Gonadotropins are hormones that play a significant role in the reproductive physiology of horses. They are primarily produced by the pituitary gland and include luteinizing hormone (LH) and follicle-stimulating hormone (FSH). These hormones regulate various aspects of equine reproduction, such as the development and function of the ovaries in mares and the testes in stallions. Gonadotropins influence processes like follicular growth, ovulation, and spermatogenesis. Their levels and activity are subject to regulation by factors such as seasonality and age, affecting reproductive efficiency in horses. This page compiles peer-reviewed research studies and scholarly articles that explore the function, regulation, and implications of gonadotropins in equine reproductive health.
Channing CP.Granulosa cells were harvested from follicles of mares at various stages of the oestrous cycle and maintained in a tissue culture medium containing 15% horse serum, 30% medium '199' and 55% Hanks's solution. Between days 4 and 10 of culture the granulosa cells harvested from small follicles (1–2 cm. diam.) of mares in the midluteal phase of the cycle secreted an average of 0·36 pg. progesterone/cell/day. Cells harvested from large follicles of mares in the late and/or early oestrous stage of the cycle secreted an average of 29·5 pg. progesterone cell/day; the cells harvested from the large...
Visutakul P, Bell ET, Loraine JA, Fisher RB.Human chorionic gonadotrophin (HCG), pregnant mare serum gonadotrophin (PMSG) and human menopausal gonadotrophin (HMG) were incubated with varying concentrations of urea at different temperatures for different times.
The luteinizing hormone (LH) activity of HCG was progressively destroyed with increasing concentrations of urea. The degree of inactivation was greater at higher temperatures but the time of incubation did not affect the results.
The follicle-stimulating activity of PMSG was reduced at high urea concentrations; the time of incubation was without effect.
Under the experime...
SAXENA BB, McSHAN WH, MEYER RK.Fresh horse-pituitary glands were extracted with 40% ethanol and the gonadotropins were recovered by increasing the alcohol concentration to 85% followed by drying with acetone. This preparation was further extracted with water at pH 5, and the extract was adjusted to pH 7 and lyophilized. The follicle-stimulating hormone in the pH-5-souluble fraction was purified by zone electrophoresis and resolved into six components by starch-gel electrophoresis. One of these components contained follicle-stimulating hormone which was recovered in the elution cell and the contaminating starch was separated...
Fitzgerald BP, Mellbye LB.Two experiments were performed to test the hypothesis that the seasonal suppression of gonadotrophin pulse frequency in anoestrous horse mares reflects inhibitory neural mechanisms. In a preliminary experiment (Exp. 1) conducted in February, 4 anoestrous mares were sedated by repeated intravenous injections of xylazine, an alpha 2-adrenergic receptor agonist. On the day of treatment, 1-2 LH pulses were observed in xylazine-treated mares. In contrast, during a 12-h period only 1/8 untreated control mares exhibited a LH pulse. In Exp. 2, the effect of xylazine-induced sedation on pulsatile gonad...
Thompson DL, McNeill DR, Wiest JJ, St George RL, Jones LS, Garza F.Sequential samples of blood were drawn via jugular catheters every 15 min for 24 h from four mares in each of five reproductive states: intact anestrous mares in winter, intact diestrous mares in summer, intact estrous mares in summer, ovariectomized mares in winter and ovariectomized mares in summer. Estrous mares were sampled on d 4 or 5 of estrus and diestrous mares on d 10 or 11 of diestrus. Each sample of plasma was assessed for concentrations of luteinizing hormone (LH) and follicle stimulating hormone (FSH) in two independent radioimmunoassays. A computer program was developed that dete...
Checura CM, Beg MA, Parrish JJ, Ginther OJ.The functional relationships among intrafollicular free insulin-like growth factor 1 (IGF1), circulatory gonadotropins, and development of the dominant follicle were studied in 40 mares in two experiments. A GnRH antagonist (Acyline) was given i.m. at the expected beginning of follicular deviation (largest follicle or F1> or =20mm; Day 0) alone (Acyline group) or in combination with intrafollicular treatment of F1 with rhIGF1 (Acyline/IGF1 group). In Experiment 1, blood samples, follicular-fluid samples, and diameter of F1 were taken on Days 1 and 2. In Experiment 2, daily follicular diamet...
