bluuebunny/crossref_metadata_2025 huggingface dataset:
THE SMALLEST ENCLOSING BALL OF BALLS: COMBINATORIAL STRUCTURE AND ALGORITHMS
Authors: FISCHER KASPAR , GÄRTNER BERND
Published: October 2004

We develop algorithms for computing the exact smallest enclosing ball of a set of n balls in d-dimensional space. Unlike previous methods, we explicitly address small cases (n≤d+2), derive the necessary primitive operations and show that they can efficiently be realized with rational arithmetic. An implementation (along with a fast and robust floating-point version) is available as part of the CGAL library.

We show that Welzl's randomized linear-time algorithm for computing the ball spanned by a set of points fails to work for balls. Consequently, the existing adaptations of the method to the ball case are incorrect. In solving the small cases we may assume that the ball centers are affinely independent. Via a geometric transformation and suitable generalization, it fits into the combinatorial model of unique sink orientations whose rich structure has recently received considerable attention. One consequence is that Welzl's algorithm does work for small instances; moreover, there is a variety of pivoting methods for unique sink orientations which have the potential of being fast in practice even for high dimensions. As a by-product, we show that the problem of finding the smallest enclosing ball of balls with a fixed point on the boundary is equivalent to the problem of finding the minimum-norm point in the convex hull of a union of balls.
POPULATION GENETICS, HISTORY, AND HEALTH PATTERNS IN NATIVE AMERICANS
Authors: Mulligan Connie J. , Hunley Keith , Cole Suzanne , Long Jeffrey C.
Published: October 2004

▪ Abstract  Over the past two decades, detailed studies of mitochondrial DNA and the Y chromosome have increased our understanding of the history and population genetics of Native American populations. Variation in autosomal DNA has also been investigated, but to a more limited extent. A low level of genetic diversity in Native American populations is a robust finding from all lines of evidence. In contrast to the previous multiple migration scenarios for the Pleistocene peopling of the Americas, it now seems that a single migration satisfactorily explains the genetic data. Native Americans show greater genetic similarity to populations in east central Asia than they do to the current easternmost Siberian populations. Recent studies on the Y chromosome indicate a date of entry (about 17,000 years ago) into the Americas roughly consistent with the archaeological record. Native Americans experienced two episodes of reduced population size: one with the peopling of the Americas and the other with European contact. The former is the more important determinant for the number of gene lineages and founding haplotypes seen in populations. It may also be an important determinant of the genetic variation underlying common complex diseases, and especially diabetes. The tribal structure of contemporary Native American populations is relevant to the distribution of rare Mendelian disorders because most tribes constitute relatively small, semi-independent gene pools. This leads us to expect that the allelic spectrum for Mendelian diseases will be simple within individual tribes but complex for Native Americans as a whole.
MAMMALIAN CIRCADIAN BIOLOGY: Elucidating Genome-Wide Levels of Temporal Organization
Authors: Lowrey Phillip L. , Takahashi Joseph S.
Published: October 2004

▪ Abstract  During the past decade, the molecular mechanisms underlying the mammalian circadian clock have been defined. A core set of circadian clock genes common to most cells throughout the body code for proteins that feed back to regulate not only their own expression, but also that of clock output genes and pathways throughout the genome. The circadian system represents a complex multioscillatory temporal network in which an ensemble of coupled neurons comprising the principal circadian pacemaker in the suprachiasmatic nucleus of the hypothalamus is entrained to the daily light/dark cycle and subsequently transmits synchronizing signals to local circadian oscillators in peripheral tissues. Only recently has the importance of this system to the regulation of such fundamental biological processes as the cell cycle and metabolism become apparent. A convergence of data from microarray studies, quantitative trait locus analysis, and mutagenesis screens demonstrates the pervasiveness of circadian regulation in biological systems. The importance of maintaining the internal temporal homeostasis conferred by the circadian system is revealed by animal models in which mutations in genes coding for core components of the clock result in disease, including cancer and disturbances to the sleep/wake cycle.
GENETICS OF ATHEROSCLEROSIS
Authors: Lusis Aldons J. , Mar Rebecca , Pajukanta Päivi
Published: October 2004

▪ Abstract  Atherosclerosis, the primary cause of coronary artery disease (CAD) and stroke, is a disorder with multiple genetic and environmental contributions. Genetic-epidemiologic studies have identified a surprisingly long list of genetic and nongenetic risk factors for CAD. However, such studies indicate that family history is the most significant independent risk factor ( 15 , 52 , 77 ). Many Mendelian disorders associated with atherosclerosis, such as familial hypercholesterolemia (FH), have been characterized, but they explain only a small percentage of disease susceptibility (although a substantial fraction of early CAD). Most cases of myocardial infarction (MI) and stroke result from the interactions of multiple genetic and environmental factors, none of which can cause disease by itself. Successful discovery of these genetic factors will require using complementary approaches with animal models, large-scale human genetic studies, and functional experiments. This review emphasizes the common, complex forms of CAD.
MEDICAL GENETICS IN DEVELOPING COUNTRIES
Authors: Christianson Arnold , Modell Bernadette
Published: October 2004

▪ Abstract  Since Watson & Crick's 1953 description of the structure of DNA, significant progress has been achieved in the control of congenital disorders, most of which has benefited industrialized countries. Little advantage accrued to developing nations, most of which in the same time frame achieved a significant epidemiological transition, resulting in congenital disorders attaining public health significance. The burden of congenital disorders in these lower-resource countries is high and they need to develop medical genetic services. We present a new pragmatic approach for the care and prevention of congenital disorders in these countries, pioneered initially by the World Health Organization.
GENETIC TESTING IN PRIMARY CARE
Authors: Burke Wylie
Published: October 2004

