Root Pulling Force Across Drought in Maize Reveals Genotype by Environment Interactions and Candidate Genes

High-throughput, field-based characterization of root systems for hundreds of genotypes in thousands of plots is necessary for breeding and identifying loci underlying variation in root traits and their plasticity. We designed a large-scale sampling of root pulling force, the vertical force required to extract the root system from the soil, in a maize diversity panel under differing irrigation levels for two growing seasons. We then characterized the root system architecture of the extracted root crowns. We found consistent patterns of phenotypic plasticity for root pulling force for a subset of genotypes under differential irrigation, suggesting that root plasticity is predictable. Using genome-wide association analysis, we identified 54 SNPs as statistically significant for six independent root pulling force measurements across two irrigation levels and four developmental timepoints. For every significant GWAS SNP for any trait in any treatment and timepoint we conducted post hoc tests for genotype-by-environment interaction, using a mixed model ANOVA. We found that 8 of the 54 SNPs showed significant GxE. Candidate genes underlying variation in root pulling force included those involved in nutrient transport. Although they are often treated separately, variation in the ability of plant roots to sense and respond to variation in environmental resources including water and nutrients may be linked by the genes and pathways underlying this variation. While functional validation of the identified genes is needed, our results expand the current knowledge of root phenotypic plasticity at the whole plant and gene levels, and further elucidate the complex genetic architecture of maize root systems.

Quantitative Trait Loci Controlling Agronomic and Biochemical Traits in Cannabis sativa

Understanding the genetic basis of complex traits is a fundamental goal of evolutionary genetics. Yet, the genetics controlling complex traits in many important species such as hemp (Cannabis sativa) remain poorly investigated. Because hemp’s change in legal status with the 2014 and 2018 U.S. Federal Farm Bills, interest in the genetics controlling its numerous agriculturally important traits has steadily increased. To better understand the genetics of agriculturally important traits in hemp, we developed an F₂ population by crossing two phenotypically distinct hemp cultivars (Carmagnola and USO31). Using whole-genome sequencing, we mapped quantitative trait loci (QTL) associated with variation in numerous agronomic and biochemical traits. A total of 69 loci associated with agronomic (34) and biochemical (35) trait variation were identified. We found that most QTL co-localized, suggesting that the phenotypic distinctions between Carmagnola and USO31 are largely controlled by a small number of loci. We identified TINY and olivetol synthase as candidate genes underlying co-localized QTL clusters for agronomic and biochemical traits, respectively. We functionally validated the olivetol synthase candidate by expressing the alleles in yeast. Gas chromatography-mass spectrometry assays of extracts from these yeast colonies suggest that the USO31 olivetol synthase is functionally less active and potentially explains why USO31 produces lower cannabinoids compared to Carmagnola. Overall, our results help modernize the genomic understanding of complex traits in hemp.

Deployment of Lidar from a Ground Platform: Customizing a Low-Cost, Information-Rich and User-Friendly Application for Field Phenomics Research

Using sensors and electronic systems for characterization of plant traits provides valuable digital inputs to support complex analytical modeling in genetics research. In field applications, frequent sensor deployment enables the study of the dynamics of these traits and their interaction with the environment. This study focused on implementing lidar (light detection and ranging) technology to generate 2D displacement data at high spatial resolution and extract plant architectural parameters, namely canopy height and cover, in a diverse population of 252 maize (Zea mays L.) genotypes. A prime objective was to develop the mechanical and electrical subcomponents for field deployment from a ground vehicle. Data reduction approaches were implemented for efficient same-day post-processing to generate by-plot statistics. The lidar system was successfully deployed six times in a span of 42 days. Lidar data accuracy was validated through independent measurements in a subset of 75 experimental units. Manual and lidar-derived canopy height measurements were compared resulting in root mean square error (RMSE) = 0.068 m and r2 = 0.81. Subsequent genome-wide association study (GWAS) analyses for quantitative trait locus (QTL) identification and comparisons of genetic correlations and heritabilities for manual and lidar-based traits showed statistically significant associations. Low-cost, field-ready lidar of computational simplicity make possible timely phenotyping of diverse populations in multiple environments.

Drought adaptation in Arabidopsis thaliana by extensive genetic loss-of-function

Interdisciplinary syntheses are needed to scale up discovery of the environmental drivers and molecular basis of adaptation in nature. Here we integrated novel approaches using whole genome sequences, satellite remote sensing, and transgenic experiments to study natural loss-of-function alleles associated with drought histories in wild Arabidopsis thaliana. The genes we identified exhibit population genetic signatures of parallel molecular evolution, selection for loss-of-function, and shared associations with flowering time phenotypes in directions consistent with longstanding adaptive hypotheses seven times more often than expected by chance. We then confirmed predicted phenotypes experimentally in transgenic knockout lines. These findings reveal the importance of drought timing to explain the evolution of alternative drought tolerance strategies and further challenge popular assumptions about the adaptive value of genetic loss-of-function in nature. These results also motivate improved species-wide sequencing efforts to better identify loss-of-function variants and inspire new opportunities for engineering climate resilience in crops.

Water shortages caused by droughts lead to crop losses that affect billions of people around the world each year. By discovering how wild plants adapt to drought, it may be possible to identify traits and genes that help to improve the growth of crop plants when water is scarce. It has been suggested that plants have adapted to droughts by flowering at times of the year when droughts are less likely to occur. For example, if droughts are more likely to happen in spring, the plants may delay flowering until the summer.

Arabidopsis thaliana is a small plant that is found across Eurasia, Africa and North America, including in areas that are prone to drought at different times of the year. Individual plants of the same species may carry different versions of the same gene (known as alleles). Some of these alleles may not work properly and are referred to as loss-of-function alleles. Monroe et al. investigated whether A. thaliana plants carry any loss-of-function alleles that are associated with droughts happening in the spring or summer, and whether they are linked to when those plants will flower.

Monroe et al. analyzed satellite images collected over the last 30 years to measure when droughts have occurred. Next, they searched genome sequences of Arabidopsis thaliana for alleles that might help the plants to adapt to droughts in the spring or summer. Combining the two approaches revealed that loss-of-function alleles associated with spring droughts were strongly predicted to be associated with the plants flowering later in the year. Similarly, loss-of-function alleles associated with summer droughts were predicted to be associated with the plants flowering earlier in the year.

These findings support the idea that plants can adapt to drought by changing when they produce flowers, and suggest that loss-of-function alleles play a major role in this process. New techniques for editing genes mean it is easier than ever to generate new loss-of-function alleles in specific genes. Therefore, the results presented by Monroe et al. may help researchers to develop new varieties of crop plants that are better adapted to droughts.

