4,441 research outputs found
Renal Function in Suckling and Fasting Pups of the Northern Elephant Seal
Elephant seals fast for prolonged periods without access to water. This is made possible, in part, by reductions in urine production. However, the mechanisms involved in reducing urine production are not understood. In this study, glomerular filtration rate (GFR) was measured in five northern elephant seal pups (Mirounga angustirostris) via the inulin clearance technique. Measurements were made during day 9 and day 18â22 of nursing and the second and eighth week of the postweaning fast. Plasma aldosterone and cortisol concentrations, quantified by radioimmunoassay, were measured in eight other weanlings during the second and eighth week of the fast. Mean GFR was 79.3±29.3 ml/min during the early suckling period and 78.2±17.1, 89.8±52.7, and 80.4±12.2 ml/min during the late suckling, early fasting and late fasting periods, respectively. Differences between nursing and fasting were insignificant, possibly because reduced protein oxidation during suckling and rapid recruitment of protein for tissue synthesis obviated the need for postprandial hyperfiltration. Alternatively, maintenance of GFR during fasting may facilitate urea concentration by compensating for reductions in the fractional excretion of urea. It is further hypothesized that aldosterone is primarily responsible for mediating renal water reabsorption in this system
Angiotensin II and Aldosterone Increase with Fasting in Breeding Adult Male Northern Elephant Seals (Mirounga angustirostris)
The reninâangiotensinâaldosterone system (RAAS) appears to contribute significantly to osmoregulation of fasting northern elephant seal (Mirounga angustirostris) pups; however, RAAS has not been characterized in fasting adult seals. Therefore, this study examined the contribution of RAAS to water turnover rates in fasting adult male northern elephant seals. Blood samples were obtained twice during their breeding fast at an interval of 6.5 wk, and water efflux rate was estimated by isotopic dilution during the same period. Serum electrolytes (Na+, K+, Clâ) and osmolality were unaltered between the two sampling periods, indicating ionic and osmotic homeostasis during the fast. Despite the lack of an increase in vasopressin, serum angiotensin II and aldosterone were increased and were significantly and positively correlated. Changes in aldosterone concentration and water efflux rate were significantly and negatively correlated, suggesting that the greater the increase in aldosterone, the smaller the loss of water. Adult male seals maintain ionic and osmotic homeostasis similar to that of fasting weaned pups, and this homeostasis appears to be mediated, at least in part, by RAAS, which probably contributes to increased water retention as well. The hormonal mechanisms by which northern elephant seals maintain water and electrolyte balance during fasting conditions appear to be similar regardless of age
Recommended from our members
Preparation and Properties of In-Situ Devices Using the SALD and SALDVI Techniques
One of the many advantages of Selective Area Laser Deposition (SALD) and Selective
Area Laser Deposition Vapor Infiltration (SALDVI) is that they can be used to embed in-situ
micro-sensors within macro-components. A single-point SiC/C thermocouple sensor embedded
within a SiC macro-component and electrically insulated with silicon nitride layers has been
demonstrated. In many applications, multi-point sensors within a single component are needed,
e.g., in monitoring the temperature gradient and distribution at different positions. In this paper,
multi-point thermocouple devices are demonstrated. The macro-component is a SiC bulk shape
made by infiltrating vapor deposited silicon carbide into a silicon carbide powder bed using the
SALDVI technique. Multiple SiC/C thermocouples are embedded in-situ in the SiC bulk shape
using the SALD technique. The transient and steady state responses ofthe embedded
thermocouples are compared to reference thermocouples probing the surfaces of the bulk shape.Mechanical Engineerin
The Effects of Children's Time Use and Home and Neighborhood Quality on their Body Weight and Cognitive/Behavioral Development
We estimate a directional distance function to assess the impacts of multiple time-varying parent and child inputs on a cluster of jointly produced child outcomes for children aged 7 to 13 years. The directional distance function specification avoids several well-known empirical problems associated with analysis of household production data, namely, the need to aggregate inputs and outputs, assume separability among inputs and outputs, or estimate reduced form equations. Using a balanced panel of families from the National Longitudinal Survey of Youth-Child Sample for 1996 to 2000, we assess the marginal contributions of home and neighborhood environmental quality and children's time allocations, on their math and reading performance, behavior problems, and body mass index. We also measure productivity growth, technical change, efficiency change, and technical efficiency for production of child outcomes. Our results indicate significant jointness among good and bad child outcomes. Significant improvements in children's good outcomes and reductions in bad outcomes are also associated with a better home and parent perceived neighborhood environment, Head Start participation, and increased family time spent together during meals. Children's productivity growth is found to be highest at age 8 years and diminishes thereafter.Health Economics and Policy, Labor and Human Capital,
