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Publication
Journal: Journal of Strength and Conditioning Research
September/9/2008
Abstract
Intense physical exercise is an important modifier of hormone metabolism. The aim of this study was to evaluate the variations in the urine profile of glucuroconjugated steroids (androgens, estrogens, and corticosteroids) as a consequence of a session of strength exercises. The subjects were a group (N = 20) of untrained male university students. They performed 3 sets of 10 repetitions, with a 3-minute recovery time between sets, at 70-75% of 1 repetition maximum (1RM). Four urine samples were collected per subject: before the session, immediately after, 3 hours after, and 48 hours after the session. They were assayed using a gas chromatograph coupled with a mass spectrometer. The concentrations of the different hormones were determined according to the urine creatinine level (ng steroid per mg creatinine). The substances assayed were testosterone, epitestosterone (Epit), androstenedione, dehydroepiandrosterone (DHEA), androsterone, etiocholanolone, beta-estradiol, estrone, tetrahydrocortisone (THE), and tetrahydrocortisol (THF). The results showed a significant decline after exercise with respect to the rested state in the urinary excretion of testosterone, Epit, DHEA, androsterone, and etiocholanolone. At 48 hours, there was a significant increase in the urinary excretion of Epit, androstenedione, androsterone, etiocholanolone, estrone, and THE. The androsterone + etiocholanolone/THE + THF ratio decreased after exercise, increased significantly (p < 0.05) at 3 hours, and returned to near resting levels at 48 hours. The data suggest that the performing a strength session at 70-75% of maximum strength provoked a state of fatigue in the subjects, from which they recovered 48 hours after the exercise.
Publication
Journal: Analytica Chimica Acta
March/28/2013
Abstract
In this research, a novel stacking capillary electrophoresis method, repetitive large volume sample injection and sweeping MEKC (rLVSI-sweeping MEKC) were developed to analyze the presence of three androgenic steroids considered as sport doping drugs, testosterone (T), epitestosterone (E) and epitestosterone glucuronide (EG) in urine. This method provides better sensitivity enhancement than the traditional large volume sample stacking-sweeping strategies due to sensitivity enhancement by repetitive injections. This multiple sampling method enhances sensitivity of monitoring of urine samples by UV detection (254 nm). Firstly, the phosphate buffer was filled into an uncoated fused silica capillary and the samples were injected into the capillary at 10 psi for 20s, and then stacked at -10 kV for 1 min using phosphate buffer containing SDS. The above injecting and stacking steps were repeated five times. Finally, separation was performed at -20 kV, using phosphate buffer containing methanol, SDS and (2-hydroxypropyl)-β-cyclodextrin. Method validation showed that calibration plots were linear (r≥0.997) over a range of 5-200 ng mL(-1) for T, 20-200 ng mL(-1) for E and 0.5-500 ng mL(-1) for EG. The limits of detection were 1.0 ng mL(-1) for T, 5.0 ng mL(-1) for E and 200.0 pg mL(-1) for EG. When evaluating precision and accuracy, values of RSD and RE in intra-day (n=3) and inter-day (n=5) analysis were found to be less than 10.0%. Compared with the simple LVSS-sweeping, which is also a stacking strategy, this method further improves sensitivity up to 25 folds (~2500 folds with MEKC without preconcentration). This method was applied to monitor 10 athletes' urine, and did not detect any analyte. The novel stacking method was feasible for monitoring of doping by sportsmen.
Publication
Journal: Steroids
August/31/2005
Abstract
Pregnenolone (PREG) can potentially be abused by athletes to maintain an equilibration of the steroidal environment after sex steroids administrations. Five men volunteers orally ingested 50 mg PREG to determine optimal urinary markers for detection of this steroid. Our findings show that ingestion of PREG has no significant effects on the testosterone/epitestosterone (T/E) and testosterone/luteinizing hormone (T/LH) ratios, whereas variable changes on the carbon isotopic values of three T metabolites: androsterone, etiocholanolone, 5beta-androstane-3alpha,17beta-diol (5beta-androstanediol) together with 16(5alpha)-androsten-3alpha-ol (androstenol) and 5beta-pregnane-3alpha,20alpha-diol (pregnanediol) have been observed. The difference between the carbon isotopic values (delta13C-values) of androstenol and pregnanediol is potentially the most reliable marker of exogenous PREG administration in males. For all subjects, the differences differ by 3.0 per thousand or more over a period of about 10 h and for both of them the detection window for positivity is extended over 40 h.
