Ultrasonographic study of ovarian function during early pregnancy and after parturition in the ewe

Transrectal ultrasonography of ovaries was performed in 11 ewes from Days 10 to 26 and on Day 30 of pregnancy to record the number, size, and position of ovarian follicles > or = 3 mm in diameter and corpora lutea (CL). Transrectal and/or transabdominal ultrasonography of the uterus was performed on Days 10 to 26, 30, 35, 40, 45 and 50 of gestation to ascertain the number and position of the conceptuses. In a second experiment, ultrasonography was conducted in 15 ewes on Days 10, 25, 30, 45 and 50 of pregnancy and from Days 13 to 29 after parturition. Ovarian data were classified into ovaries without CL (Group 1), ovaries with the CL in 1 ovary (Group 2), and ovaries with the CL in both ovaries during pregnancy (Group 3). In early pregnant ewes, the total number of follicles and the diameter of all follicles > or = 3 mm were smaller (P < 0.05) in the CL-bearing ovaries (both Group 2, n = 7 and Group 3, n = 8) than in the non-CL-bearing ovaries (Group 1, n = 7), while the largest follicle diameter was significantly smaller in Group 3 than in Group 1 or 2 ovaries. The number of 3-mm follicles in Group 2 ovaries was lower (P < 0.05) than in Group 1 or 3 ovaries, but the mean number of follicles > or = 5 mm in diameter was significantly lower in Group 3 than in Group 1. The total luteal volume per ovary was higher (P < 0.001) in Group 2 than in Group 3 ovaries of early pregnant ewes. The total follicle diameter and the number of follicles growing from 3 to > or = 5 mm in diameter was lower (P < 0.05) for Group 2 ovaries of ewes that carried twins (n = 3) compared with Group 2 ovaries from ewes with singletons (n = 4). There were no differences in follicular dynamics between Group 3 ovaries and the ovaries of Group 2 in ewes that carried twins. No follicles > 3 mm were seen in the ovaries of postpartum ewes that contained CL during gestation, until Days 21 and 25 postpartum for Groups 2 (n = 10) and 3 (n = 8), respectively, and follicles reaching > or = 5 mm in diameter were detected in only 2 ovaries (Group 2), on Days 27 and 28 postpartum, respectively. We conclude that during early pregnancy in ewes there is a suppression of antral follicle growth which appears to be exerted primarily by the developing conceptus but remains confined to CL-bearing ovaries. Residual local inhibition of follicular development extends into the postpartum period.     

Ultrasonographic imaging of the reproductive tract and surgical recovery of oocytes in Cebus apella (capuchin monkeys)

Two-dimensional real-time and Doppler ultrasonography are valuable non-invasive methods to assess reproductive anatomy and physiology. In adult, postpubertal female Cebus apella (capuchin monkeys), the objectives were to determine (1) uterine and ovarian dimensions, ovarian follicular dynamics, day of ovulation, and arterial blood flow of uterus and utero-ovarian ligament during the follicular phase of the menstrual cycle and (2) the number of oocytes aspirated from antral follicles at laparotomy. Based on two-dimensional, transabdominal B-mode ultrasonography, mean (+/- S.E.M.) length, height, width, and volume of the uterus were 17.9+/-0.4, 12.4+/-0.3, 13.6+/-0.3 mm, and 1.55+/-0.08 mL, respectively, and of the ovary were 13.4+/-0.2, 8.2+/-0.1, 7.7+/-0.1 mm, and 4.5+/-0.2 mL. Ovarian follicles were monitored for 6 days before ovulation, which occurred on day 9.3+/-0.5 (range, days 7-11; day 1=start of menses), with 10 of 12 ovulations in the right ovary. Diameter and volume of the preovulatory follicle were 10.1+/-0.2 mm and 0.55+/-0.03 mL (on the estimated day of ovulation) and of the CL were 8.1+/-0.4 mm and 0.3+/-0.05 mL. Resistivity and pulsatility indices were 0.86+/-0.02 and 2.15+/-0.11 for uterine arteries, and were 0.69+/-0.04 and 1.63+/-0.15 for the utero-ovarian ligament (UOL) artery; just prior to ovulation, both indices peaked (P<0.05) in the uterine artery ipsilateral to the side of ovulation, but both reached a nadir (P<0.05) in the UOL artery. In the absence of ovarian stimulation, 31 oocytes (diameter, 137+/-10 microm) were aspirated (average of 2 oocytes/(female attempt)) on days 5, 7, and 9. In conclusion, transabdominal ultrasonography facilitated assessment of reproductive anatomy and physiology in C. apella adult females. Resistance and pulsatility indices of uterine and UOL arteries changed near the time of ovulation. Dominant follicles were easiest to aspirate at 8-9 mm in diameter ( approximately day 9), with intact cumulus-oocyte complexes recovered from ovarian follicles 2-9 mm in diameter.     