▪ Abstract  Rapid advances in genetic research are leading to an expanding array of genetic tests. Primary care providers will increasingly be challenged to identify patients whose symptoms, physical findings, or family history indicate the need for genetic testing, and to determine how to use genetic information most effectively to improve disease prevention. In addressing these challenges, practitioners will need to consider the range of different uses of genetic testing, including diagnosis in symptomatic and asymptomatic people, risk assessment, reproductive decision-making, and population screening. They will need a set of core skills and knowledge to evaluate family history and to recognize clinical findings that indicate genetic risk. At the same time, the primary care perspective will contribute to the evaluation of appropriate uses of genetic testing. A partnership between medical genetics and primary care will help to ensure the development of effective policies, educational tools, and practice guidelines for the coming era of genomic health care.
AUTISM AS A PARADIGMATIC COMPLEX GENETIC DISORDER
Authors: Veenstra-VanderWeele Jeremy , Christian Susan L. , Cook, Jr. Edwin H.
Published: October 2004

▪ Abstract  Autism is one of the most heritable complex disorders, with compelling evidence for genetic factors and little or no support for environmental influence. The estimated prevalence of autism has increased since molecular genetic studies began, owing to loosening of diagnostic criteria and, more importantly, to more complete ascertainment strategies. This has led to a reduction in the sibling relative risk, but strong heritability estimates remain. It is essential to recognize that genetics is the only current approach to understanding the pathophysiology of autism in which there is not the usual concern about whether one is studying a consequence rather than a cause. There are hundreds, if not thousands, of patients with autism spectrum disorder with documented single-gene mutations or chromosomal abnormalities. Autism may be one of the most complex, yet strongly genetic, disorders in which chromosomal disorders, relatively rare highly penetrant mutations, and multiplicative effects of common variants all have support in different cases and families. The field of complex genetics is replete with many researchers and reviewers who want to promote their overly focused interest in one method at the exclusion of others. However, it is essential that the restricted interests of patients with autism not be reflected in overly restrictive genetic approaches if we are to better understand the genetics of autism in the most expeditious and thorough manner.
Biophysical Analyses of Designed and Selected Mutants of Protocatechuate 3,4-Dioxygenase
Authors: Brown C. Kent , Vetting Matthew W. , Earhart Cathleen A. , Ohlendorf Douglas H.
Published: October 2004

▪ Abstract  The catechol dioxygenases allow a wide variety of bacteria to use aromatic compounds as carbon sources by catalyzing the key ring-opening step. These enzymes use specifically either catechol or protocatechuate (2,3-dihydroxybenozate) as their substrates; they use a bare metal ion as the sole cofactor. To learn how this family of metalloenzymes functions, a structural analysis of designed and selected mutants of these enzymes has been undertaken. Here we review the results of this analysis on the nonheme ferric iron intradiol dioxygenase protocatechuate 3,4-dioxygenase.
The Cellulosomes: Multienzyme Machines for Degradation of Plant Cell Wall Polysaccharides
Authors: Bayer Edward A. , Belaich Jean-Pierre , Shoham Yuval , Lamed Raphael
Published: October 2004

▪ Abstract  The discrete multicomponent, multienzyme cellulosome complex of anaerobic cellulolytic bacteria provides enhanced synergistic activity among the different resident enzymes to efficiently hydrolyze intractable cellulosic and hemicellulosic substrates of the plant cell wall. A pivotal noncatalytic subunit called scaffoldin secures the various enzymatic subunits into the complex via the cohesin-dockerin interaction. The specificity characteristics and tenacious binding between the scaffoldin-based cohesin modules and the enzyme-borne dockerin domains dictate the supramolecular architecture of the cellulosome. The diversity in cellulosome architecture among the known cellulosome-producing bacteria is manifest in the arrangement of their genes in either multiple-scaffoldin or enzyme-linked clusters on the genome. The recently described three-dimensional crystal structure of the cohesin-dockerin heterodimer sheds light on the critical amino acids that contribute to this high-affinity protein-protein interaction. In addition, new information regarding the regulation of cellulosome-related genes, budding genetic tools, and emerging genomics of cellulosome-producing bacteria promises new insight into the assembly and consequences of the multienzyme complex.
Anaerobic Oxidation of Methane and Ammonium
Authors: Strous Marc , Jetten Mike S.M.
Published: October 2004

▪ Abstract  Anaerobic oxidation of methane and ammonium are two different processes catalyzed by completely unrelated microorganisms. Still, the two processes do have many interesting aspects in common. First, both of them were once deemed biochemically impossible and nonexistent in nature, but have now been identified as major factors in global carbon and nitrogen cycling. Second, the microorganisms responsible for both processes cannot be grown in pure culture yet; their detection and identification were based on molecular ecology, tracer studies, use of lipid biomarkers, and enrichment cultures. Third, these microorganisms grow extremely slowly (doubling time from weeks to months). Fourth, both processes have a good potential for application in biotechnology. Because both anaerobic methane and ammonium oxidation have been separately and excellently reviewed elsewhere, we focus on aspects of interest in the context of current developments in microbiology and explore the added value of reviewing these two processes in one place.
Biosynthesis of Nonribosomal Peptides
Authors: Finking Robert , Marahiel Mohamed A.
Published: October 2004

