formation of advanced glycosylation end products (AGEs) has been proposed as a major mechanism contributing to structural and functional changes of the vascular wall, thus leading to microangiopathy.

Methods: Laminin, a major basement membrane glycoprotein present in the microvasculature, was isolated and incubated in the presence of high glucose concentrations, in order to generate an in vitro diabetic environment. Putrescine was either present or absent from the incubation mixture. Formation of cross‐links was assessed by two independent methods: gel electrophoresis and development of characteristic fluorescence.

Results: Putrescine inhibited in a dose‐dependent manner the formation of slower mobility bands in gel electrophoresis. Quantitation of the development of fluorescence characteristic of glycosylation‐induced cross‐links demonstrated that putrescine inhibited the formation of fluorescent products.

Conclusions: Putrescine may be a promising compound for inhibition of protein cross‐linking and, therefore, could be used in the prevention of diabetic microangiopathy.