Monet-Kuntz C, Guillou F, Fontaine I, Combarnous Y.Using a suspension of seminiferous tubule cells, we had previously shown that equine FSH is superactive in the male rat, i.e. that it exhibits a higher biological potency than expected from its binding activity. In this work we investigated equine FSH superactivity in rat, pig and sheep, by comparing in each species the equine FSH with the homologous FSH, both for their binding activities (in a radioreceptor assay using a testicular membrane fraction) and for their in vitro biological potencies (in a plasminogen activator assay using a Sertoli cell-enriched population cultured on plastic). In ...
Hoque S, Senba H, Tsunoda N, Derar RI, Watanabe G, Taya K, Osawa T, Miyake Y.To clarify the endocrinological characteristics of the mares with granulosa theca cell tumor (GTCT), peripheral plasma samples from the 6 mares affected with GTCT were collected before and after the surgical removal of the affected ovary. Concentrations of testosterone (T), follicle stimulating hormone (FSH), luteinizing hormone (LH), immunoreactive-inhibin (ir-INH), progesterone (P) and estradiol-17beta (E(2)) in the plasma samples were measured by radioimmunoassay. Before removal of GTCT in all cases, the concentrations of T were significantly higher than those of normal mares at the breedin...
Ellerbrock RE, Canisso IF, Lima FS, Shipley CF, Thompson DL, Conley AJ, Kline KH.The objectives of this study were to determine the concentrations of reproductive and metabolic hormones during the peripubertal period and to assess their relationship with testicular development and body fat deposition. Blood samples were collected from 23 healthy Standardbred colts every four weeks for twelve months. Colts were weighed monthly, and percent of body fat and testicular volume estimated by ultrasound. Onset of puberty was determined as the month when testosterone was two standard deviations above the previous mean. Plasma FSH, LH, leptin, estradiol-17β, androstenedione, IGF-1,...
Löfman CO, Brännström M, Holmes PV, Janson PO.Surface cell changes at the apices of preovulatory follicles and ovulations were documented in isolated perfused ovaries from immature rats treated with pregnant mare serum gonadotropin (20 IU) and 48 h later with human chorionic gonadotropin (hCG) (10 IU). A video camera coupled to an inverted microscope and a video recorder captured the preovulatory and ovulatory events at a cellular level. At around 8 h post-hCG, the follicular apex changed from a smooth and optically homogeneous appearance into a rough surface with bleb formation and extrusions of single cells through minute perforations (...
Collingsworth MG, Fuller Z, Cox JE, Argo CM.Concentrations of gonadotrophins and prolactin were recorded in pony stallions castrated during the early breeding season, to examine the regulatory role of the gonad at a time when testosterone has been postulated to exert positive feedback on LH secretion. Further, gonadotrophin concentrations in geldings are reported to return to values within the normal range of the entire stallion. In an attempt to characterize this species-specific reversal, the gonadotrophin concentrations of 6 male ponies castrated on 25 March were monitored for 4 months, and 4 stallions were used to generate control d...
Zelli R, Sylla L, Monaci M, Stradaioli G, Sibley LE, Roser JF, Munro C, Liu IK.Granulosa-theca cell tumors (GTCTs) are able to secrete variable amounts of sex steroids and immunoreactive inhibin (ir-INH). Although the pituitary appears to be affected by the presence of a GTCT, pituitary responsiveness to exogenous GnRH has not been examined. The aims of the present study were to: (i) assess the plasma hormone concentrations of ir-INH, gonadotropins and sex steroids in eight mares with GTCT and (ii) assess the responsiveness of pituitary gonadotroph cells to exogenous GnRH stimulus both before and after tumor removal. In seven mares, the contralateral ovary was firm, smal...
