Tracer Methods Research Articles

Contribution of wood burning to PM10 in London

Ahead of measures to incentivise wood heating, the current level of wood burning in London was assessed by two tracer methods; i) a six week campaign of daily measurements of levoglucosan along a 38 km transect across the city during winter 2010, ii) a three year (2009–2011) measurement programme of black carbon and particulate matter from wood burning using differential IR and UV absorption by Aethalometer. Mean winter levoglucosan concentrations were 160 ± 17 ng m−3 in central London and 30 ± 26 ng m−3 greater in the suburbs, with good temporal correlation (r2 = 0.68–0.98) between sampling sites. Sensitivity testing found that the aethalometer wood burning tracer method was more sensitive to the assumed value of the Ångström coefficient for fossil fuel black carbon than it was to the Ångström coefficient for wood burning PM, and that the model was optimised with Ångström coefficient for fossil fuel black carbon of 0.96. The aethalometer and levoglucosan estimates of mean PM from wood burning were in good agreement during the winter campaign; 1.8 μg m−3 (levoglucosan) and 2.0 μg m−3 (aethalometer); i.e. between 7% and 9% of mean PM10 across the London transect. Analysis of wood burning tracers with respect to wind speed suggested that wood burning PM was dominated by sources within the city. Concentrations of aethalometer and levoglucosan wood burning tracers were a greatest at weekends suggesting discretionary or secondary domestic wood burning rather than wood being used as a main heating source. Aethalometer wood burning tracers suggests that the annual mean concentration of PM10 from wood burning was 1.1 μg m−3. To put this in a policy context, this PM10 from wood burning is considerably greater than the city-wide mean PM10 reduction of 0.17 μg m−3 predicted from the first two phases of the London Low Emission Zone which was introduced to reduce PM from traffic sources.

Evaluation of Bedrock Groundwater Movement in a Weathered Granite Hillslope Using Tracer Methods

Evaluation of Bedrock Groundwater Movement in a Weathered Granite Hillslope Using Tracer Methods

Sentinel node navigation surgery in gastric cancer: Current status.

The theory behind using sentinel node mapping and biopsy in gastric cancer surgery, the so-called sentinel node navigation surgery, is to limit the extent of surgical tissue dissection around the affected organ and subsequently the accompanied morbidity. However, obstacles on the clinical correspondence of sentinel node navigation surgery in everyday practice have occasionally alleviated researchers' interest on the topic. Only recently with the widespread use of minimally invasive surgical techniques, i.e., laparoscopic gastric cancer resections, surgical community's interest on the topic have been unavoidably reflated. Double tracer methods appear superior compared to single tracer techniques. Ongoing research is now focused on the invention of new lymph node detection methods utilizing sophisticated technology such as infrared ray endoscopy, florescence imaging and near-infrared technology. Despite its notable limitations, hematoxylin/eosin is still the mainstay staining for assessing the metastatic status of an identified lymph node. An intra-operatively verified metastatic sentinel lymph node will dictate the need for further conventional lymph node dissection. Thus, laparoscopic resection of the gastric primary tumor combined with the appropriate lymph node dissection as determined by the process of sentinel lymph node status characterization represents an option for early gastric cancer. Patients with T3 or more advanced disease should still be managed conventionally with resection plus standard lymph node dissection.

Heat and Solute Tracers: How Do They Compare in Heterogeneous Aquifers?

