Testosterone is a steroid hormone found in horses, primarily produced by the testes in males and, to a lesser extent, by the ovaries and adrenal glands in females. It plays a significant role in the development and maintenance of male reproductive tissues, as well as influencing secondary sexual characteristics and behavior. Testosterone levels can impact muscle mass, bone density, and overall physical condition, and they may vary due to factors such as age, season, and health status. This page compiles peer-reviewed research studies and scholarly articles that explore the production, regulation, and physiological effects of testosterone in equine biology, as well as its implications for behavior and health management in horses.
Ho EN, Kwok WH, Leung DK, Riggs CM, Sidlow G, Stewart BD, Wong AS, Wan TS.Testosterone is an endogenous steroid produced primarily in the testes. Trace levels of testosterone are found in urine samples from geldings, as testosterone is also secreted by the adrenal. An international threshold of free and conjugated testosterone in urine (20 ng/mL) was adopted by the International Federation of Horseracing Authorities (IFHA) in 1996 for controlling testosterone misuse in geldings. In view of the recent popularity of using blood in doping control testing, it is necessary to establish a threshold for testosterone in gelding plasma. A liquid chromatography-mass spectro...
Pozor MA, Zambrano G, Roser J, Hess R, Runyon S, Runcan E, Thomas BF, Dymock D, Macpherson ML, Troedsson MH, Kelleman A.The objective of this study was to evaluate acute endocrine effects as well as histological changes in testicular parenchyma induced by the contraceptive compound RTI-4587-073(l). Six miniature stallions were used in this experiment. The treatment group (n = 3) received one oral dose of 12.5 mg/kg of RTI-4587-073(l), and the control group (n = 3) received placebo only. The stallions' baseline parameters (semen, testicular dimensions, endocrine values) were collected and recorded for 5 weeks before treatment and for 6 weeks after treatment. Multiple blood samples were collected for endoc...
Arkoun B, Gautier C, Delalande C, Barrier-Battut I, Guénon I, Goux D, Bouraïma-Lelong H.Among mammals, the stallion produces the largest amount of testicular estrogens. These steroid hormones are produced mainly by Leydig and Sertoli cells in the testis and also in the epididymis. Their role in horse testicular physiology and their ability to act on spermatozoa are still unknown. In order to determine if spermatozoa are targets for estrogens, the presence of estrogen receptors in mature ejaculated spermatozoa has been investigated. The presence of a single isoform of ESR1 (66kDa) and ESR2 (61kDa) was found by Western-blot analysis in samples from seven stallions. Confocal analysi...
Schmitz A, Zielinski J, Dick B, Mevissen M.Testosterone (TES) 6-β-hydroxylation is a significant metabolic step in the biotransformation of TES in human liver microsomes and reflects cytochrome P450 (CYP) 3A4/5 specific metabolic activity. Several CYP3A enzymes have been annotated in the horse genome, but functional characterization is missing. This descriptive study investigates TES metabolism in the horse liver in vitro and the qualitative contribution of three CYP3A isoforms of the horse. Metabolism of TES was investigated by using equine hepatocyte primary cultures and liver microsomes. Chemical inhibitors were used to determine t...
Fayrer-Hosken RA, Hill NS, Heusner GL, Traylor-Wiggins W, Turner K.Ergot alkaloids cause a range of pathological conditions in mares. There is no evaluation of the effects of ergot alkaloids from endophyte-infected tall fescue on the stallion breeding soundness examination spermiogram. Objective: The objective of this study was to investigate the effect of ergot alkaloids from endophyte-infected tall fescue on the stallion's reproductive functions. Methods: Crossover toxicology experiment. Methods: Six stallions were fed either toxic endophyte-infected tall fescue seed or a nontoxic endophyte tall fescue seed (Flecha AR-542, MaxQ). The fescue seed content was...
Pearl CA, Roser JF.Lactoferrin is one of the most abundant proteins secreted by the stallion epididymis, but its cellular localization and regulation remain unknown. This study was designed to address the following objectives: (1) identify the epididymal cell types producing lactoferrin in pre-pubertal, peri-pubertal and post-pubertal animals; (2) demonstrate that lactoferrin binds to stallion sperm; and (3) determine if testosterone and estradiol regulate lactoferrin secretion in vitro. Using an immunohistochemical method, lactoferrin was localized in the cytoplasm of principal cells in the corpus and cauda of ...
Pozor MA, Macpherson ML, McDonnell SM, Nollin M, Roser JF, Love C, Runyon S, Thomas BF, Troedsson MH.The objective of this study was to determine whether an indenopyridine derivative RTI-4587-073(l) was a good candidate for male contraception in horses. We hypothesized that a single administration of RTI-4587-073(l) causes significant suppression of testicular function in stallions without affecting sexual behavior. Three Miniature horse stallions received a single dose of 12.5 mg/kg RTI-4587-073(l) orally (group "treated"), whereas three other Miniature horse stallions received placebo only (group "control"). Semen was collected and evaluated from all stallions twice a week for three baselin...