▪ Abstract  Bacteria and fungi use large multifunctional enzymes, the so-called nonribosomal peptide synthetases (NRPSs), to produce peptides of broad structural and biological activity. Biochemical studies have contributed substantially to the understanding of the key principles of these modular enzymes that can draw on a much larger number of catalytic tools for the incorporation of unusual features compared with the ribosomal system. Several crystal structures of NRPS-domains have yielded deep insight into the catalytic mechanisms involved and have led to a better prediction of the products assembled and to the construction of hybrid enzymes. In addition to the structure-function relationship of the core- and tailoring-domains of NRPSs, which is the main focus of this review, different biosynthetic strategies and essential enzymes for posttranslational modification and editing are discussed.
Viral Error Catastrophe by Mutagenic Nucleosides
Authors: Anderson Jon P. , Daifuku Richard , Loeb Lawrence A.
Published: October 2004

▪ Abstract  Riboviruses and retroviruses have the highest rates of mutations of any known organism. Increasing the mutation rate of these viruses could exceed the error threshold for viability of a viral population within a host. Recent experiments with mutagenic nucleoside analogs validate this new approach to treating infection of RNA viruses. Lethal mutagenesis with HIV-infected cells in culture has been documented and has been postulated to be the mechanism for treatment of hepatitis C with ribavirin. We consider the viral dynamics involved in the formation of a quasispecies, the choice of mutagenic nucleoside analogs, and the studies that have demonstrated the feasibility of lethal mutagenesis.
The Ecology and Genetics of Microbial Diversity
Authors: Kassen Rees , Rainey Paul B.
Published: October 2004

▪ Abstract  Natural communities of microbes are often diverse, a fact that is difficult to reconcile with the action of natural selection in simple, uniform environments. We suggest that this apparent paradox may be resolved by considering the origin and fate of diversity in an explicitly ecological context. Here, we review insights into the ecological and genetic causes of diversity that stem from experiments with microbial populations evolving in the defined conditions of the laboratory environment. These studies highlight the importance of environmental structure in governing the fate of diversity and shed light on the genetic mechanisms generating diversity. We conclude by emphasizing the importance of placing detailed molecular-level studies within the context of a sound ecological and evolutionary framework.
Herpes Vector-Mediated Gene Transfer in Treatment of Diseases of the Nervous System
Authors: Glorioso Joseph C. , Fink David J.
Published: October 2004

▪ Abstract  Vectors constructed from recombinant herpes simplex virus (HSV) have special utility for gene transfer to the nervous system. Nonreplicating vectors created by deletion of essential immediate early genes can be propagated to high titers on complementing cell lines that provide the missing gene product(s) in trans. Direct inoculation of these vectors into neural parenchyma is effective in rodent models of brain tumor, Parkinson disease, spinal cord injury, and spinal root trauma. Subcutaneous inoculation of the HSV vectors can be used to transduce neurons of the dorsal root ganglion to provide a therapeutic effect in models of polyneuropathy and chronic regional pain. In human trials, direct injection of replication-competent HSV into brain tumors has proven safe. Human trials of nonreplicating HSV gene transfer by direct inoculation for treatment of glioblastoma and HSV gene transfer by subcutaneous inoculation for the treatment of chronic intractable pain should commence soon.
Early Molecular Investigations of Lichen-Forming Symbionts: 1986–2001
Authors: DePriest Paula T.
Published: October 2004

▪ Abstract  From the mid-1980s the symbionts in lichen associations, heterotrophic fungi and photosynthetic algae or cyanobacteria, were the subject of increasing numbers of molecular investigations. Many of the studies examined the phylogenetic placement of the individual symbiotic partners with their free-living relatives, refining their nomenclature and classification. Resulting phylogenies permitted the mapping of transitions to and from lichenization and stimulated discussion of the relative ease of gaining and losing symbiotic lifestyles. Comparing symbiont phylogenies both rejected strict cospeciation and mirrored phylogenies and hinted at more complex forces of coevolution, including symbiont switching and selection. Studies at the species and population levels examined patterns of species delimitation and geographic dispersion and processes such as gene flow, self-fertilization, and founder effect. Significant genetic variation often was associated with mobile elements, group I and spliceosomal introns. This review examines the influence of molecular investigation on lichenology during this first 15 years.
Pickles, Pectin, and Penicillin
Authors: Demain Arnold L.
Published: October 2004

My professional life has been devoted to the study of microbial products and their biosynthesis, regulation, and overproduction. These have included primary metabolites (glutamic acid, tryptophan, inosinic acid, guanylic acid, vitamin B12, riboflavin, pantothenic acid, ethanol, and lactic acid) and secondary metabolites (penicillin, cephalosporins, streptomycin, fosfomycin, gramicidin S, rapamycin, indolmycin, microcin B17, fumagillin, mycotoxins, Monascus pigments, and tetramethylpyrazine). Other areas included microbial nutrition, strain improvement, bioconversions of statins and β-lactams, sporulation and germination, plasmid stability, gel microdroplets, and the production of double-stranded RNA, the polymer xanthan, and enzymes (polygalacturonase, protease, cellulase). Most of the studies were carried out with me by devoted and hardworking industrial scientists for 15 years at Merck & Co. and by similarly characterized students, postdoctorals, and visiting scientists during my 32 years at the Massachusetts Institute of Technology. I owe much of my success to my mentors from academia and industry. My recent research activities with undergraduate students at the Charles A. Dana Research Institute for Scientists Emeriti (R.I.S.E.) at Drew University have been very rewarding and are allowing me to continue my career.
Selection for Gene Clustering by Tandem Duplication
Authors: Reams Andrew B. , Neidle Ellen L.
Published: October 2004