Publication
Journal: Methods in enzymology
September/14/2017
Abstract
The misuse of anabolic-androgenic steroids (AAS) in sports aiming at enhancing athletic performance has been a challenging matter for doping control laboratories for decades. While the presence of a xenobiotic AAS or its metabolite(s) in human urine immediately represents an antidoping rule violation, the detection of the misuse of endogenous steroids such as testosterone necessitates comparably complex procedures. Concentration thresholds and diagnostic analyte ratios computed from urinary steroid concentrations of, e.g., testosterone and epitestosterone have aided identifying suspicious doping control samples in the past. These ratios can however also be affected by confounding factors and are therefore not sufficient to prove illicit steroid administrations. Here, carbon and, in rare cases, hydrogen isotope ratio mass spectrometry (IRMS) has become an indispensable tool. Importantly, the isotopic signatures of pharmaceutical steroid preparations commonly differ slightly but significantly from those found with endogenously produced steroids. By comparing the isotope ratios of endogenous reference compounds like pregnanediol to that of testosterone and its metabolites, the unambiguous identification of the urinary steroids' origin is accomplished. Due to the complex urinary matrix, several steps in sample preparation are inevitable as pure analyte peaks are a prerequisite for valid IRMS determinations. The sample cleanup encompasses steps such as solid phase or liquid-liquid extraction that are presumably not accompanied by isotopic fractionation processes, as well as more critical steps like enzymatic hydrolysis, high-performance liquid chromatography fractionation, and derivatization of analytes. In order to exclude any bias of the analytical results, each step of the analytical procedure is optimized and validated to exclude, or at least result in constant, isotopic fractionation. These efforts are explained in detail.
Publication
Journal: Drug Testing and Analysis
June/27/2010
Abstract
In order to detect the misuse of endogenous anabolic steroids such as testosterone by athletes a total of n = 1734 suspicious urine samples were investigated by gas chromatography/combustion/isotope ratio mass spectrometry throughout the years 2005, 2006 and 2007. The (13)C/(12)C ratio of a target substance (androsterone, a testosterone metabolite) was compared to the (13)C/(12)C ratio of an endogenous reference compound (11beta-hydroxyandrosterone).N = 1340 samples were investigated due to elevated testosterone/epitestosterone ratios, with n = 87 (6.5%) exceptional findings regarding their isotopic ratios. An additional n = 164 samples were investigated because of elevated dehydroepiandrosterone concentrations, with n = 2 (1.2%) exceptional findings. The remainder were subjected to isotope ratio analysis because of elevated androsterone levels or because this was requested by sports federations.Significant differences between female and male samples were found for the (13)C/(12)C ratios of androsterone and 11beta-hydroxyandrosterone but not for samples taken in or out of competition.A further n = 645 samples originating from other World Anti-Doping Agency accredited laboratories, mainly throughout Europe as well as South America, South Africa and Southeast Asia, were investigated. The (13)C/(12)C ratios of the urinary steroids differ significantly for each geographical region, reflecting the dietary status of the individuals.The system stability over time has been tested by repeated injections of a standard solution and repeated processing of frozen stored blank urine. Despite a drift over time in absolute (13)C/(12)C ratios, no significant change in the difference of (13)C/(12)C (11beta-hydroxyandrosterone) minus (13)C/(12)C (androsterone) could be observed.
Publication
Journal: Acta Endocrinologica
August/7/1968
Publication
Journal: Journal of Chromatography A
November/19/2002
Abstract
Trimethylsilylation of target substances in a mixture of N-methyl-N-trimethylsilyltrifluoroacetamide (MSTFA), ammonium iodide and ethanethiol is frequently applied for the application of gas chromatography-mass spectrometry (GC-MS) in steroid analysis. However, artifacts were formed when using this mixture to silylate the steroids androsterone and etiocholanolone obtained from a urine matrix. The artifacts were identified as ethyl thio-containing products of the respective trimethylsilyl derivatives. The conversion of the studied products increased slowly as a function of time, was dependent on the presence of the urine matrix and was significantly accelerated by adding diethyl disulfide to the reagent before incubation. Also ethyl thio-incorporation into testosterone and epitestosterone was established. A mechanism for ethyl thio-incorporation is proposed. The conversion achieved after 120-h sample storage at room temperature was insufficient to significantly influence the analysis of androsterone and etiocholanolone under the studied conditions. However, the results provide fundamental insight into the mechanism of silylation and the occurring side-reactions. Moreover, when investigating the formation of new metabolites, the ethyl thio-incorporation can lead to misinterpretation.