A comparison of groundwater velocity in heterogeneous aquifers estimated from hydraulic methods, heat and solute tracers was made using numerical simulations. Aquifer heterogeneity was described by geostatistical properties of the Borden, Cape Cod, North Bay, and MADE aquifers. Both heat and solute tracers displayed little systematic under- or over-estimation in velocity relative to a hydraulic control. The worst cases were under-estimates of 6.63% for solute and 2.13% for the heat tracer. Both under- and over-estimation of velocity from the heat tracer relative to the solute tracer occurred. Differences between the estimates from the tracer methods increased as the mean velocity decreased, owing to differences in rates of molecular diffusion and thermal conduction. The variance in estimated velocity using all methods increased as the variance in log-hydraulic conductivity (K) and correlation length scales increased. The variance in velocity for each scenario was remarkably small when compared to σ2 ln(K) for all methods tested. The largest variability identified was for the solute tracer where 95% of velocity estimates ranged by a factor of 19 in simulations where 95% of the K values varied by almost four orders of magnitude. For the same K-fields, this range was a factor of 11 for the heat tracer. The variance in estimated velocity was always lowest when using heat as a tracer. The study results suggest that a solute tracer will provide more understanding about the variance in velocity caused by aquifer heterogeneity and a heat tracer provides a better approximation of the mean velocity.

Detection of Alzheimer’s Disease Using Multitracer Positron Emission Tomography Imaging

Alzheimer's disease is characterized by impaired glucose metabolism and demonstration of amyloid plaques. Individual positron emission tomography tracers may reveal specific signs of pathology that is not readily apparent on inspection of another one. Combination of multitracer positron emission tomography imaging yields promising results. In this paper, 57 Alzheimer's disease neuroimaging initiative subjects that had FDG and PiB-positron emission tomography neuroimaging scans at the same time were used for development of proposed multitracer classification method. The subject’s brain image was automatically parcellated into 48 pre-defined regions of interest. Then, 96 features were extracted for each subject. The principal features weere extracted using principal component analysis, then they were combined based on intersection strategy. Finally, a support vector machine was adopted to evaluate the classification accuracy. Combination of two tracers with positron emission tomography scan yielded a higher diagnostic accuracy in Alzheimer's disease compared to individual tracer and other combination methods.

Advance of labeling and tracing methods for mesenchymal stem cells

Mesenchymal stem cells (MSCs) have a strong self-renewal capacity and multi-differentiation potential,which make them become ideal seed cells of tissue repair and target cells of gene therapy.However,the labeling and tracing method of MSCs transplanted in vivo is the hot spot and difficult problem of the current research.At present,the commonly used tracer methods of MSCs include fluorescence dye labeling,molecular marker,imaging marker technology.This paper summarized the advantages and disadvantages of these tracer methods. Key words: Mesenchymal stem cells; Labeling and tracing; Molecular imaging

Sentinel Lymph Node Biopsy for Risk-Reducing Mastectomy

Risk-reducing mastectomy (RRM) confers 90-95% decreased risk of breast cancer, and may reduce mortality, especially in high-risk groups such as BRCA carriers. Risk of occult disease in RRM specimen is ~5%. This demands axillary staging: sentinel lymph node (SLN) biopsy is no longer possible, axillary clearance confers significant risks and may prove negative. Contemporaneous SLN biopsy allows axillary staging with minimal further dissection. Women undergoing RRM and SLN biopsy between June 2005 and July 2010 were reviewed retrospectively from our prospectively maintained database of 1,522 SLN procedures in 1,498 patients. SLN(s) localized using routine tracer methods. SLNs and mastectomy specimens underwent routine histologic examination. Eighty-three RRMs with SLN biopsy were performed in 71 patients (12 bilateral). Indications for RRM: contralateral invasive (55), in situ (5) disease, BRCA 1/2 mutation (12), and strong family history (10). Mean number of SLNs: 1.35. Occult disease was detected in four cases (4.8%), with one case of occult invasive lobular carcinoma (1.2%). Remaining occult disease was lobular in situ neoplasia (LISN). SLNs were negative in all cases. Our findings are comparable to those in the literature: 4.8% rate of occult disease overall, 1.2% invasive. The significant risk with SLN biopsy is lymphoedema, quoted around 7%. We have had no reports of symptomatic lymphoedema in patients undergoing RRM and SLN biopsy. We propose that SLN at the time of mastectomy requires only limited further dissection, and confers minimal risk compared with secondary axillary surgery.

