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Topic:Testosterone
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.
Measurement of 19-nortestosterone and its esters in equine plasma by high-performance liquid chromatography with tandem mass spectrometry. A high-performance liquid chromatographic-tandem mass spectrometric (HPLC/MS/MS) method for the determination of 19-nortestosterone and its esters (cyclopentanepropionate, phenylpropionate, and decanoate) in equine plasma is achieved using an atmospheric pressure chemical ionization (APCI) interface in selected reaction monitoring (SRM) mode. The two internal standards used were 16,16, 17-(2)H(3)-19-nortestosterone for 19-nortestosterone and methenolone acetate for its esters. The steroids studied were extracted from plasma samples with a mixture of diethyl ether/n-hexane (9:1, v/v). The quant...
Tissue-specific localization of cytochrome P450 aromatase in the equine embryo by in situ hybridization and immunocytochemistry. Estrogen production by the preimplantation equine embryo is presumed to be important in maternal-conceptus communication in the mare. The synthesis of C(18) estrogens from C(19) androgens requires cytochrome P450 aromatase (P450(arom)) in the conceptus, but little information is available on the specific tissue location or potential developmental patterns of expression for the horse. The goal of this research was to localize P450(arom) in the equine conceptus by immunocytochemistry and in situ hybridization. Intact blastocyst-stage embryos were collected by nonsurgical flush on Days 12-15 of p...
Intrafollicular concentrations of steroids and steroidogenic enzymes in relation to follicular development in the mare. The objective of the present study was to determine the changes in follicular fluid steroid concentrations and in granulosa cell steroidogenic enzyme expression during the follicular phase, in relation to follicular size and physiological status in the mare. Follicular fluid and follicular cells were recovered by ultrasound-guided follicular punctures either around the time of emergence of the dominant follicle, at the end of the dominant follicle growth, or at the preovulatory stage, after injection of gonadotropin to induce ovulation. Cellular relative amounts of steroidogenic acute regulato...
Peripuberal sexual development of Pantaneiro stallions. Pantaneiro horses are a breed native to flood plains of Brazil, where they thrive with little human interference. The aims of this study were to characterize age-associated changes in testicular size, serum testosterone and sexual behavior and to determine age at puberty as well as to evaluate daily sperm production in the Pantaneiro stallion. After weaning the males were kept in bachelor groups away from the females, in a separated area in the natural environment of flood plains. Infantile period ended at approximately 14.4 m.o. of age. Sexual interest and breeding capability first appeared b...
Maximal exercise transiently disrupts hormonal secretory patterns in standardbred geldings. 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...
Determination of testosterone:epitestosterone ratio after pentafluorophenyldimethylsilyl-trimethylsilyl derivatisation using gas chromatography-mass spectrometry in equine urine. A highly specific method is described for measuring the testosterone:epitestosterone ratio in equine urine by gas chromatography-mass spectrometry (GC-MS) with stable isotope internal standards. The procedure was based on Serdolit Pad-1 resin extraction, enzymatic hydrolysis, and chemical derivatisation prior to instrumental analysis. The mixed derivatives, 3-trimethylsilyl-17-pentafluorophenyldimethylsilyl ether (3-TMS-17-flophemesyl) testosterone and epitestosterone, were found to have excellent analytical properties. The specificity of the derivatisation method exploits a unique feature of ...
Pituitary response to steroid replacement therapy in fertile, subfertile and infertile stallions after castration. Recent studies in our laboratory investigating plasma gonadotrophin concentrations before and after castration indicate that the hypothalamic-pituitary axis is not the original site of dysfunction in stallions with idiopathic infertility. In the present study, fertile, subfertile and infertile stallions were subjected to replacement therapy with oestradiol and testosterone 1 year after castration to investigate hypothalamic-pituitary axis function further. Fertile (n=5), subfertile (n=3) and infertile (n=2) castrated stallions of Light horse breeds, aged 11-23 years, were given either oestradi...
Testicular and hormonal changes in stallions with thermally induced testicular degeneration. The scrota of three Pony stallions and one miniature horse were insulated for 36 h. Plasma testosterone concentrations decreased gradually and were significantly (P < 0.05) lower than pretreatment values at 16, 24, 30, 38 and 44 h after onset of scrotal insulation. Plasma LH and oestradiol concentrations were significantly (P < 0.05) decreased 18 h, and 24 and 26 h, after onset of scrotal insulation, respectively. Plasma FSH concentrations were significantly (P < 0.05) decreased 4 days after the insulation was removed. Decreases in the potential daily sperm output per Pony for early p...