TSPmap, a tool making use of traveling salesperson problem solvers in the efficient and accurate construction of high-density genetic linkage maps

Background

Recent advances in nucleic acid sequencing technologies have led to a dramatic increase in the number of markers available to generate genetic linkage maps. This increased marker density can be used to improve genome assemblies as well as add much needed resolution for loci controlling variation in ecologically and agriculturally important traits. However, traditional genetic map construction methods from these large marker datasets can be computationally prohibitive and highly error prone.

Results

We present TSPmap, a method which implements both approximate and exact Traveling Salesperson Problem solvers to generate linkage maps. We demonstrate that for datasets with large numbers of genomic markers (e.g. 10,000) and in multiple population types generated from inbred parents, TSPmap can rapidly produce high quality linkage maps with low sensitivity to missing and erroneous genotyping data compared to two other benchmark methods, JoinMap and MSTmap. TSPmap is open source and freely available as an R package.

Conclusions

With the advancement of low cost sequencing technologies, the number of markers used in the generation of genetic maps is expected to continue to rise. TSPmap will be a useful tool to handle such large datasets into the future, quickly producing high quality maps using a large number of genomic markers.

Electronic supplementary material

The online version of this article (10.1186/s13040-017-0158-0) contains supplementary material, which is available to authorized users.

Screening for Natural Variation in Water Use Efficiency Traits in a Diversity Set of Brassica napus L. Identifies Candidate Variants in Photosynthetic Assimilation

Seed yield and quality of crop species are significantly reduced by water deficit. Stable isotope screening (δ13C) of a diversity set of 147 accessions of Brassica napus grown in the field identified several accessions with extremes in water use efficiency (WUE). We next conducted an investigation of the physiological characteristics of selected natural variants with high and low WUE to understand how these characteristics translate to differences in WUE. We identified an interesting Spring accession, G302 (Mozart), that exhibited the highest WUE in the field and high CO2 assimilation rates coupled with an increased electron transport capacity (Jmax) under the imposed conditions. Differences in stomatal density and stomatal index did not translate to differences in stomatal conductance in the investigated accessions. Stomatal conductance response to exogenous ABA was analyzed in selected high and low WUE accessions. Spring lines showed little variation in response to exogenous ABA, while one Semi-Winter line (SW047) showed a significantly more rapid response to exogenous ABA, that corresponded to the high WUE indicated by δ13C measurements. This research illustrates the importance of examining natural variation at a physiological level for investigation of the underlying mechanisms influencing the diversity of carbon isotope discrimination values in the field and identifies natural variants in B. napus with improved WUE and potential relevant traits.

Identification of Polymorphisms Associated with Drought Adaptation QTL in Brassica napus by Resequencing

Brassica napus is a globally important oilseed for which little is known about the genetics of drought adaptation. We previously mapped twelve quantitative trait loci (QTL) underlying drought-related traits in a biparental mapping population created from a cross between winter and spring B. napus cultivars. Here we resequence the genomes of the mapping population parents to identify genetic diversity across the genome and within QTL regions. We sequenced each parental cultivar on the Illumina HiSeq platform to a minimum depth of 23 × and performed a reference based assembly in order to describe the molecular variation differentiating them at the scale of the genome, QTL and gene. Genome-wide patterns of variation were characterized by an overall higher single nucleotide polymorphism (SNP) density in the A genome and a higher ratio of nonsynonymous to synonymous substitutions in the C genome. Nonsynonymous substitutions were used to categorize gene ontology terms differentiating the parent genomes along with a list of putative functional variants contained within each QTL. Marker assays were developed for several of the discovered polymorphisms within a pleiotropic QTL on chromosome A10. QTL analysis with the new, denser map showed the most associated marker to be that developed from an insertion/deletion polymorphism located in the candidate gene Bna.FLC.A10, and it was the only candidate within the QTL interval with observed polymorphism. Together, these results provide a glimpse of genome-wide variation differentiating annual and biennial B. napus ecotypes as well as a better understanding of the genetic basis of root and drought phenotypes.

Combining quantitative trait loci analysis with physiological models to predict genotype-specific transpiration rates

Transpiration is controlled by evaporative demand and stomatal conductance (gs ), and there can be substantial genetic variation in gs . A key parameter in empirical models of transpiration is minimum stomatal conductance (g0 ), a trait that can be measured and has a large effect on gs and transpiration. In Arabidopsis thaliana, g0 exhibits both environmental and genetic variation, and quantitative trait loci (QTL) have been mapped. We used this information to create a genetically parameterized empirical model to predict transpiration of genotypes. For the parental lines, this worked well. However, in a recombinant inbred population, the predictions proved less accurate. When based only upon their genotype at a single g0 QTL, genotypes were less distinct than our model predicted. Follow-up experiments indicated that both genotype by environment interaction and a polygenic inheritance complicate the application of genetic effects into physiological models. The use of ecophysiological or 'crop' models for predicting transpiration of novel genetic lines will benefit from incorporating further knowledge of the genetic control and degree of independence of core traits/parameters underlying gs variation.

Exploiting Differential Gene Expression and Epistasis to Discover Candidate Genes for Drought-Associated QTLs in Arabidopsis thaliana

Soil water availability represents one of the most important selective agents for plants in nature and the single greatest abiotic determinant of agricultural productivity, yet the genetic bases of drought acclimation responses remain poorly understood. Here, we developed a systems-genetic approach to characterize quantitative trait loci (QTLs), physiological traits and genes that affect responses to soil moisture deficit in the TSUxKAS mapping population of Arabidopsis thaliana. To determine the effects of candidate genes underlying QTLs, we analyzed gene expression as a covariate within the QTL model in an effort to mechanistically link markers, RNA expression, and the phenotype. This strategy produced ranked lists of candidate genes for several drought-associated traits, including water use efficiency, growth, abscisic acid concentration (ABA), and proline concentration. As a proof of concept, we recovered known causal loci for several QTLs. For other traits, including ABA, we identified novel loci not previously associated with drought. Furthermore, we documented natural variation at two key steps in proline metabolism and demonstrated that the mitochondrial genome differentially affects genomic QTLs to influence proline accumulation. These findings demonstrate that linking genome, transcriptome, and phenotype data holds great promise to extend the utility of genetic mapping, even when QTL effects are modest or complex.

