Regular and irregular characteristics of ovulation and the interovulatory interval in mares

Characteristics of regular and irregular ovarian events were studied by daily ultrasound examination in 102 non-bred mares. The mean diameter of the prevoluatory follicle on the day before a single ovulation was significantly higher in April (46 mm) and May (48 mm) than in July (40 mm). Diameter was also significantly different among single (44 mm), double unilateral (35 mm), and double bilateral (40 mm) preovulatory follicles. The incidence of apparent anovulation within the ovulatory season was 4.7%. All apparent anovulations involved filling of the follicle with blood (hemorrhagic follicles). The incidence of diestrous ovulations was 4%. Prolonged interovulatory intervals occurred in 6 of 69 (9%) intervals. In 2 intervals (30 and 33 days), both the luteal and follicular phases were prolonged and no structural ovarian or uterine irregularities were detected. Three prolonged intervals (34, 41, and 49 days) were associated with hemorrhagic follicles and 1 was associated with a late diestrous ovulation (47 days). The condition known as spontaneous persistence of the corpus luteum, which is thought to be common in nonpregnant mares, was not detected in any of 69 interovulatory intervals.     

Dopamine Antagonist Affects Luteal Function But Not Cyclicity During the Autumn Transition

The autumn transition is characterized by a number of anomalies affecting the luteal phase of the estrous cycle, such as declining progesterone secretion from the corpus luteum and increased rate of failure of luteolysis. Prolactin also decreases. We theorized that these events may be linked, possibly through dopamine. We administered domperidone, a specific dopamine D2 receptor antagonist from September 12 to anestrus or January 15, either daily (n = 8), or once per day for the first 7 days of each month (n = 7). Controls (n = 7) received no treatment. Mean progesterone and prolactin concentrations were compared with summer cycles. Time to entry into anestrus and incidence of spontaneously prolonged luteal activity was compared between groups during the autumn transition. Prolactin declined from June through October equally in all groups. There was no difference between groups in time to anestrus. Progesterone decline was prevented (daily treatment) or delayed for a prolonged period (weekly group) in autumn. The incidence of spontaneously prolonged corpus luteum activity was reduced to summer levels in both domperidone groups compared with the control. We concluded that autumn prolactin decline was not driven through dopaminergic D2 receptor inhibition of pituitary lactotrophs. Sustained progesterone synthesis through the autumn may be the result of action of the D2 receptor antagonist with dopamine receptors on the corpus luteum. Autumnal luteolytic function appears to have a dopamine-influenced component. There does not appear to be a causative relationship between autumnal progesterone and prolactin secretion.     

Lack of natural luteolysis associated with uterine horn aplasia in a heifer

A heifer with congenital left uterine horn aplasia had completely normal reproductive cycles when ovulation occurred from the right ovary. Subsequent to ovulation from the left ovary, however, the corpus luteum persisted for months unless prostaglandin F2 alpha was administered. The reproductive tract was examined after slaughter. The left oviduct ended blindly, resulting in fluid-filled cysts. Except for aplasia of the left uterine horn, the reproductive tract appeared to be morphologically normal. This natural model confirms that the luteolytic signal in cattle is sent from the uterine horn to the ipsilateral ovary, but not to the contralateral ovary. Diagnosis of this abnormality required careful palpation per rectum. The normal luteolysis that occurred with exogenous prostaglandin F2 alpha treatment provided misleading information that the heifer was normal.     

Morphological study of the corpus luteum in the rat

The cyclic related growth and regression of the corpus luteum during four consecutive oestrous cycles of the regular four-day-cycling (ie, 16 days), virgin albino Wistar rat were followed up by light and electron microscopic investigation of the ovaries. After ovulation, follicular granulosa cells differentiated into luteal cells in the newly formed corpus luteum. Based on their specific histological characteristics, four various types of corpus luteum in each stage of the oestrous cycle could be identified. As soon as the luteal cells started to degenerate, the number of fibroblasts progressively increased and apoptotic degeneration of luteal cells was initiated and became most prominent during oestrus. Complete regression of the corpus luteum was seen after 15 days. This study shows a strictly organised pattern of luteal cell growth and degeneration in the corpus luteum of the regular four-day-cycling, virgin Wistar rat. The morphological alterations may be regulated by a hormonal fluctuation.     