Lapin DR, Ginther OJ.A crude equine pituitary ethanol extract (EE) was used to induce single and miltiple ovulations in seasonally anovulatory pony mares 3-15 years of age. 12 mares were injected daily for 14 days with EE; 6 of the EE-treated mares were also treated with human chorionic gonadotropin (HCG), and 6 control mares received saline vehicle only. In a 2nd experiment designed to determine if EE treatment could induce multiple ovulations in seasonally ovulatory mares, 7 mares were treated during diestrus, 7 mares were treated beginning on Day 1 of estrus, and 7 remained untreated. The results of experiment ...
Garza F, Thompson DL, St George RL, Reville-Moroz SI.Eight long-term ovariectomized pony mares were treated with either dihydrotestosterone (DHT) benzoate (400 micrograms/kg body weight) in safflower oil or an equivalent amount of oil every other day for 21 d to determine the effects of DHT on follicle stimulating hormone (FSH) and luteinizing hormone (LH) concentrations in blood samples drawn once daily and after administration of three successive injections of gonadotropin releasing hormone (GnRH). The GnRH injections were given at 4-h intervals on the day following the last DHT or oil injection. Treatment with DHT benzoate did not alter (P gr...
Brinsko SP.Poor fertility has been associated with hormonal imbalances in the stallion. The primary cause of this imbalance is unknown, but it may be related to abnormal gonadotropin secretion. Secretion of GnRH from the hypothalamus causes the release of LH and FSH from the anterior pituitary and these gonadotropins help maintain adequate steroid levels so that normal spermatogenesis can occur. Hypogonadotropic hypogonadism has not been documented in the stallion; however, GnRH therapy has improved the fertility of a limited number of horses. Downregulation of the HPT axis readily occurs in most other s...
Henderson K, Stevens S, Bailey C, Hall G, Stewart J, Wards R.The relative merits of measuring blood concentrations of equine chorionic gonadotrophin (eCG, previously known as pregnant mare serum gonadotrophin (PMSG)), or oestrone sulphate (OS), or faecal OS concentrations for determining pregnancy status in miniature horses were investigated. Pregnant mares between 40 and 140 days after mating had serum eCG concentrations > 1 I.U. mL-1, with the highest concentrations occurring between days 50 and 120. However, eCG measurements were susceptible to returning a 'false positive' diagnosis of pregnancy. Plasma OS concentrations ranged from 0.1 to 3.6 ng ...
YoungLai EV, Jarrell JF.Granulosa cells were harvested from mares at various stages of the oestrous cycle and incubated in Krebs-Ringer bicarbonate buffer with 1 beta,2 beta[3H]androstenedione as substrate. The release of 3H2O expressed as CPM/h/mg protein varied from 44000 to 768000 in follicles from 7 mares. The release of 3H2O was not significantly altered by luteinizing hormone, follicle stimulating hormone or pregnant mare's serum gonadotrophin. There was a significant negative correlation between the release of 3H2O and the concentration of progesterone in the follicular fluid. Based on the assumption that the ...
Sairam MR, Yarney TA, Bhargavi GN, Sanford LM.A membrane preparation from the testis of maturing Dorset-Leicester-Suffolk sheep, capable of discriminating pituitary LH (lutropin) from placental gonadotropins human choriogonadotropin (hCG) and equine choriogonadotropin is described. Maximum binding of 125I-oLH (ovine lutropin) to the testicular receptors occurred at 4 degrees C in a rapid manner, attaining equilibrium in 12-16 h. Under such optimal conditions, only unlabeled ovine LH or the structurally identical bovine LH effectively competed for receptor occupation. Other highly purified pituitary LH preparations from rat and human pitui...
Martinuk SD, Bristol F, Murphy BD.Breeding trials were designed to determine the influence of the mare on serum concentrations of equine chorionic gonadotropin (eCG) from Day 39 to Day 104 of gestation. Sires were ranked according to mean eCG concentrations found in the groups of randomly selected mares to which they were mated in 1983. Mares were ranked according to their mean eCG concentrations on Days 55, 71 and 85 of gestation (Day 0 = mating), in 1983 and 1985. In the 1986 breeding season, mares that had pregnancies characterized by high eCG levels were mated to sires previously associated with low eCG concentration pregn...
