The Experts below are selected from a list of 213 Experts worldwide ranked by ideXlab platform

Vladimir Petrow - One of the best experts on this subject based on the ideXlab platform.

  • Total Suppression of Spontaneous Endometrial Carcinoma in BDII/Han Rats by Melengestrol Acetate
    Oncology, 1995
    Co-Authors: Friedrich Deerberg, Gabriele Pohlmeyer, Konrad Lörcher, Vladimir Petrow
    Abstract:

    Female virgin BDII/Han rats develop spontaneous endometrial carcinoma (EC) in incidences up to 90%. Our objective was to determine whether lifelong administration of the progestin Melengestrol Acetate (MGA) would suppress those tumors. Four groups of 20 rats aged 24-28 days were employed Group I animals were untreated controls. Groups II, III, and IV were fed 0.1, 0.2, and 0.4 mg MGA/kg daily in their diet during their lifetimes. All treated groups were free from EC during their lifetimes with an increased lifespan up to 30%. The controls, in contrast, had an EC incidence of 85%. Histologically, with one exception all tumors were classified as adenocarcinoma. While most of the control rats died from EC, nearly all animals of groups II and III died from age-related diseases. Rats in group IV showed side effects due to the glucocorticoid properties of MGA. Besides alopecia and obesity an acceleration of chronic progressive nephrosis was observed. The study establishes the validity of the prophylactic approach to spontaneous hormone-dependent cancers in a rat tumor model.

  • 1-Dehydro-Melengestrol Acetate inhibitis the growth and protein kinase C activity of androgen-independent Dunning rat prostatic tumors
    Cancer Chemotherapy and Pharmacology, 1993
    Co-Authors: Michael J. Battistone, George M. Padilla, Vladimir Petrow
    Abstract:

    Androgen-independent Dunning R3327-AT3 rat prostate tumors are considered an appropriate model of advanced prostate cancer in humans. We recently reported that the progestational steroid Melengestrol Acetate (MGA) inhibited growth of these tumors on oral administration but also induced a marked involution of adrenals and androgen target organs (prostate, seminal vesicles, and testes). We report herein that the 1-dehydro derivative of Melengestrol Acetate (dMGA) fed to rats for 21 days also inhibited the growth of Dunning AT3 tumors by ∼55% without causing a significant regression of adrenals or androgen-dependent tissues. Thus, tumor-growth inhibition was induced by dMGA in the absence of glucocorticoid activity. Cytosolic AT3 tumor fractions obtained by diethylaminoethyl (DEAE)-Sephacel batch chromatography were assayed for lipid-and Ca^2+-dependent (PKC) and-independent protein kinase activities. Prostatic cytosols had equivalent activity levels of both types of kinases (∼2 nmol γ-[^32P]-adenosine 5′-triphosphate (ATP) incorporated mg protein^−1 min^−1. The PKC activity recovered from the cytosol of untreated AT3 tumors was ∼4 times higher. Oral administration of dMGA reduced this activity by >95%. The relationship between protein-kinase activity levels and dMGA-induced growth inhibition of androgen-independent tumors in this animal model is discussed.

H H D Meyer - One of the best experts on this subject based on the ideXlab platform.

  • Non-invasive screening for treatment of heifers with the anabolic steroid Melengestrol Acetate (MGA) by feces analysis.
    Journal of immunoassay & immunochemistry, 2003
    Co-Authors: Iris G Lange, Andreas Daxenberger, M Hageleit, Michael W Pfaffl, H H D Meyer
    Abstract:

    Abstract For eight weeks, two heifers each had been orally administered daily doses of 0, 1.5, or 5 mg Melengestrol Acetate (MGA) in a feed premix. Four heifers received the labeled dose of 0.5 mg/day. Regular feces samples were taken throughout the experiment. A rapid screening method for the determination of MGA in feces was developed, consisting of liquid extraction, clean-up on solid-phase extraction cartridges and quantification by enzyme immunoassay (ELISA). Residues in feces were dose-dependent with mean values of 

