Ex Vivo Experiments Shed Light on the Innate Immune Response from Influenza Virus.

The innate immune response is recognized as a key driver in controlling an influenza virus infection in a host. However, the mechanistic action of such innate response is not fully understood. Infection experiments on ex vivo explants from swine trachea represent an efficient alternative to animal experiments, as the explants conserved key characteristics of an organ from an animal. In the present work we compare three cellular automata models of influenza virus dynamics. The models are fitted to free virus and infected cells data from ex vivo swine trachea experiments. Our findings suggest that the presence of an immune response is necessary to explain the observed dynamics in ex vivo organ culture. Moreover, such immune response should include a refractory state for epithelial cells, and not just a reduced infection rate. Our results may shed light on how the immune system responds to an infection event.

Binding Specificity of a Novel Cyclo/Maltodextrin-Binding Protein and Its Role in the Cyclodextrin ABC Importer System from Thermoanaerobacterales.

Extracellular synthesis of functional cyclodextrins (CDs) as intermediates of starch assimilation is a convenient microbial adaptation to sequester substrates, increase the half-life of the carbon source, carry bioactive compounds, and alleviate chemical toxicity through the formation of CD-guest complexes. Bacteria encoding the four steps of the carbohydrate metabolism pathway via cyclodextrins (CM-CD) actively internalize CDs across the microbial membrane via a putative type I ATP-dependent ABC sugar importer system, MdxEFG-(X/MsmX). While the first step of the CM-CD pathway encompasses extracellular starch-active cyclomaltodextrin glucanotransferases (CGTases) to synthesize linear dextrins and CDs, it is the ABC importer system in the second step that is the critical factor in determining which molecules from the CGTase activity will be internalized by the cell. Here, structure-function relationship studies of the cyclo/maltodextrin-binding protein MdxE of the MdxEFG-MsmX importer system from Thermoanaerobacter mathranii subsp. mathranii A3 are presented. Calorimetric and fluorescence studies of recombinant MdxE using linear dextrins and CDs showed that although MdxE binds linear dextrins and CDs with high affinity, the open-to-closed conformational change is solely observed after α- and ß-CD binding, suggesting that the CM-CD pathway from Thermoanaerobacterales is exclusive for cellular internalization of these molecules. Structural analysis of MdxE coupled with docking simulations showed an overall architecture typically found in sugar-binding proteins (SBPs) that comprised two N- and C-domains linked by three small hinge regions, including the conserved aromatic triad Tyr193/Trp269/Trp378 in the C-domain and Phe87 in the N-domain involved in CD recognition and stabilization. Structural bioinformatic analysis of the entire MdxFG-MsmX importer system provided further insights into the binding, internalization, and delivery mechanisms of CDs. Hence, while the MdxE-CD complex couples to the permease subunits MdxFG to deliver the CD into the transmembrane channel, the dimerization of the cytoplasmatic promiscuous ATPase MsmX triggers active transport into the cytoplasm. This research provides the first results on a novel thermofunctional SBP and its role in the internalization of CDs in extremely thermophilic bacteria.

Mining for novel cyclomaltodextrin glucanotransferases unravels the carbohydrate metabolism pathway via cyclodextrins in Thermoanaerobacterales.

Carbohydrate metabolism via cyclodextrins (CM-CD) is an uncommon starch-converting pathway that thoroughly depends on extracellular cyclomaltodextrin glucanotransferases (CGTases) to transform the surrounding starch substrate to α-(1,4)-linked oligosaccharides and cyclodextrins (CDs). The CM-CD pathway has emerged as a convenient microbial adaptation to thrive under extreme temperatures, as CDs are functional amphipathic toroids with higher heat-resistant values than linear dextrins. Nevertheless, although the CM-CD pathway has been described in a few mesophilic bacteria and archaea, it remains obscure in extremely thermophilic prokaryotes (Topt ≥ 70 °C). Here, a new monophyletic group of CGTases with an exceptional three-domain ABC architecture was detected by (meta)genome mining of extremely thermophilic Thermoanaerobacterales living in a wide variety of hot starch-poor environments on Earth. Functional studies of a representative member, CldA, showed a maximum activity in a thermoacidophilic range (pH 4.0 and 80 °C) with remarkable product diversification that yielded a mixture of α:ß:γ-CDs (34:62:4) from soluble starch, as well as G3-G7 linear dextrins and fermentable sugars as the primary products. Together, comparative genomics and predictive functional analysis, combined with data of the functionally characterized key proteins of the gene clusters encoding CGTases, revealed the CM-CD pathway in Thermoanaerobacterales and showed that it is involved in the synthesis, transportation, degradation, and metabolic assimilation of CDs.