QTL analysis of root morphology, flowering time, and yield reveals trade-offs in response to drought in Brassica napus

Drought escape and dehydration avoidance represent alternative strategies for drought adaptation in annual crops. The mechanisms underlying these two strategies are reported to have a negative correlation, suggesting a trade-off. We conducted a quantitative trait locus (QTL) analysis of flowering time and root mass, traits representing each strategy, in Brassica napus to understand if a trade-off exists and what the genetic basis might be. Our field experiment used a genotyped population of doubled haploid lines and included both irrigated and rainfed treatments, allowing analysis of plasticity in each trait. We found strong genetic correlations among all traits, suggesting a trade-off among traits may exist. Summing across traits and treatments we found 20 QTLs, but many of these co-localized to two major QTLs, providing evidence that the trade-off is genetically constrained. To understand the mechanistic relationship between root mass, flowering time, and QTLs, we analysed the data by conditioning upon correlated traits. Our results suggest a causal model where such QTLs affect root mass directly as well as through their impacts on flowering time. Additionally, we used draft Brassica genomes to identify orthologues of well characterized Arabidopsis thaliana flowering time genes as candidate genes. This research provides valuable clues to breeding for drought adaptation as it is the first to analyse the inheritance of the root system in B. napus in relation to drought.

Development of a next-generation NIL library in Arabidopsis thaliana for dissecting complex traits

Background

The identification of the loci and specific alleles underlying variation in quantitative traits is an important goal for evolutionary biologists and breeders. Despite major advancements in genomics technology, moving from QTL to causal alleles remains a major challenge in genetics research. Near-isogenic lines are the ideal raw material for QTL validation, refinement of QTL location and, ultimately, gene discovery.

Results

In this study, a population of 75 Arabidopsis thaliana near-isogenic lines was developed from an existing recombinant inbred line (RIL) population derived from a cross between physiologically divergent accessions Kas-1 and Tsu-1. First, a novel algorithm was developed to utilize genome-wide marker data in selecting RILs fully isogenic to Kas-1 for a single chromosome. Seven such RILs were used in 2 generations of crossing to Tsu-1 to create BC1 seed. BC1 plants were genotyped with SSR markers so that lines could be selected that carried Kas-1 introgressions, resulting in a population carrying chromosomal introgressions spanning the genome. BC1 lines were genotyped with 48 genome-wide SSRs to identify lines with a targeted Kas-1 introgression and the fewest genomic introgressions elsewhere. 75 such lines were selected and genotyped at an additional 41 SNP loci and another 930 tags using 2b-RAD genotyping by sequencing. The final population carried an average of 1.35 homozygous and 2.49 heterozygous introgressions per line with average introgression sizes of 5.32 and 5.16 Mb, respectively. In a simple case study, we demonstrate the advantage of maintaining heterozygotes in our library whereby fine-mapping efforts are conducted simply by self-pollination. Crossovers in the heterozygous interval during this single selfing generation break the introgression into smaller, homozygous fragments (sub-NILs). Additionally, we utilize a homozygous NIL for validation of a QTL underlying stomatal conductance, a low heritability trait.

Conclusions

The present results introduce a new and valuable resource to the Brassicaceae research community that enables rapid fine-mapping of candidate loci in parallel with QTL validation. These attributes along with dense marker coverage and genome-wide chromosomal introgressions make this population an ideal starting point for discovery of genes underlying important complex traits of agricultural and ecological significance.

A novel phototropic response to red light is revealed in microgravity

The aim of this study was to investigate phototropism in plants grown in microgravity conditions without the complications of a 1-g environment. Experiments performed on the International Space Station (ISS) were used to explore the mechanisms of both blue-light- and red-light-induced phototropism in plants. This project utilized the European Modular Cultivation System (EMCS), which has environmental controls for plant growth as well as centrifuges for gravity treatments used as a 1-g control. Images captured from video tapes were used to analyze the growth, development, and curvature of Arabidopsis thaliana plants that developed from seed in space. A novel positive phototropic response to red light was observed in hypocotyls of seedlings that developed in microgravity. This response was not apparent in seedlings grown on Earth or in the 1-g control during the space flight. In addition, blue-light-based phototropism had a greater response in microgravity compared with the 1-g control. Although flowering plants are generally thought to lack red light phototropism, our data suggest that at least some flowering plants may have retained a red light sensory system for phototropism. Thus, this discovery may have important implications for understanding the evolution of light sensory systems in plants.

The state of general surgery training: a different perspective

BACKGROUND

Much has been written about the influences of Accreditation Council for Graduate Medical Education (ACGME) work restrictions, the litigious climate in American medicine, and the proliferation of subspecialty fellowships on general surgery training. Few previous studies have addressed general surgical residents' perceptions of surgical training on a national level.

METHODS

A 38-question Institutional Review Board-approved survey was sent via e-mail to the program directors at all ACGME-approved general surgical training programs for distribution to categorical general surgery residents. Voluntary responses to statements focusing on job satisfaction, quality of life, and the influences of operative experience, work hours, fellows, physician extenders, as well as faculty and administration on resident training were solicited.

RESULTS

Overall, 997 responses were received from residents of all clinical levels from 40 states. Most respondents were from university-based programs (79%) with a broad representation of program sizes (mean of 6 graduates per year; range 2 to 11). Residents believe that they will be prepared to enter clinical practice at the conclusion of their training (86%), that the duration of surgical training is adequate (85%), and that they are exposed to sufficient case volume and complexity (85% and 84%, respectively). Only 360 respondents (36%) believe that they are financially compensated appropriately. Although most respondents support the ACGME work-hour restrictions (70%), far fewer feel that they improve their training or patient care (46.6% and 46.8%, respectively). Most respondents are proud to be surgical residents (88%), view surgery as a rewarding profession (87%), and would choose surgery as a profession again (77%).

CONCLUSIONS

Surgical residents are positive regarding the quality of their training and life, although they feel poorly compensated for their work. Most residents intend to pursue fellowship training. Survey responses were consistent irrespective of gender, ethnicity, and program type.

Shade avoidance and the regulation of leaf inclination in Arabidopsis

As a rosette plant, Arabidopsis thaliana forms leaves near to the ground, which causes the plant to be vulnerable to shading by neighbours. One mechanism to avoid such shading is the regulation of leaf inclination, such that leaves can be raised to more vertical orientations to prevent neighbouring leaves from overtopping them. Throughout Arabidopsis rosette development, rosette leaves move to more vertical orientations when shaded by neighbouring leaves, exposed to low light levels or placed in the dark. After dark-induced reorientation of leaves, returning them to white light causes the leaves to reorient to more horizontal inclinations. These light-dependent leaf movements are more robust than, and distinct from, the diurnal movements of rosette leaves. However, the movements are gated by the circadian clock. The light-dependent leaf orientation response is mediated primarily through phytochromes A, B and E, with the orientation varying with the ratio of red light to far-red light, consistent with other shade-avoidance responses. However, even plants lacking these phytochromes were able to alter leaf inclination in response to white light, suggesting a role for other photoreceptors. In particular, we found significant changes in leaf inclination for plants exposed to green light. This green light response may be caused, in part, by light-dependent regulation of abscisic acid (ABA) biosynthesis.

