909 resultados para 070301 Agro-ecosystem Function and Prediction
Resumo:
The major task of policy makers and practitioners when confronted with a resource management problem is to decide on the potential solution(s) to adopt from a range of available options. However, this process is unlikely to be successful and cost effective without access to an independently verified and comprehensive available list of options. There is currently burgeoning interest in ecosystem services and quantitative assessments of their importance and value. Recognition of the value of ecosystem services to human well-being represents an increasingly important argument for protecting and restoring the natural environment, alongside the moral and ethical justifications for conservation. As well as understanding the benefits of ecosystem services, it is also important to synthesize the practical interventions that are capable of maintaining and/or enhancing these services. Apart from pest regulation, pollination, and global climate regulation, this type of exercise has attracted relatively little attention. Through a systematic consultation exercise, we identify a candidate list of 296 possible interventions across the main regulating services of air quality regulation, climate regulation, water flow regulation, erosion regulation, water purification and waste treatment, disease regulation, pest regulation, pollination and natural hazard regulation. The range of interventions differs greatly between habitats and services depending upon the ease of manipulation and the level of research intensity. Some interventions have the potential to deliver benefits across a range of regulating services, especially those that reduce soil loss and maintain forest cover. Synthesis and applications: Solution scanning is important for questioning existing knowledge and identifying the range of options available to researchers and practitioners, as well as serving as the necessary basis for assessing cost effectiveness and guiding implementation strategies. We recommend that it become a routine part of decision making in all environmental policy areas.
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Substantial collective flow is observed in collisions between lead nuclei at Large Hadron Collider (LHC) as evidenced by the azimuthal correlations in the transverse momentum distributions of the produced particles. Our calculations indicate that the global v1-flow, which at RHIC peaked at negative rapidities (named third flow component or antiflow), now at LHC is going to turn toward forward rapidities (to the same side and direction as the projectile residue). Potentially this can provide a sensitive barometer to estimate the pressure and transport properties of the quark-gluon plasma. Our calculations also take into account the initial state center-of-mass rapidity fluctuations, and demonstrate that these are crucial for v1 simulations. In order to better study the transverse momentum flow dependence we suggest a new"symmetrized" vS1(pt) function, and we also propose a new method to disentangle global v1 flow from the contribution generated by the random fluctuations in the initial state. This will enhance the possibilities of studying the collective Global v1 flow both at the STAR Beam Energy Scan program and at LHC.
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Aims: The aims were to create clinically feasible reference intervals for thyroidstimulating hormone (TSH) and free thyroxine (FT4) and to analyze associations between thyroid function and self-rated health, neuropsychiatric symptoms, depression and dementia in the elderly. The second aim was also to establish reference intervals for sex hormones and to analyze associations between sex hormone levels and self-rated health, symptoms, depression and dementia in elderly men. Subjects and methods: The study population comprised 1252 subjects aged 65 years or over, living in the municipality of Lieto, south-western Finland. Self-rated health, life satisfaction, symptoms, depression, and dementia were assessed with specific questions, clinical examination and tools such as the Zung Self-report Depression Scale and the Mini-Mental State Examination. Independent variables were dichotomized, and associations of these variables with TSH, FT4 or sex hormone levels were assessed. Levels of TSH and FT4 in thyroid disease–free women and women treated with thyroxine were also compared. Results: Elevated concentrations of thyroid peroxidase antibodies (TPOAb) or thyroglobulin antibodies (TgAb) were found to have a marked effect on the upper reference limit for TSH among women, who were thyroid antibody positive more higher than suggested in several recent guidelines. After age adjustment, there were no associations between TSH levels and self-rated health, life satisfaction, or most neuropsychiatric symptoms in the thyroid disease-free population. Although women with thyroxine treatment for primary hypothyroidism had far higher TSH levels than thyroid disease-free women, there were no differences between thyroid-disease free women and women with stable thyroxine treatment regarding self-rated health, life satisfaction or symptoms. Age had a significant positive association with luteinizing hormone (LH), follicle 2 practice, one range in men aged 65 years or over can be used for T, E2 and FSH measured with the AutoDelfia method, but two separate reference intervals should be used for fT, LH and SHBG. After adjustment for age, higher levels of T and fT were associated with better self-rated health (SRH) in the reference population. After adjustment for age and body mass index (BMI), there were no associations between sex hormone concentrations and self-rated health, life satisfaction or most symptoms in concentration. Conclusion: Age-specific reference intervals were derived for thyroid function and sex hormones based on comprehensive data from a community-dwelling population with a high participation rate. The results do not support the need to decrease the upper reference limit for TSH or to lower the optimal TSH target in levothyroxine treatment in older adults, as recommended in recent guidelines. Older age or being overweight symptoms among elderly men. The associations of single symptoms with T levels were inconsistent among elderly men, although the association of low T level with diagnosed depression might be clinically significant.