Kaabia Z, Dervilly-Pinel G, Popot MA, Bailly-Chouriberry L, Plou P, Bonnaire Y, Le Bizec B.Nandrolone (17β-hydroxy-4-estren-3-one) is amongst the most misused endogenous steroid hormones in entire male horses. The detection of such a substance is challenging with regard to its endogenous presence. The current international threshold level for nandrolone misuse is based on the urinary concentration ratio of 5α-estrane-3β,17α-diol (EAD) to 5(10)-estrene-3β,17α-diol (EED). This ratio, however, can be influenced by a number of factors due to existing intra- and inter-variability standing, respectively, for the variation occurring in endogenous steroids concentration levels in a si...
Pereira GR, Lorenzo PL, Carneiro GF, Ball BA, Bilodeau-Goeseels S, Kastelic J, Pegoraro LM, Pimentel CA, Esteller-Vico A, Illera JC, Granado GS....The objectives of this study were to evaluate the effects of equine growth hormone (eGH) on nuclear and cytoplasmic maturation of equine oocytes in vitro, steroid production by cumulus cells, and expression and subcellular localization of eGH-receptors (eGH-R) on equine ovarian follicles. Cumulus-oocyte complexes (COCs) were recovered by aspirating follicles <30 mm in diameter from abattoir-derived ovaries. The COCs were morphologically evaluated and randomly allocated to be cultured in either a control maturation medium or supplemented with 400 ng/mL eGH, for 30 h at 38.5°C in air with 5%...
Gray BP, Viljanto M, Bright J, Pearce C, Maynard S.The detection of the abuse of anabolic steroids in equine sport is complicated by the endogenous nature of some of the abused steroids, such as testosterone and nandrolone. These steroids are commonly administered as intramuscular injections of esterified forms of the steroid, which prolongs their effects and improves bioavailability over oral dosing. The successful detection of an intact anabolic steroid ester therefore provides unequivocal proof of an illegal administration, as esterified forms are not found endogenously. Detection of intact anabolic steroid esters is possible in plasma samp...
Kaabia Z, Dervilly-Pinel G, Hanganu F, Cesbron N, Bichon E, Popot MA, Bonnaire Y, Le Bizec B.During last decades, the use of natural steroids in racing and food producing animals for doping purposes has been flourishing. The endogenous or exogenous origin of these naturally occurring steroids has since remained a challenge for the different anti-doping laboratories. The administration of these substances to animals is usually made through an intra-muscular pathway with the steroid under its ester form for a higher bioavailability and a longer lasting effect. Detecting these steroid esters would provide an unequivocal proof of an exogenous administration of the considered naturally occ...
Leung GN, Kwok WH, Wan TS, Lam KK, Schiff PJ.Formestane (4-hydroxyandrost-4-ene-3,17-dione) is an irreversible steroidal aromatase inhibitor with reported abuse in human sports. In 2011, our laboratory identified the presence of formestane in a horse urine sample from an overseas jurisdiction. This was the first reported case of formestane in a racehorse. The metabolism of formestane in humans has been reported previously; however, little is known about its metabolic fate in horses. This paper describes the in vitro and in vivo metabolic studies of formestane in horses, with the objective of identifying the target metabolite with the lon...
Almeida J, Conley AJ, Ball BA.Cryptorchidism affects 2-8% of male horses and the affected testis undergoes a disruption of normal spermatogenesis. The underlying molecular changes are poorly understood in the cryptorchid equine testis. Objective: Compare the expression of anti-Müllerian hormone (AMH), anti-Müllerian hormone receptor (AMHR2), androgen receptor (AR), cyclin kinase inhibitor (CDKN1B), connexin 43 (Cx43), 3β hydroxysteroid dehydrogenase/Δ(5) -Δ(4) - isomerase (3βHSD), P450c17 hydroxylase/lyase (P450c17) and cytochrome P450 aromatase (P450arom) in the undescended testis of cryptorchid stallions with that ...
Schönert S, Reher M, Gruber AD, Carstanjen B.This case report describes the use of a subcutaneously applied 4.7-mg deslorelin acetate implant in a three-year-old Arabian crossbred stallion showing unwanted strong male behaviour. Following deslorelin acetate implantation the stallion showed a short transitional increase in male behaviour. A 'gelding-like' behaviour was noted 15 days (D15) after treatment. The horse was surgically castrated at the owners request at D52 after treatment. Serum testosterone, oestradiol-17β and oestrone sulphate values decreased after deslorelin acetate implantation, but serum LH and FSH levels remained uncha...