Phytochrome modulation of blue light-induced chloroplast movements in Arabidopsis

Photometric analysis of chloroplast movements in various phytochrome (phy) mutants of Arabidopsis showed that phyA, B, and D are not required for chloroplast movements because blue light (BL)-dependent chloroplast migration still occurs in these mutants. However, mutants lacking phyA or phyB showed an enhanced response at fluence rates of BL above 10 micromol m-2 s-1. Overexpression of phyA or phyB resulted in an enhancement of the low-light response. Analysis of chloroplast movements within the range of BL intensities in which the transition between the low- and high-light responses occur (1.5-15 micromol m-2 s-1) revealed a transient increase in light transmittance through leaves, indicative of the high-light response, followed by a decrease in transmittance to a value below that measured before the BL treatment, indicative of the low-light response. A biphasic response was not observed for phyABD leaves exposed to the same fluence rate of BL, suggesting that phys play a role in modulating the transition between the low- and high-light chloroplast movement responses of Arabidopsis.

Root phototropism: how light and gravity interact in shaping plant form

The interactions among tropisms can be critical in determining the final growth form of plants and plant organs. We have studied tropistic responses in roots as an example of these type of interactions. While gravitropism is the predominant tropistic response in roots, phototropism also plays a role in the oriented growth in this organ in flowering plants. In blue or white light, roots exhibit negative phototropism, but red light induces positive phototropism. In the flowering plant Arabidopsis, the photosensitive pigments phytochrome A (phyA) and phytochrome B (phyB) mediate this positive red-light-based photoresponse in roots since single mutants (and the double phyAB mutant) were severely impaired in this response. While blue-light-based negative phototropism is primarily mediated by the phototropin family of photoreceptors, the phyA and phyAB mutants (but not phyB) were inhibited in this response relative to the WT. The differences observed in phototropic responses were not due to growth limitations since the growth rates among all the mutants tested were not significantly different from that of the WT. Thus, our study shows that the blue-light and red-light systems interact in plants and that phytochrome plays a key role in integrating multiple environmental stimuli.

Phytochromes A and B mediate red-light-induced positive phototropism in roots

The interaction of tropisms is important in determining the final growth form of the plant body. In roots, gravitropism is the predominant tropistic response, but phototropism also plays a role in the oriented growth of roots in flowering plants. In blue or white light, roots exhibit negative phototropism that is mediated by the phototropin family of photoreceptors. In contrast, red light induces a positive phototropism in Arabidopsis roots. Because this red-light-induced response is weak relative to both gravitropism and negative phototropism, we used a novel device to study phototropism without the complications of a counteracting gravitational stimulus. This device is based on a computer-controlled system using real-time image analysis of root growth and a feedback-regulated rotatable stage. Our data show that this system is useful to study root phototropism in response to red light, because in wild-type roots, the maximal curvature detected with this apparatus is 30 degrees to 40 degrees, compared with 5 degrees to 10 degrees without the feedback system. In positive root phototropism, sensing of red light occurs in the root itself and is not dependent on shoot-derived signals resulting from light perception. Phytochrome (Phy)A and phyB were severely impaired in red-light-induced phototropism, whereas the phyD and phyE mutants were normal in this response. Thus, PHYA and PHYB play a key role in mediating red-light-dependent positive phototropism in roots. Although phytochrome has been shown to mediate phototropism in some lower plant groups, this is one of the few reports indicating a phytochrome-dependent phototropism in flowering plants.

Phytochromes play a role in phototropism and gravitropism in Arabidopsis roots

Phototropism as well as gravitropism plays a role in the oriented growth of roots in flowering plants. In blue or white light, roots exhibit negative phototropism, but red light induces positive phototropism in Arabidopsis roots. Phytochrome A (phyA) and phyB mediate the positive red-light-based photoresponse in roots since single mutants (and the double phyAB mutant) were severely impaired in this response. In blue-light-based negative phototropism, phyA and phyAB (but not phyB) were inhibited in the response relative to the WT. In root gravitropism, phyB and phyAB (but not phyA) were inhibited in the response compared to the WT. The differences observed in tropistic responses were not due to growth limitations since the growth rates among all the mutants tested were not significantly different from that of the WT. Thus, our study shows that the blue-light and red-light systems interact in roots and that phytochrome plays a key role in plant development by integrating multiple environmental stimuli.

Genetic analysis of the gravitropic set-point angle in lateral roots of Arabidopsis

Research on gravity responses in plants has mostly focused on primary roots and shoots, which typically orient to a vertical orientation. However, the distribution of lateral organs and their characteristically non-vertical growth orientation are critical for the determination of plant form. For example, in Arabidopsis, when lateral roots emerge from the primary root, they grow at a nearly horizontal orientation. As they elongate, the roots slowly curve until they eventually reach a vertical orientation. The regulation of this lateral root orientation is an important component affecting overall root system architecture. We found that this change in orientation is not simply due to the onset of gravitropic competence, as non-vertical lateral roots are capable of both positive and negative gravitropism. Thus, the horizontal growth of new lateral roots appears to be determined by what is called the gravitropic set-point angle (GSA). This developmental control of the GSA of lateral roots in Arabidopsis provides a useful system for investigating the components involved in regulating gravitropic responses. Using this system, we have identified several Arabidopsis mutants that have altered lateral root orientations but maintain normal primary root orientation.

Spatial separation of light perception and growth response in maize root phototropism

Although the effects of gravity on root growth are well known and interactions between light and gravity have been reported, details of root phototropic responses are less documented. We used high-resolution image analysis to study phototropism in primary roots of Zea mays L. Similar to the location of perception in gravitropism, the perception of light was localized in the root cap. Phototropic curvature away from the light, on the other hand, developed in the central elongation zone, more basal than the site of initiation of gravitropic curvature. The phototropic curvature saturated at approximately 10 micromoles m-2 s-1 blue light with a peak curvature of 29 +/- 4 degrees, in part due to induction of positive gravitropism following displacement of the root tip from vertical during negative phototropism. However, at higher fluence rates, development of phototropic curvature is arrested even if gravitropism is avoided by maintaining the root cap vertically using a rotating feedback system. Thus continuous illumination can cause adaptation in the signalling pathway of the phototropic response in roots.

Root gravitropism in response to a signal originating outside of the cap

We have developed image analysis software linked to a rotating stage, allowing constraint of any user-selected region of a root at a prescribed angle during root gravitropism. This device allows the cap of a graviresponding root to reach vertical while maintaining a selected region within the elongation zone at a gravistimulated angle. Under these conditions gravitropic curvature of roots of Zea mays L. continues long after the root cap reaches vertical, indicating that a signal from outside of the cap can contribute to the curvature response.