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Regular aerobic exercise training, which is touted as a way to ameliorate metabolic diseases, increases aerobic capacity. Aerobic capacity usually declines with advanced age. The decline in aerobic capacity is typically associated by a decrease in the quality of skeletal muscle. At the molecular level, this decreased quality comes in part from perturbations in skeletal muscle mitochondria. Of particular is a decrease in the total amount of mitochondria that occupy the skeletal muscle volume. What is not well established is if this decrease in mitochondrial content is due to inactive lifestyle or the process of aging. Herein, the work of the thesis shows a clear connection between mitochondrial content and aerobic capacity. This indicates that active individuals with higher VChmax levels also contain higher volumes of mitochondria inside their muscle as opposed to sedentary counterparts who have lower levels of mitochondrial content. Upon taking these previously sedentary individuals and entering them into an aerobic exercise intervention, they are able to recover their mitochondrial content as well as function to similar levels of lifelong athletes of the same age. Furthermore, the results of this thesis show that mitochondrial content and function also correlate with exercise efficiency. If one is more efficient, he/she is able to expend less energy for a similar power output. Furthermore, individuals who increase in efficiency also increase in the ability to oxidize and utilize fat during pro-longed exercise. This increased reliance on fat after the intervention is associated with an increased amount of mitochondria, particularly in the intermyofibrillar region of skeletal muscle. Therefore, elderly adults who were once sedentary were able to recover mitochondrial content and function and are able to reap other health benefits from regular aerobic exercise training. Aging per se does not seem to be the culprit that will lead to metabolic diseases but rather it seems to be a lack of physical activity. -- Un entraînement sportif d'endurance, connu pour réduire le risque de développer des maladies métaboliques, augmente notre capacité aérobie. La capacité aérobie diminue généralement avec l'âge. Ce déclin est typiquement associé d'une diminution de la qualité du muscle squelettique. Au niveau moléculaire, cette diminution est due à des perturbations dans les mitochondries du muscle squelettique,, ce qui conduit à une diminution de la quantité totale des mitochondries présentes dans le muscle squelettique. Il n'a pas encore été établi si cette diminution de la teneur mitochondriale est due à un mode de vie sédentaire ou au processus du vieillissement. Ce travail de thèse montre un lien clair entre le contenu mitochondrial et la capacité aérobie. Il indique que des personnes âgées actives, avec des niveaux de V02max plus élevés, possèdent également un volume plus élevé de mitochondries dans leurs muscles en comparaison à leurs homologues sédentaires. En prenant des individus sédentaires et leur faisant pratiquer une activité physique aérobie, il est possible d'accroître leur contenu de même que leur fonction mitochondriale à des niveaux similaires à ceux d'athlètes du même âge ayant pratiqué une activité physique tout au long de leur vie. De plus, les résultats de ce travail démontrent que le contenu et la fonction mitochondriale sont en corrélation avec l'efficiscience lors d'exercice physique. En agumentant l'effiscience, les personnes sont alors capables de dépenser moins d'énergie pour une puissance d'exercice similaire. Donc, un volume mitochondrial accru dans le muscle squelettique, associé à une fonction mitochondriale améliorée, est associté à une augmentation de l'effiscience. En outre, les personnes qui augmentent leur effiscience, augmentent aussi leur capacité à oxyder les graisses durant l'exercice prolongé. Une augmentation du recours au graisses après l'intervention est associée à une quantité accrue de mitochondries, en particulier dans la région inter-myofibrillaire du muscle squelettique. Par conséquent, les personnes âgées autrefois sédentaires sont en mesure de récupérer leur contenu et leur fonction mitochondriale ainsi que d'autres avantages pour la santé grâce à un entraînement aérobie régulier. Le vieillissement en soi ne semble donc pas être le coupable conduisant aux maladies métaboliques qui semblent plutôt être lié à un manque d'activité physique.