Employing phylogenetic tree shape statistics to resolve the underlying host population structure.

BACKGROUND: Host population structure is a key determinant of pathogen and infectious disease transmission patterns. Pathogen phylogenetic trees are useful tools to reveal the population structure underlying an epidemic. Determining whether a population is structured or not is useful in informing the type of phylogenetic methods to be used in a given study. We employ tree statistics derived from phylogenetic trees and machine learning classification techniques to reveal an underlying population structure. RESULTS: In this paper, we simulate phylogenetic trees from both structured and non-structured host populations. We compute eight statistics for the simulated trees, which are: the number of cherries; Sackin, Colless and total cophenetic indices; ladder length; maximum depth; maximum width, and width-to-depth ratio. Based on the estimated tree statistics, we classify the simulated trees as from either a non-structured or a structured population using the decision tree (DT), K-nearest neighbor (KNN) and support vector machine (SVM). We incorporate the basic reproductive number ([Formula: see text]) in our tree simulation procedure. Sensitivity analysis is done to investigate whether the classifiers are robust to different choice of model parameters and to size of trees. Cross-validated results for area under the curve (AUC) for receiver operating characteristic (ROC) curves yield mean values of over 0.9 for most of the classification models. CONCLUSIONS: Our classification procedure distinguishes well between trees from structured and non-structured populations using the classifiers, the two-sample Kolmogorov-Smirnov, Cucconi and Podgor-Gastwirth tests and the box plots. SVM models were more robust to changes in model parameters and tree size compared to KNN and DT classifiers. Our classification procedure was applied to real -world data and the structured population was revealed with high accuracy of [Formula: see text] using SVM-polynomial classifier.

Transmission dynamics and forecasts of the COVID-19 pandemic in Mexico, March-December 2020.

Mexico has experienced one of the highest COVID-19 mortality rates in the world. A delayed implementation of social distancing interventions in late March 2020 and a phased reopening of the country in June 2020 has facilitated sustained disease transmission in the region. In this study we systematically generate and compare 30-day ahead forecasts using previously validated growth models based on mortality trends from the Institute for Health Metrics and Evaluation for Mexico and Mexico City in near real-time. Moreover, we estimate reproduction numbers for SARS-CoV-2 based on the methods that rely on genomic data as well as case incidence data. Subsequently, functional data analysis techniques are utilized to analyze the shapes of COVID-19 growth rate curves at the state level to characterize the spatiotemporal transmission patterns of SARS-CoV-2. The early estimates of the reproduction number for Mexico were estimated between Rt ~1.1-1.3 from the genomic and case incidence data. Moreover, the mean estimate of Rt has fluctuated around ~1.0 from late July till end of September 2020. The spatial analysis characterizes the state-level dynamics of COVID-19 into four groups with distinct epidemic trajectories based on epidemic growth rates. Our results show that the sequential mortality forecasts from the GLM and Richards model predict a downward trend in the number of deaths for all thirteen forecast periods for Mexico and Mexico City. However, the sub-epidemic and IHME models perform better predicting a more realistic stable trajectory of COVID-19 mortality trends for the last three forecast periods (09/21-10/21, 09/28-10/27, 09/28-10/27) for Mexico and Mexico City. Our findings indicate that phenomenological models are useful tools for short-term epidemic forecasting albeit forecasts need to be interpreted with caution given the dynamic implementation and lifting of social distancing measures.

Custom Optical Coherence Tomography Parameters for Distinguishing Papilledema from Pseudopapilledema.