Two distinct regions of response drive differential growth in Vigna root electrotropism

Although exogenous electric fields have been reported to influence the orientation of plant root growth, reports of the ultimate direction of differential growth have been contradictory. Using a high-resolution image analysis approach, the kinetics of electrotropic curvature in Vigna mungo L. roots were investigated. It was found that curvature occurred in the same root toward both the anode and cathode. However, these two responses occurred in two different regions of the root, the central elongation zone (CEZ) and distal elongation zone (DEZ), respectively. These oppositely directed responses could be reproduced individually by a localized electric field application to the region of response. This indicates that both are true responses to the electric field, rather than one being a secondary response to an induced gravitropic stimulation. The individual responses differed in the type of differential growth giving rise to curvature. In the CEZ, curvature was driven by inhibition of elongation, whereas curvature in the DEZ was primarily due to stimulation of elongation. This stimulation of elongation is consistent with the growth response of the DEZ to other environmental stimuli.

Kinetics of constant gravitropic stimulus responses in Arabidopsis roots using a feedback system

The study of gravitropism is hindered by the fact that as a root responds, the gravitational stimulus changes. Using a feedback system to connect a rotating stage platform to a video digitizer system, we were able to maintain a constant angle of gravistimulation to Arabidopsis roots for long time periods. The rate of curvature approximated the sine rule for angles of stimulation between 20 degrees and 120 degrees. For a given angle of stimulation, the rate of curvature also remained constant, with no observed diminishment of the response. Although previous reports of Arabidopsis root gravitropism suggest latent periods of approximately 30 min, using a smooth mechanical stage to reorient the root, we observed a mean time lag of approximately 10 min. This more rapid onset of curvature can, in part, be explained by reduced mechanical perturbation during the process of gravistimulation. This suggests that mechanical stimulation associated with rapid root re-orientation may confound investigations of early gravitropic events.

Inhibition of root elongation in microgravity by an applied electric field

Roots grown in an applied electric field demonstrate a bidirectional curvature. To further understand the nature of this response and its implications for the regulation of differential growth, we applied an electric field to roots growing in microgravity. We found that growth rates of roots in microgravity were higher than growth rates of ground controls. Immediately upon application of the electric field, root elongation was inhibited. We interpret this result as an indication that, in the absence of a gravity stimulus, the sensitivity of the root to an applied electric stimulus is increased. Further space experiments are required to determine the extent to which this sensitivity is shifted. The implications of this result are discussed in relation to gravitropic signaling and the regulation of differential cell elongation in the root.

Inhibition of root elongation in microgravity by an applied electric field

Roots grown in an applied electric field demonstrate a bidirectional curvature. To further understand the nature of this response and its implications for the regulation of differential growth, we applied an electric field to roots growing in microgravity. We found that growth rates of roots in microgravity were higher than growth rates of ground controls. Immediately upon application of the electric field, root elongation was inhibited. We interpret this result as an indication that, in the absence of a gravity stimulus, the sensitivity of the root to an applied electric stimulus is increased. Further space experiments are required to determine the extent to which this sensitivity is shifted. The implications of this result are discussed in relation to gravitropic signaling and the regulation of differential cell elongation in the root.

Root-growth behavior of the Arabidopsis mutant rgr1. Roles of gravitropism and circumnutation in the waving/coiling phenomenon

In this study we investigated the kinetics of the gravitropic response of the Arabidopsis mutant rgr1 (reduced root gravitropism). Although the rate of curvature in rgr1, which is allelic to axr4, was smaller than in the wild type (ecotype Wassilewskija), curvature was initiated in the same region of the root, the distal elongation zone. The time lag for the response was unaffected in the mutant; however, the gravitropic response of rgr1 contained a feature not found in the wild type: when roots growing along the surface of an agar plate were gravistimulated, there was often an upward curvature that initiated in the central elongation zone. Because this response was dependent on the tactile environment of the root, it most likely resulted from the superposition of the waving/coiling phenomenon onto the gravitropic response. We found that the frequency of the waving pattern and circumnutation, a cyclic endogenous pattern of root growth, was the same in rgr1 and in the wild type, so the waving/coiling phenomenon is likely governed by circumnutation patterns. The amplitudes of these oscillations may then be selectively amplified by tactile stimulation to provide a directional preference to the slanting.

Analysis of changes in relative elemental growth rate patterns in the elongation zone of Arabidopsis roots upon gravistimulation

Although Arabidopsis is an important system for studying root physiology, the localized growth patterns of its roots have not been well defined, particularly during tropic responses. In order to characterize growth rate profiles along the apex of primary roots of Arabidopsis thaliana (L.) Heynh (ecotype Columbia) we applied small charcoal particles to the root surface and analyzed their displacement during growth using an automated video digitizer system with custom software for tracking the markers. When growing vertically, the maximum elongation rate occurred 481 +/- 50 microns back from the extreme tip of the root (tip of root cap), and the elongation zone extended back to 912 +/- 137 microns. The distal elongation zone (DEZ) has previously been described as the apical region of the elongation zone in which the relative elemental growth rate (REGR) is < or = 30% of the peak rate in the central elongation zone. By this definition, our data indicate that the basal limit of the DEZ was located 248 +/- 30 microns from the root tip. However, after gravistimulation, the growth patterns of the root changed. Within the first hour of graviresponse, the basal limit of the DEZ and the position of peak REGR shifted apically on the upper flank of the root. This was due to a combination of increased growth in the DEZ and growth inhibition in the central elongation zone. On the lower flank, the basal limit of the DEZ shifted basipetally as the REGR decreased. These factors set up the gradient of growth rate across the root, which drives curvature.

Automated, eight-cage indirect calorimetry in rats

We have constructed an automated, eight-cage indirect calorimeter (AIC) for the measurement of energy expenditure in rats. We compared the measurements of resting energy expenditure (REE) in rats during a 30-h fast obtained with the AIC with those obtained with a manual indirect calorimetry (MIC) system. There was both a high degree of correlation between the two techniques during the initial 18 h of the fast (r = 0.90, P < 0.05) and strong intertechnique agreement. REE (AIC) decreased during the final 12 h of the 30-h fast (79.6 +/- 2.7-72.0 +/- 4.4 kcal.kg-0.75.d-1 [mean +/- SD, P < 0.01]). REE (MIC) did not show a significant decrease during this part of the fast (79.7 +/- 2.6 - 75.2 +/- 4.7 kcal.kg-0.75.d-1 [P = NS]). During the final 12 h of the fast agreement between the two systems gradually dissipated and correlation was poor (r = 0.375, P < 0.05). The frequency of animal handling necessitated by MIC may have resulted in a stress-induced increase in metabolic work that would mask the animals' adaptive response to starvation. This investigation demonstrates the advantages of the AIC and calls into question the accuracy of manual methods under long-term starvation conditions.

Resting energy expenditure of patients with gynecologic malignancies

OBJECTIVE

To evaluate resting energy expenditure compared to predicted energy expenditure in patients with cervical or ovarian carcinoma who require specialized nutritional support.