Induction of ovulation in proestrous ewes: Identification of the ovulatory follicle and functional status of the corpus luteum

Ewes were treated with a luteolytic agent on Day 14 of the estrous cycle. Their largest follicle was identified 30 hr later. Thirty-six hr post-treatment, ewes received an injection of an analog of luteinizing hormone-releasing hormone (LHRHa). The peak in the induced surge of LH occurred 2 to 4 hr after injection of LHRHa. Ovulation occurred from the largest follicle approximately 24 hr following administration of LHRHa. During the subsequent luteal phase, serum concentrations of progesterone were normal. The treatment regimen described is well-suited for collection of follicles at precisely-timed periovulatory intervals. Perhaps information gained by using this model will be useful in ultimately understanding the follicular events associated with ovulation and function of the corpus luteum.     

Use of synchronized heifer-recipients in view of the effectiveness of embryo transfer in cattle

A possibility was investigated of using heifers prepared for embryo reception by i. m. double application of Oestrophan (Spofa) luteolytic preparation. After a clinical examination of ovaries and corpus luteum, out of the total number of 2894 animals synchronized for nonsurgical ipsilateral transfer in the D7 stage only 2038 (70.4%) recipients were used. Almost 30% (856) heifers were discarded from the role of recipients, mostly due to the functional disorders of the cyclic activity of ovaries manifesting themselves as luteal cysts (22.5%), cysts of corpus luteum (16.5%), small or young corpora lutea (12.7%), postovulation states (4.5%), and also as a high frequency of the follicular activity without the presence of corpus luteum (37.9%). The occurrence of follicular cysts (1.4%) and nonfunctional ovaries (2.8%) was considerably lower. The high number of discarded recipients which results, in the complex of causes, from qualitative nutritional disorders, husbandry and zoo-hygienic shortcomings and stress-inducing factors in the course of recipient selection and preparation, diminishes the transfer efficiency and considerably increases the claims for the numbers of recipient prepared for ovulation. In the conditions of our workplace where 10.6 to 12.8 transferable embryos are recorded from one successful superovulation and their survival is 65 to 68.6%, it will be necessary, at the present level of recipient discarding, to prepare 13.8 to 16.6 heifers per donor to make full use of the superovulation effect.     

Fate of conceptus and corpus luteum after induced embryonic loss in heifers

Ultrasonography was performed to determine the fate of the conceptus and the corpus luteum after induced embryonic loss in heifers. When embryonic loss was induced by administration of prostaglandin F2 alpha (25 mg, IM) on day 28 (n = 10) or day 42 (n = 10), embryonic death occurred 2.3 +/- 0.2 (mean +/- SEM) and 2.6 +/- 0.2 days, respectively, after treatment, and subsequent ovulation occurred 2.4 +/- 0.3 and 2.7 +/- 0.2 days, respectively, after embryonic death. Administration of a mitotic inhibitor (1 mg of colchicine, intrauterine; n = 4) on day 42 resulted in embryonic death in 1.2 +/- 0.2 days and ovulation in 20.8 +/- 3.1 days after embryonic death. Rupture of the amnion on day 42 (n = 3) resulted in immediate death of the embryo and ovulation in 35 +/- 3.5 days. In prostaglandin-treated heifers, area of the corpus luteum decreased (P less than 0.01) between days -2 and -1, relative to day of embryonic death. Volume of uterine contents remained approximately constant for 2 or 3 days after treatment, then decreased greater than 75% between examinations on consecutive days. Embryonic death apparently resulted from luteolysis and was characterized by rapid loss of the conceptus with minimal conceptus degeneration; an intact conceptus was recovered from the vagina of 3 heifers treated on day 42. In heifers treated with colchicine or in which the amnion was ruptured, embryonic death was associated with maintenance of the corpus luteum and prolonged retention of the conceptus, which underwent extensive degeneration.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of homogenized embryos on IUD-induced luteal regression in the ewe