SIGNIFICANCE: Causes of papilledema can be life-threatening; however, distinguishing papilledema from pseudopapilledema is often challenging. The conventional optical coherence tomography (OCT) scan for assessing the optic nerve often fails to detect mild papilledema. Our study suggests that parameters derived from volumetric OCT scans can provide additional useful information for detecting papilledema. PURPOSE: Optical coherence tomography analysis of the optic nerve commonly measures retinal nerve fiber layer thickness (RNFLT) along a 1.73-mm-radius scan path. This conventional scan, however, often fails to detect mild papilledema. The purpose of this study was to evaluate additional OCT-derived measures of the optic nerve head (ONH) and peripapillary retina for differentiating papilledema (all grades and mild) from pseudopapilledema. METHODS: Cirrus OCT ONH volume scans were acquired from 21 papilledema (15 mild papilledema), 27 pseudopapilledema, and 42 control subjects. Raw scan data were exported, and total retinal thickness within Bruch's membrane opening (BMO) plus RNFLT and total retinal thickness at the following eccentricities were calculated using custom algorithms: BMO to 250, 250 to 500, 500 to 1000, and 1000 to 1500 µm. Minimum rim width was calculated, and BMO height was measured from a 4-mm Bruch's membrane reference plane centered on the BMO. RESULTS: Retinal nerve fiber layer thickness from BMO to 250 µm, minimum rim width, and BMO height had significantly greater areas under the receiver operating characteristic curve than did conventional RNFLT for differentiating mild papilledema from pseudopapilledema (P < .0001) and greater sensitivities at 95% specificity. Using cutoff values at 95% specificity, custom parameters detected 10 mild papilledema patients, and conventional RNFLT detected only 1. Bruch's membrane opening heights above the reference plane were observed in papilledema only, although many papilledema cases had a neutral or negative BMO height. CONCLUSIONS: Using OCT volumetric data, additional parameters describing peripapillary tissue thickness, neuroretinal rim thickness, and ONH position can be calculated and provide valuable measures for differentiating mild papilledema from pseudopapilledema.

Epidemiologia de la hipertensión pulmonar en Colombia / Epidemiology of pulmonary hypertension in Colombia

Resumen Objetivo: Estimar la prevalência e incidencia de la hipertensión pulmonar (HTP) en Colombia entre el periodo comprendido entre 2010 y 2014. Metodologia: Estudio de corte transversal utilizando la Bodega de Datos del Sistema Integral de Información de la Protección Social (SISPRO) del Ministerio de Salud y Protección Social (MSPS). Se incluyeron todas las personas atendidas a nivel nacional que tenían registrado los diagnósticos de Hipertensión Pulmonar Primaria (Clasificación Internacional de Enfermedades CIE-101270), durante el periodo establecido para el estudio. Resultados: Se estimó que la prevalencia e incidencia de HTP es de aproximadamente 52 y 20 casos por cada millón de habitantes, respectivamente. Predomina en el sexo femenino y en los grupos de edad mayores de 60 años. Conclusión: Las estimaciones epidemiológicas de la HTP en Colombia son compatibles con la definición de enfermedades huérfanas o raras.

Abstract Objective: To estimate the prevalence and incidence of pulmonary hypertension (PH) in Colombia between the period between 2010 and 2014. Methodology: Cross-sectional study using the Data Warehouse of the Social Protection Information System (SISPRO) of the Ministry of Health and Social Protection (MSPS). We included all the nationwide patients who had registered the diagnoses of Primary Pulmonary Hypertension (ICD-101270) during the period established for the study. Results: It was estimated that the prevalence and incidence of PH is approximately 52 and 20 cases per million inhabitants, respectively. It predominates in the female sex and in the age groups over 60 years. Conclusion: Epidemiological estimates of PH in Colombia are consistent with the definition of orphan or rare diseases.

Use of A-scan Ultrasound and Optical Coherence Tomography to Differentiate Papilledema From Pseudopapilledema.