  • non invasive screening for treatment of heifers with the anabolic steroid Melengestrol Acetate mga by feces analysis
    Journal of Immunoassay & Immunochemistry, 2003
    Co-Authors: Iris G Lange, Andreas Daxenberger, M Hageleit, Michael W Pfaffl, H H D Meyer
    Abstract:

    Abstract For eight weeks, two heifers each had been orally administered daily doses of 0, 1.5, or 5 mg Melengestrol Acetate (MGA) in a feed premix. Four heifers received the labeled dose of 0.5 mg/day. Regular feces samples were taken throughout the experiment. A rapid screening method for the determination of MGA in feces was developed, consisting of liquid extraction, clean-up on solid-phase extraction cartridges and quantification by enzyme immunoassay (ELISA). Residues in feces were dose-dependent with mean values of < 0.25, 2.0, 4.4, or 15.4 ng/g for 0, 0.5, 1.5, and 5 mg/day doses, respectively. In contrast to urine analysis, feces analysis appeared to be a suitable means of non-invasive screening before slaughter for surveillance of MGA treatment and verification of its compliance with labeled dosage.

  • Quantitative assessment of foetal exposure to trenbolone Acetate, zeranol and Melengestrol Acetate, following maternal dosing in rabbits.
    Xenobiotica; the fate of foreign compounds in biological systems, 2002
    Co-Authors: Iris G Lange, H H D Meyer, A Daxenberger, E. Rajpert-de Meyts, N E Skakkebaek, D. N. R. Veeramachaneni
    Abstract:

    1. Residues of commonly used growth-promoting agents found in animal meat can be hormonally active and they have been implicated as possible endocrine disruptors in man. Although these compounds could be potentially detrimental to the developing foetus, it is not clear whether and to what extent they pass through placental barrier. 2. This issue was addressed using the rabbit as an animal model. Pregnant rabbits were treated with trenbolone Acetate, zeranol or Melengestrol Acetate beginning at gestation day 14. Levels of active substances in plasma were screened by means of specific ELISA systems. The residues of parent compounds and their metabolites were quantified in maternal and foetal tissues on gestation day 27 using validated, sensitive HPLC/ELISA methods. 3. All three compounds crossed the placental barrier and were detectable in foetal tissues. The extent of tissue concentration varied depending on the compound and tissue analysed. Gender differences were observed in some instances.

  • Detection of Melengestrol Acetate residues in plasma and edible tissues of heifers.
    The veterinary quarterly, 1999
    Co-Authors: Andreas Daxenberger, M Hageleit, Karsten Meyer, H H D Meyer
    Abstract:

    The aim of this study was to gain knowledge of residue formation after the use of Melengestrol Acetate (MGA) as a growth-promoting agent. Two Holstein-Friesian heifers each received a daily dose through the feed of 0, 0.5 mg (2 heifers with and without withdrawal each), 1.5 mg or 5.0 mg MGA for 8 weeks. MGA residues in plasma were screened by enzyme immuno-assay (EIA). Concentrations in kidney, liver, and muscle were quantified by liquid-chromatography-mass spectrometry (LC-MS), and in fat by gas chromatography-mass spectrometry (GC-MS). MGA levels in plasma were 40, 128, and 280 ng/L, respectively. Residues accumulated in muscle and kidney (5-fold), liver (20-to-40-fold), and fat (200-fold). After administration of 1.5 mg per day the mean MGA concentration in fat was 29 micrograms/kg and thus violated USA regulations which specify a limit of 25 ppb. Therefore the labelled use of MGA (0.5 mg per day) has to be officially controlled.