The effect of homogenized embryos on IUD-induced luteal regression in the ewe was studied. Plastic spiral IUDs were inserted in an uterine horn adjacent to an ovary containing a corpus luteum during various times of the estrous cycle. The ewes were sacrificed on Day 6 for examination of the corpus luteum. Estrous Cycle Day 3 was the last day in which the IUD insertion induced luteal regression. Corpus luteum was maintained in ewes when the IUD was inserted on Day 4, 5, or 6. Corpus luteum regression was not prevented when homogenized 14- or 15-day-old embryos were injected into the uterus at the time of IUD insertion. Ewes which received an IUD, a cannula, and an infusion of saline or homogenized embryos on Days 3, 4, and 5 maintained corpora lutea in 4 of 7 embryo-infused ewes and in none of 7 saline-infused ewes (p less than .05). It was determined that the IUD must remain in the uterine horn for longer than 1 day to induce corpus luteum regression and that embryos can sometimes prevent the IUD-induced regression.     

绵羊妊娠识别、建立和维持的信号系统

妊娠的建立和维持归因于胚体的信号和黄体对孕酮的产生,在反刍动物,胚体滋养层分泌的激素抑制子宫内膜产生前列腺素PGF2α。在发情周期的绵羊,孕酮下调子宫内膜腔上皮和子宫腺上皮孕酮受体基因的表达,并伴随着上皮雌激素受体和催产素受体的增加。在催产素的作用下,子宫开始分泌溶黄体作用的前列腺素F2α。在妊娠绵羊,孕体滋养层产生的干扰素可作用于子宫内膜而直接抑制雌激素受体基因和催产素受体基因的转录。孕酮、干扰素、胎盘催乳素和生殖激素共同组成了一个"作用网络"来调节子宫的功能分化和子宫腺的形态发生,从而维持绵羊妊娠。本文综述了绵羊妊娠识别、建立和维持的信号系统。     

排卵延迟奶牛发情后不同阶段B超黄体相关指标变化规律分析

为研究排卵延迟奶牛发情配种后黄体的变化规律及其差异性,本研究在临床症状观察、直肠检查和B超辅助检查诊断的基础上,选取8头排卵延迟奶牛(排卵延迟组)、5头健康正常发情奶牛(对照组),应用B超对黄体的相关指标(直径、面积、周长和体积)进行了测量及分析,对获得的不同阶段典型黄体声像图进行了描述。结果显示,与对照组相比,排卵延迟组与对照组奶牛黄体的直径、面积、周长和体积在发情配种后7~15 d差异均不显著(P>0.05)。在发情配种后第9和13天排卵延迟组奶牛黄体相关指标(直径、体积、面积和周长)大于对照组奶牛,而在第11天小于对照组奶牛。结果表明,排卵延迟奶牛发情后不同阶段B超黄体直径、面积、周长和体积与正常发情排卵后的相应指标没有显著差别。     

哺乳动物发情周期黄体的组织学研究进展

黄体是排卵后形成的暂时性的内分泌组织 ,在一个较短的存在期限中经历了一系列的结构变化和分泌阶段 ,对于哺乳动物维持正常的生殖功能具有重要作用。人们对黄体细胞的来源、组成、形态及大小持有不同的观点。近年来 ,人们就黄体细胞的功能和退化、溶解进行了较为深入的研究 ,发现不同动物黄体细胞的功能各有不同 ,黄体退化、溶解与细胞凋亡有密切关系。了解哺乳动物发情周期黄体的组织结构对于控制动物的繁殖具有重要意义。文章对哺乳动物发情周期黄体中不同类型黄体细胞的来源、组成、形态、功能及退化、溶解 ,黄体细胞的分泌方式和超声波在黄体研究中的运用作了概述     