▪ Abstract  In prokaryotic genomes, related genes are frequently clustered in operons and higher-order arrangements that reflect functional context. Organization emerges despite rearrangements that constantly shuffle gene and operon order. Evidence is presented that the tandem duplication of related genes acts as a driving evolutionary force in the origin and maintenance of clusters. Gene amplification can be viewed as a dynamic and reversible regulatory mechanism that facilitates adaptation to variable environments. Clustered genes confer selective benefits via their ability to be coamplified. During evolution, rearrangements that bring together related genes can be selected if they increase the fitness of the organism in which they reside. Similarly, the benefits of gene amplification can prevent the dispersal of existing clusters. Examples of frequent and spontaneous amplification of large genomic fragments are provided. The possibility is raised that tandem gene duplication works in concert with horizontal gene transfer as interrelated evolutionary forces for gene clustering.
Bacterial Iron Sources: From Siderophores to Hemophores
Authors: Wandersman Cécile , Delepelaire Philippe
Published: October 2004

▪ Abstract  Iron is an essential element for most organisms, including bacteria. The oxidized form is insoluble, and the reduced form is highly toxic for most macromolecules and, in biological systems, is generally sequestrated by iron- and heme-carrier proteins. Thus, despite its abundance on earth, there is practically no free iron available for bacteria whatever biotope they colonize. To fulfill their iron needs, bacteria have multiple iron acquisition systems, reflecting the diversity of their potential biotopes. The iron/heme acquisition systems in bacteria have one of two general mechanisms. The first involves direct contact between the bacterium and the exogenous iron/heme sources. The second mechanism relies on molecules (siderophores and hemophores) synthesized and released by bacteria into the extracellular medium; these molecules scavenge iron or heme from various sources. Recent genetic, biochemical, and crystallographic studies have allowed substantial progress in describing molecular mechanisms of siderophore and hemophore interactions with the outer membrane receptors, transport through the inner membrane, iron storage, and regulation of genes encoding biosynthesis and uptake proteins.
Ribosomal Crystallography: Initiation, Peptide Bond Formation, and Amino Acid Polymerization are Hampered by Antibiotics
Authors: Yonath Ada , Bashan Anat
Published: October 2004

▪ Abstract  High-resolution structures of ribosomal complexes revealed that minute amounts of clinically relevant antibiotics hamper protein biosynthesis by limiting ribosomal mobility or perturbing its elaborate architecture, designed for navigating and controlling peptide bond formation and continuous amino acid polymerization. To accomplish this, the ribosome contributes positional rather than chemical catalysis, provides remote interactions governing accurate substrate alignment within the flexible peptidyl-transferase center (PTC) pocket, and ensures nascent-protein chirality through spatial limitations. Peptide bond formation is concurrent with aminoacylated-tRNA 3′ end translocation and is performed by a rotatory motion around the axis of a sizable ribosomal symmetry-related region, which is located around the PTC in all known crystal structures. Guided by ribosomal-RNA scaffold along an exact pattern, the rotatory motion results in stereochemistry that is optimal for peptide bond formation and for nascent protein entrance into the exit tunnel, the main target of antibiotics targeting ribosomes. By connecting the PTC, the decoding center, and the tRNA entrance and exit regions, the symmetry-related region can transfer intraribosomal signals, guaranteeing smooth processivity of amino acid polymerization.
Cell-Mediated Immunity and the Outcome of Hepatitis C Virus Infection
Authors: Shoukry Naglaa H. , Cawthon Andrew G. , Walker Christopher M.
Published: October 2004

▪ Abstract  The hepatitis C virus (HCV) infects approximately three percent of the world's population. Some individuals resolve the infection spontaneously, but the majority develop persistent viremia that often causes progressive liver disease. There is an emerging consensus that cellular immune responses are essential for spontaneous resolution of acute hepatitis C and long-term protection from persistent infection. This review focuses on the recent advances in understanding mechanisms of protective immunity and why they fail in most infected individuals. The distinct yet complementary role of CD4+ and CD8+ T lymphocytes in this process is highlighted.
Mechanisms of MAdCAM-1 gene expression in human intestinal microvascular endothelial cells
Authors: Ogawa Hitoshi , Binion David G. , Heidemann Jan , Theriot Monica , Fisher Pamela J. , Johnson Nathan A. , Otterson Mary F. , Rafiee Parvaneh
Published: October 2004