DESIGN

Women with biopsy-proven cervical or ovarian carcinoma referred to the Nutrition Support Service were studied. Resting energy expenditure was measured by indirect calorimetry and compared to predicted energy expenditure (PEE) as determined by the Harris-Benedict equation for females.

RESULTS

Sixty one patients were studied. Patients with ovarian cancer (n = 31) had a significantly higher measured resting energy expenditure (% PEE) than patients with cervical cancer (109 +/- 18% vs. 98 +/- 16%, p < 0.02, respectively). This difference in measured resting energy expenditure between groups could not be explained by differences in the extent of disease, nutritional status, body temperature, or nutrient intake between groups. A greater proportion of patients with ovarian cancer were hypermetabolic (> 110% of predicted) in comparison to patients with cervical cancer (55% vs. 13%, p < 0.01, respectively). Measured resting energy expenditure varied between 53% and 157% of predicted for the entire population.

CONCLUSION

Ovarian cancer patients are more hypermetabolic than cervical cancer patients. The Harris-Benedict equation for females is a unreliable estimate of caloric expenditure in patients with cervical or ovarian cancer receiving specialized nutritional support.

Long-term enteral access in aspiration-prone patients

Aspiration pneumonia is a serious complication of enteral feeding. Many critically ill patients are particularly at risk for aspiration. Few studies have rigorously compared various access devices. Risk factors for aspiration and studies examining aspiration associated with enteral feeding devices are reviewed. We recommend a surgical jejunostomy for all patients at high risk for aspiration who require more than 3 weeks of enteral nutrition support.

The button jejunostomy for long-term jejunal feeding: results of a prospective randomized trial

Low profile, self-retaining feeding conduits ("buttons") inserted percutaneously through a mature gastrostomy stoma are ideal for prepyloric feeding. We tested the efficacy of a surgically inserted button (Button, C.R. Bard, Inc) in the jejunum for long-term postpyloric feeding. Forty-two aspiration risk patients were prospectively randomized to receive a standard No. 14 French red rubber catheter (n = 21, mean age 68 +/- 17 years) or the button (n = 21, mean age 68 +/- 18 years). Common indications for jejunal feeding were aphagia due to obtundation (41%) and esophageal dysmotility (41%). All feeding devices were inserted 20 cm distal to the ligament of Treitz via a serosal tunnel (catheter) or double pursestring (button) technique. No patient required reoperation, and cardiopulmonary failure was the most frequent cause of death, occurring in 11 patients (26%). Goal feedings were obtained in 91% of the catheter patients and 100% of the button patients by postoperative day 4.7 +/- 1.9 and 4.2 +/- 2.2, respectively. At a follow-up of 43 +/- 13 days, 12 (92.3%) of 13 catheter patients and 9 (81.8%) of 11 button patients were receiving goal feedings. Three patients in the catheter group and four patients in the button group had resumed an oral diet. Device-related complications (dislodgment, occlusion, peritubular leak, or bowel obstruction) and total number of patients with complications were significantly lower in the button group (one [5%] vs eight [38%] for device-related complications and one [5%] vs six [29%] for incidence of complications for the button and catheter groups, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Home parenteral nutrition after near total enterectomy

Six patients with extreme short bowel syndrome (4.2 +/- 4.9 cm of residual small bowel) were provided home parenteral nutrition (HPN) for 14,397 days. The average age at onset of HPN was 38 years (18-64 years). Patients maintained body weight at 97% of ideal (86-112%) with mean serum albumin of 3.7 +/- 0.6 g/dL (normal 3.5-5.8 g/dL), serum transferrin of 341 +/- 104 mg/dL (normal 200-400 mg/dL), and mean serum pre-albumin of 27.5 +/- 12.6 mg/dL (normal 16.6-43 mg/dL). Hospital admission for HPN-related complications was required 10.3 times/patient for a total of 864 hospital days and was catheter related in 71% of episodes. Catheter sepsis occurred once per 436 catheter days and required catheter removal in only 33% of instances. Five patients were able to resume an oral diet, five had returned to work or school, and three were married with family. HPN allowed return to a quality productive life with acceptable morbidity following catastrophic massive bowel resection.

Total quality management: one way to get started

Continuous QI requires our hospitals to undergo a fundamental change in values, beliefs, and ways to manage. Process improvement changes must start with senior managers, who create the environment for continuous improvement and then enable department managers and employees to improve their processes. Persistent poor quality does not respect organizational boundaries, and HQIP provides an opportunity to manage all the resources necessary to make improvements. As pharmacy managers, we must identify processes under our control that can be continuously improved based on documented customer judgments. We must stop asking employees to work harder in a flawed system and empower them to improve those processes within their control. It may be easy to become frustrated if it seems to take a long time to implement TQM. Remember, transforming our departments and hospitals will not happen overnight. We are embarking on a new style of leadership and management, one that will help pharmacies implement our pharmaceutical care vision.

Laparoscopic-guided jejunostomy

The proximal jejunum is the preferred site for long-term enteral access in the patient at risk for aspiration. Herein we describe a laparoscopic technique for the creation of a feeding tube jejunostomy. This minimally invasive approach is an alternative for patients requiring chronic postpyloric enteral feeding.

Contribution of skeletal muscle atrophy to exercise intolerance and altered muscle metabolism in heart failure

BACKGROUND

The purpose of this study was to investigate the prevalence of skeletal muscle atrophy and its relation to exercise intolerance and abnormal muscle metabolism in patients with heart failure (HF).

METHODS AND RESULTS

Peak VO2, percent ideal body weight (% IBW), 24-hour urine creatinine (Cr), and anthropometrics were measured in 62 ambulatory patients with HF. 31P magnetic resonance spectroscopy (MRS) and imaging (MRI) of the calf were performed in 15 patients with HF and 10 control subjects. Inorganic phosphorus (Pi), phosphocreatine (PCr), and intracellular pH were measured at rest and during exercise. Calf muscle volume was determined from the sum of the integrated area of muscle in 1-cm-thick contiguous axial images from the patella to the calcaneus. A reduced skeletal muscle mass was noted in 68% of patients, as evidenced by a decrease in Cr-to-height ratio of less than 7.4 mg/cm and/or upper arm circumference of less than 5% of normal. Calf muscle volume (MRI) was also reduced in the patients with HF (controls, 675 +/- 84 cm3/m2; HF, 567 +/- 112 cm3/m2; p less than 0.05). Fat stores were largely preserved with triceps skinfold of less than 5% of normal and/or IBW of less than 80% in only 8% of patients. Modest linear correlations were observed between peak VO2 and both calf muscle volume per meter squared (r = 0.48) and midarm muscle area (r = 0.36) (both p less than 0.05). 31P metabolic abnormalities during exercise were observed in the patients with HF, which is consistent with intrinsic oxidative abnormalities. The metabolic changes were weakly correlated with muscle volume (r = -0.42, p less than 0.05).