Direct flux and 15N tracer methods for measuring denitrification in forest soils

Estimates of denitrification are one of the key uncertainties in the terrestrial nitrogen (N) cycle, primarily because reliable measurements of this highly variable process—especially the production of its terminal product (N2)—are difficult to obtain. We evaluated the ability of gas-flow soil core and 15N tracer methods to provide reliable estimates of denitrification in forest soils. Our objectives were to: (1) describe and present typical results from new gas-flow soil core and in situ 15N tracer methods for measuring denitrification, (2) discuss factors that affect the relevance of these methods to actual in situ denitrification, and (3) compare denitrification estimates produced by the two methods for a series of sites in a northern hardwood forest ecosystem. Both methods were able to measure accumulations of N2 over relatively short (2–5 h) incubations of either unamended or tracer-amended intact soils. Denitrification rates measured by the direct flux soil core method were very sensitive to incubation oxygen (O2) concentration and decreased with increased O2 levels. Denitrification rates measured by the in situ 15N tracer method were very sensitive to the 15N content of the nitrate (NO3 −) pool undergoing denitrification, which limits the applicability of this method for quantifying denitrification in N-poor ecosystems. While its ability to provide accurate estimates of denitrification was limited, the 15N tracer method provided estimates of the short-term abiotic and biotic transformations of atmospheric N deposition to gas. Furthermore, results suggest that denitrification is higher and that N2O:N2 ratios are lower (<0.02) than previously thought in the northern hardwood forest and that short-term abiotic and biotic transformations of atmospheric N deposition to gas are significant in this ecosystem.

Variations in surface water-ground water interactions along a headwater mountain stream: Comparisons between transient storage and water balance analyses

[1] The accumulation of discharge along a stream valley is frequently assumed to be the primary control on solute transport processes. Relationships of both increasing and decreasing transient storage, and decreased gross losses of stream water have been reported with increasing discharge; however, we have yet to validate these relationships with extensive field study. We conducted transient storage and mass recovery analyses of artificial tracer studies completed for 28 contiguous 100 m reaches along a stream valley, repeated under four base-flow conditions. We calculated net and gross gains and losses, temporal moments of tracer breakthrough curves, and best fit transient storage model parameters (with uncertainty estimates) for 106 individual tracer injections. Results supported predictions that gross loss of channel water would decrease with increased discharge. However, results showed no clear relationship between discharge and transient storage, and further analysis of solute tracer methods demonstrated that the lack of this relation may be explained by uncertainty and equifinality in the transient storage model framework. Furthermore, comparison of water balance and transient storage approaches reveals complications in clear interpretation of either method due to changes in advective transport time, which sets a the temporal boundary separating transient storage and channel water balance. We have little ability to parse this limitation of solute tracer methods from the physical processes we seek to study. We suggest the combined analysis of both transient storage and channel water balance more completely characterizes transport of solutes in stream networks than can be inferred from either method alone.

Bias of Apparent Tracer Ages in Heterogeneous Environments

The interpretation of apparent ages often assumes that a water sample is composed of a single age. In heterogeneous aquifers, apparent ages estimated with environmental tracer methods do not reflect mean water ages because of the mixing of waters from many flow paths with different ages. This is due to nonlinear variations in atmospheric concentrations of the tracer with time resulting in biases of mixed concentrations used to determine apparent ages. The bias of these methods is rarely reported and has not been systematically evaluated in heterogeneous settings. We simulate residence time distributions (RTDs) and environmental tracers CFCs, SF6 , (85) Kr, and (39) Ar in synthetic heterogeneous confined aquifers and compare apparent ages to mean ages. Heterogeneity was simulated as both K-field variance (σ(2) ) and structure. We demonstrate that an increase in heterogeneity (increase in σ(2) or structure) results in an increase in the width of the RTD. In low heterogeneity cases, widths were generally on the order of 10 years and biases generally less than 10%. In high heterogeneity cases, widths can reach 100 s of years and biases can reach up to 100%. In cases where the temporal variations of atmospheric concentration of individual tracers vary, different patterns of bias are observed for the same mean age. We show that CFC-12 and CFC-113 ages may be used to correct for the mean age if analytical errors are small.