R. Harland - One of the best experts on this subject based on the ideXlab platform.

  • Effects of immunization against GnRH, Melengestrol Acetate, and a trenbolene Acetate/estradiol implant on growth and carcass characteristics of beef heifers.
    Theriogenology, 2001
    Co-Authors: R.b. Cook, J. D. Popp, Tim A. Mcallister, John P. Kastelic, R. Harland
    Abstract:

    Abstract A 2 × 3 factorial experiment was conducted to determine the effects of an implant (trenbolene Acetate/estradiol or no implant) and method of estrus suppression (immunization against GnRH, Melengestrol Acetate, or no suppression) on growth performance and carcass characteristics of heifers fed for slaughter. At the start of a 21 -d feed adaption phase, crossbred beef heifers (n = 144, 390 ± 2.8 kg) were given their first dose of an anti-GnRH vaccine or started on Melengestrol Acetate (MGA). Thereafter, heifers were fed a high-concentrate diet (78% barley grain) for 84 d (Days 0 to 83), received implants on Day 0, a second vaccination on Day 21, and were slaughtered on Days 84 or 85. Implanting increased average daily gain (1.72 vs 1.50 kg/d, P 0.05) on dry matter intake, grade fat thickness. marbling score, or lean yield. Compared to heifers fed MGA, those immunized against GnRH had a greater ribeye area (90.0 vs 84.6 cm2) and lean yield (63 vs 61%), and had thinner grade fat (7.5 vs 8.6 mm; P 0.05) preslaughter weight, average daily gain, dry matter intake, feed efficiency, carcass weight, or marbling score. In conclusion, implanting significantly increased growth performance and preslaughter and carcass weights. Compared to heifers fed MGA, immunization against GnRH significantly increased ribeye area and lean yield, and reduced grade fat thickness.

  • effects of immunization against gnrh Melengestrol Acetate and a trenbolene Acetate estradiol implant on growth and carcass characteristics of beef heifers
    Theriogenology, 2001
    Co-Authors: R.b. Cook, J. D. Popp, Tim A. Mcallister, John P. Kastelic, R. Harland
    Abstract:

    Abstract A 2 × 3 factorial experiment was conducted to determine the effects of an implant (trenbolene Acetate/estradiol or no implant) and method of estrus suppression (immunization against GnRH, Melengestrol Acetate, or no suppression) on growth performance and carcass characteristics of heifers fed for slaughter. At the start of a 21 -d feed adaption phase, crossbred beef heifers (n = 144, 390 ± 2.8 kg) were given their first dose of an anti-GnRH vaccine or started on Melengestrol Acetate (MGA). Thereafter, heifers were fed a high-concentrate diet (78% barley grain) for 84 d (Days 0 to 83), received implants on Day 0, a second vaccination on Day 21, and were slaughtered on Days 84 or 85. Implanting increased average daily gain (1.72 vs 1.50 kg/d, P 0.05) on dry matter intake, grade fat thickness. marbling score, or lean yield. Compared to heifers fed MGA, those immunized against GnRH had a greater ribeye area (90.0 vs 84.6 cm2) and lean yield (63 vs 61%), and had thinner grade fat (7.5 vs 8.6 mm; P 0.05) preslaughter weight, average daily gain, dry matter intake, feed efficiency, carcass weight, or marbling score. In conclusion, implanting significantly increased growth performance and preslaughter and carcass weights. Compared to heifers fed MGA, immunization against GnRH significantly increased ribeye area and lean yield, and reduced grade fat thickness.

Heinrich H. D. Meyer - One of the best experts on this subject based on the ideXlab platform.

