Home About us Contact
|
Home About us Contact | ||
|
|
||
Allometric Scaling (allometric + scaling)
Selected AbstractsAllometric scaling of maximum population density: a common rule for marine phytoplankton and terrestrial plantsECOLOGY LETTERS, Issue 5 2002Andrea Belgrano A primary goal of macroecology is to identify principles that apply across varied ecosystems and taxonomic groups. Here we show that the allometric relationship observed between maximum abundance and body size for terrestrial plants can be extended to predict maximum population densities of marine phytoplankton. These results imply that the abundance of primary producers is similarly constrained in terrestrial and marine systems by rates of energy supply as dictated by a common allometric scaling law. They also highlight the existence of general mechanisms linking rates of individual metabolism to emergent properties of ecosystems. [source] Allometric scaling of maximum metabolic rate: the influence of temperatureFUNCTIONAL ECOLOGY, Issue 4 2008C. R. White Summary 1Maximum aerobic metabolic rate, measured in terms of rate of oxygen consumption during exercise (), is well known to scale to body mass (M) with an exponent greater than the value of 0·75 predicted by models based on the geometry of systems that supply nutrients. 2Recently, the observed scaling for (,M0·872) has been hypothesized to arise because of the temperature dependence of biological processes, and because large species show a greater increase in muscle temperature when exercising than do small species. 3Based on this hypothesis, we predicted that will be positively related to ambient temperature, because heat loss is restricted at high temperatures and body temperature is likely to be elevated to a greater extent than during exercise in the cold. 4This prediction was tested using a comparative phylogenetic generalized least-squares (PGLS) approach, and 34 measurements of six species of rodent (20·5,939 g) maximally exercising at temperatures from ,16 to 30 °C. 5 is unrelated to testing temperature, but is negatively related to acclimation temperature. We conclude that prolonged cold exposure increases exercise-induced by acting as a form of aerobic training in mammals, and that elevated muscle temperatures of large species do not explain the scaling of across taxa. [source] Allometric scaling of marbofloxacin, moxifloxacin, danofloxacin and difloxacin pharmacokinetics: a retrospective analysisJOURNAL OF VETERINARY PHARMACOLOGY & THERAPEUTICS, Issue 5 2007S. K. COX The purpose of this study was to examine the allometric analyses of marbofloxacin, moxifloxacin, danofloxacin and difloxacin using pharmacokinetic data from the literature. The parameters of interest (half-life, clearance and volume of distribution) were correlated across species as a function of body weight using an allometric approach (Y = aWb). Results of the allometric analysis indicated similarity between clearance and volume of distribution as they relate to body weight for all drugs. The elimination half-life was independent of body mass for all fluoroquinolones except moxifloxacin. Results of the analysis suggest that allometric scaling can be used as a tool for predicting pharmacokinetic parameters for fluoroquinolones. [source] Pharmacokinetics and allometric scaling of levormeloxifene, a selective oestrogen receptor modulatorBIOPHARMACEUTICS AND DRUG DISPOSITION, Issue 3 2003O. Østerberg Abstract The pharmacokinetics of a new selective oestrogen receptor modulator levormeloxifene was investigated in mice, rats, cynomolgus monkeys and humans by compartmental pharmacokinetics. Levormeloxifene was administered as an oral solution in all studies. Allometric scaling was used to predict human pharmacokinetic parameters and the performance of the approach was evaluated. Mean values of clearance confounded by F(CL/F) were 0.073, 0.29, 3.18 and 2.4 l/h in mice, rats, monkeys and humans, respectively. Values of distribution volume at steady state confounded by F(Vss/F) were 0.073 and 7.5 l in mice and rats. In monkeys, values of the central volume F(Vc/F) and volume at steady state F(Vss/F) were 28.9 and 57.9 l, respectively. In humans, values of Vc/F and Vss/F were 106 and 587 l, respectively. Predicted CL/F and Vss/F showed a linear relationship when plotted vs BW on a log,log scale; for CL/F, r was 0.95,0.98 and for Vss/F, r was 0.99. Using allometric scaling the predicted human Vss/F deviated 3-fold from the experimentally determined values. Observed values of CL/F deviated 21,25 fold from the predicted, the latter depending on the scaling method. Confidence intervals for the predicted parameters showed major lack of precision for all the allometric scaling methods. Copyright © 2003 John Wiley & Sons, Ltd. [source] Community heterogeneity and single-cell