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Osteoclasts are multinucleated bone degrading cells. Phosphate is an important constituent of mineralized bone and released in significant quantities during bone resorption. Molecular contributors to phosphate transport during the resorptive activity of osteoclasts have been controversially discussed. This study aimed at deciphering the role of sodium-dependent phosphate transporters during osteoclast differentiation and bone resorption. Our studies reveal RANKL-induced differential expression of sodium-dependent phosphate transport protein IIa (NaPi-IIa) transcript and protein during osteoclast development, but no expression of the closely related NaPi-IIb and NaPi-IIc SLC34 family isoforms. In vitro studies employing NaPi-IIa-deficient osteoclast precursors and mature osteoclasts reveal that NaPi-IIa is dispensable for bone resorption and osteoclast differentiation. These results are supported by the analysis of structural bone parameters by high-resolution microcomputed tomography that yielded no differences between adult NaPi-IIa WT and KO mice. By contrast, both type III sodium-dependent phosphate transporters Pit-1 and Pit-2 were abundantly expressed throughout osteoclast differentiation, indicating that they are the relevant sodium-dependent phosphate transporters in osteoclasts and osteoclast precursors. We conclude that phosphate transporters of the SLC34 family have no role in osteoclast differentiation and function and propose that Pit-dependent phosphate transport could be pivotal for bone resorption and should be addressed in further studies.
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Cardiovascular mortality is 15 to 30 times higher in patients with chronic kidney disease than in the age-adjusted general population. Even minor renal dysfunction predicts cardiovascular events and death in the general population. In patients with atherosclerotic renovascular disease the annual cardiovascular event and death rate is even higher. The abnormalities in coronary and peripheral artery function in the different stages of chronic kidney disease and in renovascular disease are still poorly understood, nor have the cardiac effects of renal artery revascularization been well characterized, although considered to be beneficial. This study was conducted to characterize myocardial perfusion and peripheral endothelial function in patients with chronic kidney disease and in patients with atherosclerotic renovascular disease. Myocardial perfusion was measured with positron emission tomography (PET) and peripheral endothelial function with brachial artery flow-mediated dilatation. It has been suggested that the poor renal outcomes after the renal artery revascularization could be due to damage in the stenotic kidney parenchyma; especially the reduction in the microvascular density, changes mainly evident at the cortical level which controls almost 80% of the total renal blood flow. This study was also performed to measure the effect of renal artery stenosis revascularization on renal perfusion in patients with renovascular disease. In order to do that a PET-based method for quantification of renal perfusion was developed. The coronary flow reserve of patients with chronic kidney disease was similar to the coronary flow reserve of healthy controls. In renovascular disease the coronary flow reserve was, however, markedly reduced. Flow-mediated dilatation of brachial artery was decreased in patients with chronic kidney disease compared to healthy controls, and even more so in patients with renovascular disease. After renal artery stenosis revascularization, coronary vascular function and renal perfusion did not improve in patients with atherosclerotic renovascular disease, but in patients with bilateral renal artery stenosis, flow-mediated dilatation improved. Chronic kidney disease does not significantly affect coronary vascular function. On the contrary, coronary vascular function was severely deteriorated in patients with atherosclerotic renovascular disease, possibly because of diffuse coronary artery disease and/or diffuse microvascular disease. The peripheral endothelial function was disturbed in patients with chronic kidney disease and even more so in patient with atherosclerotic renovascular disease. Renal artery stenosis dilatation does not seem to offer any benefits over medical treatment in patients with renovascular disease, since revascularization does not improve coronary vascular function or renal perfusion.