Mucosal addressin cell adhesion molecule-1 (MAdCAM-1) is a homing receptor preferentially expressed on gut-associated endothelial cells that plays a central role in leukocyte traffic into the mucosal immune compartment. Although the molecular mechanisms underlying endothelial ICAM-1 or E-selectin expression have been intensively investigated, the mechanisms that regulate human MAdCAM-1 expression have not been defined. We report MAdCAM-1 gene and protein expression in primary cultures of human intestinal microvascular endothelial cells (HIMEC) that was not demonstrated in human umbilical vein endothelial cells. Similar to ICAM-1 and E-selectin expression, MAdCAM-1 gene expression in HIMEC was inducible with TNF-α, IL-1β, or LPS activation. However, in striking contrast to ICAM-1 and E-selectin expression, MAdCAM-1 mRNA and protein expression in HIMEC was heavily dependent on culture duration and/or cellular density, suggesting a prominent role for cell-cell interaction among these endothelial cells in the expression of the mucosal addressin. MAdCAM-1 expression was inhibited by both SN-50 (NF-κB inhibitor) and LY-294002 [phosphatidylinositol 3-kinase (PI3-K) inhibitor], whereas ICAM-1 and E-selectin expression was inhibited by SN-50 but not by LY-294002. The Akt phosphorylation by TNF-α or LPS was greater at higher cell density, demonstrating a pattern similar to that of MAdCAM-1 expression. NF-κB activation was not affected by cellular density in HIMEC. MAdCAM-1 expression in human gut endothelial cells is regulated by distinct signaling mechanisms involving both NF-κB and PI3-K/Akt. These data also suggest that PI3-K/Akt is involved in the gut-specific differentiation of HIMEC, which results in expression of the mucosal addressin MAdCAM-1.
Role of vagus nerve in postprandial antropyloric coordination in conscious dogs
Authors: Ueno Tomio , Uemura Kenichiro , Harris Mary B. , Pappas Theodore N. , Takahashi Toku
Published: October 2004

It is generally believed that gastric emptying of solids is regulated by a coordinated motor pattern between the antrum and pylorus. We studied the role of the vagus nerve in mediating postprandial coordination between the antrum and pylorus. Force transducers were implanted on the serosal surface of the body, antrum, pylorus, and duodenum in seven dogs. Dogs were given either a solid or a liquid meal, and gastroduodenal motility was recorded over 10 h. Gastric emptying was evaluated with radiopaque markers mixed with a solid meal. Dogs were treated with hexamethonium, NG-nitro-l-arginine methyl ester (l-NAME), or transient vagal nerve blockade by cooling. A postprandial motility pattern showed three distinct phases: early, intermediate, and late. In the late phase, profound pyloric relaxations predominantly synchronized with giant antral contractions that were defined as postprandial antropyloric coordination. A gastric emptying study revealed that the time at which gastric contents entered into the duodenum occurred concomitantly with antropyloric coordination. Treatment by vagal blockade or hexamethonium significantly reduced postprandial antral contractions and pyloric relaxations of the late phase. l-NAME changed pyloric motor patterns from relaxation dominant to contraction dominant. Solid gastric emptying was significantly attenuated by treatment with hexamethonium, l-NAME, and vagal blockade. Postprandial antropyloric coordination was not seen after feeding a liquid meal. It is concluded that postprandial antropyloric coordination plays an important role to regulate gastric emptying of a solid food. Postprandial antropyloric coordination is regulated by the vagus nerve and nitrergic neurons in conscious dogs.
Impaired cytoprotective function of muscle in human gallbladders with cholesterol stones
Authors: Xiao Zuo-Liang , Amaral Joseph , Biancani Piero , Behar Jose
Published: October 2004

Acute cholecystitis develops in gallbladders (GB) with excessive bile cholesterol (Ch). Increased membrane Ch content affects membrane function and may affect PGE2receptors involved in the cytoprotection against acute inflammation. This study was aimed at determining whether the cytoprotective response to PGE2is affected by lithogenic bile with Ch. Muscle cells from human GB with cholesterol stones (ChS) or pigment stones (PS) were obtained by enzymatic digestion. PGE2levels were measured by radioimmunoassay, and activities of superoxide dismutase (SOD) and catalase were assayed by spectrophotometry. The contraction in response to H2O2in muscle cells from PS was 14 ± 0.3%, not different from normal controls, and decreased after the cells were incubated with Ch-rich liposomes ( P < 0.05), which increase the Ch content in the plasma membranes. In muscle cells from GB with ChS, H2O2-induced contraction was only 9.2 ± 1.3% and increased to 14 ± 0.2% after Ch-free liposome treatment to remove Ch from the plasma membranes ( P < 0.01). H2O2caused a similar increase in the levels of lipid peroxidation and PGE2content in muscle cells from GBs with ChS and PS. However, the activities of SOD and catalase were significantly lower in muscle cells from GBs with ChS compared with those with PS. The binding capacity of PGE2receptors was also significantly lower in muscle cells from GBs with ChS compared with those with PS. In conclusion, the cytoprotective response to reactive oxygen species is reduced in muscle cells from GBs with ChS despite a normal increase in the cellular levels of PGE2. This impaired cytoprotective response may be due to a dysfunction of PGE2receptors with decreased binding capacity resulting from excessive Ch levels in the plasma membrane.
Enteroendocrine cell expression of a cholecystokinin gene construct in transgenic mice and cultured cells
Authors: Lay Jean M. , Bane Gina , Brunkan Cynthia S. , Davis Jennifer , Lopez-Diaz Lymari , Samuelson Linda C.
Published: October 2004