Publication
Journal: Biochemistry and Cell Biology
February/9/1994
Abstract
Mare granulosa cells and cyclic corpus luteum microsomes are reported to aromatize 19-norandrogens more efficiently than androgens. However, 16 alpha-hydroxytestosterone and epitestosterone were not aromatized by the equine corpus luteum microsomal estrogen synthetase. These results indicate that the equine aromatase system would be different from the human placental microsomal estrogen synthetase, which aromatizes 16 alpha-hydroxyandrogens and epitestosterone but not 19-norandrogens. Furthermore, our data show that the rates of aromatization of androgens and 19-norandrogens were not additive and that 19-norandrogens competitively inhibited the aromatization of androgens, suggesting that a single enzymic system would be involved in the aromatization of androstenedione, 19-norandrostenedione, testosterone, and 19-nortestosterone. Our findings, which are identical to those previously reported for stallion testis and mare placental estrogen synthetases, provide evidence for a strong species specificity of the equine aromatase system.
Publication
Journal: Journal of Clinical Endocrinology and Metabolism
July/18/1973
Publication
Journal: Journal of Separation Science
April/30/2007
Abstract
A simple method is described for the measurement of testosterone (T) and epitestosterone (ET) in human urine samples. The deconjugated steroids were extracted directly from the samples by stir bar sorptive extraction (SBSE) and derivatized in situ on the stir bar by headspace acylation prior to thermal desorption and GC/MS. Extraction and derivatization parameters, namely salt addition, temperature, and time, were optimized to improve the recovery of T and ET by SBSE. The limits of quantification (S/N 10) were 0.9 ng/mL for T and 2.8 ng/mL for ET. Quantification of the steroids in urine samples was performed using standard addition to avoid the influence of matrix effects. The method was applied for the measurement of urinary T and ET in a group of healthy volunteers and HIV+ patients. Decreased levels of T were detected in the HIV+ group, whereas the excretion of ET was comparable for the two groups. Further clinical research is required to elucidate the biomarker significance of the T/ET ratio in HIV infection.
Publication
Journal: Forensic Science International
November/26/2006
Abstract
The case of seven urine samples collected for anti-doping purposes during a cycling stage race with moderately elevated testosterone and epitestosterone ratio (T/E) is reported. The very low probability of having all seven urine samples with such similar elevated T/E ratio (from 3.2 to 4.7) was very suspicious. Different pattern classification tools were tested to categorize the most similar steroid profiles, but none of the models enabled a clear classification of the different urine samples. Subsequently, genetic profiling of all urine samples was performed and demonstrated that three of the seven samples were collected from the same cyclist. Finally, the International Federation confirmed DNA profiling results. This suggests that urinary steroid data using several methodologies are not appropriate for identification purposes and to an extent not unique to individuals.
Publication
Journal: Journal of Analytical Toxicology
December/16/1998
Abstract
Dehydroepiandrosterone (DHEA) is an endogenous androgenic steroid produced by the ovaries and adrenal glands. Research suggests that DHEA can be converted to testosterone in peripheral tissues. Classified as a nutritional supplement, this compound may be purchased without a prescription. The military and international sports organizations prohibit the use of exogenous androgenic/anabolic steroids. Steroid-screening results are considered "positive" when the urinary ratio of testosterone to epitestosterone (T/E), an inactive synthetic byproduct, exceeds 6:1. Human volunteers ingested the recommended daily dose of 50 mg each morning for 30 days to determine if DHEA causes an adverse effect on this ratio. Urinary samples were collected before ingestion and 2-3 h after ingestion. Urine samples were extracted using solid-phase columns and analyzed using a previously developed gas chromatography-mass spectrometry method. T/E results were compared to an average baseline generated from three urine samples obtained before the study. Mean baseline T/E ratios averaged 0.67 for the seven subjects (range 0.1-1.2). The mean T/E ratio after DHEA ingestion ranged from 0.03 to 2.11. Individual postdose T/E ratios ranged from 0.01 to 3.7. The results from these individuals indicate that the administration of DHEA at this dose, for this period of time, has a minimal effect on urine T/E ratios and would not be expected to result in a positive screen for testosterone abuse. One subject agreed to take a single dose of 250 mg. This acute, high dose caused his T/E ratio to increase by 40% relative to the predose value.
