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PubMed2005

Tree measures and the number of segregating sites in time-structured population samples.

BACKGROUND: Time-structured genetic samples are a valuable source of information in population genetics because they provide several correlated observations of the underlying evolutionary processes. In this paper we study basic properties of the genetic variation in time-structured samples as reflected in the genealogies relating individuals and the number of segregating sites observed. Our emphasis is on "measurably evolving populations" i.e. populations from which it is possible to obtain time-structured samples that span a significant interval of evolutionary time. RESULTS: We use results from the coalescent process to derive properties of time-structured samples. In the first section we extend existing results to attain measures on coalescent trees relating time-structured samples. These include the expected time to a most recent common ancestor, the expected total branch length and the expected length of branches subtending only ancient individuals. The effect of different sampling schemes on the latter measure is studied. In the second section we study the special case where the full sample consists of a group of contemporary extant samples and a group of contemporary ancient samples. As regards this case, we present results and applications concerning the probability distribution of the number of segregating sites where a mutation is unique to the ancient individuals and the number of segregating sites where a mutation is shared between ancient and extant individuals. CONCLUSION: The methodology and results presented here is of use to the design and interpretation of ancient DNA experiments. Furthermore, the results may be useful in further development of statistical tests of e.g. population dynamics and selection, which include temporal information.

Animals↗
PubMed2006

Screening of pesticide residues in soil and water samples from agricultural settings.

BACKGROUND: The role of agricultural practices in the selection of insecticide resistance in malaria vectors has so far been hypothesized without clear evidence. Many mosquito species, Anopheles gambiae in particular, lay their eggs in breeding sites located around agricultural settings. There is a probability that, as a result of farming activities, insecticide residues may be found in soil and water, where they exercise a selection pressure on the larval stage of various populations of mosquitoes. To confirm this hypothesis, a study was conducted in the Republic of Benin to assess the environmental hazards which can be generated from massive use of pesticides in agricultural settings. METHODS: Lacking an HPLC machine for direct quantification of insecticide residues in samples, this investigation was performed using indirect bioassays focussed on the study of factors inhibiting the normal growth of mosquito larvae in breeding sites. The speed of development was monitored as well as the yield of rearing An. gambiae larvae in breeding sites reconstituted with water and soil samples collected in agricultural areas known to be under pesticide pressure. Two strains of An. gambiae were used in this indirect bioassay: the pyrethroid-susceptible Kisumu strain and the resistant Ladji strain. The key approach in this methodology is based on comparison of the growth of larvae in test and in control breeding sites, the test samples having been collected from two vegetable farms. RESULTS: Results obtained clearly show the presence of inhibiting factors on test samples. A normal growth of larvae was observed in control samples. In breeding sites simulated by using a few grams of soil samples from the two vegetable farms under constant insecticide treatments (test samples), a poor hatching rate of Anopheles eggs coupled with a retarded growth of larvae and a low yield of adult mosquitoes from hatched eggs, was noticed. CONCLUSION: Toxic factors inhibiting the hatching of anopheles eggs and the growth of larvae are probably pesticide residues from agricultural practices. Samples used during this indirect assay have been stored in the laboratory and will be analysed with HPLC techniques to confirm hypothesis of this study and to identify the various end products found in soil and water samples from agricultural settings under pesticide pressure.

Agriculture↗
PubMed2006

Variation in fiberoptic bead-based oligonucleotide microarrays: dispersion characteristics among hybridization and biological replicate samples.