Hormone and Metabolite Changes associated with Extended Breeding Fasts in Male Northern Elephant Seals (Mirounga Angustirostris)
We measured metabolic hormones and several key metabolites in breeding adult male northern elephant seals to examine the regulation of fuel metabolism during extended natural fasts of over 3 months associated with high levels of energy expenditure. Males were sampled twice, early and late in the fast, losing an average of 23% of body mass and 47% of adipose stores between measurements. Males exhibited metabolic homeostasis over the breeding fast with no changes in glucose, non-esterified fatty acids, or blood urea nitrogen. Ketoacids increased over the fast but were very low when compared to other fasting species. Changes within individuals in total triiodothyronine (tT3) were positively related to daily energy expenditure (DEE) and protein catabolism. Differences in levels of thyroid hormones relative to that observed in weaned pups and females suggest a greater deiodination of T4 to support the high DEE of breeding males. Relative levels of leptin and ghrelin were consistent with the suppression of appetite but a significant reduction in growth hormone across the fast was contrary to expectation in fasting mammals. The lack of the increase in cortisol during fasting found in conspecific weaned pups and lactating females may contribute to the ability of breeding males to spare protein despite high levels of energy expenditure. Together these findings reveal significant differences with conspecifics under varying nutrient demands, suggesting metabolic adaptation to extended high energy fasts
Comment on "Long-range electrostatic interactions between like-charged colloids: Steric and confinement effects"
In a recent study [Phys. Rev. E 60, 6530 (1999)], Trizac and Raimbault showed
that the effective pair interaction between like charged colloids immersed in a
cylindrically confined electrolyte remains repulsive even when the size of the
micro-ions or the finite longitudinal extension of the confining cylinder are
taken into account. Contrary to their claim, we argue that the case of finite
longitudinal confinement doesn't always generate repulsive interactions and to
illustrate this point we also provide a simple example.Comment: 3 pages, 1 figure. Accepted for publication in Phys. Rev. E 200
Specificity and entropy reduction in situated referential processing
In situated communication, reference to an entity in the shared visual context can be established using eitheranexpression that conveys precise (minimally specified) or redundant (over-specified) information. There is, however, along-lasting debate in psycholinguistics concerningwhether the latter hinders referential processing. We present evidence from an eyetrackingexperiment recordingfixations as well asthe Index of Cognitive Activity âa novel measure of cognitive workload âsupporting the view that over-specifications facilitate processing. We further present originalevidence that, above and beyond the effect of specificity,referring expressions thatuniformly reduce referential entropyalso benefitprocessin
The Clerkship-Academia Continuum
In the spring 2021 edition of Judicature (Vol. 105 No. 1), Florida International University Law Professor Howard Wasserman published data analyzing the number of current law professors who have served in clerkships and for which judges those professors clerked. His study offered a compelling picture of âacademic feeder judges,â or those on the bench whose clerks tended to matriculate professionally in large numbers within the halls of the academy.
We asked two law professors, Merritt McAlister at the University of Florida, and Katherine Mims Crocker of William & Mary Law School, to reflect on Wassermanâs findings and to offer a personal account of how their clerkships shaped their lives
Diffusion of Point Defects in Two-Dimensional Colloidal Crystals
We report the first study of the dynamics of point defects, mono and
di-vacancies, in a confined 2-D colloidal crystal in real space and time using
digital video microscopy. The defects are introduced by manipulating individual
particles with optical tweezers. The diffusion rates are measured to be
Hz for mono-vacancies and
Hz for di-vacancies. The elementary diffusion
processes are identified and it is found that the diffusion of di-vacancies is
enhanced by a \textit{dislocation dissociation-recombination} mechanism.
Furthermore, the defects do not follow a simple random walk but their hopping
exhibits memory effects, due to the reduced symmetry (compared to the
triangular lattice) of their stable configurations, and the slow relaxation
rates of the lattice modes.Comment: 6 pages (REVTEX), 5 figures (PS
- âŠ