Davis SD, Sharp DC.This experiment investigated steroid production by ovarian tissues, in vitro, of pony mares during vernal transition from anoestrus to the breeding season. Follicular dynamics were monitored to detect the first, second, third or fourth transition follicle, greater than or equal to 30 mm diameter or the first large post luteal follicle of the breeding season. Twenty-four hours after a large follicle was detected, theca (T) and granulosa (G) tissues were harvested. Separate and co-incubations of these tissues were conducted to determine steroid production in early transition (ET), late transitio...
Hines KK, Fitzgerald BP, Loy RG.Changes in the pattern of LH and FSH in serum were studied in 6 mares foaling during the summer. Samples were collected frequently (every 15 min) for 24 h twice before foaling, -33 +/- 2 and -12 +/- 2 days, and for 12 h after foaling, on Day 0 and Day 4. Simultaneous pulses of FSH and LH were observed before foaling (r2 = 0.99). Before foaling, gonadotrophin pulses were infrequent (6 in 264 h of observation). On the day of foaling, LH and FSH pulse frequency increased (P less than 0.005) with 2-4 pulses per mare. The amplitudes of pulses of LH and FSH were higher before parturition than for th...
Logan NL, McCue PM, Alonso MA, Squires EL.Superovulation could potentially increase embryo recovery for immediate transfer or cryopreservation. The objectives were to evaluate the effect of pretreatment with progesterone and estradiol (P+E) on follicular response to eFSH and compare doses of eFSH and ovulatory agents on follicular development and ovulation in mares. In Experiment 1, 40 mares were assigned to one of four treatment groups. Group 1 consisted of untreated controls. Group 2 mares were administered eFSH without pretreatment with P+E. Group 3 mares were administered P+E for 10 days starting in mid-diestrus followed by eFSH t...
Tan JH, Nanbo Y, Oikawa M, Kiso Y, Sasaki F.To analyze the sex difference in 6 kinds of adenohypophyseal cells of Mongolian ponies and the effect of prepubertal orchidectomy on adenohypophyseal cells. Methods: Pituitary glands collected from 15 adult Mongolian ponies, 5 to 10 years old: 5 stallions, 5 mares, and 5 geldings, orchidectomized between the ages of 1 and 2 years. Methods: Morphologic comparison of 6 kinds of adenohypophyseal cells among mares, stallions, and geldings was done, using immunocytochemistry and morphometry. Results: A sex difference was evident in the percentage of somatotrophs, gonadotrophs (follicle-stimulating ...
Huber MJ, Roser JF, Riebold TW, Schmotzer WB, Grubb TL, Crisman RO.Seven pregnant mares underwent general anaesthesia, laparotomy, hysterotomy and removal of a 50-day conceptus. Eversion of the uterine horn through the hysterotomy site allowed direct visualisation and electrosurgical removal of endometrial cup tissue from 5 randomly selected mares (Nos 1-5), while cup tissue in 2 mares (Nos 6 and 7) was left intact. Two pregnant mares served as unoperated controls (Nos 8 and 9). Efforts to re-establish pregnancy were initiated 20 days after surgery. Serum samples collected before surgery and during the post-operative period were analysed for concentration of ...
Fitzgerald BP.The purpose of this experiment was to investigate whether N-methyl-D,L-aspartate stimulated gonadotropin secretion in mares and to determine the response in two experimental paradigms where gonadotropin secretion is low or elevated. In Experiment 1, conducted during the breeding season (summer), eight long-term ovariectomized mares were treated daily for 21 d with progesterone plus estradiol (n = 4) or oil vehicle. Beginning on Day 14, each mare received, in a randomized design on alternate days, an intravenous injection of either 0, 0.5, 1.0, or 5.0 mg/kg NMA. Treatment with NMA was not accom...
Chopineau M, Stewart F.Reverse transcription-PCR was used to clone the coding region of the donkey (Equus asinus) glycoprotein hormone alpha-subunit transcript from pituitary gland RNA. The donkey alpha-subunit sequence demonstrated considerable identity with the horse (97% at the nucleotide level), confirming the very close evolutionary linkage between these two species. The predicted amino acid sequence revealed that the donkey alpha-subunit has the same unusual C-terminus as the horse alpha-subunit, when compared with all other mammalian alpha-subunits, including a Tyr-His transposition between positions 87 and 9...