Torres A, Silva JF, Bernardes N, Sales Luís J, Lopes da Costa L.Here is reported a disorder of sex development found in the Portuguese Lusitano horse breed. The complex genital phenotype included mammary glands, abdominal testes without epididymis, connected through oviducts to pelvic hypoplastic uterine horns and fused vulvar labia majora from which protruded ventrally a penis-like structure. This structure was presented in a reversed position, the urethral opening placed dorsally in the glans. However, it was functional both for micturition and erection. The horse exhibited female micturition posture and aggressive male-like behaviour, including flehmen,...
Herrera-Luna CV, Budik S, Helmreich M, Walter I, Aurich C.Glucocorticoids (GCs) as mediators of the stress response may affect Leydig cell function by inhibiting either luteinizing hormone receptor expression or testosterone biosynthesis. The isozymes 11β-hydroxysteroid dehydrogenase (11βHSD) 1 and 11βHSD2 control the intracellular cortisol levels. Little is known about the effects of stress on fertility in the equine. The objective of the present study was to determine the presence and cellular localization of glucocorticoid receptors (GCR) and glucocorticoid-metabolizing enzymes (11βHSD1 and 11βHSD2) in equine epididymal and testicular tissue ...
Kwok WH, Ho EN, Leung GN, Tang FP, Wan TS, Wong HN, Yeung JH.1-Testosterone (17β-hydroxy-5α-androst-1-en-3-one), a synthetic anabolic steroid, has been described as one of the most effective muscle-building supplements currently on the market. It has an anabolic potency of 200 as compared to 26 for testosterone. Apart from its abuse in human sports, it can also be a doping agent in racehorses. Metabolic studies on 1-testosterone have only been reported for human in the early seventies, whereas little is known about its metabolic fate in horses. This paper describes the studies of in vitro and in vivo metabolism of 1-testosterone in horses, with the ai...
Sato F, Hirota K, Tozaki T, Ito K, Dhakal P, Taya K, Endo Y, Murase H, Nambo Y.A Thoroughbred colt with ambiguous external genitalia was presented for clinical and histological examinations. The colt had a short penis that faced backward between his hind limbs. The measurements of luteinizing hormone, follicle stimulating hormone, testosterone and ir-inhibin showed a tendency to increase gradually from April. Both the sex-determining region of the Y chromosome and amelogenin gene fragments were detected by the PCR method. A cytogenetic analysis revealed the 63,XO/64,XY mosaic karyotype (ratio 83:17). In autopsy, immature symmetrical subcutaneous testes were found in the ...
Dhakal P, Hirama A, Nambo Y, Harada T, Sato F, Nagaoka K, Watanabe G, Taya K.The present study was conducted to elucidate the profile of circulating gonadotropins and gonadal hormones from birth to puberty and relationship between gonadal seasonality and hormonal secretion in both sexes of Thoroughbred horses. Spring-born colts (n=6) and fillies (n=9) were blood sampled weekly from jugular vein from birth to 60 weeks of age. Circulating FSH, LH, prolactin, testosterone, progesterone, estradiol-17β, and immunoreactive (ir)-inhibin were measured by radioimmunoassay. In both sexes, the steroid hormones levels were remarkably high at birth, rapidly dropped within a week a...
Leme DP, Papa FO, Roser JF.The objective of this study was to investigate reproductive characteristics of stallions at a tropical zone in the breeding and non-breeding seasons. The following parameters were assessed: testicular volume; semen quality; and serum concentrations of LH, FSH, and testosterone; in addition to the percentages of germ cells and proportions of germ cells/Sertoli cells by testicular cytology in stallions. Semen was collected from eight adult stallions twice a week during a 12-week period in both seasons (6 weeks before and 6 weeks after the summer and winter solstices). Jugular blood samples were ...
Gee EK, Dicken M, Archer RM, Herdan CL, Pauwels FE, Drayton BM.A 14-year-old Thoroughbred mare was presented for evaluation of a rapidly enlarging ovary at 73 days gestation. The mare's owner reported behavioural changes in the mare since she returned from stud, notably aggression towards other horses. Results: Transrectal palpation and ultrasonography of the reproductive tract revealed a viable pregnancy, an enlarged, multiloculated right ovary, and a normal-sized left ovary with a corpus luteum present. Concentrations of inhibin and testosterone in serum were 13.8 ng/mL and 1,150 pg/mL, respectively, being markedly higher than reference ranges. Concentr...