CONCLUSIONS

These findings indicate that patients with chronic HF frequently develop significant skeletal muscle atrophy and metabolic abnormalities. Atrophy contributes modestly to both the reduced exercise capacity and altered muscle metabolism.

Surgical jejunostomy in aspiration risk patients

One hundred patients underwent laparotomy for independent jejunal feeding tube placement. Neurologic disease was present in 50%, and obtundation (28) and oropharyngeal dysmotility (25) were the most common indications for enteral feeding. The post-pyloric route was chosen because of aspiration risk in almost all (94%) patients. Postoperative (30-day) mortality rate was 21%, because of cardiopulmonary failure in most (18). One death resulted directly from aspiration of tube feeds. Two surgical complications required reoperation: one wound dehiscence and one small bowel obstruction. Four wound infections occurred. Two patients underwent reoperation after tube removal, and four tubes required fluoroscopically guided reinsertion for peritubular drainage (2), removal (1), and occlusion (1). Aspiration pneumonia was present in 18 patients preoperatively and in eight postoperatively. None of the patients with feeding-related preoperative aspiration pneumonia (13) had a recurrence while fed by jejunostomy. Three patients developed postoperative aspiration pneumonia before initiation of jejunostomy feedings. Jejunostomy may be performed with low morbidity rate and substantial reduction of feeding-related aspiration pneumonia, and is the feeding route of choice in aspiration risk patients.

Early-onset repeated dieting reduces food intake and body weight but not adiposity in dietary-obese female rats

As dieting behavior and attempts at weight loss are becoming increasingly common in adolescent girls, we wished to determine whether early-onset repeated dieting influenced the development of obesity and its metabolic correlates. Female rats were fed a high-fat diet and subjected to six cycles of dieting and regain, beginning in the peripubertal period. Although dieted rats weighted less than nondieted high-fat fed controls at the completion of the sixth cycle, body composition analysis revealed that the two groups were equally obese. Cumulative caloric intake was less in dieted rats, suggesting that the pattern of consumption promoted by dieting helped to establish the obesity. Resting metabolic rate did not differ between the two groups. These data suggest that although early-onset repeated dieting may result in reduced body weight, the eventual level of adiposity may be unknowingly elevated, potentially leading to long-term health risks.

Nutritional support in renal failure

Adequate protein intake is necessary in renal failure to reduce morbidity. The desire to avoid dialysis should not be a justification to starve patients, particularly because fed patients have better survival rates in acute renal failure. The treatment techniques for renal failure may be used secondarily as a delivery route for nutrients.

Nutritional assessment and indications for nutritional support

The goal of nutritional assessment is to identify prospectively all those patients who would develop a nutrition-related complication. In practical terms, there is no single test capable of achieving this goal. At present, the best method of nutritional assessment is an organized step-by-step multifactorial approach. This involves assessment of the primary illness, the patient history, and the prognosis. A nutritional status examination is done, and the current intake is compared with the nutritional goals. A decision is then made whether to force feed. If forced feeding is initiated, the effectiveness of the therapy must be monitored frequently until the patient recovers and is able to be sustained by volitional oral intake.

Resting energy expenditure in patients with pancreatitis

OBJECTIVE

To assess the resting energy expenditure of hospitalized patients with pancreatitis.

DESIGN

Prospective, case-referent study.

SETTING

Nutrition support service in a university tertiary care hospital.

PATIENTS

Patients referred to the Nutrition Support Service with the diagnosis of pancreatitis. Excluded from study entry included those with cancer, obesity (greater than 150% ideal body weight), those measured within 3 postoperative days, or patients requiring ventilator support with an FIO2 of greater than 0.5. Forty-eight patients with either acute pancreatitis (n = 13), chronic pancreatitis (n = 24), acute pancreatitis with sepsis (n = 7), or chronic pancreatitis with sepsis (n = 7) were studied. The two septic groups were combined into a single pancreatitis-with-sepsis group, since no significant differences among measured variables were observed between individual septic groups.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Resting energy expenditure was measured by indirect calorimetry and compared with the predicted energy expenditure, as determined by the Harris-Benedict equations. Resting energy expenditure (percent of predicted energy expenditure) was significantly (p less than .02) greater for patients with pancreatitis complicated by sepsis (120 +/- 11%) compared with the nonseptic chronic pancreatitis group (105 +/- 14%). Resting energy expenditure for the nonseptic acute pancreatitis patients (112 +/- 17%) was not significantly different from the other groups. The septic pancreatitis group had the largest percentage (82%) of hypermetabolic (resting energy expenditure greater than 110% of predicted energy expenditure) patients, whereas 61% and 33% of the acute and chronic pancreatitis groups were hypermetabolic, respectively (p less than .02).

CONCLUSIONS

Resting energy expenditure is variable in patients with pancreatitis (77% to 139% of predicted energy expenditure). The Harris-Benedict equations are an unreliable estimate of caloric expenditure. Septic complications are associated with hypermetabolism and may be the most important factor influencing resting energy expenditure in pancreatitis patients.

Long-term effects of dieting on resting metabolic rate in obese outpatients

There is growing concern that dieting may adversely affect the metabolic rate and exacerbate efforts to control weight. In this study we measured the resting metabolic rate nine times over 48 weeks in 18 obese women (108.0 +/- 3.1 kg) who were randomly assigned to one of two dietary conditions. Nine patients consumed approximately 5021 kJ/d (1200 kcal/d) throughout the 48 weeks, while the other nine consumed a 1757-kJ/d (420-kcal/d) diet for 16 of the first 17 weeks and a conventional reducing diet for the remainder of treatment. All patients increased their physical activity, primarily by walking. During the first 5 weeks, the fall in metabolic rate was more than double the relative reduction in weight. By contrast, at week 48, the metabolic rate of patients in the two conditions was reduced by 9.4% +/- 4.0% and 8.3% +/- 2.2%, respectively, while weight was reduced by 16.6% +/- 2.7% and 19.5% +/- 2.7%, respectively. Thus, neither dietary regimen, combined with modest physical activity, was associated with long-term reductions in resting metabolic rate that exceeded decreases anticipated with the achievement of a lower body weight.