BACKGROUND: Gene expression microarray technology continues to evolve and its use has expanded into all areas of biology. However, the high dimensionality of the data makes analysis a difficult challenge. Evaluating measurements and estimating the significance of the observed differences among samples remain important issues that must be addressed for each technology platform. In this work we use a consecutive sampling method to characterize the dispersion patterns of data generated from Illumina fiberoptic bead-based oligonucleotide arrays. RESULTS: To describe general properties of the dispersion we used a linear function SD = a + bY(mean), approximating the standard deviation across arrays (Y(mean) is the mean expression of a given consecutive sample). First we examined three levels of variability: 1) same cell culture, same reverse transcription, duplicate hybridizations; 2) same cell culture, reverse transcription replicates; 3) parallel cultures. Each higher level is expected to introduce a new source of variability. We observed minor differences in the constant term: the mean values are 3.5, 3.1 and 3.5, respectively. However, the mean coefficient b increased from 0.045 to 0.147 and 0.133. We compared the coefficients derived from the consecutive sampling to those obtained from the standard deviation of individual gene expressions and found them in good agreement. In the second experiment samples we detected 11 genes with systematically different expressions between the experiment samples treated with glucose oxidase and controls and corroborated the selection using the Mann-Whitney and other tests. We also compared the consecutive sampling and coincidence method to t-test: the average percentage of consistency was above 80 for the former and below 50 for the latter. CONCLUSION: Our results indicate that the consecutive sampling method and standard deviation function provide a convenient description of the overall dispersion of Illumina arrays. We observed that the constant term of the standard deviation function is at average approximately the same for duplicate hybridization as for the assays with additional sources of variability. Furthermore, among the genes affected by glucose oxidase treatment we identified 6 genes in oxidative stress pathways and 5 genes involved in DNA repair. Finally, we noted that the consecutive sampling and coincidence test provide, under given conditions, more consistent results than the t-test. REVIEWERS: This article was reviewed by Alexander Karpikov (nominated by Mark Gerstein), Jordan King and Eugene V. Koonin.

Journal Article↗
PubMed2006

Prevalence of Salmonella species in various raw meat samples of a local market in Kathmandu.

A cross-sectional study of raw meat samples from the local meat market of Kathmandu Metropolitan City was carried out during September 2002 to May 2003 with special emphasis on isolation and identification of Salmonella bacteria. A total of 123 raw meat samples (55 chicken, 37 buffalo, and 31 goat) were collected and analyzed relative to season. Salmonella spp was found in 11.4% (14/123) meat samples. Eight samples of chicken, that is, 14.5%, five samples of buffalo (13.5%), and one sample of goat (3.3%) were found to be positive for Salmonella. Salmonella prevalence revealed Salmonella (S.) pullorum in 3.3% samples, S. gallinarum in 0.8%, S. typhi in 1.6%, S. choleraesuis in 0.8%, and Salmonella of subgenus I or II group in 4.9% samples. More than 80% meat samples microbiologically processed indicated coliform contamination. Seasonal prevalence of Salmonella was highest in the months of April/May. Surveys revealed unsatisfactory conditions of sanitation in the local meat markets of Kathmandu.

Animals↗
PubMed1984

Intensified rates of venous sampling unmask the presence of spontaneous, high-frequency pulsations of luteinizing hormone in man.

To test the validity of venous sampling rates that are generally used to characterize pulsatile LH release in man (e.g. sampling every 15-20 min), we characterized apparent LH pulse frequency in blood withdrawn variously at 20- or 4-min intervals in 19 men, at 2-min intervals in 14 men, and at 1-min intervals in 6 men. In an effort to minimize detection bias, significant LH pulses were evaluated objectively using a computerized pulse-detection algorithm, which tended to maximize recognition of true-positive LH pulses, and minimize false-positive and false-negative pulses. Under these conditions, intensified rates of venous sampling at 4-, 2-, and 1-min intervals exposed approximately 3.6, 4.9, and 13.7-fold more LH pulses, respectively, than could be discerned at a 20-min sampling frequency. In addition, more rapid rates of venous sampling disclosed a previously unobserved pattern of LH pulses, in which higher frequency, lower amplitude LH pulsations were interposed among low frequency, high amplitude LH peaks. Quantitatively, LH pulses unmasked by intensified rates of venous sampling exhibited significantly lower pulse amplitudes, expressed either as a fractional (%) or absolute (mIU/ml) increment, than pulses identified at 20-min intervals. In conclusion, we demonstrated that intensified rates of venous sampling unmask a significant number of otherwise unrecognized LH pulses in the circulation of normal men. Moreover, because generally employed sampling rates overlooked these more rapid physiological fluctuations in LH concentrations, patterns of both high and low frequency LH pulsations must now be characterized in various states of health and disease using more rapid sampling paradigms.

Adult↗
PubMed2003

Mass spectrometric analysis of chemical warfare agents and their degradation products in soil and synthetic samples.