Analysis of B-ultrasound Luteal Variation Related Indicators of Delayed Ovulation Dairy Cows after Estrus at Different Stages

The study was aimed to observe the variation and differences of corpus luteum of delayed ovulation cows after estrus.Based on the observation of clinical symptoms, rectal examination and diagnosis of B-ultrasound scanning, 8 delayed ovulation dairy cows with the variation (delayed ovulation group) and 5 healthy and normal dairy cows with estrus (control group) were selected, and the related indicators of the corpus luteum (diameter, area, perimeter and volume) were measured by B-ultrasound scanning.These luteal indicators were compared and analyzed further, and the luteal typical sonography obtained of the different stages were described.The results showed that the diameter, area, perimeter and volume during 7 to 15 d after estrus of the corpus luteum had no significant differences between delayed ovulation group and control group (P>0.05).However, on the 9th and 13th day after estrus, the luteal relevant indicators of delayed ovulation group cows (diameter, volume, area and perimeter) were greater than that of control group cows and less than normal dairy cows on the 11th day.There were no significant differences in diameter, area, circumference and volume of corpus luteum at the different stages after estrus between the delayed ovulation dairy cows and the normal ones.     

Luteotropic influence of the ovine uterus.

Preliminary observations indicated that the ovine uterus might play a contributing role in the development of the corpus luteum. In order to better define this putative relationship, we monitored luteal function in mature ewes that were hysterectomized or sham-operated at different intervals following induction of ovulation. Corpora lutea formed following hysterectomy carried out immediately after ovulation were subnormal. Circulatory concentrations of progesterone in these animals began to ascend normally, but then achieved a plateau level less than that of control animals. This was attributed to reduced size of the luteal gland, and not to anomalies per unit tissue in morphology or content of progesterone. Luteal activity was not altered in ewes hysterectomized later in the estrous cycle (Day 5). However, when such a luteal phase was terminated by exogenous luteolysin, corpora lutea formed subsequently were defective. It appears that the ovine uterus produces a hormonal factor during metestrus that augments the growth potential of the corpus luteum.     

Ovarian, uterine and embryo dynamics in horses versus ponies

Characteristics of the internal genitalia were compared between horses and ponies contemporaneously in a single study by asingle operator. Diameter of the preovulatory follicle for 10 days before ovulation (Day 0) and cross-sectional area of the corpus luteum for 10 days after ovulation were measured in 12 horses and 12 ponies. Follicle growth rate and maximum diameter attained during growth and luteal tissue area were not different between mare types. However, ultrasonic echogenicity of luteal tissue was less on Day 0 (P<0.09) and Day 1 (P<0.01) in ponies than in horses, suggesting that under field conditions mare type should be considered when using the extent of luteal gland echogenicity for estimating the number of days postovulation and luteal function. Circulating concentrations of progesterone averaged over Days 3 to 10 were greater in ponies (10.3 ng/ml) than in horses (8.7 ng/ml) as suggested by a tendency (P<0.1) towards a type-by-day interaction.Luteal, uterine and embryonic characteristics during Days 0 to 40 of pregnancy were compared between 7 horses and 9 ponies. Luteal tissue area of the primary corpus luteum was not different between mare types during Days 0 to 30 and during luteal resurgence after Day 30. The interaction between mare type and day was significant for circulating progesterone concentrations; the interaction seemed to result primarily from higher progesterone levels in ponies during Days 6 to 12 and Days 34 to 40. Progesterone concentrations were about 25% higher in ponies on the approximate days that levels were at their highest in the two types of mares. These results indicate, a need for further studies on the effect of mare size or type on circulating concentrations of progesterone, and the consideration of size or type in clinically evaluating progesterone levels in pregnant mares. Apparent partial recovery of the corpus luteum of the previous estrous cycle occurred during early pregnancy in one pony.Increasing diameter of the embryonic vesicle and the extent of uterine tone were similar between horses and ponies. Although diameter of the uterine horns decreased in parallel for the two mare types during Days 0 to 40, the diameter was significantly less (2.2 mm difference averaged over all days) for ponies than horses. The temporal relationship between an expanding embryonic vesicle concurrently with decreasing uterine horn size and enhanced uterine turgidity is compatible with the postulated mechanism of embryo fixation. The smaller uterus in ponies with no difference in size of the conceptus between mare types could account for earlier fixation of the embryonic vesicle in ponies than in horses.     