SIGNIFICANCE: Differentiating papilledema from pseudopapilledema reflecting tilted/crowded optic discs or disc drusen is critical but can be challenging. Our study suggests that spectral-domain optical coherence tomography (OCT) peripapillary retinal nerve fiber layer thickness and retrobulbar optic nerve sheath diameter (ONSD) measured by A-scan ultrasound provide useful information when differentiating the two conditions. PURPOSE: To evaluate the use of A-scan ultrasound and spectral-domain OCT retinal nerve fiber layer thickness (RNFLT) in differentiating papilledema associated with idiopathic intracranial hypertension from pseudopapilledema. METHODS: Retrospective cross-sectional analysis included 23 papilledema and 28 pseudopapilledema patients. Ultrasound-measured ONSD at primary gaze, percent change in ONSD at lateral gaze (30° test), and peripapillary RNFLT were analyzed. Receiver operating characteristic curves were constructed using one eye from each subject. RESULTS: Compared with pseudopapilledema, papilledema eyes showed larger mean ONSD (5.4 ± 0.6 vs. 4.0 ± 0.3 mm, P < .0001), greater change of ONSD at lateral gaze (22.4 ± 8.4% vs. 2.8 ± 4.8%, P < .0001), and thicker retinal nerve fiber layer (219.1 ± 104.6 vs. 102.4 ± 20.1 µm, P < .0001). Optic nerve sheath diameter and 30° test had the greatest area under the receiver operating characteristic curve, 0.98 and 0.97, respectively; followed by inferior quadrant (0.90) and average RNFLT (0.87). All papilledema eyes with Frisén scale greater than grade II were accurately diagnosed by ONSD, 30° test, or OCT. In mild papilledema (Frisén scale grades I and II, n = 15), area under the receiver operating characteristic curve remained high for ONSD (0.95) and 30° test (0.93) but decreased to 0.61 to 0.71 for RNFLT. At 95% specificity, sensitivities for ONSD, 30° test, and RNFLT were 91.3%, 91.3%, and 56.5%, respectively, for the entire papilledema group and 80.0%, 86.7%, and 13.3% for the mild papilledema subgroup. CONCLUSIONS: Retinal nerve fiber layer thickness can potentially be used to detect moderate to severe papilledema. A-scan may further assist differentiation of mild papilledema from pseudopapilledema.

Tracking changes over time in retinal nerve fiber layer and ganglion cell-inner plexiform layer thickness in multiple sclerosis.

BACKGROUND: Neurodegeneration plays an important role in permanent disability in multiple sclerosis (MS). OBJECTIVE: The objective of this paper is to determine whether progressive neurodegeneration occurs in MS eyes without clinically evident inflammation. METHODS: Retinal nerve fiver layer thickness (RNFLT) and ganglion cell-inner plexiform layer thickness (GCIPT) were measured using Cirrus optical coherence tomography (OCT) in 133 relapsing-remitting MS (RRMS) patients (149 non-optic neuritis (ON), 97 ON eyes, last ON ≥6 months). Ninety-three patients were scanned at two visits. Percentages of abnormal GCIPT vs RNFLT (<5% of machine norms) in cross-sectional data were compared. Relations between RNFLT/GCIPT and MS duration (cross-sectional) and follow-up time (longitudinal) were assessed. RESULTS: GCIPT was abnormal in more eyes than RNFLT (27% vs 16% p = 0.004 in non-ON, 82% vs 72% p = 0.007 in ON). RNFLT and GCIPT decreased with MS duration by -0.49 µm/yr (p = 0.0001) and -0.36 (p = 0.005) for non-ON; -0.52 (p = 0.003) and -0.41 (p = 0.007) for ON. RNFLT and GCIPT decreased with follow-up time by -1.49 µm/yr (p < 0.0001) and -0.53 (p = 0.004) for non-ON, -1.27 (p = 0.002) and -0.49 (p = 0.04) for ON. CONCLUSIONS: In RRMS eyes without clinically evident inflammation, progressive loss of RNFLT and GCIPT occurred, supporting the need for neuroprotection in addition to suppression of autoimmune responses and inflammation.

Nested model reveals potential amplification of an HIV epidemic due to drug resistance.

The use of antiretroviral therapy (ART) is the most efficient measure in controlling the HIV epidemic. However, emergence of drug-resistant strains can reduce the potential benefits of ART. The viral dynamics of drug-sensitive and drug-resistant strains at the individual level may play a crucial role in the emergence and spread of drug resistance in a population. We investigate the effect of the viral dynamics within an infected individual on the epidemiological dynamics of HIV using a nested model that links both dynamical levels. A time-dependent between-host transmission rate that receives feedback from a model of two-strain virus dynamics within a host is incorporated into an epidemiological model of HIV. We analyze the resulting dynamics of the model and identify model parameters such as time when ART is initiated, fraction of cases treated, and the probability that a patient develops drug resistance, as having the greatest impact on total infection and prevalence of drug resistance. Importantly, for small values of the risk of a patient developing drug resistance, increasing the fraction of cases treated can increase the cumulative number of infected individuals. Such a pattern is the result of the balance between not treating a patient and having future cases still sensitive to treatment, and treating the patient and increasing the chances for future (untreatable) drug-resistant infections. The current modeling framework incorporates important aspects of virus dynamics within a host into an epidemic model. This approach provides useful insights on the drug resistance dynamics of an epidemic of HIV, which may assist in identifying an optimal use of ART.