Almeida J, Conley AJ, Mathewson L, Ball BA.Sertoli cells are essential in development of a functional testis. During puberty, Sertoli cell maturation can be characterized by a number of markers, including anti-Müllerian hormone (AMH) and its receptor (AMHR2), androgen receptor (AR), cyclin-dependent kinase inhibitor (CDKN1B), and connexin 43 (Cx43). In the present study, immunohistochemistry (IHC) and real-time quantitative polymerase chain reaction (RT-qPCR) were used to characterize changes in expression of AMH, AMHR2, AR, CDKN1B, and Cx43 in prepubertal, postpubertal, and adult equine testes. During puberty, AMH expression decrease...
Guan F, Uboh CE, Soma LR, You Y, Li X, McDonnell S.19-Norandrostenedione (NAED) and nandrolone are anabolic-androgenic steroids (AASs). Nandrolone was regarded solely as a synthetic AAS until the 1980s when trace concentrations of apparently endogenous nandrolone were detected in urine samples obtained from intact male horses (stallions). Since then, its endogenous origin has been reported in boars and bulls; endogenous NAED and nandrolone have been identified in plasma and urine samples collected from stallions. More recently, however, it was suggested that NAED and nandrolone detected in urine samples from stallions are primarily artifacts d...
Dhakal P, Tsunoda N, Nakai R, Kitaura T, Harada T, Ito M, Nagaoka K, Toishi Y, Taniyama H, Gen W, Taya K.Changes in follicle-stimulating hormone (FSH), luteinizing hormone (LH), prolactin, immunoreactive(ir)-inhibin, testosterone, estradiol-17β, and insulin-like growth factor (IGF)-I in Thoroughbred stallions along with changes in prolactin secretion in geldings were studied. The correlations of day-length with changes in the concentrations of these hormones were also studied. Five stallions and thirteen geldings were employed to draw blood samples in monthly basis and radioimmunoassay was performed to measure these hormones. All hormones showed a seasonal pattern, the levels being highest durin...
Leleu C, Haentjens F.The demands in the Standardbred trotters industry require young, still growing horses, to be trained well above light exercise level. During that period, the risk of occurrence of energy imbalance and maladaptation to training is high. In man, the lack of energy homeostasis is considered as the basic problem in the development of chronic fatigue. Objective: To find objective biomarkers of early maladaptation to training in young racehorses under field conditions. Methods: Sixty-five 2-year-old Standardbreds were followed during their first 3 months of training in 5 different training centres. ...
Yoon MJ, Roser JF.Localization of IGF-I and IGF-IR were observed in Leydig cells of horses using immunohistochemistry (IHC), suggesting IGF-I may play a role in equine Leydig cell steroidogenesis. Previous studies in other species have indicated that IGF-I increases basal and/or LH/hCG-induced testosterone production. The objectives of this study were to (1) test the synergistic effect of IGF-I on eLH-induced testosterone production in cultured equine Leydig cells and (2) determine if this effect is reproductive stage-dependent. Testes were collected from five pubertal (1.1±0.1 year; 1-1.5 year) and eight post...
You Y, Uboh CE, Soma LR, Guan F, Li X, Liu Y, Rudy JA, Chen J, Tsang D.The potential for using testosterone and nandrolone esters in racehorses to boost the biological concentrations of these steroids and enhance athletic performance is very compelling and should be seriously considered in formulating regulatory policies for doping control. In order to regulate the use of these esters in racehorses, a sensitive and validated method is needed. In this paper, we report such a method for simultaneous separation, screening, quantification and confirmation of 16 testosterone and nandrolone esters in equine plasma by ultra high performance liquid chromatography-tandem ...
Dhakal P, Tsunoda N, Nakai R, Nagaoka K, Nambo Y, Sato F, Taniyama H, Taya K.The aim of present study was to clarify the post-natal profile of follicle-stimulating hormone (FSH), luteinizing hormone (LH), immunoreactive (ir)-inhibin, progesterone, testosterone, and estradiol-17β, and their relationships in Thoroughbred colts. Six hundred and thirty-six colts were used for the study. Single plasma samples from each animal were harvested from the blood drawn through jugular venipuncture. The subjects were born with high amounts of progesterone, testosterone, and estradiol-17β, all of which dropped significantly and remained at lower levels till the end of 6 months. FSH...
Soma LR, Uboh CE, You Y, Guan F, McDonnell S.Pennsylvania (PA) State Racing Commissions regulate the endogenous androgenic steroid, testosterone (TES), in racing intact males (RIM) by quantification of TES in post-race samples. Post-race plasma samples (2209) collected between March 2008 and November 2010 were analyzed for TES, nandrolone (NAN), and other anabolic steroids (ABS). Of the 2209 plasma samples, 2098 had quantifiable TES ≥ 25 pg/mL. Plasma (mean ± SD) concentrations of TES and NAN in RIM were 329.2 ± 266.4 and 96.0 ± 67.8 pg/mL, respectively. Only 64.6% of RIM had quantifiable concentration of NAN, and there was no relat...