Beta-carotene uptake and changes in ovarian steroids and uterine proteins during the estrous cycle in the canine

The uptake of beta-carotene by reproductive tissues and the effects of beta-carotene on reproductive function in the dog are unknown. We studied the uptake of beta-carotene by blood, corpus luteum, and uterine endometrium and the role of dietary beta-carotene in influencing ovarian steroid and uterine protein production during the estrous cycle in the dog. Mature female Beagle dogs (n = 56) were fed diets containing 0, 2, 20, or 50 mg of beta-carotene daily for approximately 6 wk before estrus detection. Blood was sampled at regular intervals from estrus through d 45 after ovulation (d 0 = ovulation), when laparotomy was performed. The ovaries were obtained for the isolation of corpus luteum. The uterus was flushed with phosphate-buffered saline and the endometrium obtained by scraping. Beta-carotene was not detectable in plasma, corpus luteum, or endometrium of unsupplemented dogs. However, beta-carotene and alpha-carotene in plasma, corpus luteum, and uterine endometrium increased in a dose-dependent manner. Alpha-carotene made up a high percentage of total carotenoids even though the alpha-carotene content in the dietary source was very low. Dogs fed 50 mg of beta-carotene had significantly higher concentrations of plasma progesterone between d 12 and 26 compared with unsupplemented dogs. Dietary beta-carotene did not influence plasma estradiol-17beta and total uterine proteins. Therefore, beta-carotene is absorbed into plasma, corpus luteum, and uterine endometrium of dogs. Furthermore, dietary beta-carotene increased plasma progesterone concentrations during the estrous cycle. It is possible that dietary beta-carotene may improve reproductive function in the canine.     

Pituitary Hormone Responses to Luteal Regression after Administration of Prostaglandin F2α-Analogue

As an experiment to elucidate the canine luteal function maintenance system, a PGF2alpha-analogue, fenprostalene (PGF-F), was administered 24 and 54 days after ovulation to induce luteal regression, and the responses of luteinizing hormone (LH) and prolactin (PRL), which are considered to support the canine corpus luteum, were investigated. The plasma progesterone (P(4)) level was rapidly decreased, by which the plasma PRL level was increased, but no change was observed in the plasma LH level. The decrease in the plasma P(4) level after PGF-F administration may have induced positive feedback to the superior system, and stimulated secretion of the pituitary hormones. These findings suggested that the canine corpus luteum is maintained by PRL, not by LH.     

Species-related differences in the mechanism of apoptosis during structural luteolysis

Luteolysis is defined as the loss of function and subsequent involution of the luteal structure. The luteolytic process is usually subdivided, whereby the decline in progesterone is described as functional luteolysis and the structural involution is described as structural luteolysis. After the corpus luteum ceases to produce progesterone, it decreases in size, experiences a loss of cellular integrity, and then disappears from the ovary as a result of apoptosis of luteal cells. However, the control mechanisms responsible for initiating and mediating apoptosis during structural luteolysis seem more complex than originally envisioned. Furthermore, efforts to elucidate the apoptotic mechanisms have been complicated by the fact that different mammalian species have different mechanisms for controlling luteal function. Therefore, it is of interest to know whether different mammalian species have different apoptotic mechanisms. The goal of this review was to focus on species-related differences in the mechanism of apoptosis during structural luteolysis in rodents, cattle and humans, the species that are used most for luteolysis research.     