  • Articles The Fate of Trenbolone Acetate and Melengestrol Acetate after Application as Growth Promoters in Cattle: Environmental Studies
    2013
    Co-Authors: Bettina Schiffer, Andreas Daxenberger, Karsten Meyer, Heinrich H. D. Meyer
    Abstract:

    The steroids trenbolone Acetate (TbA) and Melengestrol Acetate (MGA) are licensed as growth promoters for farm animals in several meat-exporting countries. Although many studies have explored their safety for both animals and consumers, little is known about their fate after excretion by the animal. Our study aimed to determine the residues and degradation of trenbolone and MGA in solid dung, liquid manure, and soil. In animal experiments lasting 8 weeks, cattle were treated with TbA and MGA. Solid dung and, in case of trenbolone, liquid manure were collected and spread on maize fields after 4.5 and 5.5 months of storage, respectively. Determination of the hormone residues in all samples included extraction, clean-up (solid-phase extraction), separation of metabolites and interfering substances by HPLC (RP-18), and quantification by sensitive enzyme immunoassay. Procedures were validated by mass spectrometry (MS) methods. During storage of liquid manure the level of trenbolone decreased from 1,700 to 1,100 pg/g (17α-isomer), corresponding to a half-life of 267 days. Before storage, the concentrations in the dung hill ranged from 5 to 75 ng/g TbOH and from 0.3 to 8 ng/g MGA. After storage, levels up to 10 ng/g trenbolone, and 6 ng/g MGA were detected. In the soil samples trenbolone was traceable up to 8 weeks after fertilization, and MGA was detected even until the end of the cultivation period. The results show that these substances should be investigated further concerning their potential endocrine-disrupting activity in agricultural ecosystems. Key words: degradation, dung, growth promoter, manure, Melengestrol Acetate, soil, trenbolone. Environ Health Perspect 109:1145–1151(2001). [Online 2 November 2001

  • Mobility of the growth promoters trenbolone and Melengestrol Acetate in agricultural soil: column studies
    The Science of the total environment, 2004
    Co-Authors: Bettina Schiffer, Karsten Meyer, Kai Uwe Totsche, Steffen Jann, Ingrid Kögel-knabner, Heinrich H. D. Meyer
    Abstract:

    There is growing concern about environmentally released man-made chemicals suspected to be responsible for a number of adverse effects on endocrine function in wildlife species and possibly also in humans. Sex hormones are of particular interest due to their regulatory role in developmental processes such as sexual differentiation. Endogenous hormones of human or animal origin as well as exogenous sex steroids used for contraception or as anabolics for farm animals are excreted and reach the environment. We investigated the transport of the synthetic growth promoters trenbolone (TbOH) and Melengestrol Acetate (MGA) in agricultural soil by means of column experiments with aggregated soil materials (Ap and Bt horizons of a Luvisol). Column effluent concentrations and depth profiles of TbOH and MGA were determined with sensitive enzyme immunoassay systems and HPLC (RP-18), respectively. All procedures were confirmed by liquid chromatography-mass spectrometry. Small amounts of TbOH and MGA passed the columns very quickly. However, both hormones exhibited a high affinity to the organic matter of both horizons leading to a high retardation within the upper layers of the soil columns. Although we cannot deduce whether hormones of animal origin reach the ground water under field conditions, our model experiments show that their transition can be presumed.

R.b. Cook - One of the best experts on this subject based on the ideXlab platform.

  • Effects of immunization against GnRH, Melengestrol Acetate, and a trenbolene Acetate/estradiol implant on growth and carcass characteristics of beef heifers.
    Theriogenology, 2001
    Co-Authors: R.b. Cook, J. D. Popp, Tim A. Mcallister, John P. Kastelic, R. Harland
    Abstract:

    Abstract A 2 × 3 factorial experiment was conducted to determine the effects of an implant (trenbolene Acetate/estradiol or no implant) and method of estrus suppression (immunization against GnRH, Melengestrol Acetate, or no suppression) on growth performance and carcass characteristics of heifers fed for slaughter. At the start of a 21 -d feed adaption phase, crossbred beef heifers (n = 144, 390 ± 2.8 kg) were given their first dose of an anti-GnRH vaccine or started on Melengestrol Acetate (MGA). Thereafter, heifers were fed a high-concentrate diet (78% barley grain) for 84 d (Days 0 to 83), received implants on Day 0, a second vaccination on Day 21, and were slaughtered on Days 84 or 85. Implanting increased average daily gain (1.72 vs 1.50 kg/d, P 0.05) on dry matter intake, grade fat thickness. marbling score, or lean yield. Compared to heifers fed MGA, those immunized against GnRH had a greater ribeye area (90.0 vs 84.6 cm2) and lean yield (63 vs 61%), and had thinner grade fat (7.5 vs 8.6 mm; P 0.05) preslaughter weight, average daily gain, dry matter intake, feed efficiency, carcass weight, or marbling score. In conclusion, implanting significantly increased growth performance and preslaughter and carcass weights. Compared to heifers fed MGA, immunization against GnRH significantly increased ribeye area and lean yield, and reduced grade fat thickness.

  • effects of immunization against gnrh Melengestrol Acetate and a trenbolene Acetate estradiol implant on growth and carcass characteristics of beef heifers
    Theriogenology, 2001
    Co-Authors: R.b. Cook, J. D. Popp, Tim A. Mcallister, John P. Kastelic, R. Harland
    Abstract:

    Abstract A 2 × 3 factorial experiment was conducted to determine the effects of an implant (trenbolene Acetate/estradiol or no implant) and method of estrus suppression (immunization against GnRH, Melengestrol Acetate, or no suppression) on growth performance and carcass characteristics of heifers fed for slaughter. At the start of a 21 -d feed adaption phase, crossbred beef heifers (n = 144, 390 ± 2.8 kg) were given their first dose of an anti-GnRH vaccine or started on Melengestrol Acetate (MGA). Thereafter, heifers were fed a high-concentrate diet (78% barley grain) for 84 d (Days 0 to 83), received implants on Day 0, a second vaccination on Day 21, and were slaughtered on Days 84 or 85. Implanting increased average daily gain (1.72 vs 1.50 kg/d, P 0.05) on dry matter intake, grade fat thickness. marbling score, or lean yield. Compared to heifers fed MGA, those immunized against GnRH had a greater ribeye area (90.0 vs 84.6 cm2) and lean yield (63 vs 61%), and had thinner grade fat (7.5 vs 8.6 mm; P 0.05) preslaughter weight, average daily gain, dry matter intake, feed efficiency, carcass weight, or marbling score. In conclusion, implanting significantly increased growth performance and preslaughter and carcass weights. Compared to heifers fed MGA, immunization against GnRH significantly increased ribeye area and lean yield, and reduced grade fat thickness.

  • Melengestrol Acetate, estradiol-17β and GnRH for synchronization of estrus and ovulation in beef cows
    Canadian Journal of Animal Science, 1999
    Co-Authors: J. Thundathil, R.b. Cook, John P. Kastelic, W. O. Olson, Reuben J. Mapletoft
    Abstract:

    Three experiments were conducted with suckled crossbred beef cows to determine the efficacy of various short-term regimens for synchronizing estrus or ovulation and to determine whether feeding Melengestrol Acetate (MGA) after timed AI will increase pregnancy rate. In exp. 1, all cows (n = 141) were given 0.5 mg MGA head−1 d−1 for 7 d (days 1 to 7), 1 or 5 mg E17β (and 100 mg progesterone) or 100 µg GnRH on day 1, and 500 µg cloprostenol on day 7. There were no significant differences among groups for estrous or synchronized conception rates (average, 84.4 and 52.1%, respectively). With an identical protocol in exp. 2 (78 cows), by day 11, cows given 5 mg E17β had the highest estrous and synchronized pregnancy rates (65.4 and 42.3%), compared to 1 mg E17β (46.2 and 15.4%) and GnRH (34.6 and 11.5%). Cows not detected in estrus were timed-inseminated and given 100 µg GnRH, 100 h after cloprostenol. There were no significant differences among groups for synchronized conception rate to timed AI (65.0%) or syn...