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Early identification of beginning readers at risk of developing reading and writing difficulties plays an important role in the prevention and provision of appropriate intervention. In Tanzania, as in other countries, there are children in schools who are at risk of developing reading and writing difficulties. Many of these children complete school without being identified and without proper and relevant support. The main language in Tanzania is Kiswahili, a transparent language. Contextually relevant, reliable and valid instruments of identification are needed in Tanzanian schools. This study aimed at the construction and validation of a group-based screening instrument in the Kiswahili language for identifying beginning readers at risk of reading and writing difficulties. In studying the function of the test there was special interest in analyzing the explanatory power of certain contextual factors related to the home and school. Halfway through grade one, 337 children from four purposively selected primary schools in Morogoro municipality were screened with a group test consisting of 7 subscales measuring phonological awareness, word and letter knowledge and spelling. A questionnaire about background factors and the home and school environments related to literacy was also used. The schools were chosen based on performance status (i.e. high, good, average and low performing schools) in order to include variation. For validation, 64 children were chosen from the original sample to take an individual test measuring nonsense word reading, word reading, actual text reading, one-minute reading and writing. School marks from grade one and a follow-up test half way through grade two were also used for validation. The correlations between the results from the group test and the three measures used for validation were very high (.83-.95). Content validity of the group test was established by using items drawn from authorized text books for reading in grade one. Construct validity was analyzed through item analysis and principal component analysis. The difficulty level of most items in both the group test and the follow-up test was good. The items also discriminated well. Principal component analysis revealed one powerful latent dimension (initial literacy factor), accounting for 93% of the variance. This implies that it could be possible to use any set of the subtests of the group test for screening and prediction. The K-Means cluster analysis revealed four clusters: at-risk children, strugglers, readers and good readers. The main concern in this study was with the groups of at-risk children (24%) and strugglers (22%), who need the most assistance. The predictive validity of the group test was analyzed by correlating the measures from the two school years and by cross tabulating grade one and grade two clusters. All the correlations were positive and very high, and 94% of the at-risk children in grade two were already identified in the group test in grade one. The explanatory power of some of the home and school factors was very strong. The number of books at home accounted for 38% of the variance in reading and writing ability measured by the group test. Parents´ reading ability and the support children received at home for schoolwork were also influential factors. Among the studied school factors school attendance had the strongest explanatory power, accounting for 21% of the variance in reading and writing ability. Having been in nursery school was also of importance. Based on the findings in the study a short version of the group test was created. It is suggested for use in the screening processes in grade one aiming at identifying children at risk of reading and writing difficulties in the Tanzanian context. Suggestions for further research as well as for actions for improving the literacy skills of Tanzanian children are presented.