Ultrasonic evaluation of the reproductive tract of the mare: Ovaries

Ultrasonography is useful for monitoring the dynamic follicular and luteal changes of equine ovaries, since it permits rapid, visual, non-invasive access to the reproductive tract. A 5 MHz transducer has greater resolving power and is far more suitable for evaluation of ovaries than a 3–3.5 MHz transducer. Follicles as small as 2–3 mm can be seen and the corpus luteum can usually be identified throughout its functional life. In a study involving daily ovarian examinations, there was a pronounced change in shape of the preovulatory follicle from a roughly spherical to a pear-shaped or oblong form in 66% of the ovulatory periods, This change usually occurred on the day preceding ovulation. The occurrence of ovulation was detectable by the disappearance of a large follicle. In addition, the ovulation site on day 0 was characterized by an intense echogenic area in 88% of 32 ovulations. The developing corpus luteum retained the echogenicity for a mean of 2.4 days. In a blind study, the location of the corpus luteum, as determined by ultrasound, agreed with a previous independent determination of the side of ovulation by palpation in 88% of the 40 bred mares on days 0–14. In all of the 12 mares that were in estrus, the location of the corpus luteum could not be ascertained. In another study, the corpus luteum was identified for a mean of 16 days in 14 estrous cycles. One or more days before the corpus luteum became ultrasonically unidentifiable, it developed increased echogenicity in 36% of the mares, indicating greater tissue density. It is concluded that ultrasonic evaluation of the corpus luteum is superior to digital evaluation by rectal palpation. Some of the potential applications of ultrasonic examination of the ovaries include: 1) obtaining important, sometimes definitive, information by a single examination for judging whether a mare has entered the ovulatory season, 2) aiding in estimating the stage of the estrous cycle, 3) detecting double preovulatory-sized follicles which are in close apposition and difficult to discern by palpation, 4) detecting failure of ovulation or anovulatory estrus by the absence of a corpus luteum, 5) differentiating a persistent corpus luteum from anovulatory or anestrous conditions, 6) diagnosing certain pathological conditions such as peri-ovarian cysts and ovarian tumors, and 7) diagnosing anovulatory hemorrhagic follicles.     

Hormonal control of the bovine oestrous cycle

The role of hormones in controlling the estrous cycle of cows is reviewed in the context of current research, specifically on endocrinal functions. This is central as the follicles grow on the ovaries in response to the pituitary's follicular stimulating hormone. When the ovaries produce sufficient estrogens, an ovulatory surge of luteinizing hormone is released by the pituitary. This causes the ovulation of 1 of the follicles and the growth of a corpus luteum in the follicular cavity. This corpus luteum secretes progesterone for about 2 weeks until its activity is terminated by uterine luteolysin. Control of the estrous cycle thus depends on alternate signals from the pituitary and ovaries with the end of the cycle caused by the nonpregnant uterus.     

Regulation of Luteal Function and Corpus Luteum Regression in Cows: Hormonal Control, Immune Mechanisms and Intercellular Communication

The main function of the corpus luteum (CL) is production of progesterone (P4). Adequate luteal function to secrete P4 is crucial for determining the physiological duration of the oestrous cycle and for achieving a successful pregnancy. The bovine CL grows very fast and regresses within a few days at luteolysis. Mechanisms controlling development and secretory function of the bovine CL may involve many factors that are produced both within and outside the CL. Some of these regulators seem to be prostaglandins (PGs), oxytocin, growth and adrenergic factors. Moreover, there is evidence that P4 acts within the CL as an autocrine or paracrine regulator. Each of these factors may act on the CL independently or may modify the actions of others. Although uterine PGF_2α is known to be a principal luteolytic factor, its direct action on the CL is mediated by local factors: cytokines, endothelin-1, nitric oxide. The changes in ovarian blood flow have also been suggested to have some role in regulation of CL development, maintenance and regression.