CCK is predominantly expressed in subsets of endocrine cells in the intestine and neurons in the brain. We evaluated the expression of a CCK gene construct in transgenic mice and cultured cells to identify a genomic region that directs correct tissue- and cell-specific expression in enteroendocrine cells. The CCKL1 transgene contained 6.4 kb of mouse Cck fused to lacZ. Expression was evaluated in three transgenic lines (J11, J12, J14) by measurement of β-galactosidase in tissue homogenates and frozen sections. Correct tissue-specific expression was observed, with β-galactosidase activity detected in intestine and brain. However, there were differences seen in cell-specific expression in the intestine. Line J14 exhibited expression in CCK-endocrine cells, with expressing cells arising at the normal time during fetal development. However, transgene expression in line J12 intestine was limited to neurons of the enteric nervous system, which reflect an early fetal expression pattern for CCK. Analysis of an additional 15 transgenic founder mice demonstrated intestinal expression in 40% of transgenics, with expressing mice following either an endocrine cell pattern or a neuronal pattern in approximately equal numbers. CCKL1 transfection analysis in cultured cells also demonstrated enteroendocrine cell expression, with 100-fold enhanced activity in the enteroendocrine cell line STC-1 compared with nonendocrine cell lines. The results suggest that the minimal cis-regulatory DNA elements necessary for appropriate CCK expression in enteroendocrine cells reside within the 6.4-kb mouse genomic fragment.
Plasma volume restoration with salt tablets and water after bed rest prevents orthostatic hypotension and changes in supine hemodynamic and endocrine variables
Authors: Waters Wendy W. , Platts Steven H. , Mitchell Brett M. , Whitson Peggy A. , Meck Janice V.
Published: October 2004

Head-down bed rest changes the values of many cardiovascular and endocrine variables and also elicits significant hypovolemia. Because previous studies had not controlled for hypovolemia, it is unknown whether the reported changes were primary effects of bed rest or secondary effects of bed rest-induced hypovolemia. We hypothesized that restoring plasma volume with salt tablets and water after 12 days of head-down bed rest would result in an absence of hemodynamic and endocrine changes and a reduced incidence of orthostatic hypotension. In 10 men, we measured changes from pre-bed-rest to post-bed-rest in venous and arterial pressures; heart rate; stroke volume; cardiac output; vascular resistance; plasma norepinephrine, epinephrine, vasopressin, renin activity (PRA), and aldosterone responses to different tilt levels (0°, −10°, 20°, 30°, and 70°); and plasma volume and platelet α2- and lymphocyte β2-adrenoreceptor densities and affinities (0° tilt only). Fluid loading at the end of bed rest restored plasma volume and resulted in the absence of post-bed-rest orthostatic hypotension and changes in supine hemodynamic and endocrine variables. Fluid loading did not prevent post-bed-rest increases in β2-adrenoreceptor density or decreases in the aldosterone-to-PRA ratio ( P = 0.05 for each). Heart rate, epinephrine, and PRA responses to upright tilt after bed rest were increased ( P < 0.05), despite the fluid load. These results suggest that incidents of orthostatic hypotension and many of the changes in supine hemodynamic and endocrine variables in volume-depleted bed-rested subjects occur secondarily to the hypovolemia. Despite normovolemia after bed rest, β2-adrenoreceptors were upregulated, and heart rate, epinephrine, and PRA responses to tilt were augmented, indicating that these changes are independent of volume depletion.
Cyclooxygenase inhibition and baroreflex sensitivity in humans
Authors: Monahan Kevin D. , Ray Chester A.
Published: October 2004

Animal studies suggest that prostanoids (i.e., such as prostacyclin) may sensitize or impair baroreceptor and/or baroreflex responsiveness depending on the site of administration and/or inhibition. We tested the hypothesis that acute inhibition of cyclooxygenase (COX), the rate-limiting enzyme in prostanoid synthesis, impairs baroreflex regulation of cardiac period (R-R interval) and muscle sympathetic nerve activity (MSNA) in humans and augments pressor reactivity. Baroreflex sensitivity (BRS) was determined at baseline (preinfusion) and 60 min after (postinfusion) intravenous infusion of a COX antagonist (ketorolac; 45 mg) (24 ± 1 yr; n = 12) or saline (25 ± 1 yr; n = 12). BRS was assessed by using the modified Oxford technique (bolus intravenous infusion of nitroprusside followed by phenylephrine). BRS was quantified as the slope of the linear portion of the 1) R-R interval-systolic blood pressure relation (cardiovagal BRS) and 2) MSNA-diastolic blood pressure relation (sympathetic BRS) during pharmacological changes in arterial blood pressure. Ketorolac did not alter cardiovagal (19.4 ± 2.1 vs. 18.4 ± 2.4 ms/mmHg preinfusion and postinfusion, respectively) or sympathetic BRS (−2.9 ± 0.7 vs. −2.6 ± 0.4 arbitrary units·beat−1·mmHg−1) but significantly decreased a plasma biomarker of prostanoid generation (plasma thromboxane B2) by 53 ± 11%. Cardiovagal BRS (21.3 ± 3.8 vs. 21.2 ± 3.0 ms/mmHg), sympathetic BRS (−3.4 ± 0.3 vs. −3.2 ± 0.2 arbitrary units·beat−1·mmHg−1), and thromboxane B2(change in −1 ± 12%) were unchanged in the control (saline infusion) group. Pressor responses to steady-state incremental (0.5, 1.0, and 1.5 μg·kg−1·min−1) infusion (5 min/dose) of phenylephrine were not altered by ketorolac ( n = 8). Collectively, these data indicate that acute pharmacological antagonism of the COX enzyme does not impair BRS (cardiovagal or sympathetic) or augment pressor reactivity in healthy young adults.
Effect of simvastatin on left ventricular mass in hypercholesterolemic rabbits
Authors: Lee Tsung-Ming , Lin Mei-Shu , Chou Tsai-Fwu , Chang Nen-Chung
Published: October 2004