Female sex steroid effects on basal muscle protein synthesis rates in postmenopausal women

We recently reported a greater basal, postabsorptive rate of muscle protein synthesis (MPS) in post‐compared with premenopausal women. This finding suggests that ovarian hormones suppress MPS. In the current study, we tested this hypothesis by measuring the basal rate of MPS (by using stable isotope‐labeled tracer methods) in postmenopausal women before and after treatment with either estradiol (Mylan Pharmaceuticals; 0.1 mg/d delivered transdermally; n=6) or progesterone (Endometrin®; 100 mg/d delivered vaginally; n =5). The MPS rate was unaffected by estrogen treatment (0.063±0.006 vs. 0.063±0.010 %/h, before and after treatment respectively; P=0.99) but was markedly increased after progesterone treatment (0.102±0.018 %/h vs. 0.055±0.007; P=0.02). We conclude that the menopause associated decline in ovarian female sex hormone production is not responsible for the age‐associated increase in MPS in old women.Supported by grants from the NIH.

Clinical Implementations of Preoperative Computed Tomography Lymphography in Gastric Cancer: A Comparison with Dual Tracer Methods in Sentinel Node Navigation Surgery

Current sentinel node (SN) detection techniques require a learning period and tracers have many disadvantages for practical use. The purpose of this study was to evaluate the feasibility of preoperative computed tomography (CT) lymphography using lipiodol for detecting SNs in gastric cancer. A total of 24 patients who underwent laparoscopic surgery for early gastric cancer were enrolled in this study. Noncontrast CT images were obtained 1-2 h after endoscopic submucosal peritumoral injection of 1 mL of lipiodol the day before surgery. The final sentinel basins (SBs) were decided by the dual tracer method (indocyanine green plus (99m)Tc-antimony sulfur colloid) during laparoscopic gastrectomy. SN detection rate by preoperative CT lymphography using lipiodol and agreement between CT lymphography versus dual tracer method were evaluated. The agreement was confirmed with soft X-ray radiography of detected SBs. Technical failure of endoscopic lipiodol injection occurred in one patient. SNs were successfully detected in the remaining 23 patients (95.8 %), whereas the intraoperative SB detection rate using the dual method was 100 %. The agreement rate, defined as the concordance between two methods or inclusion of SNs detected by CT lymphography in SBs by the dual tracer method, was 87 %. Our initial experience of CT lymphography using lipiodol shows good potential in predicting SBs of gastric cancer preoperatively. However, SN detection by CT lymphography and the dual method should be applied complementarily in gastric cancer because discrepancies between these methods occur.

Wear measurement of highly cross-linked UHMWPE using a7Be tracer implantation technique

The very low wear rates achieved with the current highly cross-linked ultrahigh molecular weight polyethylenes (UHMWPE) used in joint prostheses have proven to be difficult to measure accurately by gravimetry. Tracer methods are therefore being explored. The purpose of this study was to perform a proof-of-concept experiment on the use of the radioactive tracer beryllium-7 ((7)Be) for the determination of in vitro wear in a highly cross-linked orthopedic UHMWPE. Three cross-linked and four conventional UHMWPE pins made from compression-molded GUR 1050, were activated with 10(9) to 10(10) (7)Be nuclei using a new implantation setup that produced a homogenous distribution of implanted nuclei up to 8.5 μm below the surface. The pins were tested for wear in a six-station pin-on-flat apparatus for up to 7.1 million cycles (178 km). A Germanium gamma detector was employed to determine activity loss of the UHMWPE pins at preset intervals during the wear test. The wear of the cross-linked UHMWPE pins was readily detected and estimated to be 17 ± 3 μg per million cycles. The conventional-to-cross-linked ratio of the wear rates was 13.1 ± 0.8, in the expected range for these materials. Oxidative degradation damage from implantation was negligible; however, a weak dependence of wear on implantation dose was observed limiting the number of radioactive tracer atoms that can be introduced. Future applications of this tracer technology may include the analysis of location-specific wear, such as loss of material in the post or backside of a tibial insert.