Clay CM, Squires EL, Amann RP, Pickett BW.To investigate the influence of daylength on the seasonal reproductive cycle of stallions, 21 stallions were assigned to one of three treatments: control, ambient (natural) photoperiod; S-L, 8 h light and 16 h dark (8:16) for 20 wk beginning July 16, 1982 then 16:8 from December 2, 1982 until March 5, 1984; S-S, 8:16 from July 16, 1982 until March 1984. Temperature was not controlled and was similar for all groups. Total scrotal width (TSW) was measured every 4 wk throughout the experiment. During 10 periods, semen was collected and evaluated every other day for 3 wk and sexual behavior was as...
Hess MF, Roser JF.There are several hormones and local testicular factors involved in the initiation and control of steroidogenesis and spermatogenesis during puberty. GH and its mediator, IGF-I, increase substantially during puberty, and in addition to LH, these growth-promoting hormones can have direct effects upon testicular function. The objective of this work was to investigate the effects of eLH, eGH and hrIGF-I upon Leydig cells derived from testes of colts and stallions representing different stages of development. Testes were obtained from 48 light horse colts and stallions at the time of routine castr...
Malmgren L, Andresen O, Dalin AM.The aim of this study was to investigate the effect of gonadotrophin-releasing hormone (GnRH) immunisation on mature stallions that had been used for breeding. Four Standardbred stallions were used in the study: 3 experimental animals and 1 control animal. Semen was collected regularly, i.e. twice/week, during the 4 months prior to the experimental period. The stallions were immunised against GnRH with a GnRH-BSA conjugate. Equimune was used as the adjuvant. The stallions were immunised on 5 occasions, 4 at 2 week intervals, and the fifth 4 weeks after the fourth. Blood samples were taken once...
Waddington B, Penitente-Filho JM, Neves J, Pinho RO, Chaya AY, Maitan PP, Silveira CO, Neves MG, Guimarães S, de Carvalho GR, Guimarães JD.This study was conducted to characterize the daily profile of testosterone secretion and its mean concentrations in the four seasons as well as to evaluate the semen characteristics and testicular biometry of Mangalarga Marchador stallions throughout the year in a tropical region. Three stallions were submitted to semen collections and evaluation of testicular biometry every 14 days along a year. Blood samples were collected once at the middle of each season, in a 20-min interval during 24 hr in order to evaluate the testosterone secretion profiles among seasons. Testosterone concentrations ...
Boyer S, Garcia P, Popot MA, Steiner V, Lesieur M.A sensitive and specific method has been developed to detect semi-quantitatively testosterone in horse hair samples. The method involved a washing step with sodium dodecylsulfate aqueous solution. The mane and tail hair samples (100mg) were dissolved in 1 mL of sodium hydroxide for 15 min at 95 degrees C in the presence of d3-boldenone used as internal standard. The next three steps involved diethyl ether extraction and a solid phase extraction on Isolute C18 (EC) cartridges eluted with methanol. The residue was derivatized by adding 100 microL of acetonitrile and 30 microL of PFPA then incuba...
Johnson L, Varner DD, Thompson DL.To determine the age at which adult values for hormonal and testicular characteristics are established, testes and blood from 123 slaughtered horses, aged 1-5 years, were compared. Serum concentrations of follicle-stimulating hormone (FSH), luteinizing hormone (LH) and testosterone (T) and intratesticular testosterone (ITT) were determined by radio-immunoassay. Specimens were obtained in the non-breeding (n = 46) or breeding (n = 43) season in Experiment 1 (Exp. 1) and in the breeding (n = 34) season in Experiment 2 (Exp. 2). Testicular parenchyma was fixed in glutaraldehyde and homogenized to...
Koskinen E, Katila T.The long-term effect of anabolic steroid was investigated in 3 experiments. In experiment I, 500 mg of 19-norandrostenololylaurate was given to 5 colts and a dose of 100 mg to another 5 colts every 3rd week. Six colts served as untreated controls. The animals were 12-16 months old at the start, and 24 months at the end of treatment. In experiment II, a dose of 1 mg/kg was given every 3rd week to 4 colts and 0.3 mg/kg every week to another 4 colts. Six colts served as controls. The colts were treated from 7 months to 12 months of age. In experiment III, 1 mg/kg of steroid was given every 3rd we...
Gautier C, Schmidt K, Aurich J, Aurich C.The hypothesis in this study was continuous treatment of stallions with the GnRH agonist deslorelin inhibits reproductive functions. A 2-week pre-experimental period was followed by an 11-week deslorelin implant treatment. Stallions received 4.7 (D1, n = 7), or 18.8 mg deslorelin (D2, n = 5) or remained untreated (C, n = 5). Libido, sperm motility, membrane integrity, DNA fragmentation, estrogen receptors, basal plasma testosterone and Anti Muellerian hormone (AMH) concentrations were evaluated once weekly during the treatment period. The testosterone response to the GnRH agonist buserelin a...