Epidemiological studies showed that hypercholesterolemia is associated with higher left ventricular mass. Endothelin signaling is activated in hyperlipidemic animals and may contribute to progressive ventricular hypertrophy. Simvastatin has been shown to inhibit endothelin-1. However, the behavior of simvastatin on ventricular hypertrophy in hyperlipidemic animals is not well understood. In this study, we evaluated the hemodynamic, biochemical, and morphological responses to simvastatin in cholesterol-fed (1%) rabbits. The left ventricular weight increased 8 wk after cholesterol feeding compared with that in normocholesterolemic rabbits. Simvastatin at a clinical therapeutic dose (1.2 mg·kg−1·day−1) significantly decreased left ventricular weight by 14% and left ventricular myocyte sizes by 14% as isolated by enzymatic dissociation. Hypercholesterolemia upregulated ventricular preproendothelin-1 mRNA as assessed by real-time quantitative RT-PCR and elevated production of cardiac endothelin-1 concentration. The increased endothelin-1 responses can be inhibited after simvastatin administration. Left ventricular mass indexed by body weight positively correlated with tissue endothelin-1 levels ( P = 0.0003). In Langendorff-perfused rabbit hearts, hyperlipidemia led to significant QT prolongation compared with normocholesterolemia, which can be reversed by administering simvastatin. In contrast, simvastatin-induced beneficial effects were reversed by the addition of mevalonate. The addition of bosentan, a nonspecific endothelin receptor blocker, improved the response in hypercholesterolemic rabbits and did not have additional beneficial effects in simvastatin-treated rabbits. The results of the present study suggest that the antihypertropic and electrocardiographic effects of simvastatin at a clinical therapeutic dose are mediated through inhibition of tissue endothelin-1 expression, which is linked to mevalonate metabolism, and result in an amelioration of cardiomyocyte hypertrophy development by an atherogenic diet.
Hypertension attenuates cell-to-cell communication in hamster retractor muscle feed arteries
Authors: Kurjiaka David T. , Bender Shawn B. , Nye Darin D. , Wiehler William B. , Welsh Donald G.
Published: October 2004

This study examined whether hypertension attenuated cell-to-cell communication in skeletal muscle resistance arteries. Briefly, arteries feeding the retractor muscle of normotensive and hypertensive hamsters were cannulated, pressurized, and superfused with a physiological saline solution. Cell-to-cell communication was functionally assessed by application of vasoactive stimuli (via micropipette) to a small portion of a feed artery while diameter at sites distal to the point of agent application was monitored. In keeping with past observations, discrete application of a smooth muscle depolarizing agent (phenylephrine or KCl) elicited a localized vasoconstriction that conducted poorly along feed arteries from normotensive hamsters. In contrast, acetylcholine, an agent known to hyperpolarize endothelial cells, elicited a vasodilation in normotensive feed arteries that conducted with little decay. Whereas smooth muscle depolarizing agents continued to elicit a localized response, conduction of endothelium-dependent vasodilation was attenuated in hypertensive hamsters. This decrease occurred in the absence of changes in vessel reactivity to intravascular pressure or to global application of phenylephrine, U-46619, or acetylcholine. We propose, on the basis of these physiological observations, quantitative mRNA measurements of connexins 37, 40, 43, and 45, and analysis of the literature, that an increase in endothelial-to-endothelial or smooth muscle-to-endothelial coupling resistance is likely responsible for hypertension-induced impairment in vascular communication. We hypothesize that this attenuation could contribute to the rise in total peripheral resistance characteristically observed in hypertension.
MRI-determined left ventricular “crescent effect”: a consequence of the slight deviation of contents of the pericardial sack from the constant-volume state
Authors: Waters Emily A. , Bowman Andrew W. , Kovács Sándor J.
Published: October 2004

During one cardiac cycle, the volume encompassed by the pericardial sack in healthy subjects remains nearly constant, with a transient ±5% decrease in volume at end systole. This “constant-volume” attribute defines a constraint that the longitudinal versus radial pericardial contour dimension relationship must obey. Using cardiac MRI, we determined the extent to which the constant-volume attribute is valid from four-chamber slices (two-dimensional) compared with three-dimensional volumetric data. We also compared the relative percentage of longitudinal versus radial (short-axis) change in cross-sectional area (dimension) of the pericardial contour, thereby assessing the fate of the ±5% end-systolic volume decrease. We analyzed images from 10 normal volunteers and 1 subject with congenital absence of the pericardium, obtained using a 1.5-T MR scanner. Short-axis cine loop stacks covering the entire heart were acquired, as were single four-chamber cine loops. In the short-axis and four-chamber slices, relative to midventricular end-diastolic location, end-systolic pericardial (left ventricular epicardial) displacement was observed to be radial and maximized at end systole. Longitudinal (apex to mediastinum) pericardial contour dimension change and pericardial area change on the four-chamber slice were negligible throughout the cardiac cycle. We conclude that the ±5% end-systolic decrease in the volume encompassed by the pericardial sack is primarily accounted for by a “crescent effect” on short-axis views, manifesting as a nonisotropic radial diminution of the pericardial/epicardial contour of the left ventricle. This systolic drop in cardiac volume occurs primarily at the ventricular level and is made up during the subsequent diastole when blood crosses the pericardium in the pulmonary venous Doppler D wave during early rapid left ventricular filling.
Salt-induced ANG II suppression impairs the response of cerebral artery smooth muscle cells to prostacyclin
Authors: Zhu Jiaxuan , Yu Ming , Friesema Jill , Huang Tianjian , Roman Richard J. , Lombard Julian H.
Published: October 2004

