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Topic:Ovarian Follicles
Ovarian follicles in horses are structures within the ovaries that contain the developing oocyte, or egg, and are essential for reproduction. These follicles undergo a series of growth stages, from primordial to preovulatory, influenced by hormonal changes within the mare's reproductive cycle. The development and maturation of ovarian follicles are regulated by hormones such as follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Monitoring follicular development is integral to understanding reproductive physiology and managing breeding in equine practice. This page compiles peer-reviewed research studies and scholarly articles that explore the physiology, development, and clinical management of ovarian follicles in horses.
Soluble oestrogen and progesterone receptors in the endometrium of the mare. Receptors for progesterone and oestrogen were measured in cytosol extracted from the endometrium of mares. Samples of endometrium were obtained from mares during the oestrous cycle and during other physiological and pathological states, and from mares with persistent endometritis. The concentration of binding sites was high around oestrus and early in dioestrus and was low by mid- to late dioestrus. Numbers of receptors were low in mares sampled on Day 15 of pregnancy and in mares in prolonged dioestrus, whereas receptor concentrations in ovariectomized mares were high. In 2 mares with endomet...
Measurements of glycosaminoglycans in follicular, oviductal and uterine fluids of mares. Eighteen fertile mares were used to determine the effects of the oestrous cycle and location in the reproductive tract on the amount and concentration of glycosaminoglycans in luminal fluids. Ovariohysterectomies were performed in 3 groups of 6 mares on Day 3 of behavioural oestrus, within 6 h after ovulation or on Day 8 of dioestrus. The lumina of the uterine horns and oviducts ipsilateral and contralateral to the active ovary were flushed and fluid was aspirated from the dominant follicle in the oestrous preovulation group. Glycosaminoglycans and protein concentrations were measured in these...
Ovarian response in mares to prolonged treatment with exogenous equine pituitary gonadotrophins. Twelve anoestrous mares were treated with an intravaginal sponge containing 0.5 g allyl trembolone (Regumate; Roussel UCLAF, Paris) and 50 mg oestradiol benzoate for 7 days, followed by daily intramuscular (i.m.) injections of 25 mg crude equine pituitary extract (CEG), with (n = 6) or without (n = 6) 0.25 mg porcine growth hormone (pGH). No difference in ovarian response to this superovulation treatment was observed between the 2 groups (2.2 +/- 0.4 vs 2.3 +/- 0.4 ovulations per mare, respectively). CEG treatment was then combined with allyl trembolone (40 mg per os per day) and prolonged in ...
Intra-follicular and peripheral steroid characteristics during vernal transition in the pony mare. 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...
Equine granulosa-theca cell tumors express inhibin alpha- and beta A-subunit messenger ribonucleic acids and proteins. The association of equine granulosa-theca cell tumors with atrophied contralateral ovaries and abnormal estrous cycles suggests that these tumors produce hormones that affect pituitary gonadotropin production. Because inhibin, a heterodimer protein secreted by granulosa cells, decreases FSH production, we examined the presence of inhibin alpha- and beta A-subunits and their mRNAs in ovarian tumors obtained from three mares. These tumors contained neoplastic cords and nodules, multiple fluid-filled cysts, and a predominance of neoplastic granulosa cells. Reduced proteins from tumor-conditioned ...
Developmental changes in steroidogenesis by equine preovulatory follicles: effects of equine LH, FSH, and CG. Ovulation in mares is preceded by a long and variable estrous period. The differentiation of equine preovulatory follicles with respect to steroidogenic capacity and responsiveness to equine gonadotropins was studied by culturing pieces of follicle wall (FW = theca + attached granulosa cells) from preovulatory follicles isolated during late diestrus (day 14 of cycle, n = 5 mares), early estrus (1st-2nd day of estrus, n = 6) or late estrus (4th or 5th day of estrus, n = 6). FW was cultured with or without equine LH, FSH, LH + FSH, or CG (10 or 100 ng/ml) and medium was collected and replaced at...
Granulosa cell tumor in a mare with a functional contralateral ovary. A functional corpus luteum was found in the ovary contralateral to the ovary with a granulosa cell tumor in a 24-year-old Standardbred mare. The mare was ovariectomized because she was to be used as a jump mare for collection of semen from stallions. The blood concentration of progesterone was 2.2 ng/ml, and the luteal tissue progesterone concentration was 6.3 micrograms/mg. Atrophy of the contralateral ovary is one of the major signs used in diagnosis of granulosa cell tumor; however, our findings indicate that the ovary contralateral to a granulosa cell tumor is not invariably nonfunctional....
Folliculogenesis during the transitional period and early ovulatory season in mares. Individual follicles were monitored by ultrasonography in 15 mares during the transitional period preceding the first ovulation of the year and in 9 mares during the first interovulatory interval. During the transitional period, 7 mares developed 1-3 anovulatory follicular waves characterized by a dominant follicle (maximum diameter greater than or equal to 38 mm) that had growing, static, and regressing phases. The emergence of a subsequent wave (anovulatory or ovulatory) did not occur until the dominant follicle of the previous wave was in the static phase. After the emergence of the subsequ...