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Matrix metalloproteinase-13 (MMP-13) is a potent proteolytic enzyme, whose expression has been previously associated with fetal bone development and postnatal bone remodeling and with adult gingival wound healing. MMP-13 is also known to be involved in the growth and invasion of various cancers including squamous cell carcinoma (SCC) of the skin. The aim of this study was to further elucidate the function and regulation of MMP-13 in wound repair and cancer. In this study, it was shown that fetal skin fibroblasts express MMP-13 in response to transforming growth factor-β in a p38 MAP kinase dependent manner. In addition, MMP-13 was found to be expressed in vivo by wound fibroblasts in human fetal skin grafted on SCID mice. Adenovirally delivered expression of MMP-13 enhanced collagen matrix contraction by fibroblasts in vitro in association with altered cytoskeletal structure, enhanced proliferation and survival. These results indicate that MMP-13 is involved in cell-mediated collagen matrix remodeling and suggest a role for MMP-13 in superior matrix remodeling and scarless healing of fetal skin wounds. Using an MMP-13 deficient mouse strain, it was shown that MMP-13 is essential for the normal development of experimental granulation tissue in mice. MMP-13 was implicated in the regulation of myofibroblast function and angiogenesis and the expression of genes involved in cellular proliferation and movement, immune response, angiogenesis and proteolysis. Finally, epidermal mitogen, keratinocyte growth factor (KGF) was shown to suppress the malignant properties of skin SCC cells by downregulating the expression of several target genes with potential cancer promoting properties, including MMP-13, and by reducing SCC cell invasion. These results provide evidence that MMP-13 potently regulates cell viability, myofibroblast function and angiogenesis associated with wound healing and cancer. In addition, fibroblasts expressing MMP-13 show high collagen reorganization capacity. Moreover, the results suggest that KGF mediates the anti-cancer effects on skin SCC
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Objective: To evaluate the influence of end-stage liver disease and orthotopic liver transplantation in the pituitary function and hormone metabolism before and after liver transplantation.Methods: In a prospective study, serum levels of follicle stimulating hormone (FSH), luteinizing hormone (LH), estradiol (E2) and prolactin (PRL) of 30 male patients with cirrhosis were determined two to four hours before and six months after liver transplantation. The results were compared according to the Model for End-stage Liver Disease (MELD).Results: male patients with liver cirrhosis have hypogonadism. FSH was normal, but inappropriately low due to androgen failure; E2 and PRL, on their turn, were high. After liver transplantation, FSH and LH levels increased (p < 0.05), whereas E2 and PRL normalized (p < 0.05). The MELD score did not influence changes in FSH, PRL and LH, however, the more severe the cirrhosis was, the more significant was the normalization of E2 (p = 0.01).Conclusion: Patients with cirrhosis and male hypogonadism have inappropriately normal levels of FSH and LH, associated with an increase in E2 and LRP. After liver transplantation, FSH and LH increased, while E2 and PRL returned to normal. Changes in E2 levels were most pronounced in patients with MELD > 18. The severity of cirrhosis had no influence on FSH, PRL and LH.
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The biological variation in nature is called biodiversity. Anthropogenic pressures have led to a loss of biodiversity, alarming scientists as to what consequences declining diversity has for ecosystem functioning. The general consensus is that diversity (e.g. species richness or identity) affects functioning and provides services from which humans benefit. The aim of this thesis was to investigate how aquatic plant species richness and identity affect ecosystem functioning in terms of processes such as primary production, nutrient availability, epifaunal colonization and properties e.g. stability of Zostera marina subjected to shading. The main work was carried out in the field and ranged temporally from weeklong to 3.5 months-long experiments. The experimental plants used frequently co-occur in submerged meadows in the northern Baltic Sea and consist of eelgrass (Z. marina), perfoliate pondweed (Potamogeton perfoliatus), sago pondweed (P. pectinatus), slender-leaved pondweed (P. filiformis) and horned pondweed (Zannichellia palustris). The results showed that plant richness affected epifaunal community variables weakly, but had a strong positive effect on infaunal species number and functional diversity, while plant identity had strong effects on amphipods (Gammarus spp.), of which abundances were higher in plant assemblages consisting of P. perfoliatus. Depending on the starting standardizing unit, plant richness showed varying effects on primary production. In shoot density-standardized plots, plant richness increased the shoot densities of three out of four species and enhanced the plant biomass production. Both positive complementarity and selection effects were found to underpin the positive biodiversity effects. In shoot biomass-standardized plots, richness effects only affected biomass production of one species. Negative selection was prevalent, counteracting positive complementarity, which resulted in no significant biodiversity effect. The stability of Z. marina was affected by plant richness in such that Z. marina growing in polycultures lost proportionally less biomass than Z. marina in monocultures and thus had a higher resistance to shading. Monoculture plants in turn gained biomass faster, and thereby had a faster recovery than Z. marina growing in polycultures. These results indicate that positive interspecific interactions occurred during shading, while the faster recovery of monocultures suggests that the change from shading stress to recovery resulted in a shift from positive interactions to resource competition between species. The results derived from this thesis show that plant diversity affects ecosystem functioning and contribute to the growing knowledge of plant diversity being an important component of aquatic ecosystems. Diverse plant communities sustain higher primary productivity than comparable monocultures, affect faunal communities positively and enhance stability. Richness and identity effects vary, and identity has generally stronger effects on more variables than richness. However, species-rich communities are likely to contain several species with differing effects on functions, which renders species richness important for functioning. Mixed meadows add to coastal ecosystem functioning in the northern Baltic Sea and may provide with services essential for human well-being.