The role of backward mutations on the within-host dynamics of HIV-1.

The quality of life for patients infected with human immunodeficiency virus (HIV-1) has been positively impacted by the use of antiretroviral therapy (ART). However, the benefits of ART are usually halted by the emergence of drug resistance. Drug-resistant strains arise from virus mutations, as HIV-1 reverse transcription is prone to errors, with mutations normally carrying fitness costs to the virus. When ART is interrupted, the wild-type drug-sensitive strain rapidly out-competes the resistant strain, as the former strain is fitter than the latter in the absence of ART. One mechanism for sustaining the sensitive strain during ART is given by the virus mutating from resistant to sensitive strains, which is referred to as backward mutation. This is important during periods of treatment interruptions as prior existence of the sensitive strain would lead to replacement of the resistant strain. In order to assess the role of backward mutations in the dynamics of HIV-1 within an infected host, we analyze a mathematical model of two interacting virus strains in either absence or presence of ART. We study the effect of backward mutations on the definition of the basic reproductive number, and the value and stability of equilibrium points. The analysis of the model shows that, thanks to both forward and backward mutations, sensitive and resistant strains co-exist. In addition, conditions for the dominance of a viral strain with or without ART are provided. For this model, backward mutations are shown to be necessary for the persistence of the sensitive strain during ART.

Quantifying transmission of highly pathogenic and low pathogenicity H7N1 avian influenza in turkeys.

Outbreaks of avian influenza in poultry can be devastating, yet many of the basic epidemiological parameters have not been accurately characterised. In 1999-2000 in Northern Italy, outbreaks of H7N1 low pathogenicity avian influenza virus (LPAI) were followed by the emergence of H7N1 highly pathogenic avian influenza virus (HPAI). This study investigates the transmission dynamics in turkeys of representative HPAI and LPAI H7N1 virus strains from this outbreak in an experimental setting, allowing direct comparison of the two strains. The fitted transmission rates for the two strains are similar: 2.04 (1.5-2.7) per day for HPAI, 2.01 (1.6-2.5) per day for LPAI. However, the mean infectious period is far shorter for HPAI (1.47 (1.3-1.7) days) than for LPAI (7.65 (7.0-8.3) days), due to the rapid death of infected turkeys. Hence the basic reproductive ratio, [Formula: see text] is significantly lower for HPAI (3.01 (2.2-4.0)) than for LPAI (15.3 (11.8-19.7)). The comparison of transmission rates and [Formula: see text] are critically important in relation to understanding how HPAI might emerge from LPAI. Two competing hypotheses for how transmission rates vary with population size are tested by fitting competing models to experiments with differing numbers of turkeys. A model with frequency-dependent transmission gives a significantly better fit to experimental data than density-dependent transmission. This has important implications for extrapolating experimental results from relatively small numbers of birds to the commercial poultry flock size, and for how control, including vaccination, might scale with flock size.

Dynamics of influenza virus infection and pathology.

A key question in pandemic influenza is the relative roles of innate immunity and target cell depletion in limiting primary infection and modulating pathology. Here, we model these interactions using detailed data from equine influenza virus infection, combining viral and immune (type I interferon) kinetics with estimates of cell depletion. The resulting dynamics indicate a powerful role for innate immunity in controlling the rapid peak in virus shedding. As a corollary, cells are much less depleted than suggested by a model of human influenza based only on virus-shedding data. We then explore how differences in the influence of viral proteins on interferon kinetics can account for the observed spectrum of virus shedding, immune response, and influenza pathology. In particular, induction of high levels of interferon ("cytokine storms"), coupled with evasion of its effects, could lead to severe pathology, as hypothesized for some fatal cases of influenza.