A novel index of whole body antilipolytic insulin action

Assessment of antilipolytic insulin action is important in obesity research, but extensive isotopic tracer studies are not always feasible. We evaluated whether an index of antilipolytic insulin action could be derived from readily available insulin and glycerol concentrations obtained during clamps or oral glucose tolerance tests (OGTT). We evaluated data collected from 29 subjects who had undergone a 3-stage hyperinsulinemic-euglycemic clamp (4, 8, and 40 mU/m(2)/min) with infusion of [(2) H5 ]glycerol to calculate the glycerol rate of appearance (GLYRA). Exponential decay curves for GLYRA across insulin concentrations were generated for each individual and suppression of lipolysis was calculated as the insulin concentration needed to half-maximally suppress GLYRA (GLYRA EC50). Areas under the curve for glycerol (GLYAUC) and insulin (INSAUC) were calculated and their products (INSAUC × GLYAUC) were calculated as an index of insulin suppression of lipolysis. The clamp index was highly correlated with GLYRA EC50 (r = 0.862, P < 0.001), as was an OGTT-derived index (r = 0.720, P < 0.01). These findings suggest that the products of the insulin and glycerol AUC from either a clamp or an OGTT are good biomarkers of the antilipolytic action of insulin and are comparable with direct measurement by isotopic tracer methods.

Dating groundwater in the Bohemian Cretaceous Basin: Understanding tracer variations in the subsurface

The northern section of the Bohemian Cretaceous Basin has been the site of intensive U exploitation with harmful impacts on groundwater quality. The understanding of groundwater flow and age distribution is crucial for the prediction of the future dispersion and impact of the contamination. State of the art tracer methods (3H, 3He, 4He, 85Kr, 39Ar and 14C) were, therefore, used to obtain insights to ageing and mixing processes of groundwater along a north–south flow line in the centre of the two most important aquifers of Cenomanian and middle Turonian age. Dating of groundwater is particularly complex in this area as: (i) groundwater in the Cenomanian aquifer is locally affected by fluxes of geogenic and biogenic gases (e.g. CO2, CH4, He) and by fossil brines in basement rocks rich in Cl and SO4; (ii) a thick unsaturated zone overlays the Turonian aquifer; (iii) a periglacial climate and permafrost conditions prevailed during the Last Glacial Maximum (LGM), and iv) the wells are mostly screened over large depth intervals.Large disagreements in 85Kr and 3H/3He ages indicate that processes other than ageing have affected the tracer data in the Turonian aquifer. Mixing with older waters (>50a) was confirmed by 39Ar activities. An inverse modelling approach, which included time lags for tracer transport throughout the unsaturated zone and degassing of 3He, was used to estimate the age of groundwater. Best fits between model and field results were obtained for mean residence times varying from modern up to a few hundred years. The presence of modern water in this aquifer is correlated with the occurrence of elevated pollution (e.g. nitrates).An increase of reactive geochemical indicators (e.g. Na) and radiogenic 4He, and a decrease in 14C along the flow direction confirmed groundwater ageing in the deeper confined Cenomanian aquifer. Radiocarbon ages varied from a few hundred years to more than 20ka. Initial 14C activity for radiocarbon dating was calibrated by means of 39Ar measurements. The 14C age of a sample recharged during the LGM was further confirmed by depleted stable isotope signatures and near freezing point noble gas temperature. Radiogenic 4He accumulated in groundwater with concentrations increasing linearly with 14C ages. This enabled the use of 4He to validate the dating range of 14C and extend it to other parts of this aquifer. In the proximity of faults, 39Ar in excess of modern concentrations and 14C dead CO2 sources, elevated 3He/4He ratios and volcanic activity in Oligocene to Quaternary demonstrate the influence of gas of deeper origin and impeded the application of 4He, 39Ar and 14C for groundwater dating.