digestive activity of estuarine heterotrophic nanoflagellates assessed using lysotracker and flow cytometryENVIRONMENTAL MICROBIOLOGY, Issue 7 2010Eva Sintes Summary Heterotrophic nanoflagellates (HNFs) are an essential component of all aquatic microbial food webs, and yet the exploration of the numerical and single-cell responses of these organisms in mixed assemblages still represents a major technical challenge. LysoTracker Green staining combined with flow cytometry was recently proposed for the enumeration of aquatic HNFs. Here we show that LysoTracker Green not only allows the enumeration of HNFs in estuarine samples with a wide range of HNF abundances, but also allows the discrimination of distinct HNF populations in mixed assemblages. In addition, the resulting cytometric parameters can be used to characterize cell size and the level of activity of the cells in the different populations that are detected. LysoTracker Green accumulates preferentially in lysosomes, and we demonstrate that the green fluorescence emission from HNF cells stained with LysoTracker strongly correlates with cell-specific ,-glucosaminidase (,-Gam) activity, a key digestive enzyme of lysosomal origin in eukaryotic cells. Our results further show that different populations that develop in estuarine regrowth cultures are characterized by different intrinsic ranges of size and of feeding activity, and that there is a wide range of single-cell responses within these HNF populations. We found a large degree of uncoupling between cell size and feeding activity, both between and within HNF populations, and there appears to be no clear allometric scaling of feeding activity. We were able to reconstruct the succession of distinct HNF populations that developed during the regrowth experiments, and explore the complex interactions that occurred between numerical (change in abundance of the cytometric populations) and single-cell HNF responses. [source] Red Cell Pulmonary Transit Times Through the Healthy Human LungEXPERIMENTAL PHYSIOLOGY, Issue 2 2003G. S. Zavorsky It has previously been postulated that rapid red cell capillary transit through the human lung plays a role in the mechanism of diffusion limitation in some endurance athletes. Methodological limitations currently prevent researchers from directly measuring pulmonary capillary transit times in humans during exercise; however, first pass radionuclide cardiography allows direct measurement of red blood cell (RBC) transit times through the whole lung at various exercise intensities. We examined the relationship between mean whole lung red cell pulmonary transit times (cardiopulmonary transit times or CPTT) and different levels of flow in 88 healthy humans (76 males, 12 females) from several studies (mean age 31 years). The pooled data suggest that the relationship between CPTT and cardiac index (CI), beginning at rest and progressing through to maximum exercise demonstrates that CPTT reaches its minimum value when CI is about 8.1 l m2 min,1 (2.5-3 times the CI value at rest), and does not significantly change with further increases in CI. Cardiopulmonary blood volume (CPBV) index also does not change significantly until CI reaches 2.5 to 3 times the CI value at rest and then increases roughly linearly after that point. Consequently, the systematic increase in CPBV index with increasing pulmonary blood flow between 8.1 and 20 l m2 min,1 displays an adaptive response of the cardiopulmonary system by augmenting CPBV (and perhaps pulmonary capillary blood volume through distension and recruitment) to offset the reduction in CPTT, as no significant difference in mean CPTT is observed between these levels of flow (P > 0.05). Therefore, these data demonstrate that CPBV does not reach maximum capacity during strenuous or maximum exercise. This does not support the principle of quarter-power allometric scaling for flow when explaining modifications during exercise. Therefore, we speculate that the observed relationships between CPTT, CBPV index and flow may prevent mean CPTT (and perhaps mean pulmonary capillary transit times) from decreasing below the threshold time required for oxygenation. [source] Ontogenic changes in the allometric scaling of the mass and length relationship in Sprattus sprattusJOURNAL OF FISH BIOLOGY, Issue 3 2005M. A. Peck An analysis of mass (M) and standard length (LS) data for larval, juvenile and adult sprat (Sprattus sprattus; Clupeidae) revealed marked changes in the allometric scaling factor (b in ). For sprat <44 mm LS, b was 5·0, whereas in larger juveniles and adults, b was c. 3·4 indicating a relatively protracted metamorphic period for this species. [source] A global examination of allometric scaling for predicting human drug clearance and the prediction of large vertical