Immunosuppressive properties of follicular fluid from preovulatory horse follicles. Fluid was aspirated from the preovulatory follicles of mares before and 12, 24 and 36 h after intravenous administration of hCG. Follicular fluid significantly (P less than 0.001) reduced lymphocyte blastogenesis in vitro and, at a dilution of 1:100, fluid collected at 36 h after administration of hCG was significantly more suppressive (P less than 0.01) than fluid collected before 36 h. Suppression of blastogenesis was reduced by extracting the follicular fluid with ether or by charcoal treatment (P less than 0.01) or by heating at 56 degrees C for 30 min (P less than 0.05). Preincubation of ...
[Ovarian structure and function in the mare from the clinical viewpoint with special regard to ultrasonography]. Ultrasonography is a good means of monitoring follicular development in the mare and allows objective observation and measurement of follicular growth as well as identification of corpora lutea and hematoma in the ovary. The significance of ultrasonography in this field lies in the specific anatomical structure of the mare's ovary and the different phenomena preceding and accompanying ovulation, which are described in this paper. The last part deals with the handling and use of ultrasonography.
Effect of GnRH treatment during the anovulatory season on multiple ovulation rate and on follicular development during the ensuing pregnancy in mares. Seasonally anovulatory mares were injected, i.m., twice daily with a GnRH analogue (GnRH-A), and hCG was given when the largest follicle reached 35 mm in diameter. In Exp. 1, treatment was initiated on 23 December when the largest follicle per mare was less than or equal to 17 mm. An ovulatory response (ovulation within 21 days) occurred in 17 of 30 (57%) GnRH-A-treated mares on a mean of 15.8 days. The shortest interval to ovulation in control mares (N = 10) was 57 days. The diameter of the largest follicle first increased significantly 6 days after start of treatment. In Exp. 2, treatment wa...
Ovulation in the isolated perfused rat ovary as documented by intravital microscopy. 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 (...
The effects of pregnant mare serum gonadotropin on follicular development, mating and pregnancy in mink. Forty-four female ranch mink, maintained out-of-doors under standard conditions, were exposed to natural photoperiod supplemented with a period of artificial light from approximately 2300 hr to 0300 hr from early January to mid February. Breeding was initiated on March 1. After repeated attempts to breed the animals, it was determined that the likelihood of their breeding was very low, presumably due to the artificial and asynchronous long-day photoperiod. In an attempt to induce breeding, the mink were randomly assigned to one of four treatment groups: saline, 25 International Units (IU) PMSG...
Regulation of ovarian function by catecholestrogens: current concepts. Development of the ovarian follicle(s) destined for ovulation appears to be a process in which antral follicles undergo a recruitment, selection and subsequent dominance phase. Several intraovarian or autocrine/paracrine regulatory mechanisms have been evoked to explain these processes. One of these potential autocrine/paracrine regulators is a catecholestrogen, 2-hydroxy-estradiol (2-OH-E2). Evidence implicating 2-OH-E2 as an autocrine/paracrine regulator of follicular function is reviewed. Studies have shown 2-OH-E2 to be present in nanomolar concentrations in fluid of human and equine folli...
Primary ovarian adenocarcinoma associated with teratomatous elements in a mare. An ovarian adenocarcinoma with teratomatous elements was removed from a 9-year-old mare. Although no other lesions were detected at ovariectomy, multifocal metastatic masses led to cachexia and euthanasia 2 months later. This case reaffirms the need to exercise caution when removing ovarian masses to prevent seeding of the abdomen. This report includes discussion of the WHO system of classification of ovarian tumors.
Predicting ovulation in the mare on the basis of follicular growth and serum oestrone sulphate and progesterone levels. Follicular growth and hormone determinations were used to predict ovulation in the mare. Thirty Finnhorse mares were used for the investigation and 38 oestrous cycles were studied. The mares were examined by rectal palpation and ultrasonography every 6 hours during late oestrus. Daily blood samples were obtained for progesterone and oestrone sulphate determination. The preovulatory follicle grew 3 mm a day up to 2 days before ovulation. The size then remained constant, before diminishing by 2-3 mm during the last 12 hours. The maximal diameter of the follicle was 43 +/- 4 mm. In 89% of the fol...
Serous cystadenoma in a normally cyclic mare with high plasma testosterone values. Serous cystadenoma was diagnosed by histologic examination of a large ovary removed from a 16-year-old Thoroughbred mare with normal estrous cycles. Palpation and ultrasound examination per rectum had revealed an excessive number of follicles in the right ovary. The ovulation fossa was palpable on the right ovary, and the left ovary appeared to have normal activity. Plasma testosterone values were high at the time of examination (0.15 ng/ml), but decreased to normal values (0.09 ng/ml) after removal of the cystadenoma.