Use of magnetic tracer and radio-cesium methods to determine past cropland soil erosion amounts and rates

Abstract The primary objective of this research was to determine the soil erosion rates in cropland of west central Illinois using a magnetic tracer (fly ash) and radio-cesium (cesium-137). The fly ash and cesium-137 accumulation on a stable cropland/hayland summit was determined using a spiral transect. This reference site was used as a baseline and then compared with the fly ash and cesium-137 levels in adjacent cropland landscape positions to estimate loss from erosion. The cesium-137 and fly ash data suggests that cropland lost significant sediment, fly ash and cesium-137 to erosion process especially from the upper and lower backslopes and footslope. The amount and rate of erosion predicted for each cropland landscape position using the fly ash and cesium-137 methods were determine for the 1910 to 1960, 1960 to 2009 and for the entire 100-year time periods. The fly ash and cesium-137 determined erosion amounts and annual soil erosion rate for cropland landscapes positions were highest for the upper and lower backslopes. Past backslope annual erosion rates for three different time periods were 51 Mt ha− 1 yr− 1 or less and above the tolerable soil loss rate of 11 Mt ha− 1 yr− 1 for Hickory soils. However, the predicted fly ash annual erosion rates for the last for the last 50 years using cesium-137 deposition was higher than annual erosion rates for the 1910 to 1960 time period using the difference between the two methods. The reason for the higher erosion rates for the 50 years after 1960 than before was most likely the continued use of moldboard plowing, up and down the slope plowing and the more intensive corn–soybean rotation without forages and small grains. These methods provide a way to document past cropland soil erosion amount and rates for three different time periods (1910 to 1960, 1960 to 2009 and 1910 to 2009).

Isotopic and modeling investigation of long-term protein turnover in rat tissues

Fractional synthesis rates (FSR) of tissue proteins (P) are usually measured using labeled amino acid (AA) tracer methods over short periods of time under acute, particular conditions. By combining the long-term and non-steady-state (15)N labeling of AA and P tissue fractions with compartmental modeling, we have developed a new isotopic approach to investigate the degree of compartmentation of P turnover in tissues and to estimate long-term FSR values under sustained and averaged nutritional and physiological conditions. We measured the rise-to-plateau kinetics of nitrogen isotopic enrichments (δ(15)N) in the AA and P fractions of various tissues in rats for 2 mo following a slight increase in diet δ(15)N. Using these δ(15)N kinetics and a numerical method based on a two-compartment model, we determined reliable FSR estimates for tissues in which P turnover is adequately represented by such a simple precursor-product model. This was the case for kidney, liver, plasma, and muscle, where FSR estimates were 103, 101, 58, and 11%/day, respectively. Conversely, we identified tissues, namely, skin and small intestine, where P turnover proved to be too complex to be represented by a simple two-compartment model, evidencing the higher level of subcompartmentation of the P and/or AA metabolism in these tissues. The present results support the value of this new approach in gaining cognitive and practical insights into tissue P turnover and propose new and integrated FSR values over all individual precursor AA and all diurnal variations in P kinetics.