Bibliometría: conceptos y utilidades para el estudio médico y la formación profesional / Bibliometrics: concepts and utility to study and medical training

El crecimiento de la investigación científica en los últimos tiempos ha hecho necesario el desarrollo y la implementación de diversos indicadores que ayuden a medir la importancia de la investigación de cara a la propia comunidad científica. En la formación profesional del médico general y el residente de especialidades médicas se encuentra a menudo un desconocimiento o déficit en el manejo de temas sobre la producción, manejo y publicación de información científica, que conlleva a la pérdida de ideas, proyectos y tesis; que se quedan en el archivo de las bibliotecas o de los laboratorios de investigación de las universidades, sin que pasen a ser parte del desarrollo intelectual de los centros de formación o trasciendan como aportes al conocimiento científico y de la comunidad médica mundial. Uno de estos temas de vital importancia para todos aquellos interesados en la producción científica y la publicación de la misma en medios de información idóneos, revistas médicas indexadas a buenas bases de datos, que evalúan permanentemente la calidad de los trabajos, así como los requisitos para acceder a ellas sea como fuente de información veraz o como medio de publicación de gran trascendencia, es la Bibliometría. Para objetivar y hacer tangible la calidad y cantidad de la producción científica es necesario recurrir a la bibliometría como herramienta necesaria para lograr un resultado medible de la producción científica. Por tal razón se hace una revisión en la literatura médica sobre la importancia de la bibliometría, su historia, sus diferentes conceptos y aplicaciones...

The growth of scientific research in recent times has needed the development and application of various indicators to help measure the importance of research for the scientific community. In the training of general practitioners and medical's resident, there is often a lack or deficit in handling issues concerning the production, management and publication of scientific information, these issues leads to loss of ideas an projects, which are in many libraries and research labs of universities, waiting to become part of the intellectual development in training or to contribute knowledge beyond the scientific and medical community worldwide. One of the main issues of vital importance to anyone interested in the scientific output, research result in medical journals indexed on databases, which determine the quality of work, is their access as a source of truthful information or as a means of publication; this is of great importance to Bibliometrics. It is tangible and objective to makes the quality and quantity of scientific production to necessary use bibliometrics as a tool to achieve a measurable outcome of the scientific literature. Therefore, a revision is made in the medical literature on the importance of bibliometrics, its history, its concepts and applications, in addition to its technical and bibliometric indicators in order to illustrate and provide incentives to doctors in training to understand the world of production and scientific publication...

Confined animal feeding operations as amplifiers of influenza.

Influenza pandemics occur when a novel influenza strain, often of animal origin, becomes transmissible between humans. Domestic animal species such as poultry or swine in confined animal feeding operations (CAFOs) could serve as local amplifiers for such a new strain of influenza. A mathematical model is used to examine the transmission dynamics of a new influenza virus among three sequentially linked populations: the CAFO species, the CAFO workers (the bridging population), and the rest of the local human population. Using parameters based on swine data, simulations showed that when CAFO workers comprised 15-45% of the community, human influenza cases increased by 42-86%. Successful vaccination of at least 50% of CAFO workers cancelled the amplification. A human influenza epidemic due to a new virus could be locally amplified by the presence of confined animal feeding operations in the community. Thus vaccination of CAFO workers would be an effective use of a pandemic vaccine.

Competing species models with an infectious disease.

The frequency-dependent (standard) form of the incidence is used for the transmission dynamics of an infectious disease in a competing species model. In the global analysis of the SIS model with the birth rate independent of the population size, a modified reproduction number R(1) determines the asymptotic behavior, so that the disease dies out if R(1) 1. Because the disease-reduced reproduction and disease-related death rates are often different in two competing species, a shared disease can change the outcome of the competition. Models of SIR and SIRS type are also considered. A key result in all of these models with the frequency-dependent incidence is that the disease must either die out in both species or remain endemic in both species.

Mechanisms for aldosterone and spironolactone-induced positive inotropic actions in the rat heart.