Differential expression of steroidogenic enzymes by the primary corpora lutea of pregnant mares during equine chorionic gonadotrophin secretion. At the onset of equine chorionic gonadotrophin (eCG) secretion, eCG stimulates luteal androgen and oestrogen production. Although eCG concentrations increase exponentially from day 37 to day 60 of gestation and eCG is detectable in maternal serum until about day 120-150 of gestation, luteal androgen and oestrogen production peaks between 5 and 10 days after initial exposure to eCG and then decreases gradually. It is not clear how eCG regulates luteal androgen and oestrogen production. In the present study, the steady-state mRNA expression of 3beta-hydroxysteroid dehydrogenase (3beta-HSD), cyto...
Testicular secretion of inhibin in stallions. In this study, clear seasonal changes in the circulating concentrations of immunoreactive inhibin were observed in stallions throughout the year. The highest plasma concentrations of immunoreactive inhibin were observed during the breeding season and the lowest concentrations were observed during the nonbreeding season. There was positive correlation between the circulating concentrations of immunoreactive inhibin, steroid hormones and gonadotrophins. Inhibin alpha subunit positive staining was observed in Sertoli cells and more clearly in Leydig cells. Both cell types also stained positively ...
Testicular biopsy in stallions: diagnostic potential and effects on prospective fertility. Testicular biopsy was performed as a standing procedure on fertile, mature stallions (n=7) under sedation and local anaesthesia. The 'Biopty' instrument was used to collect three samples from the left testis of each stallion. The oestradiol, testosterone and inhibin content in each testis were assessed by validated radioimmunoassay (RIA); protein concentrations were determined and the testes were prepared histologically for haematoxylin and eosin staining. The fertility status of each stallion was assessed before and after testicular biopsy by semen evaluation, changes in total scrotal width, ...
Inhibin localization in equine granulosa-theca cell tumours and inhibin forms in tumour fluid. The aim of this study was to examine inhibin production in granulosa-theca cell tumours (GTCT). The experimental aims were: (i) to determine GTCT cell types that produce inhibin alpha- and betaA-subunits; (ii) to determine whether alpha- and betaA-subunit forms differ in GTCT fluid and normal equine follicular fluid (eFF); and (iii) to determine whether dimeric inhibin (alpha betaA) is present in GTCT plasma and tumour fluid. Plasma, tumour fluid and tumour tissue were collected from mares (n=6) with GTCT. Plasma and eFF were collected during the follicular phase from mares (n=4) undergoing no...
Possible role of autoimmunity to spermatozoa in idiopathic infertility of stallions. Testicular degeneration is a major cause of subfertility in stallions, although an aetiological diagnosis cannot be made in most cases. In the present study, autoimmune testicular degeneration was induced and evaluated in stallions by immunizing stallions with their own spermatozoa mixed with an adjuvant. The factors evaluated included changes in semen quality and testicular histology. A large decrease in sperm number and quality was observed in response to sperm autoantigens. An ELISA test specific for antisperm antibodies was developed which enabled antibody titres in serum, seminal plasma a...
Secular sperm trends in stallions between 1981 and 1996. Several reports have suggested that human semen quality has declined throughout the world over the last few decades. Chemicals in the environment acting as endocrine disrupters have been implicated as a possible cause. If this is indeed the case, then similar effects may be observed in animals. We analyzed 1489 ejaculates collected from 390 Breton draught stallions between 1981 and 1996. Semen was collected from all the stallions at a single center, according to standardized semen collection protocols and laboratory methods. Semen volume decreased slightly but significantly and there was an in...
Testicular endocrine function, seasonality and semen quality of the stallion. To gain further information on gonadal function of the stallion, concentrations of testicular steroids in blood plasma (bpl) and seminal plasma (spl) and their distribution in the ejaculate were determined. Blood and semen samples from a total of 11 stallions were collected from November to July. Estrone (E1), estrone sulfate (E1S), estradiol-17beta (E2beta) and testosterone (T) were determined in bpl and spl, and in addition androstenedione (A), dehydroepiandrosterone (DHEA) and 5alpha-dihydrotestosterone (5alpha-DHT) were measured in spl. At certain points of time, aliquots of an ejaculate w...