Recent studies have demonstrated that cerebral arteries from rats fed a high-salt (HS) diet exhibit impaired vasodilation and altered electrophysiological response to reduction in Po2. The present study examined whether an increase in salt intake alters the response of vascular smooth muscle cells (VSMC) to prostacyclin, a crucial mediator of hypoxic dilation in cerebral arteries. VSMC were isolated from cerebral arteries of male Sprague-Dawley rats maintained on an HS (4% NaCl) or a low-salt diet (0.4% NaCl) for 3 days. The stable prostacyclin analog iloprost (10 ng/ml) inhibited serotonin (0.1–10 μM)-induced contractions and the increase in intracellular Ca2+concentration ([Ca2+]i) in VSMC isolated from arteries of animals fed the low-salt diet. In contrast, iloprost had no effect on serotonin-induced contractions and increases in [Ca2+]iin VSMC isolated from arteries of rats fed the HS diet. Preventing the fall in ANG in rats fed the HS diet by infusion of a low dose of ANG II (5 ng·kg−1·min−1iv) restored the inhibitory effect of iloprost on serotonin-induced contractions and increases in [Ca2+]iin VSMC from animals fed the HS diet. These effects were reversed by AT1receptor blockade with losartan. These results indicate that ANG II suppression secondary to elevated dietary salt intake impairs vascular relaxation and Ca2+regulation by prostacyclin.
Myocardium tolerant to an adenosine-dependent ischemic preconditioning stimulus can still be protected by stimuli that employ alternative signaling pathways
Authors: Liem David A. , te Lintel Hekkert Maaike , Manintveld Olivier C. , Boomsma Frans , Verdouw Pieter D. , Duncker Dirk J.
Published: October 2004

Clinical studies on cardioprotection by preinfarct angina are ambiguous, which may involve development of tolerance to repeated episodes of ischemia. Not all preconditioning stimuli use identical signaling pathways, and because patients likely experience varying numbers of episodes of preinfarct angina of different degrees and durations, it is important to know whether myocardium tolerant to a particular preconditioning stimulus can still be protected by stimuli employing alternative signaling pathways. We tested the hypothesis that development of tolerance to a particular stimulus does not affect cardioprotection by stimuli that employ different signaling pathways. Anesthetized rats underwent classical, remote or pharmacological preconditioning. Infarct size (IS), produced by a 60-min coronary artery occlusion (CAO), was determined after 120 min of reperfusion. Preconditioning by two 15-min periods of CAO (2CAO15, an adenosine-dependent stimulus) limited IS from 69 ± 2% to 37 ± 6%, but when 2CAO15 was preceded by 4CAO15, protection by 2CAO15 was absent (IS = 68 ± 1%). This development of tolerance coincided with a loss of cardiac interstitial adenosine release, whereas two 15-min infusions of adenosine (200 μg/min iv) still elicited cardioprotection (IS = 40 ± 4%). Furthermore, cardioprotection was produced when 4CAO15 was followed by the adenosine-independent stimulus 3CAO3 (IS = 50 ± 8%) or the remote preconditioning stimulus of two 15-min periods of mesenteric artery occlusion (IS = 49 ± 6%). In conclusion, development of tolerance to cardioprotection by an adenosine-dependent preconditioning stimulus still allows protection by pharmacological or ischemic stimuli intervention employing different signaling pathways.
Interaction between endothelial heme oxygenase-2 and endothelin-1 in altered aortic reactivity after hypoxia in rats
Authors: Govindaraju Vasanthi , Teoh Hwee , Hamid Qutayba , Cernacek Peter , Ward Michael E.
Published: October 2004

The aim of this study was to determine whether increased expression of heme oxygenase (HO) contributes to impairment of aortic contractile responses after hypoxia through effects on reactivity to endothelin-1 (ET-1). Thoracic aortas from normoxic rats and rats exposed to hypoxia (10% O2) for 16 or 48 h were mounted in organ bath myographs for contractile studies, fixed in paraformaldehyde, or frozen in liquid nitrogen for protein extraction. In rings from normoxic rats, the HO inhibitor tin protoporphyrin IX (SnPP IX, 10 μM) did not alter the response to phenylephrine or ET-1. In rings from rats exposed to 16-h hypoxia, maximum tension generated in response to these agonists was higher in endothelium-intact but not -denuded rings in the presence of SnPP IX. In rings from rats exposed to 48-h hypoxia SnPP IX increased contraction in endothelium-intact but not -denuded rings. In endothelium-intact aortic rings from rats exposed to 16-h hypoxia incubated with endothelin A receptor-specific antagonist BQ-123 (10−7 M), SnPP IX did not alter phenylephrine-induced contraction. Aortic ET-1 protein levels, measured by radioimmunoassay, were increased in rats exposed to hypoxia for 16 and 48 h. Western blotting showed that HO-1 and HO-2 protein were increased after 16 h of hypoxia and returned to near-control levels after 48 h. Increase in HO-1 protein was detected in endothelium-intact and -denuded rings. Removal of endothelium abolished the increase in HO-2 immunoreactivity. Immunohistochemistry localized expression of HO-1 protein to vascular smooth muscle, whereas HO-2 was only detected in endothelium. HO-2 is expressed by aortic endothelial cells early during hypoxic exposure and impairs ET-1-mediated potentiation of contraction to α-adrenoceptor stimulation.