Tracking fatty acid kinetics in distinct lipoprotein fractions in vivo: a novel high-throughput approach for studying dyslipidemia in rodent models

Isotopic tracers have been used to examine lipid trafficking for many years, and data from those studies have typically yielded novel insight regarding the pathophysiology of dyslipidemia. Previous experimental designs were suitable for studies in humans because relatively large volumes of plasma could be regularly sampled. We have expanded on the earlier logic by applying high-throughput analytical methods that require reduced sample volumes. Specifically, we have examined the possibility of coupling gel-based separations of lipoproteins (e.g., lipoprint) with LC-MS/MS analyses of complex lipid mixtures as a way to routinely measure the labeling profiles of distinct lipids in discrete lipoprotein subfractions. We demonstrate the ability to measure the incorporation of [U-(13)C]oleate into triglycerides (TG), PLs (PL), and cholesterol esters (CE) in VLDL, LDL, and HDL particles in mice. Although rodent models of dyslipidemia are inherently different from humans because of alterations in enzyme activities and underlying metabolism, rodent models can be used to screen novel compounds for efficacy in altering a given biochemical pathway and therein enable studies of target engagement in vivo. We expect that it is possible to translate our approach for application in other systems, including studies in humans.

A pore network model study of the fluid‐fluid interfacial areas measured by dynamic‐interface tracer depletion and miscible displacement water phase advective tracer methods

Fluid‐fluid interfacial areas in porous media are of considerable interest due to the impact they have on a wide range of practical applications involving mass transfer between phases, as well as for their importance in understanding unsaturated and multiphase flow behaviors in porous media. Tracer methods provide a low‐cost experimental approach for determining interfacial areas in porous media. Although a number of different tracer methods have been developed, uncertainty remains as to exactly what areas they measure. The work presented here uses pore network model simulations to study the behavior of tracers during simulated tracer measurements for two different specific water‐phase tracer methods: the dynamic‐interface tracer depletion method and the miscible displacement tracer method. The hypothesis driving this work was that different tracer methods likely measure different areas as a result of the very different ways tracers are used. Experimental data sets for six different porous media were used to validate the model and provide comparison with model‐simulated tracer‐based area measurements. Results of the work suggest that areas measured using the dynamic‐interface tracer depletion method closely match total fluid‐fluid interfacial areas, as long as the extent of tracer depletion during the method is relatively small. However, areas measured with the miscible displacement method likely fall somewhere between capillary and total fluid‐fluid areas. Calculations conducted with realistic diffusion coefficients and film thicknesses indicate that diffusion and head‐driven flow in films are insufficient to allow significant tracer access to film area, suggesting the potential importance of other mechanisms. Calculations conducted as a part of the work suggest that Leverett estimates of maximum area formed during drainage may be closer to total areas than previously reported.

Suppression in growth hormone during overeating ameliorates the increase in insulin resistance and cardiovascular disease risk

Previously, we reported that overeating for only a few days markedly suppressed the secretion of growth hormone (GH). The purpose of the present study was to determine the role of this reduction in GH concentration on key metabolic adaptations that occur during 2 wk of overeating. Nine nonobese, healthy adults were admitted to the hospital for 2 wk, during which time they ate ∼4,000 kcal/day (70 kcal·kg fat-free mass(-1)·day(-1); 50% carbohydrate, 35% fat, and 15% protein), and their plasma GH concentration was allowed to decline naturally (control). An additional eight subjects underwent the same overeating intervention and received exogenous GH treatment (GHT) administered in four daily injections to mimic physiological GH secretion throughout the 2-wk overeating period. We measured plasma insulin and glucose concentrations in the fasting and postprandial state as well as fasting lipolytic rate, proteolytic rate, and fractional synthetic rate (FSR) using stable-isotope tracer methods. GHT prevented the fall in plasma GH concentration, maintaining plasma GH concentration at baseline levels (1.2 ± 0.2 ng/ml), which increased fasting and postprandial assessments of insulin resistance (P < 0.05) and increased fasting lipidemia (all P < 0.05 vs. control). In addition, preventing the suppression in GH with overeating also blunted the increase in systemic proteolysis (P < 0.05 GHT vs. control). However, GHT did not alter lipolysis or FSR in response to overeating. In conclusion, our main findings suggest that the suppression in GH secretion that naturally occurs during the early stages of overeating may help attenuate the insulin resistance and hyperlipidemia that typically accompany overeating.