allometry,JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 8 2006Huadong Tang Abstract Allometrically scaled data sets (138 compounds) used for predicting human clearance were obtained from the literature. Our analyses of these data have led to four observations. (1) The current data do not provide strong evidence that systemic clearance (CLs; n,=,102) is more predictable than apparent oral clearance (CLpo; n,=,24), but caution needs to be applied because of potential CLpo prediction error caused by differences in bioavailability across species. (2) CLs of proteins (n,=,10) can be more accurately predicted than that of non-protein chemicals (n,=,102). (3) CLs is more predictable for compounds eliminated by renal or biliary excretion (n,=,33) than by metabolism (n,=,57). (4) CLs predictability for hepatically eliminated compounds followed the order: high CL (n,=,11),>,intermediate CL (n,=,17),>,low CL (n,=,29). All examples of large vertical allometry (% error of prediction greater than 1000%) occurred only when predicting human CLs of drugs having very low CLs. A qualitative analysis revealed the application of two potential rules for predicting the occurrence of large vertical allometry: (1) ratio of unbound fraction of drug in plasma (fu) between rats and humans greater than 5; (2) C logP greater than 2. Metabolic elimination could also serve as an additional indicator for expecting large vertical allometry. © 2006 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 95: 1783,1799, 2006 [source] Allometric scaling of marbofloxacin, moxifloxacin, danofloxacin and difloxacin pharmacokinetics: a retrospective analysisJOURNAL OF VETERINARY PHARMACOLOGY & THERAPEUTICS, Issue 5 2007S. K. COX The purpose of this study was to examine the allometric analyses of marbofloxacin, moxifloxacin, danofloxacin and difloxacin using pharmacokinetic data from the literature. The parameters of interest (half-life, clearance and volume of distribution) were correlated across species as a function of body weight using an allometric approach (Y = aWb). Results of the allometric analysis indicated similarity between clearance and volume of distribution as they relate to body weight for all drugs. The elimination half-life was independent of body mass for all fluoroquinolones except moxifloxacin. Results of the analysis suggest that allometric scaling can be used as a tool for predicting pharmacokinetic parameters for fluoroquinolones. [source] Interspecies allometric scaling: prediction of clearance in large animal species: Part II: mathematical considerationsJOURNAL OF VETERINARY PHARMACOLOGY & THERAPEUTICS, Issue 5 2006M. MARTINEZ Interspecies scaling is a useful tool for the prediction of pharmacokinetic parameters from animals to humans, and it is often used for estimating a first-time in human dose. However, it is important to appreciate the mathematical underpinnings of this scaling procedure when using it to predict pharmacokinetic parameter values across animal species. When cautiously applied, allometry can be a tool for estimating clearance in veterinary species for the purpose of dosage selection. It is particularly valuable during the selection of dosages in large zoo animal species, such as elephants, large cats and camels, for which pharmacokinetic data are scant. In Part I, allometric predictions of clearance in large animal species were found to pose substantially greater risks of inaccuracies when compared with that observed for humans. In this report, we examine the factors influencing the accuracy of our clearance estimates from the perspective of the relationship between prediction error and such variables as the distribution of body weight values used in the regression analysis, the influence of a particular observation on the clearance estimate, and the ,goodness of fit' (R2) of the regression line. Ultimately, these considerations are used to generate recommendations regarding the data to be included in the allometric prediction of clearance in large animal species. [source] Resting breathing frequency in aquatic birds: a comparative analysis with terrestrial speciesJOURNAL OF ZOOLOGY, Issue 2 2009J. P. Mortola Abstract Several studies have indicated that in birds breathing frequency (f, breaths min,1) scales to the ,1/3 of body weight (W, kg); this is different from the ,1/4 of mammals. We wondered if this discrepancy was due to the peculiar scaling pattern of aquatic birds, as is the case of aquatic mammals. In fact, we had noted previously that the allometric scaling of f differs considerably between aquatic and terrestrial mammals, respectively, W,0.42 and W,0.25. Measurements of f were obtained in 48 aquatic birds of 22 species and in 35 terrestrial birds of 27 species, during resting conditions on land. Additional data from 11 aquatic and 14 terrestrial