Hannan MA, Murase H, Sato F, Tsogtgerel M, Kawate N, Nambo Y.The peripheral blood concentrations of insulin-like peptide 3 (INSL3) have been detected in many mammalian species, but the level of INSL3 in horse remains unknown. The objectives were to develop a time-resolved fluorescence immunoassay (TRFIA) to detect INSL3 concentrations from horse blood as well as to determine the age-related and seasonal changes of plasma concentrations of INSL3 and testosterone from birth to early-puberty in Thoroughbred male horse (n = 11). Monthly blood sample and measurement of body weight, height, chest and cannon bone size were done from birth until 16 mo. Th...
Golland LC, Evans DL, Stone GM, Tyler-McGowan CM, Hodgson DR, Rose RJ.Basal concentrations of cortisol (CORT), beta-endorphin (beta EP), growth hormone (GH) and testosterone (T) and their disruption during 32 h of recovery after treadmill exercise were investigated in 4 geldings. Blood samples were collected from resting horses every 20 min between 0600-1000 and 1500-1900 h, and hourly between 1000-1500 h on 3 consecutive days. Treadmill exercise tests comprising 2 min intervals at 30, 50, and 70% VO2max then to fatigue at 100% VO2max were conducted between 1020-1130 h on Day 2. Blood was collected before, during and 15, 30, 60 and 90 min after exercise. Mean (C...
Škerlová J, Ismail A, Lindström H, Sjödin B, Mannervik B, Stenmark P.Organotin compounds are highly toxic environmental pollutants with neurotoxic and endocrine-disrupting effects. They are potent inhibitors of glutathione transferases (GSTs), thus impeding their detoxication and antioxidant functions. Several GSTs, including equine GST A3-3 (EcaGST A3-3), exhibit steroid double-bond isomerase activity and are involved in the biosynthesis of testosterone and progesterone. We have performed enzyme kinetics analyses of the inhibition of EcaGST A3-3 by organotin compounds. We have also solved crystal structures of EcaGST A3-3 in complexes with glutathione, and wit...
Rabb MH, Thompson DL, Barry BE, Colborn DR, Garza F, Hehnke KE.Six lighthorse stallions with previous sexual experience were used to determine the short-term effects of sexual stimulation (SS; 5 min exposure to an estrous mare), SS plus ejaculation (SSE), and no stimulation (control) on serum concentrations of LH, FSH, testosterone, cortisol and prolactin. Stallions received one treatment per day on d 1, 4 and 7. Treatments were assigned such that each stallion 1) received each treatment once and 2) experienced a unique sequence of treatments. Neither SS nor SSE had any consistent effects on LH or FSH concentrations. Testosterone concentrations during con...
Dowsett KF, Pattie WA, Knott LM, Jackson AE, Hoskinson RM, Rigby RP, Moss BA.This study tested the effectiveness of a conjugated GnRH vaccine for stimulating antibody production, suppressing testosterone secretion and depressing testicular development in yearling colts. Two colts were allocated to each of three groups, (1) control, (2) subcutaneous and (3) intramuscular vaccinations. Two injections of the vaccine were given 11 weeks apart. Liveweight gain was not affected by vaccination but plasma testosterone concentrations in the treated colts were suppressed and their antibody titres to GnRH were greater than 1:1000. Testicular development in the treated colts also ...
Kavak A, Lundeheim N, Aidnik M, Einarsson S.Evaluation of testicular measurements and daily sperm output (DSO) yields valuable information for predicting the reproductive capacity of stallions. The present study evaluated testicular measurements (height, length, width and circumference) and DSO of eight Tori and eight Estonian breed stallions. One ejaculate of semen was collected daily for 10 subsequent days from each stallion. The gel-free volume of semen was measured with a graduated glass cylinder and the sperm concentration was assessed with a Chorjajev chamber. The volume of gel-free fraction was multiplied by the sperm concentrati...
Laughlin AM, Welsh TH, Love CC, Varner DD, Parrish AR, Forrest DW, Ing NH.In vitro culture systems are valuable tools for investigating reproductive mechanisms in the testis. Here, we report the use of the precision-cut in vitro system using equine testicular slices. Testes were collected from immature light breed stallions (n=3) and cut into slices (mean slice weight= 13.85 ± 0.20 mg; mean slice thickness=515.00 ± 2.33 μm) using the precision-cut tissue-slicing method. Four tissue slices were placed on a grid floating on medium in individual vials. After a 1-h preincubation, they were exposed to medium containing ovine luteinizing hormone (oLH) at concentrations...