A packed capillary liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) method was developed for the identification of chemical warfare agents, their degradation products and related compounds in synthetic tabun samples and in soil samples collected from a former mustard storage site. A number of organophosphorus and organosulfur compounds that had not been previously characterized were identified, based on acquired high-resolution ESI-MS data. At lower sampling cone voltages, the ESI mass spectra were dominated by protonated, sodiated and protonated acetonitrile adducts and/or their dimers that could be used to confirm the molecular mass of each compound. Structural information was obtained by inducing product ion formation in the ESI interface at higher sampling cone voltages. Representative ESI-MS mass spectra for previously uncharacterized compounds were incorporated into a database as part of an on-going effort in chemical warfare agent detection and identification. The same samples were also analyzed by capillary column gas chromatography (GC)-MS in order to compare an established method with LC-ESI-MS for chemical warfare agent identification. Analysis times and full-scanning sensitivities were similar for both methods, with differences being associated with sample matrix, ease of ionization and compound volatility. GC-MS would be preferred for organic extracts and must be used for the determination of mustard and relatively non-polar organosulfur degradation products, including 1,4- thioxane and 1,4-dithiane, as these compounds do not ionize during ESI-MS. Diols, formed following hydrolysis of mustard and longer-chain sulfur vesicants, may be analyzed using both methods with LC-ESI-MS providing improved chromatographic peak shape. Aqueous samples and extracts would, typically, be analyzed by LC-ESI-MS, since these analyses may be conducted directly without the need for additional sample handling and/or derivatization associated with GC-MS determinations. Organophosphorus compounds, including chemical warfare agents, related compounds and lower volatility hydrolysis products may all be determined during a single LC-ESI- MS analysis. Derivatization of chemical warfare agent hydrolysis products and other compounds with hydroxyl substitution would be required prior to GC-MS analysis, giving LC-ESI-MS a definite advantage over GC-MS for the analysis of samples containing chemical warfare agents and/or their hydrolysis products.

Biodegradation, Environmental↗
PubMed2002

Discrepancy between visual and spectrophotometric assessment of sample haemolysis.

BACKGROUND: This study assessed the agreement between visual grading of sample haemolysis with automated haemolysis index (H index) measurement on the Roche 917 clinical chemistry analyser. METHODS: The H indices of 800 serum potassium samples and 800 EDTA plasma troponin I samples were compared with routine visual grading of sample haemolysis by technologists. Photographs of mild (haemoglobin 1 g/L), moderate (2.5 g/L) and severe (5 g/L) haemolysis were available for reference. RESULTS: For serum samples, the weighted kappa coefficient was 0.42 with an 8.0% haemolysis rate determined by visual inspection and 3.4% by H index. For EDTA-plasma samples, the weighted kappa coefficient was 0.35 with a 4.5% haemolysis rate determined by visual inspection and 7.9% by H index. CONCLUSION: Visual assessment of sample haemolysis is unreliable and can give variable results depending on sample type. Laboratories should consider investigating sample haemolysis using automated haemolysis index measurement as an alternative to visual grading whenever it is available.

Clinical Laboratory Techniques↗
PubMed2001

The detection of Chlamydia trachomatis by DNA amplification methods in urine samples from men with urethritis.

Our objective was to compare 3 deoxyribonucleic acid (DNA) amplification methods for the diagnosis of chlamydial infection with an enhanced enzyme immunoassay (EIA) method for antigen detection in urine samples, from men with non-gonococcal urethritis (NGU) attending a busy inner city genitourinary medicine centre. Urethral swabs and urine samples were collected from 346 male patients with NGU attending the clinic. All swabs and urines were tested for chlamydial infection (CT) using the EIA (Dako PCE immunoassay). Three aliquots of the urine samples were stored immediately at -70 degrees C for subsequent testing by: Amplicor polymerase chain reaction (PCR) (Hoffmann-La Roche, Switzerland); the amplified Chlamydia trachomatis assay (AMP CT) using transcription mediated amplification (TMA) (GenProbe, USA); and BDProbeTecET using the strand displacement assay (SDA) (Becton Dickinson, USA). The positive rate for the 3 amplified assays PCR, TMA and SDA (on urine) was 88/346 (25.4%), 80/346 (23.1%) and 88/346 (25.4%), respectively compared to 56/346 (16.2%) by EIA on urethral swabs, the current means of diagnosis in this laboratory. Thirty-one samples were positive in 2 or more of the amplification assays but negative in the EIA, 50 positives (53% sensitivity) detected in the urine samples by the EIA assay were detected by all 3 of the amplified assays. Three samples were positive by PCR only, 5 were positive by TMA only and 7 were positive by SDA only. DNA amplification assays are superior to standard immunoassays for the diagnosis of C. trachomatis infections in urine samples. Urine samples are suitable for use in these amplified assays to detect C. trachomatis. Freezing of samples before testing reduces the rate of inhibition reported in other published studies.