Publication
Journal: Clinical Chemistry
February/23/1994
Abstract
Combined self-administration of testosterone (T) and epitestosterone (ET) by athletes counteracts the efficiency of the corresponding urinary glucuronides (G) ratio, (T/ET)G, as an indicator of T abuse. I therefore propose 5-androstene-3 beta, 17 alpha-diol (5A3 beta 17 alpha), the immediate metabolic precursor of ET, as a new reference compound for the expression of relative excretions of T and ET. Thus (T/5A3 beta 17 alpha)G and (ET/5A3 beta 17 alpha)G become potential criteria to indicate joint administration of T and ET, since their respective threshold values (2.5 and 1.5) are exceeded even when (T/ET)G remains below the critical value of 6.
Authors
Publication
Journal: Steroids
July/28/2011
Abstract
A series of molecularly imprinted polymers have been prepared and investigated as stationary phases in high performance liquid chromatography for the separation of testosterone and epitestosterone using non-polar mobile phases. The polymers were imprinted using 5α-dihydrotestosterone as template, and all retain testosterone more strongly than its 17α-OH epimer. The best polymer was prepared using trifluoromethylacrylic acid as functional monomer (interacting with the template via hydrogen bonds), divinylbenzene as 'inert' cross-linker, and chloroform as porogen. It also included a steroid-based cross-linker, which may interact with the template via van der Waals interactions to lend additional 'shape selectivity'. A 250×4.6mm column packed with this polymer gave baseline resolution of testosterone and epitestosterone (15 μg each) in under 20 min. Preparation of the steroid based cross-linker included the selective reduction of 5α-dihydrotestosterone (17β-hydroxy-5α-androstan-3-one) to the 3α,17β-diol using K-selectride.
Publication
Journal: Drug Testing and Analysis
July/4/2010
Abstract
The primary screening method for the detection of doping by athletes using synthetic versions of endogenous steroids such as testosterone relies on measurement of the ratio of testosterone (T) to epitestosterone (E) in urine. In 2005 the World Anti-Doping Agency (WADA) lowered the T/E value at which samples undergo further investigation from six to four. This has resulted in a large increase in the number of athletes with naturally elevated T/E ratios undergoing investigation without a corresponding increase in the number of proven doping offences involving testosterone.Our objective was to develop a new simple screening protocol that can, with high probability, not only distinguish athletes whose natural T/E values exceed four from those whose T/E values have been elevated by testosterone doping but also detect those athletes with naturally low T/E values that do not exceed four despite being administered testosterone.Testosterone (250 mg Sustanon) was administered weekly to a group of 47 young adult males for five weeks in a double-blind placebo controlled study and urine samples collected. The samples were analysed for steroid concentrations using GC/MS and for luteinizing hormone (LH) by immunoassay.The elevation of T/E that occurred in all subjects was accompanied by a significant reduction in urinary LH concentrations to levels that are rare in normal subjects.The appropriate measurement of urinary LH, with the measurement of T/E values, can markedly improve the efficiency of detection of doping with testosterone by male athletes, particularly those who have low natural T/E ratios.
Publication
Journal: Journal of Chromatography B: Analytical Technologies in the Biomedical and Life Sciences
January/8/2007
Abstract
A simple method using liquid chromatography-linear ion trap mass spectrometry for simultaneous determination of testosterone glucuronide (TG), testosterone sulfate (TS), epitestosterone glucuronide (EG) and epitestosterone sulfate (ES) in urine samples was developed. For validation purposes, a urine containing no detectable amount of TG, TS and EG was selected and fortified with steroid conjugate standards. Quantification was performed using deuterated testosterone conjugates to correct for ion suppression/enhancement during ESI. Assay validation was performed in terms of lower limit of detection (1-3ng/mL), recovery (89-101%), intraday precision (2.0-6.8%), interday precision (3.4-9.6%) and accuracy (101-103%). Application of the method to short-term stability testing of urine samples at temperature ranging from 4 to 37 degrees C during a time-storage of a week lead to the conclusion that addition of sodium azide (10mg/mL) is required for preservation of the analytes.