Cahoreau C, Combarnous Y.A number of horse chorionic gonadotrophin (CG) preparations of different purities and from diverse sources have been compared in radioimmuno-, radioreceptor, in-vitro cell culture, and in-vivo assays. The relative activities of the great majority of the preparations tested were consistent in the 4 assay systems. Moreover, their relative activities in the 4 assays were consistent with those found for unfractionated plasmas. These preparations were therefore considered to represent the native form of hormone. The second International Reference Preparation (IRP2) was among the few preparations ex...
Merchant-Larios H.The establishment and sexual differentiation of the gonads of horse embryos were studied using high-resolution techniques. The most dramatic observation is the early cytodifferentiation of the somatic cells into steroidogenic cells which takes place before sexual differentiation of the gonads. A unique morphogenetic pattern is established during this process: the seminiferous cords of the testis are completely segregated from the steroidogenic tissue by a basal lamina, while in the medulla of the ovary, steroidogenic cells differentiate inside the epithelial cords which contain germ cells. Thi...
Hinrichs K, Rand WM, Palmer E.Follicular fluid from small- to medium-sized follicles has been shown to have an inhibiting effect on luteinization of granulosa cells in vitro. This study was conducted to investigate the effect of in vivo removal of follicular fluid on luteinization, peripheral gonadotropin concentrations, and ovulation of secondary follicles in the mare. Follicular fluid was aspirated from the preovulatory follicles of mares when the diameter of the follicle was 30-34 mm (Group A), 35-39 mm (Group B), or 40-44 mm (Group C). Mares in Group D served as controls and the preovulatory follicle was not aspirated....
Matteri RL, Baldwin DM, Lasley BL, Papkoff H.Previous studies from this laboratory have described the properties of purified luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from horse and donkey anterior pituitary glands. The present study afforded the opportunity to further characterize these previously purified hormone preparations and to compare them with enriched gonadotropin fractions from zebra pituitary glands. Although a single LH and FSH fraction was usually obtained for each pool of pituitaries, two separate zebra LH and two donkey FSH preparations were generated. Purified hormone preparations from the horse wer...
Grosskopf JF, Smuts EG.Blood was collected from 28 zebra mare (Equus burchellia antiquorum) immediately after being shot in the Kruger National Park. The serum was separated within two hours after collection and then stored at -15 degrees C for later assay. Of these, thirteen selected samples were tested for gonadotrophic activity. The stage of pregnancy was determined from a foetal growth curve. Blood samples from pregnant horse mares were collected by venipuncture. Nine mares were sampled. Seven blood samples at different stages of pregnancy were collected from one mare, four from another and only one sample each ...
Blanco ID, Devito LG, Ferreira HN, Araujo GH, Fernandes CB, Alvarenga MA, Landim-Alvarenga FC.This study examined the effect of treating mares with equine pituitary extract (EPE) alone or in combination with hCG on the recovery rate of immature follicles by transvaginal follicular aspiration (ovum pick-up; OPU). Ten normally cycling crossbred mares aged 3-15 years and weighing 350-400 kg were subjected to each of three treatments in a random sequence with each exposure to a new treatment separated by a rest cycle during which a spontaneous ovulation occurred. The treatments were (1) superovulated with 25mg EPE and treated with 2500 IU hCG, (2) superovulation with 25mg EPE, and (3) cont...
Thway TM, Wolfe MW.Equids and primates are the only species known to express the placental hormone chorionic gonadotropin (CG). CG is a member of the heterodimeric glycoprotein family and is composed of an alpha subunit linked to a hormone-specific beta subunit. Previously, we have reported that epidermal growth factor (EGF) regulates the equine glycoprotein hormone alpha subunit promoter through a protein kinase C (PKC)/mitogen-activated protein kinase (MAPK) signal transduction pathway in trophoblasts. The current study investigates the regulatory element/factors involved in the induction of equine glycoprotei...