Cox JE, Redhead PH, Dawson FE.The results of performing 1720 blood tests for equine cryptorchidism are described. Using the paired sample human chorionic gonadotrophin (hCG) stimulation test and measuring testosterone, 6.7 per cent of tests did not give a clear result. If only the testosterone concentration in the pre-hCG blood sample was used, this percentage rose to 14 per cent. The paired sample hCG stimulation test was 94.6 per cent accurate. A comparison was made between the paired hCG stimulation test and the measurement of conjugated oestrogen in a single sample. The latter did not give as many doubtfuls but gave fa...
Fouchécourt S, Dacheux F, Dacheux JL.Microsequencing after two-dimensional electrophoresis revealed a major protein, glutathione-independent prostaglandin D2 synthase (PGDS) in the anterior epididymal region fluid of the ram and stallion. In this epididymal region, PGDS was a polymorphic compound with a molecular mass around 30 kDa and a range of pI from 4 to 7. PGDS represented 15% and 8% of the total luminal proteins present in this region in the ram and stallion, respectively. The secretion of the protein as judged by in vitro biosynthesis, and the presence of its mRNA as studied by Northern blot analysis, were limited to the ...
Roser JF, McCue PM, Hoye E.An overnight double antibody RIA, employing a rabbit antiserum raised to bovine 31 kDa inhibin (rAs-#1989, NICHD) and purified bovine 31 kDa inhibin (bINH-I-90/1, NICHD) as trace and standard, was validated to measure immunoreactive inhibin (iINH) concentrations in equine peripheral plasma, follicular fluid (FF), ovarian vein (OV) plasma, testicular tissue extracts (TTE) and testicular vein (TV) plasma. The dynamic relationship of iINH and follicle stimulating hormone (FSH) was investigated during the estrous cycle of the mare and the annual reproductive cycle of the stallion. In the RIA, para...
Dintinger T, Gaillard JL, Moslemi S, Zwain I, Silberzahn P.The ability of equine and human placental microsomes to aromatize testosterone and 19-nortestosterone was studied. When 3 microM [1 beta,2 beta-3H]testosterone was used as substrate, the specific activity of equine placental microsomal aromatase was 2.5 times higher than that of the human microsomal enzyme. Although 19-nortestosterone was aromatized 67 times more rapidly by equine than by human aromatase, we found that equine aromatase exhibited a markedly weaker affinity for this substrate than did the human enzyme. Competitive inhibition of testosterone aromatization by 19-nortestosterone oc...
Zielinski J, Mevissen M.Testosterone hydroxylation was investigated in human, canine and equine liver microsomes and in human and canine single CYPs. The contribution of the CYP families 1, 2 and 3 was studied using chemical inhibitors. Testosterone metabolites were analyzed by HPLC. The metabolites androstenedione, 6β- and 11β-hydroxytestosterone were found in microsomes of all species, but the pattern of metabolites varied within species. Androstenedione was more prominent in the animal species, and an increase over time was seen in equines. Testosterone hydroxylation was predominantly catalyzed by the CYP3A subf...
Haffner JC, Fecteau KA, Eiler H, Tserendorj T, Hoffman RM, Oliver JW.Traditionally, analysis of blood cortisol alone has been used to evaluate adrenal function. Currently, multisteroid analyses are considered more informative than analysis of a single hormone to assess adrenal function. The objective of the present research was to create a database for steroid reference values for domestic Mongolian horses. Seven adrenal steroid levels were determined in the blood of 18 colts, 34 stallions, 25 geldings, 17 fillies, and 29 mares. Results were as follows (lowest and highest group median, in nanograms per milliliter): progesterone: <0.030 (fillies), 4.30 (mares), ...
Bolzon C, Joonè CJ, Schulman ML, Harper CK, Villagómez DA, King WA, Révay T.Disorders of sex development (DSD) have long been documented in domestic animal species including horses. However, there is only a single report of an androgen receptor (AR) mutation causative of such a DSD syndrome in a horse pedigree. Here, we present a new familial AR mutation in horses. A missense mutation (c.2042G>C) at AR exon 4 explains the segregation of the DSD in a Thoroughbred horse pedigree. The mutation, expected to affect the ligand-binding domain of the AR protein, led to complete androgen insensitivity of 64,XY SRY+, testicular DSD individuals. Additionally, the design of a ...