Chlamydia Infections↗
PubMed1999

Evaluation of self-taken samples for the presence of genital Chlamydia trachomatis infection in women using the ligase chain reaction assay.

The aim of this study was to evaluate the sensitivity and acceptability of self-taken vulval-introital (VI) samples, first-catch urine (FCU) samples and clinician-obtained cervical samples for the presence of genital Chlamydia trachomatis infections in women using the ligase chain reaction (LCR) assay. One hundred and four patients were enrolled, of whom 54 patients had chlamydial DNA in at least one of the samples tested. The sensitivity of the cervical sample was 96.3%, vulval-introital sample in LCR buffer 92.6%, vulval-introital swab collected dry 88.9%, FCU stored at +2-8 degrees C 81.5%, FCU stored at room temperature 77.8% and FCU stored with 2% w/v boric acid at room temperature 87.0%. Self-taken vulval-introital LCR samples were shown to be an acceptable alternative to a clinician-obtained LCR sample. The addition of boric acid may overcome the need for a continuous cold chain for FCU samples.

Adolescent↗
PubMed2004

Perfluorooctane sulfonate (PFOS) and related perfluorinated compounds in human maternal and cord blood samples: assessment of PFOS exposure in a susceptible population during pregnancy.

Fluorinated organic compounds (FOCs), such as perfluorooctane sulfonate (PFOS), perfluoro-octanoate (PFOA), and perfluorooctane sulfonylamide (PFOSA), are widely used in the manufacture of plastic, electronics, textile, and construction material in the apparel, leather, and upholstery industries. FOCs have been detected in human blood samples. Studies have indicated that FOCs may be detrimental to rodent development possibly by affecting thyroid hormone levels. In the present study, we determined the concentrations of FOCs in maternal and cord blood samples. Pregnant women 17-37 years of age were enrolled as subjects. FOCs in 15 pairs of maternal and cord blood samples were analyzed by liquid chromatography-electrospray mass spectrometry coupled with online extraction. The limits of quantification of PFOS, PFOA, and PFOSA in human plasma or serum were 0.5, 0.5, and 1.0 ng/mL, respectively. The method enables the precise determination of FOCs and can be applied to the detection of FOCs in human blood samples for monitoring human exposure. PFOS concentrations in maternal samples ranged from 4.9 to 17.6 ng/mL, whereas those in fetal samples ranged from 1.6 to 5.3 ng/mL. In contrast, PFOSA was not detected in fetal or maternal samples, whereas PFOA was detected only in maternal samples (range, < 0.5 to 2.3 ng/mL, 4 of 15). Our results revealed a high correlation between PFOS concentrations in maternal and cord blood (r2 = 0.876). However, we did not find any significant correlations between PFOS concentration in maternal and cord blood samples and age bracket, birth weight, or levels of thyroid-stimulating hormone or free thyroxine. Our study revealed that human fetuses in Japan may be exposed to relatively high levels of FOCs. Further investigation is required to determine the postnatal effects of fetal exposure to FOCs. Key words: cord blood, fluorinated organic compounds, human, PFOA, PFOS, PFOSA, pregnancy.

Adolescent↗
PubMed2006

Sample size for regression analyses of theory of planned behaviour studies: case of prescribing in general practice.