Equine castration: review of anatomy, approaches, techniques and complications in normal, cryptorchid and monorchid horses. Complications associated with equine castration are the most common cause of malpractice claims against equine practitioners in North America. An understanding of the embryological development and surgical anatomy is essential to differentiate abnormal from normal structures and to minimise complications. Castration of the normal horse can be performed using sedation and regional anaesthesia while the horse is standing, or under general anaesthesia when it is recumbent. Castration of cryptorchid horses is best performed under general anaesthesia at a surgical facility. Techniques for castratio...
Nortestosterone: endogenous in urine of goats, sheep and mares? For a number of species it is known that nortestosterone, either the alpha- or beta-epimer, can be of endogenous origin. For goats and mares similar results have not yet been published. As a follow-up on the experiments with cattle, a large number of urine samples per animal were collected from pregnant goats, sheep and mares. These samples were analysed for the presence of alpha- and beta-nortestosterone and alpha-estradiol using GC-MS. The results show that in the goats and mares studied alpha-nortestosterone is present during pregnancy. In this study no alpha-nortestosterone could be demons...
Effects of anabolic steroid (19-nortestosterone) on the secretion of testicular hormones in the stallion. The aim of this study was to clarify the effect of anabolic steroids on the testicular endocrine function of mature stallions. Mature thoroughbred stallions were treated with 800 mg nandrolone decanoate every 3 weeks for 3 months. After the first treatment, plasma concentrations of LH, immunoreactive inhibin and testosterone decreased rapidly to the nadir. These hormones were maintained at significantly lower concentrations compared with concentrations in intact stallions. Histology of the testicular tissue indicated the arrest of advanced spermatogenesis in the seminiferous tubules and a seve...
[Diagnosis, therapy and endocrinologic parameters of persistent follicles in mares in comparison with preovulatory follicles]. During the 1997 breeding season persistent follicles were diagnosed in 17 mares. In 16 of these mares a total of 17 follicles were transabdominally punctured and the steroids oestradiol, progesterone and testosterone were measured in the follicular fluid and in blood serum. In ten mares serving as a control group preovulatory follicles were punctured. The follicular fluid of the persistent follicles revealed a very high variability of the steroid concentrations. Depending on the steroid ratio within the follicles, eight follicles were rated as being intact, three follicles were undergoing atre...
Glutathione-independent prostaglandin D2 synthase in ram and stallion epididymal fluids: origin and regulation. 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 ...
Viability of an inguinal testis after laparoscopic cauterization and transection of its blood supply. A 25-month-old castrated horse was admitted for evaluation of stallion-like behavior. Twelve months earlier, bilateral cryptorchidism had been diagnosed, and the horse underwent a laparoscopic castration. At that time, the left testis was removed from the abdominal cavity, but the right testis, which was located in the inguinal ring, was left in place to undergo avascular necrosis after laparoscopic cauterization and transection of the testicular vasculature. On physical examination, an apparently clinically normal right testis was palpated within the scrotum. Administration of human chorionic...
[Experiences with spermatic cord ligation as a method of castration in the stallion. The surgical castration of the testicle in situ appears to be of value]. In 22 stallions the surgically prepared spermatic cord was crushed and ligated. Preoperative and postoperative plasma-testosterone concentrations were measured and 60 days after surgery a HCG-stimulation test was carried out in 12 horses. In these 12 horses the testosterone production had ceased. In all 22 horses the wounds healed by primary intention. Ligation of the spermatic cord is a castration technique without surgical complications, at least in this study.
Testicular inhibin in the stallion: cellular source and seasonal changes in its secretion. The cellular localization of inhibin alpha, betaA, and betaB subunits, 3beta-hydroxysteroid dehydrogenase (3beta-HSD), and cytochrome P450 aromatase (aromatase) in stallion testes was investigated. In addition, detailed seasonal changes in circulating immunoreactive (ir)-inhibin were investigated in correlation with testosterone, estradiol, LH, and FSH. Inhibin alpha subunit-positive staining was observed in Sertoli cells, and more clearly positive staining was noted in Leydig cells. Inhibin betaA and betaB subunits were also stained in both types of cells. Immunoreactivity of 3beta-HSD and ar...