Melrose PA, Walker RF, Douglas RH.Catecholamine concentrations (pg/ml) in the cerebrospinal fluid (CSF) of prepubertal (n = 9) and adult (n = 18) horses were determined by radioenzymatic assay. Norepinephrine was low or non detectable in all CSF samples. In contrast, measurable CSF dopamine concentrations were effected by age, reproductive status and exogenous steroid treatments. The concentration of dopamine in the CSF of prepubertal females (733 +/- 92) was greater (p less than 0.05) than the concentration in the CSF of prepubertal males (117 +/- 67). Prepubertal male horses which were treated with testosterone for 5 days (5...
Coryn M, De Morr A, Bouters R, Vandeplassche M.The authors analysed clinical, histological and hormonal data obtained from 205 cryptorchid horses. The majority of the unilaterally and bilaterally retained testes were located in the inguinal canal; however, the ratio of inguinal vs abdominal retention appeared to decrease with advancing age. In unilateral cryptorchidism, a pronounced preference was noted for left abdominal retention, whereas for inguinal cryptorchids, the retained testes occurred equally on both sides. Right inguinal retention was found to decrease with advancing age. Histology of cryptorchid testes revealed apparently norm...
Illera JC, Silván G, Munro CJ, Lorenzo PL, Illera MJ, Liu IK, Illera M.An amplified enzymeimmunoassay (EIA) was validated for androstenedione in the serum of male horses. We will use the assay as a tool for the diagnosis of equine cryptorchidism. We will compare androstenedione EIA to the currently used methods (testosterone and estrone sulphate determinations). The study was conducted on 115 horses of pure Spanish and Arabian breeds, that included 30 geldings, 60 bilateral cryptorchids and 25 stallions. Androstenedione standard curve covered a range between 0 and 1 ng per well. Low detection limit was 1.54 pg/ml. Intra- and inter-assay coefficients of variation ...
Barreto RSN, Romagnolli P, Mess AM, Rigoglio NN, Sasahara THC, Simões LS, Fratini P, Matias GSS, Jacob JCF, Gastal EL, Miglino MA.In horses, pregnancy is characterized by high levels of maternal estrogens that are produced largely by the interstitial tissue inside the gonads of the offspring, associated with a physiological gonadal hyperplasia, that is uncommon in other species. However, a detailed structural-functional understanding of the early stages of gonadal development and hyperplasia has remained elusive in horse pregnancy because of the lack of substantial data. The goal of this study was to describe the genital organs' development in 19 early horse embryos and fetuses (days 20-140 of gestation) of both sexes by...
Kwok WH, Leung GN, Wan TS, Curl P, Schiff PJ.Androsta-1,4,6-triene-3,17-dione (ATD) is an irreversible steroidal aromatase inhibitor and is marketed as a supplement. It has been reported to effectively reduce estrogen biosynthesis and significantly increase the levels of endogenous steroids such as dihydrotestosterone and testosterone in human. ATD abuses have been reported in human sports. Its metabolism in human has been studied, and the in vitro metabolic study of ATD in horses has been reported, however, little is known about its biotransformation and elimination in horses. This paper describes the in vitro and in vivo metabolism stu...
Zavy MT, Vernon MW, Sharp DC, Bazer FW.Comparisons of estrone, 17 beta-estradiol, and plasma progestin concentrations were made in uterine fluid and peripheral blood of nonpregnant and pregnant pony mares. Concentrations of these steroids were also measured within yolk sac fluid from blastocysts on days 12, 14, 16, and 18 of pregnancy to obtain more complete analyses of the uterine environment (uterine fluid plus yolk sac fluid) of early pregnancy. Thirty mares were randomly assigned to six treatment groups (n = 5/group), and uterine fluid and peripheral blood samples were obtained on days 8, 12, 14, 16, 18, and 20 postovulation. A...
Spicer LJ, Santiago CA, Davidson TR, Bridges TS, Chamberlain CS.The objective of the present study was to evaluate changes in concentrations of free insulin-like growth factor (IGF)-I in follicular fluid (FFL) during follicle development in the mare. Mares (n = 14) were classified as either in the follicular phase (n = 8) or luteal phase (n = 6). Follicles (n = 92) were categorized as small (6-15 mm; n = 54), medium (16-25 mm; n = 23) or large (>25 mm; n = 15) and FFL was collected. Free IGF-I levels in FFL in large follicles of follicular phase mares were greater (P < 0.05) than in large follicles of luteal phase mares and small or medium follicles ...
Fouchécourt S, Charpigny G, Reinaud P, Dumont P, Dacheux JL.Prostaglandin D2 synthase (PGDS) is a major epididymal secretory protein in several species. We quantified PGDS in ram and bull semen using a specific antiserum. Strong variations in PGDS concentration existed between animals. In the bull, the highest concentrations were found preferentially in animals with normal or high fertility, as was previously suggested. However, low concentrations were found in males with all ranges of fertility, suggesting that the function of PGDS either is not necessary for male fertility or can be assumed by other proteins when its concentration is low. In the ram ...