OBJECTIVES: Interest has been growing in the use of the theory of planned behaviour (TBP) in health services research. The sample sizes range from less than 50 to more than 750 in published TPB studies without sample size calculations. We estimate the sample size for a multi-stage random survey of prescribing intention and actual prescribing for asthma in British general practice. To our knowledge, this is the first systematic attempt to determine sample size for a TPB survey. METHODS: We use two different approaches: reported values of regression models' goodness-of-fit (the lambda method) and zero-order correlations (the variance inflation factor or VIF method). Intra-cluster correlation coefficient (ICC) is estimated and a socioeconomic variable is used for stratification. We perform sensitivity analysis to estimate the effects of our decisions on final sample size. RESULTS: The VIF method is more sensitive to the requirements of a TPB study. Given a correlation of .25 between intention and behaviour, and of .4 between intention and perceived behavioural control, the proposed sample size is 148. We estimate the ICC for asthma prescribing to be around 0.07. If 10 general practitioners were sampled per cluster, the sample size would be 242. CONCLUSIONS: It is feasible to perform sophisticated sample size calculations for a TPB study. The VIF is the appropriate method. Our approach can be used with adjustments in other settings and for other regression models.

Asthma↗
PubMed2007

Is supine rest necessary before blood sampling for plasma metanephrines?

BACKGROUND: The impact of blood sampling in sitting vs supine positions on measurements of plasma metanephrines for diagnosis of pheochromocytoma is unknown. METHODS: We compared plasma concentrations of free metanephrines in samples from patients with primary hypertension obtained after supine rest with those obtained in the sitting position without preceding rest. We also assessed the effects on diagnostic test performance retrospectively in patients with and without pheochromocytoma, and we calculated cost-effectiveness for pheochromocytoma testing. RESULTS: Upper reference limits of plasma free metanephrines were higher in samples obtained from seated patients without preceding rest than from supine patients with preceding rest. Application of these higher upper reference limits to samples from supine patients with pheochromocytoma decreased the diagnostic sensitivity from 99% to 96%. In patients without pheochromocytoma, adjusting the plasma concentration for the effects of sitting while preserving the 99% sensitivity by use of the supine upper reference limits increased the number of false-positive test results from 9% to 25%. CONCLUSIONS: To preserve high diagnostic sensitivity we recommend the use of upper reference limits determined from blood samples collected in the supine position. Under these conditions, negative test results for blood samples obtained with patients sitting are as effective for ruling out pheochromocytoma as negative results from samples obtained after supine rest. Repeat testing with samples obtained in the supine position offers a cost-effective approach for dealing with the increased numbers of false-positive results expected after initial sampling in the sitting position.

Adrenal Gland Neoplasms↗
PubMed2001

Analysis of large and small samples of biochemical and clinical data.

Statistical software often offers a list of various descriptive statistics of location and scale, but rarely selects an efficient estimate that is statistically adequate for an actual univariate sample. The sample interval estimate for a specified degree of uncertainty seems to be more meaningful if it covers an unknown value of the population parameter. The concept of an interval estimate in medicine is then used for medical decision-making. The proposed methodology, which uses the S-Plus algorithm for biochemical, biological and clinical data analysis contains the following steps: (i) Exploratory data analysis identifies basic statistical features and patterns of the data, the distributions of which are mostly non-normal, non-homogeneous and often corrupted by outliers. (ii) Sample assumptions about data, independence of sample elements, normality and homogeneity are examined. (iii) Power transformation and the Box-Cox transformation to improve sample symmetry and stabilize the spread. (iv) Classical and robust statistics for both large (n>30) and medium-sized samples (15<n<30), point and interval estimates for the parameters of location, scale and shape. For an analysis of small samples (4<n<20) the Horn procedure of pivot measures is recommended. The proposed methodology is demonstrated in two case studies, a large sample analysis of mean pregnenolone concentrations in the umbilical blood of newborns, and a small sample analysis of mean haptoglobin concentrations in human serum.

Adult↗
PubMed2005

Occurrence of Giardia cysts and Cryptosporidium oocysts in activated sludge samples in Campinas, SP, Brazil.