Alterations in the cell cycle characteristics of granulosa cells during the periovulatory period: evidence of ovarian and oviductal influences. Granulosa cells at different stages of differentiation were collected from ovarian follicles and oviducts during the periovulatory period, and their nuclear DNA content was monitored by flow cytometry to establish their cell cycle characteristics (G0 + G1, S, G2 + M). The proportion of cells in the three phases of the cell cycle varied in characteristics patterns depending upon the time they were collected, before or following ovulation. Granulosa (cumulus) cells recovered from ovulated oocytes were mitotically inactive as shown by the large proportion of cells with a 2C amount of DNA and the ...
Hemoperitoneum caused by rupture of a juvenile granulosa cell tumor in an equine neonate. A neonatal foal was examined because of apparent abdominal pain and distention, anemia, and hemoperitoneum. Exploratory laparotomy was performed, and a large spherical mass, which had ruptured, was found in the area of the left ovary. Left salpingo-oophorectomy was performed. The mass was determined to be a juvenile granulosa cell tumor.
Changes in the concentrations of steroids and prostaglandin F in preovulatory follicles of the mare after administration of hCG. Fluid was aspirated from the preovulatory follicle of Group 1 mares (N = 6) when follicles reached 32-34 mm in diameter. Group 2 mares each received an i.v. injection of hCG when the preovulatory follicle reached 35 mm. Aspiration of follicular fluid was performed 28-32 h after treatment. Follicular fluid was aspirated from Group 3 mares 28-32 h after the preovulatory follicle reached 35 mm in diameter. Concentrations of progesterone were significantly higher in follicular fluid from Group 2 mares than in that from mares in Groups 1 and 3. Testosterone was significantly higher in follicular fl...
Effect of ovarian steroids on migration of uterine lumenal neutrophils and on chemokinetic factors in uterine secretions from mares. Incubation of blood neutrophils with uterine flushings collected from ovariectomised mares treated with oestradiol, stimulated migration under agarose, whereas flushings from mares treated with progesterone or oily vehicle, inhibited migration. After intra-uterine infusion of bacteria, however, flushings from oestradiol-treated and vehicle-treated mares inhibited migration, whereas progesterone treatment stimulated migration. Migration of uterine-derived neutrophils under agarose was less than that of blood neutrophils and was not influenced by treatment with ovarian steroids. Uterine suscepti...
Ultrasonic imaging of equine ovarian follicles and corpora lutea. One of the most profound theriogenology applications of transrectal diagnostic ultrasonography in mares involves the imaging of ovarian follicles and corpora lutea. The resolving capabilities (frequency) and quality of the scanner directly affect the minimal size of a structure that can be imaged and the quality of the image. High-frequency scanners (5 or 7.5 MHz) of good quality can image a 2-mm follicle and the corpus luteum throughout its functional life. A low-frequency scanner (3 or 3.5 MHz) can image a 6-mm follicle and the corpus luteum for several days after ovulation. Equine follicles...
Effect of exogenous ovarian steroids on the uterine luminal prostaglandins in ovariectomised mares with experimental endometritis. Prostaglandins (PGs) F and E2 were measured in lavage fluid from the uterus of ovariectomised mares after experimental induction of uterine inflammation. Treatment with progesterone alone, or progesterone followed by oestradiol, significantly increased the concentrations of these PGs in the lavage compared with mares treated with oestradiol or control mares. Ovarian steroids, therefore, influenced uterine PG synthesis in response to an inflammatory stimulus. To determine whether the uterine lavage procedure might contribute to the concentrations of prostaglandins in the lavage, the procedure w...
Anesthetic considerations for emergency equine abdominal surgery. The physiologic changes that take place in horses presented for emergency abdominal surgery and the effects of these changes on the horse's anesthetic management are discussed.
Gonadotropin secretion in ovariectomized pony mares treated with dexamethasone or progesterone and subsequently with dihydrotestosterone. Twelve long-term ovariectomized (OVX) pony mares were used to determine the effects of dexamethasone (DEX) or progesterone (PR) on concentrations of follicle stimulating hormone (FSH) and luteinizing hormone (LH) in daily blood samples and after administration of gonadotropin releasing hormone (GnRH). All mares were subsequently administered dihydrotestosterone (DHT) to determine if DEX or PR treatment altered the FSH or LH response to this androgen. Daily blood sampling was started on day 1. After a pretreatment injection of GnRH on day 5, four mares were administered DEX at 125 micrograms/kg...
Use of stapling instruments to aid in the removal of ovarian tumours in mares. Ovarian granulosa theca cell tumours were removed surgically in 10 mares. Stapling instruments were used to facilitate haemostasis of the ovarian pedicle in five out of 10 cases and as a sole method of haemostasis in the remaining five cases. Postoperative haemorrhage from the ovarian pedicle was suspected in only one case. All cases survived long term follow-up from six months to four years. Results from this series of cases indicate that stapling instruments provide a rapid, easy and efficient means of ligating ovarian pedicles when performing ovariectomy in the mare.