species, different from the ones measured, were obtained from the literature. The allometric curve of all species combined (terrestrial and aquatic, n=74) was f=13.3W,0.36, similar to what is reported in previous studies. However, the allometric curve of the aquatic species (n=33, f=14.5W,0.56) differed greatly (P<0.001) from that of the terrestrial species (n=41, f=13.4W,0.26). On average, f of aquatic birds of the 3,5 kg range was 63%, and that of birds of larger size was 57%, of the values of terrestrial birds of similar W. We conclude that, as in mammals, also in terrestrial birds f scales to the ,1/4 exponent of W. The similarity of the scaling patterns of f between aquatic birds and mammals suggests a common breathing adaptation to life in the aquatic environment irrespective of phylogenetic relations. [source] An analysis and review of models of the sociobiology of the MustelidaeMAMMAL REVIEW, Issue 3-4 2000Dominic D. P. Johnson ABSTRACT Classical models of social organization in mustelids suggest that female ranging patterns are determined by the dispersion of resources, whereas those of males are determined by the dispersion of females. However, mating systems and social spacing patterns vary widely both between and within species. For example, European Badgers exhibit a continuum from the classical mustelid model of intra-sexual territoriality and inter-sexual overlap to very large, mixed-sex, promiscuous groups. We evaluated hypotheses and existing data to explain this variation, using comparative analyses and Principal Components Analysis of life history and ecological variables. In addition, we applied a null model of allometric scaling to test for associations between group mass and residual home range size. We found that: (1) the degree of social behaviour and breeding group size increased with life history variables indicative of K-selected strategies of parental investment. (2) Absolute home range size and residual home range size (derived from allometric home range scaling) decreased, paradoxically, with breeding group size and group mass, respectively. These results provide support for ecological theories of social grouping in general and, in particular, for the importance of dispersed resource-rich patches as developed in the Resource Dispersion Hypothesis. [source] Pharmacokinetics and its role in small molecule drug discovery researchMEDICINAL RESEARCH REVIEWS, Issue 5 2001Graham R. Jang Abstract Pharmacokinetics (PK), which describes the disposition of a drug in the body, should be a primary consideration in the selection of a drug candidate, ultimately contributing to its eventual clinical success or failure. Accordingly, a sound understanding of PK concepts and an appreciation of the judicious use of PK and related (e.g., metabolism, transporter) data in drug discovery can be beneficial to those involved in the process. This review defines important PK parameters (e.g., clearance, volume of distribution, half-life), describes methods of PK data analysis (noncompartmental vs. compartmental) and provides an overview of additional concepts such as allometric scaling, PK/pharmacodynamic modeling, and nonlinear PK. Furthermore, the role and strategic use of PK screens in drug discovery are discussed. © 2001 John Wiley & Sons, Inc. Med Res Rev, 21, No. 5, 382,396, 2001 [source] Detecting selection on morphological traits in social insect castes: the case of the social wasp Vespula maculifronsBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 1 2010JENNIFER L. KOVACS Highly social insects dominate terrestrial ecosystems because society members belong to discrete castes that undertake distinct tasks. The distinct functional roles of members of different castes may lead to divergent selective regimes, which may ultimately lead to morphological specialization and differentiation of the castes. This study used morphological and genetic analyses to identify traits that experienced caste-specific selection in the social wasp Vespula maculifrons (Buysson, 1905). Traits putatively under selection were identified based on their degree of caste dimorphism, levels of variability, strength of correlations with other traits, and patterns of allometric scaling. Analyses of trait characteristics suggested that queen thorax length, thorax width, and possibly mass, have experienced queen-specific selection. Additionally, trait dimorphism and intercaste phenotypic correlation values were negatively correlated, as expected if some morphological traits were subject to selection, leading to alternate phenotypic optima in the two castes. Overall, our analyses demonstrate how techniques used to identify selection between dimorphic groups can be applied to social species with distinct castes. In addition, our analyses suggest the operation of selection may be stronger in reproductive than in non-reproductive castes. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101, 93,102. [source] Prediction of human clearance of therapeutic proteins: simple allometric scaling method revisitedBIOPHARMACEUTICS AND DRUG DISPOSITION, Issue 4 2010Weirong Wang Abstract In this report, the utility of a commonly used interspecies scaling method to predict the systemic clearance (CL) of therapeutic proteins in humans was evaluated. Based on analysis of a pharmacokinetic data set of 34 therapeutic proteins, including 12 monoclonal antibodies (mAbs) and Fc fusion proteins, human CL can generally be predicted reasonably well with simple allometric scaling and a fixed exponent of 0.8:,95% of the cases predicted values within 2-fold of the observed values when using CL data from multiple species, or,90% simply using CL from monkeys. Specific to mAbs/Fc fusion proteins, scaling from monkey CL using a fixed exponent of 0.8 gave an excellent prediction; all predicted CL values were within 2-fold of the corresponding observed values. Compared with the simple allometric scaling method that uses a fitted exponent from CL data of ,3 preclinical species, the fixed exponent approach with 1,2 preclinical species is simple, resource-saving and minimizes systematic bias. Together with its overall satisfactory prediction accuracy, especially in the absence of non-linear pharmacokinetics and species-specific clearance mechanisms, this fixed exponent method affords a viable alternative to other published allometric methods, including the Rule of Exponents (ROE). Copyright © 2010 John Wiley & Sons, Ltd. [source] Prediction of human oral pharmacokinetics using nonclinical data: examples involving four proprietary compoundsBIOPHARMACEUTICS AND DRUG DISPOSITION, Issue 8 2008Aberra Fura Abstract The oral pharmacokinetics (concentration-time profile) of four proprietary compounds in humans were predicted using the Cvss - MRT method. The first step was to demonstrate superposition of intravenous (i.v.) pharmacokinetic profiles of preclinical species following mathematical transformation of their respective concentration-time curves using the corresponding Cvss (where Cvss=dose/Vss; Vss is the volume of distribution at steady state) and mean residence time (MRT) values. The resultant profiles were then back-transformed to estimate human i.v. plasma concentration-time profiles using human Cvss and MRT values. Human Cvss and MRT values were estimated from projected human Vss and CL values. Projection of CL was based on scaled (in vitro) metabolic clearance, simple allometry with and without various correction factors and the unbound fraction corrected intercept method. Vss values were estimated by allometric scaling with and without correction for interspecies differences in plasma protein binding. The predicted human i.v. profiles, in combination with the estimated mean absorption rate constants and bioavailability, were then used to simulate the oral pharmacokinetics in human using one- or multi-compartment kinetic models. Overall, with this approach, key oral pharmacokinetic parameters such as AUC, Cmax, Cmin and oral plasma T½ were projected to be within two-fold of the actual values in humans. Copyright © 2008 John Wiley & Sons, Ltd. [source] Pharmacokinetics and allometric scaling of levormeloxifene, a selective oestrogen receptor modulatorBIOPHARMACEUTICS AND DRUG DISPOSITION, Issue 3 2003O. Østerberg Abstract The pharmacokinetics of a new selective oestrogen receptor modulator levormeloxifene was investigated in mice, rats, cynomolgus monkeys and humans by compartmental pharmacokinetics. Levormeloxifene was administered as an oral solution in all studies. Allometric scaling was used to predict human pharmacokinetic parameters and the performance of the approach was evaluated. Mean values of clearance confounded by F(CL/F) were 0.073, 0.29, 3.18 and 2.4 l/h in mice, rats, monkeys and humans, respectively. Values of distribution volume at steady state confounded by F(Vss/F) were 0.073 and 7.5 l in mice and rats. In monkeys, values of the central volume F(Vc/F) and volume at steady state F(Vss/F) were 28.9 and 57.9 l, respectively. In humans, values of Vc/F and Vss/F were 106 and 587 l, respectively. Predicted CL/F and Vss/F showed a linear relationship when plotted vs BW on a log,log scale; for CL/F, r was 0.95,0.98 and for Vss/F, r was 0.99. Using allometric scaling the predicted human Vss/F deviated 3-fold from the experimentally determined values. Observed values of CL/F deviated 21,25 fold from the predicted, the latter depending on the scaling method. Confidence intervals for the predicted parameters showed major lack of precision for all the allometric scaling methods. Copyright © 2003 John Wiley & Sons, Ltd. [source] | ||||||||||||||||