Giardia and Cryptosporidium have caused several outbreaks of gastroenteritis in humans associated with drinking water. Contaminated sewage effluents are recognized as a potential source of waterborne protozoa. Due to the lack of studies about the occurrence of these parasites in sewage samples in Brazil, we compared the efficiency of two procedures for concentrating cysts and oocysts in activated sludge samples of one sewage treatment plant. For this, the samples were submitted to i) concentration by the ether clarification procedure (ECP) and to ii) purification by sucrose flotation method (SFM) and aliquots of the pellets were examined by immunofluorescence. Giardia cysts were present in all samples (100.0%; n = 8) when using ECP and kit 1 reagents, while kit 2 resulted in six positive samples (85.7%; n = 7). As for SFM, cysts were detected in 75.0% and 100.0% of these samples (for kit 1 and 2, respectively). Regarding Cryptosporidium, two samples (25.0%; kit 1 and 28.5% for kit 2) were detected positive by using ECP, while for SFM, only one sample (examined by kit 1) was positive (12.5%). The results of the control trial revealed Giardia and Cryptosporidium recovery efficiency rates for ECP of 54.5% and 9.6%, while SFM was 10.5% and 3.2%, respectively. Considering the high concentration detected, a previous evaluation of the activated sludge before its application in agriculture is recommended and with some improvement, ECP would be an appropriate simple technique for protozoa detection in sewage samples.

Animals↗
PubMed2000

[Detection of antibodies against Trypanosoma cruzi in Somoto, Nicaragua, using indirect ELISA and IFI on blood samples on filter paper].

We standardized a solid-phase enzyme-linked immunosorbent assay (ELISA) in order to study the presence of Trypanosoma cruzi antibodies in asymptomatic persons who live in an area of Nicaragua endemic for Chagas' disease. The test was standardized to analyze filter-paper blood samples, which are easy to transport. In the first phase of our investigation, ELISA was used to study 18 samples of total serum and 18 eluates of blood from patients with chronic Chagas' disease; 30 samples of serum and 30 eluates of blood from healthy people, used as negative controls; and 14 samples of serum and 14 eluates of blood from patients with cutaneous or visceral leishmaniasis, which were used to study cross-reactions. Both with the total-serum and the blood-eluate samples, the ELISA test provided 100% sensitivity and 90% specificity. Cross-reactions in the patient samples were observed only with visceral leishmaniasis. The second phase of our investigation was a population study that included eight rural communities in the area of Somoto, Nicaragua. Through random sampling, filter-paper blood samples were collected from 2,434 people (1,335 men and 1,099 women) from the communities of Aguas Calientes, El Brocal, La Manzana, Las Playas, Los Canales, Santa Isabel, Santa Rosa, and Santa Teresa. Studied by ELISA and by indirect immunofluorescence (IIF), the samples included 260 found seropositive by ELISA (10.7%), of which 207 were positive according to IIF (8.5%). With both techniques, the majority of seropositives were among women, but the difference between men and women was not statistically significant. There was a high level of agreement between the results obtained with the two techniques. There was an upward trend with age, with 5.4% of those found seropositive by ELISA being persons 10 years of age or younger and 42.7% of those found seropositive being older than 50. The vast majority of the individuals analyzed were asymptomatic.

Adolescent↗
PubMed2003

Fixed precision sequential sampling plans for the greenbug and bird cherry-oat aphid (Homoptera: Aphididae) in winter wheat.

The numbers of greenbugs, Schizaphis graminum (Rondani), and bird cherry-oat aphids, Rhopalosiphum padi L., per wheat tiller (stem) were estimated in 189 production winter wheat (Triticum aestivum L.) fields located throughout Oklahoma. Taylor's power law regressions were calculated from these data and used to construct fixed precision sequential sampling schemes for each species. An evaluation data set was constructed from 240 samples taken during three growing seasons from winter wheat fields at four locations in Oklahoma. Wheat cultivar and growth stage were recorded for each field on the day of sampling. Taylor's power law parameters for evaluation fields differed significantly for both species among growing seasons, locations, and plant growth stages. Median precision achieved using the fixed precision sequential sampling schemes for each species departed <20% from expected precision over the range population intensity in the evaluation data. For the 10% of samples with greatest deviation between observed and expected precision, observed precision was 13.8-81.8% greater than that expected precision depending on aphid species and population intensity. For the greenbug, the distribution of the percentage deviation between observed and expected precision was positively skewed, so that the sampling scheme tended to over-predict precision. For the bird cherry-oat aphid, the distribution was more symmetric. Even though precision observed using the sampling schemes frequently varied from expected precision, because of the inevitable consequence of sampling error and environmental variation, the sampling schemes yielded median observed precision levels close to expected precision levels over a broad range of population intensity.