Publication
Journal: Journal of chromatography. B, Biomedical applications
April/10/1997
Abstract
The effect of alcohol (1.2 and 2.0 g/kg) on the urinary testosterone-to-epitestosterone (T/E) ratio was studied by two experiments each conducted with four healthy females and males. The intake of 2.0 g/kg of ethanol within 5 h in the evening significantly increased plasma testosterone concentration and ratio of T/E in urine collected next morning in females. The results suggest that alcohol increases the T/E ratio more in females than in males. The effect of high doses of alcohol on urinary T/E ratio must be kept in mind when doping tests are performed during training periods.
Publication
Journal: Journal of Chromatography A
November/21/2006
Abstract
Separation of anabolic and androgenic steroids by micellar electrokinetic chromatography (MEKC) has been little studied. Simultaneous separation of the endogenous alpha-epimers testosterone and epitestosterone has not been achieved with any electroseparation technique. Here, a partial filling micellar electrokinetic chromatographic (PF-MEKC) method is described for the analysis of three endogenous steroid hormones (androstenedione, testosterone, epitestosterone) and two synthetic anabolic steroids (fluoxymesterone, methyltestosterone). The resolution efficiency of single-isomer sulphated gamma-cyclodextrins and the surfactants sodium dodecyl sulphate and sodium taurocholate was exploited. The method is based on the sequential introduction of short plugs of two different pseudostationary phases into the capillary. The separation was completed in less than 10 min. The method can be used in quantitative analysis. Linear correlation was obtained between concentration and peak area of 0.996 or better. The repeatability (RSD) of the compound peak areas ranged from 3.6% (methyltestosterone) to 6.2% (androstenedione). Limits of detection were between 73 microg/L (testosterone) and 160 microg/L (fluoxymesterone). As a demonstration of the method, androstenedione, testosterone and epitestosterone were determined in a spiked urine sample.
Publication
Journal: Hormone and Metabolic Research
September/17/2013
Abstract
Epitestosterone is the 17α-epimer of testosterone. This steroid possesses antiandrogenic activities. The mechanism of action of epitestosterone has not been elucidated. The aim of this study was to investigate the nonclassical effect of epitestosterone on the membrane of Sertoli cells in proliferative phase (rats aged 15 days) and in nonproliferative phase (rats aged 21 and 35 days). The membrane potential of Sertoli cells was recorded using a standard single microelectrode technique. Epitestosterone (0.5, 1, and 2 μM) or testosterone (1 μM) was administered alone and after infusion with flutamide (1 μM), verapamil (100 μM), or U-73122 (2 μM). The testes of rats aged 12-15 days were preincubated with 45Ca2+ with or without flutamide (1 μM) and incubated with epitestosterone (1 μM) or testosterone (1 μM). Epitestosterone and testosterone produced a depolarization in the membrane potential and increased the membrane input resistance on Sertoli cells from rats of all 3 ages. The effect of epitestosterone did not change after perfusion with flutamide. Epitestosterone increased 45Ca2+ uptake within 5 min and this effect was not inhibited by flutamide. The absence of an effect by flutamide suggests that epitestosterone acts independently of the intracellular androgen receptor. The depolarizing effect was inhibited by verapamil, a voltage-dependent calcium channel blocker, and by U-73122, a phospholipase C inhibitor. These results indicate that epitestosterone acts on the membrane via a nonclassical signaling pathway; the effect was similar to the testosterone action on membrane of Sertoli cells in whole seminiferous tubules from rat testes.
Publication
Journal: Clinical Chemistry
August/18/1988
Abstract
The testosterone/epitestosterone weight ratio in urine is used to detect cases of doping when an athlete has treated himself with exogenous testosterone. When this ratio exceeds 6, it is considered evidence of testosterone doping. We show here that intake of ethanol can affect this ratio. Ingestion of 110-160 g of ethanol, about 2 g per kilogram body weight, increased the ratio between testosterone and epitestosterone in urine from 1.14 +/- 0.07 to 1.52 +/- 0.09 in four healthy male volunteers. The increase ranged from 30% to 90% in the different subjects studied (mean 41%). In cases where doping with testosterone is suspected, the possibility should be considered that at least part of an observed increased testosterone/epitestosterone ratio in urine is ascribable to previous ingestion of ethanol.