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The aim of this dissertation is to bridge and synthesize the different streams of literature addressing ecosystem architecture through a multiple‐lens perspective. In addition, the structural properties of and processes to design and manage the architecture will be examined. With this approach, the oft‐neglected actor‐structure duality is addressed and both the position and structure, and action and process are under scrutiny. Further, the developed framework and empirical evidence offer valuable insights on how firms collectively create value and individually appropriate value. The dissertation is divided into two parts. The first part comprises a literature review, as well as the conclusions of the whole study, and the second part includes six research publications. The dissertation is based on three different reasoning logics: abduction, induction and deduction; related qualitative and quantitative methodologies are utilized in the empirical examination of the phenomenon in the information and communication technology industry. The results suggest firstly that there are endogenous and exogenous structural properties of the ecosystem architecture. Out of these, the former ones can be more easily influenced by a particular actor whereas the latter ones are taken more or less for granted. Secondly, the exogenous ecosystem design properties influence the value creation potential of the ecosystem whereas the endogenous ecosystem design properties influence the value appropriation potential of a particular actor in the ecosystem. Thirdly, the study suggests that there is a relationship between endogenous and exogenous structural properties in that the endogenous properties can be leveraged to create and reconfigure the exogenous properties whereas the exogenous properties prose opportunities and restrictions on the use of endogenous properties. In addition, the study suggests that there are different emergent and engineered processes to design and manage ecosystem architecture and to influence both the endogenous and exogenous structural properties of ecosystem architecture. This study makes three main contributions. First, on the conceptual level, it brings coherence and direction to the fast growing body of literature on novel inter‐organizational arrangements, such as ecosystems. It does this by bridging and synthetizing three different streams of literature, namely the boundary, design and orchestration conception. Secondly, it sets out a framework that enhances our understanding of the structural properties of ecosystem architecture; of the processes to design and manage ecosystem architecture; and of their influence on the value creation potential of the ecosystem and the value capture potential of a particular firm. Thirdly, it offers empirical evidence of the structural properties and processes.
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Cystic fibrosis (CF) is a lethal autosomal recessive genetic disease caused by mutations in the CF transmembrane conductance regulator (CFTR). Mutations in the CFTR gene may result in a defective processing of its protein and alter the function and regulation of this channel. Mutations are associated with different symptoms, including pancreatic insufficiency, bile duct obstruction, infertility in males, high sweat Cl-, intestinal obstruction, nasal polyp formation, chronic sinusitis, mucus dehydration, and chronic Pseudomonas aeruginosa and Staphylococcus aureus lung infection, responsible for 90% of the mortality of CF patients. The gene responsible for the cellular defect in CF was cloned in 1989 and its protein product CFTR is activated by an increase of intracellular cAMP. The CFTR contains two membrane domains, each with six transmembrane domain segments, two nucleotide-binding domains (NBDs), and a cytoplasmic domain. In this review we discuss the studies that have correlated the role of each CFTR domain in the protein function as a chloride channel and as a regulator of the outwardly rectifying Cl- channels (ORCCs).