Agriculture↗
PubMed1999

Dihydrotestosterone, stanozolol, androstenedione and dehydroepiandrosterone sulphate inhibit leptin secretion in female but not in male samples of omental adipose tissue in vitro: lack of effect of testosterone.

Leptin, the product of the Ob gene, is a polypeptide hormone expressed in adipocytes which acts as a signalling factor from the adipose tissue to the central nervous system, regulating food intake and energy expenditure. It has been reported that circulating leptin levels are higher in women than in men, even after correction for body fat. This gender-based difference may be conditioned by differences in the levels of androgenic hormones. To explore this possibility, a systematic in vitro study with organ cultures from human omental adipose tissue, either stimulated or not with androgens (1 microM), was undertaken in samples obtained from surgery on 44 non-obese donors (21 women and 23 men). The assay was standardized in periods of 24 h, ending at 96 h, with no apparent tissue damage. Leptin results are expressed as the mean+/-s.e.m. of the integrated secretion into the medium, expressed as ng leptin/g tissue per 48 h. Spontaneous leptin secretion in samples from female donors (4149+/-301) was significantly higher (P<0.01) than that from male donors (2456+/-428). Testosterone did not exert any significant effect on in vitro leptin secretion in either gender (4856+/-366 in women, 3322+/-505 in men). Coincubation of adipose tissue with dihydrotestosterone (DHT) induced a significant (P<0.05) leptin decrease in samples taken from women (3119+/-322) but not in those taken from men (2042+/-430). Stanozolol, a non-aromatizable androgen, decreased (P<0.05) leptin secretion in female samples (2809+/-383) but not in male (1553+/-671). Dehydroepiandrosterone sulphate (DHEA-S) induced a significant (P<0.01) leptin decrease in female samples (2996+/-473), with no modifications in samples derived from males (1596+/-528). Exposure to androstenedione also resulted in a significant reduction (P<0.01) of leptin secretion in samples taken from women (2231+/-264), with no effect on male adipose tissue (1605+/-544). In conclusion, DHT, stanozolol, DHEA-S and androstenedione induced a significant inhibition of in vitro leptin secretion in samples from female donors, without affecting the secretion in samples from men. Testosterone was devoid of activity in either gender.

Adipose Tissue↗
PubMed2006

Survey of carbamate and organophosphorous pesticide export from a south Florida (U.S.A.) agricultural watershed: implications of sampling frequency on ecological risk estimation.

The objectives of the present study were to characterize the presence of selected carbamate and organophosphorous pesticides in Ten Mile Creek (Fort Pierce, FL, U.S.A.) and to evaluate the implications of sampling frequency on ecological risk estimates. Ten Mile Creek originates in a predominately agricultural watershed that is drained by an extensive network of cross-linked canals. Water samples were collected daily or every other day and were analyzed for azinphos-methyl, chlorpyrifos, diazinon, dimethoate, ethion, fenamiphos, malathion, methidathion, carbaryl, carbofuran, 3-hydroxycarbofuran, methiocarb, methomyl, oxamyl, and propoxur. A total of 457 samples were analyzed for the carbamate suite, and a total of 332 samples were analyzed for the organophosphorous suite. Carbaryl was detected in eight samples; half of these detections occurred on four consecutive days (October 26-29, 2001) at concentrations ranging from 0.33 to 0.95 microg/L. Methomyl was detected in samples collected on five consecutive days (March 30-April 3, 2002) at concentrations ranging from 1.0 to 2.2 microg/L. Oxamyl was detected in four samples, three of which occurred on three consecutive days (February 17-19, 2002) at concentrations ranging from 6.2 to 6.8 microg/L. The carbamates propoxur, 3-hydroxycarbofuran, carbofuran, and methiocarb were not detected. Diazinon and ethion were the only organophosphorous pesticides detected. Diazinon was detected at 0.9 and 0.7 microg/L on January 5, 2002, and on January 6, 2002, respectively. Ethion was detected in 18 consecutive samples (August 3-20, 2001). The mean, maximum, minimum, and median detected concentrations were 0.38, 0.61, 0.30, and 0.33 microg/L, respectively. Results indicate that frequent sampling is necessary to characterize the presence of these pesticides in this intensively drained watershed. This conclusion also may apply to similar canalized watersheds.

Agriculture↗