Components of energy expenditure in tumor-bearing animals

Single snapshot measurements of resting energy expenditure (REE) suggest that hypermetabolism contributes to cancer cachexia, but tumor impact on total 24-hr energy expenditure (TEE) is unknown. Automated multicage indirect calorimetry was employed to measure daily energy expenditure in adult Buffalo rats (n = 16) randomized to tumor inoculation or controls. Measurements included baseline REE, activity EE (AEE), thermic response to food (TEF), and TEE. Rats (n = 16) were randomized. Metabolic measurements, tumor size, and body weight were recorded weekly. Animals were sacrificed at Week 5 for analysis of host and tumor composition. Significant depletion of total lean body mass occurred in TB rats (greater than 15% wt loss, ANOVA P less than 0.001) which inversely correlated with tumor growth (r = -0.81, P less than 0.001). REE, TEF, AEE, and TEE did not change in controls (ANOVA P = n.s.). In TB rats, a 19.5% increase in REE occurred (119.4 +/- 3.3 to 138.7 +/- 1.8 kcal/kg LBM/day, P less than 0.01). TEE remained unchanged (157.3 +/- 5.6 vs 152.9 +/- 3.6 kcal/kg LBM/day, P = n.s.) due to a 66% decrease in AEE (32.9 +/- 3.1 to 10.5 +/- 1.7 kcal/kg LBM/day, P = 0.01). TEF did not change (4.7 +/- 0.8 vs 5.0 +/- 0.3 kcal/kg LBM/day, P = n.s.). Both TB and controls demonstrated a decreased REE in response to a 24-hr fast (7.9% vs 4.8%, P = n.s.). Respiratory quotient decreased in both groups when comparing fed to fasted values: TB (0.86 to 0.76) and controls (0.86 to 0.71), but the decline was greater in controls (P = 0.04).(ABSTRACT TRUNCATED AT 250 WORDS)

Efficacy of thrombolytic therapy for occlusion of long-term catheters

Nineteen ambulatory outpatients requiring a tunneled central venous access device with catheter occlusion were studied. Mean catheter life was 7.9 +/- 8.2 months (range, from 1-36 months) at the time of the occlusion. Urokinase (5000 units/ml) was injected in sufficient amount to fill the internal volume of the catheter and allowed to stay for 5 to 10 min before attempting to aspirate. Repeated aspiration attempts were performed every 5 to 10 min for a maximum of 30 to 60 min or patency. In the event catheter patency was not restored, the thrombolytic solution was aspirated from the catheter and a maximum of two additional trials were instituted. Results included clearance of four out of 15 withdrawal occlusions (27%) and two out of four resistance to infusion occlusions (50%). Overall, successful catheter clearance occurred in six out of 19 occlusions (32%). The efficacy rate of thrombolytic therapy for successfully clearing occluded catheters at our institution using conventional low-dose thrombolytic therapy is markedly lower than previously reported rates of 57 to 100%. The reasons for this discrepancy may reflect differences in dosage of thrombolytic agent, method of administration, frequency of monitoring of catheter patency, and catheter life.

Effects of nonglucose substrates (xylitol, medium-chain triglycerides, long-chain triglycerides) and carnitine on nitrogen metabolism in stressed rats

To evaluate the efficacy of nonglucose energy substrates in promoting nitrogen retention and survival in stressed states, two series of studies were done. In study 1, 50 rats underwent cecal ligation/perforation and subsequent infusion for 24 hr with one of four isocaloric (220 kcal/kg/day), isonitrogenous (1.4 g/N/kg/day), isovolemic regimens which differed in caloric source: Glucose (GLU) + long-chain triglycerides (LCT) (50%:50%), GLU + LCT + medium-chain triglycerides (MCT) (50%:32%:18%), GLU + LCT/Carnitine (10 mg/dl) or GLU + LCT + Xylitol (XYL) (33%:33%:33%). The nitrogen-sparing effect of GLU + LCT was not enhanced by the addition of carnitine to facilitate LCT mitochondrial uptake or by MCT to bypass carnitine-dependent transport. In contrast, relative to GLU + LCT GLU + LCT + XYL decreased urinary 3-methylhistidine (3MH) excretion (p less than 0.01), and enhanced nitrogen retention (p less than 0.01 vs GLU + LCT). For study 2, 24 male rats were anesthetized, cannulated for TPN, and given a 25% burn. They were then randomized into three dietary groups. The diets were isocaloric (103 kcal/kg/day) and isonitrogenous (2.0 g N/kg/day) but differed in nonprotein calorie source: GLU + LCT (51%:49%), GLU + Glycerol (51%:49%) and XYL + LCT (51%:49%). As in the septic animals, N balance was best with the xylitol regimen (p less than 0.01). The polyol, xylitol, appears to have a significant nitrogen sparing effect in stressed animals.

Antibiotic therapy of catheter infections in patients receiving home parenteral nutrition

Fifty-eight episodes of catheter-related sepsis in 21 patients receiving home parenteral nutrition were retrospectively studied. Of 81 organisms isolated from the blood, 59% were Gram-positive cocci, 25% were Gram-negative bacilli, and 16% were yeast. Attempts to treat bacterial infections at home with antibiotic therapy while the catheter remained in place were made; fungal isolation resulted in immediate hospitalization and catheter removal. Gram-negative infections more often resulted in eventual hospitalization (92%) and catheter removal (50%) than Gram-positive infections (57% hospitalization and 23% catheter removal). Empiric therapy with 1 g of cefazolin intravenously every 12 hr was successful in only 33% of episodes caused by coagulase-negative staphylococci, whereas vancomycin was successful in 62%. Sensitivity testing was not a reliable guide for antibiotic choice for treatment of these infections. Cefazolin, 1 g, intravenously every 12 hr was successful in only 25% of Gram-negative episodes treated empirically with this regimen. We conclude that our home parenteral nutrition patients should be hospitalized for a few days upon presentation with a catheter infection for clinical evaluation and aggressive antibiotic therapy. Vancomycin is the preferred drug for treatment of catheter-related infections caused by coagulase-negative staphylococcus.

Ablation of abnormal energy expenditure by curative tumor resection

Resting energy expenditure is abnormal in most patients with cancer and may contribute to cancer cachexia. These metabolic abnormalities may be a direct measure of tumor metabolism, or represent alterations in the size or activity of the body cell mass, or both. To unravel this pathogenesis, we prospectively studied 68 preoperative patients with cancer about to undergo curative resection by measuring resting energy expenditure before and after tumor resection. The preoperative measured resting energy expenditure was compared with expected resting energy expenditure based on Harris-Benedict resting energy expenditure predictions: 10 patients were hypometabolic (less than 90% Harris-Benedict); 35 were normometabolic (90% to 110% Harris-Benedict); and 23 were hypermetabolic (greater than 110% Harris-Benedict). Using each patient as his or her own control, resting energy expenditure normalized or remained normal following curative resection. In contrast, after palliative resection, resting energy expenditure remained hypermetabolic or significantly increased toward hypermetabolism. Tumor induces an abnormal metabolic rate, since tumor removal results in prompt normalization of resting energy expenditure. The abnormal energy expenditure of patients with cancer cannot be solely attributed to abnormal host body composition.