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The effects of strenuous exercise before and during pregnancy on the renal function and morphological alterations of the progeny were determined in a study on female Wistar rats. This research was done based on a previous study carried out in our laboratory, which showed morphological alterations in rats submitted to this kind of exercise. As the form is related to the function, the physiological relevance of submitting a pregnant female to a high-intensity exercise training regimen could be explained by the fact that morphological alterations can influence kidney function. The animals were assigned to one of two groups: control animals that did not exercise during pregnancy and trained animals that swam for 120 min 5 days a week for 8 weeks before pregnancy and daily for 60 min over a period of 8 weeks starting on the second day of pregnancy. Seven rats of each group were analyzed for morphological alterations and for renal function. The progeny of the rats used for morphological evaluation were born by cesarean section and the progeny of the animals used to evaluate renal function were born normally. The progeny were two months old when renal function was evaluated. Fertility and morbidity were the same for both groups. Strenuous maternal exercise had no significant influence on glomerular filtration rate (GFR) but renal plasma flow was lower in the progeny of the trained group (mean ± SD, 16.65 ± 3.77 ml min-1 kg-1) compared to the progeny of the control group (33.42 ± 2.56 ml min-1 kg-1). Antidiuretic and antinatriuretic effects on the progeny of the trained group were observed, since urine flow as percentage of GFR and the fraction of urinary sodium excretion were lower in this group (1.38 ± 0.10 and 0.60 ± 0.04%, respectively) compared to the progeny of the control group (2.36 ± 0.11 and 1.55 ± 0.20%, respectively). Moreover, in this exercise program, fetuses from trained animals were small-sized (2.45 ± 0.19 vs 4.66 ± 2.45 g for control animals) and showed lower differentiation compared to fetuses from the control group. These effects were probably caused by caloric restriction, hypoxia and reduction of umbilical cord length.
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The objective of the present study was to determine contrast sensitivity curves of concentric circular patterns with radial frequencies of 0.25, 0.5, 1.0, 2.0, and 4.0 cycles per degree in young and older adult volunteers. These parameters were also compared with sensitivity contrasts for sine-wave gratings. All participants had normal acuity vision and were free of identifiable ocular illness. Contrast sensitivity was measured in 6 young adults aged 19 to 23 years and 6 older adults aged 60 to 69 years using the psychophysical forced-choice method. In this paradigm the volunteers had to decide which of two stimuli contained the above radial frequencies at low contrast levels. The other neutral stimulus was gray with homogeneous luminance. We detected a decline in contrast sensitivity for older adults at all radial frequencies compared to young adults. Also, contrast sensitivity for sine-wave gratings at all measured frequencies was better, as predicted, for all young adults. Maximum sensitivities in the radial frequency contrast sensitivity function and contrast sensitivity function occurred at 0.25 and 0.5 cycles per degree, respectively, for both young and older adults. These results suggest age-related changes in the contrast sensitivity function for concentric symmetrical stimuli.
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Heart failure is a common endpoint for many forms of cardiovascular disease and a significant cause of morbidity and mortality. Chronic neurohumoral excitation (i.e., sympathetic hyperactivity) has been considered to be a hallmark of heart failure and is associated with a poor prognosis, cardiac dysfunction and remodeling, and skeletal myopathy. Aerobic exercise training is efficient in counteracting sympathetic hyperactivity and its toxic effects on cardiac and skeletal muscles. In this review, we describe the effects of aerobic exercise training on sympathetic hyperactivity, skeletal myopathy, as well as cardiac function and remodeling in human and animal heart failure. We also discuss the mechanisms underlying the effects of aerobic exercise training.