Relationship between plasma testosterone concentrations and age, breeding season and harem size in Misaki feral horses. Jugular vein blood samples were collected from 23 young and sexual mature feral stallions to examine the relationship between plasma testosterone concentration and age, breeding season or harem size. Testosterone concentration increased with the age of the stallions until they formed their own harems, at about 4 to 6 years old. Seasonal variations in testosterone concentrations were observed, and found to be significantly higher (P<0.001) throughout the breeding season than non-breeding season, from 3 years of age. Testosterone levels were correlated with harem size for individual stallions...
A comparison of the biochemical composition of equine follicular fluid and serum at four different stages of the follicular cycle. Samples of blood and follicular fluid were recovered from 27 Welsh Pony mares at 4 distinct stages of follicular development. Eighteen biochemical parameters were measured in each sample, including sodium, potassium, chloride, glucose, urea, creatinine, calcium, inorganic phosphate, total bilirubin, total protein, albumin, magnesium, triglyceride, total cholesterol, nonesterified fatty acids, alkaline phosphatase, gamma-glutamyltransferase and aspartate aminotransferase. The concentrations of progesterone, 17beta oestradiol and testosterone, pH and osmolarity, were also measured in all the fol...
Gonadal and pituitary responsiveness of stallions is not down-regulated by prolonged pulsatile administration of GnRH. The objective of this study was to determine if prolonged pulsatile administration of homologous gonadotropin-releasing hormone (GnRH) at therapeutic or 5x therapeutic doses would cause down-regulation of the stallion's hypothalamic-pituitary-testicular axis. Fifteen stallions were randomly assigned to three treatment groups (n=5/group) and received a 0.5 ml subcutaneous dose of saline (group 1), 50 microg GnRH (group 2), or 250 microg GnRH (group 3) every 2 hours for 75 days. Weekly evaluations of follicle stimulating hormone, luteinizing hormone, and testosterone and monthly evaluations of d...
Inhibin secretion in the stallion. To examine the physiological role of inhibin in the stallion, a heterologous radioimmunoassay (RIA) based on a bovine RIA was validated and used to measure immunoreactive (ir)-inhibin concentrations in plasma and testicular homogenates. The bioactivity of equine testicular inhibin was also examined using an assay for suppression of FSH secretion from rat anterior pituitary cells. In addition, to identify the cell responsible for secreting testicular inhibin, the localisation of inhibin in the testis was investigated by an immunohistochemical method using a polyclonal antibody against (Tyr30)-p...
Effects of age, season, and fertility status on plasma and intratesticular immunoreactive (IR) inhibin concentrations in stallions. The nature of the relationship between inhibin and reproductive function in the stallion is yet to be elucidated. Blood and testes from 51 light horse stallions ranging in age from 2 mo to 25 years were collected during the breeding and nonbreeding seasons to study the effects of testicular maturation, aging, season, and fertility status on peripheral and intratesticular concentrations of Ir inhibin and other reproductive hormones. Of the 51 stallions, 12 age-matched stallions (6 fertile, 3 subfertile, and 3 infertile) were used in the fertility study. Blood samples were taken before castratio...
Inhibition and inactivation of equine aromatase by steroidal and non-steroidal compounds. A comparison with human aromatase inhibition. In order to approach the detailed structure-function relationships of aromatase, we studied the inhibitory and inactivatory potencies of several steroidal androstenedione analogues (1: 4-hydroxyandrostenedione, 2: 4-acetoxyandrostenedione and 3: 7 alpha-(4'-amino)phenylthio-4-androstene-3, 17-dione) and non-steroidal imidazole derivatives (4: ketoconazole, 5: miconazole and 6: fadrozole) on equine aromatase in placental microsomes, a well established mammalian model. Human placental microsomes and the purified enzyme from equine testis were also used to compare inhibition by 1 and 2. In equine...
Purification and characterization of equine testicular cytochrome P-450 aromatase: comparison with the human enzyme. Cytochrome P-450 aromatase was purified by five chromatographic steps from adult stallion testis. It was first separated from NADPH-cytochrome P-450 reductase (reductase) on omega-aminohexyl-Sepharose 4B then purified to homogeneity on concanavalin A-Sepharose 4B, hydroxyapatite-Sepharose 4B, DEAE-Sepharose CL-6B and on a second hydroxyapatite-Sepharose 4B. On the other hand, purifications of the equine testicular and rat liver reductases, which allowed the reconstitution of aromatase activity in vitro, were achieved for each species in one chromatographic step on an adenosine 2',5'-diphosphat...