Publication
Journal: Steroids
January/8/2012
Abstract
The screening of testosterone misuse in the doping control field is normally performed by the measurement of the ratio between the concentrations of testosterone and epitestosterone excreted as glucuronides (T/E). Despite the satisfactory results obtained with this approach, the measurement of T/E presents some limitations like the long-term detection of oral testosterone administration. Recently, several testosterone metabolites released after basic treatment of the urine have been reported (androsta-1,4-dien-3,17-dione, androsta-4,6-dien-3,17-dione, 17β-hydroxy-androsta-4,6-dien-3-one and 15-androsten-3,17-dione). In the present work, the usefulness of these metabolites for the detection of oral testosterone misuse has been evaluated and compared with the conventional T/E measurement. For this purpose, 173 urine samples collected from healthy volunteers were analysed in order to obtain reference concentrations for the four metabolites released after alkaline treatment. On the other hand, urine samples collected from five volunteers before and after testosterone undecanoate administration were also analysed. Concentrations of androsta-4,6-dien-3,17-dione and 17β-hydroxy-androsta-4,6-dien-3-one showed a similar behaviour as the T/E, allowing the detection of the misuse for several hours after administration. More promising results were obtained by quantifying androsta-1,4-dien-3,17-dione and 15-androsten-3,17-dione. The time in which the concentrations of these analytes could be differentiated from the basal level was between 3 and 6 times longer than the obtained with T/E, as a result, an improvement in the detection of testosterone abuse can be achieved. Moreover, several ratios between these compounds were evaluated. Some of them improved the detection of testosterone misuse when comparing with T/E. The best results were obtained with those ratios involving androsta-1,4-dien-3,17-dione.
Publication
Journal: Pathologie-biologie
March/5/1991
Abstract
Testing for illicit self-administration of testosterone by athletes requires quantitative analysis by gas chronomatography-mass spectrometry combined with stable isotope dilution. International Sports Authorities have adopted the ratio of urinary excretions of testosterone and epitestosterone for drug testing. This ratio is required to be under 6. The authors studied the statistical distribution of this ratio in teenage athletes and found that the likelihood of false-positive results is 15/10,000.
Publication
Journal: Clinical Chemistry
June/16/1997
Abstract
Our goal in this study was to determine whether the urinary ratio of testosterone to luteinizing hormone (T/LH) as an indicator of exogenous anabolic steroid (AS) use is superior to the urinary ratio of testosterone to epitestosterone (T/E). After 2 weekly placebo injections, 19 subjects were given testosterone cypionate (TC) injections of 250 or 500 mg/week for 14 weeks followed by 14 weekly placebo injections. Patients were considered to have ceased taking TC if they tested negative 9 weeks after their last injection. For detection of illicit or supraphysiological TC (AS) use, the urinary T/E ratio of>> or = 6 yielded a false-negative rate of 46% and a false-positive rate of 4%. However, a urinary T/LH ratio of>> or = 30 produced a false-negative rate of only 24% and a false-positive rate of 13%. We conclude that the urinary T/LH ratio of>> or = 30 is a more sensitive marker of AS use than the urinary T/E ratio of>> or = 6 and remains sensitive for twice as long as urinary T/E.
Publication
Journal: Rapid Communications in Mass Spectrometry
May/24/2000
Abstract
The detection of exogenous testosterone in bovine urine was investigated by using gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). The carbon isotopic ratio measurement of epitestosterone, etiocholanolone (testosterone metabolite) and DHEA (testosterone precursor) in female bovine urines after testosterone enanthate administration was carried out. An important modification in the 13C/12C ratio of testosterone metabolites was observed, such that significant differences between precursor and metabolites of testosterone occurred until three weeks after intramuscular administration of testosterone enanthate. The factors influencing the 13C/12C of endogenous steroids were studied especially through cattle feeding and age. The DHEA mean delta13C value was found to vary between -25 and -26/1000 when hay and concentrate diet were used for fattening. On the other hand the delta13C value observed when maize silage was used increased to -20/1000. Testosterone metabolites showed the same delta13C increase as their precursor. Moreover, we observed a clear relationship between age and efficiency of misuse determination. Indeed, because of the lower concentration of natural hormones in young animals, the contribution of exogenous molecules increases significantly compared with older subjects. Consequently, demonstration of administration is easier to achieve in calves than in mature animals.
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