Previously, we reported that aldosterone and spironolactone have inotropic effects in the isolated perfused heart. To address the mechanisms underlying these inotropic effects, we examined the effects of aldosterone and spironolactone on isolated cardiac myocyte shortening, intracellular calcium ([Ca+2]i), pHi, and calcium-dependent actinomyosin ATPase activity. Aldosterone significantly increased shortening in cardiac myocytes (8.0+/-1.0 versus 16.0+/-1.3%, P<0.01) but neither diastolic [Ca+2]i (61.0+/-1.1 versus 66.0+/-4.4 nmol/L) nor peak systolic [Ca+2]i (302+/-11 versus 304+/-17 nmol/L) was affected. Spironolactone-increased shortening was also not coupled with changes in peak systolic calcium; however, diastolic calcium was significantly increased by spironolactone. Aldosterone, but not spironolactone, increased pHi from 7.23+/-0.03 to 7.59+/-0.02 (P<0.01); this was completely blocked by coadministration of 100 micromol/L of ethyl-isopropyl amiloride (EIPA), an inhibitor of the Na+/H+ exchanger (P<0.01). Consistent with this finding, aldosterone increased cytosolic sodium concentration ([Na+]i) from 9.2+/-0.15 to 11.4+/-0.2 mmol/L and produced a leftward shift in the pCa ATPase curve (pCa=5.82+/-0.02 versus 6.35+/-0.02, P<0.01) without affecting maximal myosin ATPase activity. Conversely, spironolactone, but not aldosterone, significantly increases maximal actomyosin ATPase activity (837+/-59 versus 355+/-52 nmol inorganic phosphate (P(i)) x min(-1) x g tissue(-1)). Collectively, these data strongly suggest that the inotropic actions of aldosterone and spironolactone are caused by different mechanisms of action. Aldosterone appeared to increase inotropy primarily through increased cytosolic pH, whereas spironolactone increased myosin ATPase calcium sensitivity and diastolic calcium concentration.

Monarch butterfly spatially discrete advection model.

We study the population cycles of the Monarch butterfly using one of the simplest systems incorporating both migration and local dynamics. The annual migration of the Monarch involves four generations. Members of Generations 1-3 (occasionally 4) migrate from the over-wintering site in Central Mexico to breeding grounds that extend as far north as the Northern United States and Southern Canada. A portion of the Generation 3 and all members of the Generation 4 butterflies begin their return to the over-wintering grounds in August through October where they enter reproductive diapause for several months. We developed a simple discrete-time island chain model in which different fecundity functions are used to model the reproductive strategies of each generation. The fecundity functions are selected from broad classes of functions that capture the effects of either contest or scramble intraspecific competition in the Monarch population. The objectives of our research are multiple and include the study of the generationally dependent intraspecific competition and its effect on the pool size of migrants as well as the persistence of the overall butterfly populations. The stage structure used in modeling the Monarch butterfly dynamics and their generationally dependent reproductive strategies naturally support fluctuating patterns and multiple attractors. The implications of these fluctuations and attractors on the long-term survival of the Monarch butterfly population are explored.

Rapid effects of aldosterone and spironolactone in the isolated working rat heart.

Chronic administration of aldosterone promotes myocardial fibrosis in rats. The Randomized Aldactone Evaluation Study reported that the aldosterone antagonist spironolactone improved outcome in patients with congestive heart failure, suggesting a deleterious effect of aldosterone in the heart. Aldosterone has been shown to have rapid nongenomic effects in different tissues including the heart. However, the hemodynamic actions of aldosterone and spironolactone are not well characterized. In this study, we examined the hemodynamic effects of aldosterone and its receptor antagonist, spironolactone, in the isolated rat heart by use of the Langendorff-Neely technique. Perfusion with 10 nmol/L aldosterone increased contractility by 45% within 2 to 4 minutes (P<0.01). Similar to the aldosterone effect, 10 nmol/L spironolactone increased contractility by 41% (P<0.01). Furthermore, 100-fold molar excess of spironolactone did not block the aldosterone effect. Perfusion of aldosterone plus spironolactone resulted in the highest increase in contractility 106% (P<0.01). The threshold response for aldosterone occurred within physiological concentrations (0.5 to 1 nmol/L), and maximal contractility was achieved with 10 nmol/L aldosterone. For spironolactone, the threshold and maximal contractile responses occurred at concentrations readily achieved with clinical dosing, 0.1 to 0.5 nmol/L and 1.0 nmol/L, respectively. These data demonstrate that aldosterone and spironolactone have rapid, positive inotropic actions on the myocardium. Moreover, addition of spironolactone to aldosterone increased contractility beyond the maximal responses elicited by each agent when perfused alone, thus suggesting different pathways of action. Furthermore, the intrinsic inotropic effects of spironolactone might be relevant to the apparent beneficial effect this compound has in patients with congestive heart failure.