Expression of prostasin serine protease and protease nexin-1 (PN-1) in rhesus monkey ovary during menstrual cycle and early pregnancy.

Serine proteases and their cognate serpin-class inhibitors are involved in the controlled proteolytic events during follicular development, ovulation, formation, and maintenance of the corpus luteum (CL). In this study, we investigated the expression patterns of prostasin serine protease and protease nexin-1 (PN-1), a serine protease inhibitor also called serpin-E2, in rhesus monkey ovaries during the menstrual cycle and early pregnancy, by using in situ hybridization and immunohistochemistry. Expression of prostasin was localized in oocyte, granulosa cells, and/or theca cells of early antral follicles and antral follicles, with high levels observed in preovulatory follicles. Prostasin was also localized at high levels of abundance in the CL during the menstrual cycle and early pregnancy. During the menstrual cycle, PN-1 was coordinately localized with prostasin in oocytes, granulosa cells, and theca cells of antral follicles and preovulatory follicles and in the CL. In addition, the PN-1 expression level in macaque CL during early pregnancy increased as pregnancy proceeded. We propose that prostasin may be involved in follicular development, ovulation, and CL formation, whereas PN-1 may be present to regulate the proteolysis in these processes.     

Antral follicle count reliably predicts number of morphologically healthy oocytes and follicles in ovaries of young adult cattle

Methods to predict numbers of healthy oocytes in the ovaries of young adults could have important diagnostic relevance in family planning and animal agriculture. We have observed that peak antral follicle count (AFC) determined by serial ovarian ultrasonography during follicular waves is very highly reproducible within individual young adult cattle, despite 7-fold variation among animals. Herein, we tested the hypothesis that AFC is positively associated with the number of morphologically healthy oocytes and follicles in ovaries and with serum concentrations of anti-Müllerian hormone (AMH), an indirect marker for number of healthy follicles and oocytes in ovaries. In the present study, age-matched young adult cattle (12-18 mo old) were subjected to serial ultrasonography to identify animals with a consistently high (> or =25 follicles that were > or =3 mm in diameter) or low (< or =15 follicles) AFC during follicular waves. Differences in serum AMH concentrations, ovary weight, and number of morphologically healthy and atretic follicles and oocytes were determined. The phenotypic classifications of cattle based on AFC during follicular waves or AMH concentrations both predict reliably the relative number of morphologically healthy follicles and oocytes in ovaries of age-matched young adult cattle.     

Evaluation of ultrasonography for monitoring follicular growth in rhesus monkeys

The purpose of this study was to determine if the ovaries and uterus of rhesus monkeys could be visualized by ultrasonography and to detect changes associated with follicular growth and ovulation. Animals were examined during 15 menstrual cycles, for an average of nine consecutive days. Ultrasonic recordings were correlated with hormonal parameters (estradiol 17beta, E(2); luteinizing hormone, LH; and progesterone, P) and laparoscopic findings. The uterus and both ovaries were observed in more than 90% of the examinations. A dominant follicle (DF) was identified during all ovulatory cycles, on average 1 d preceding the E(2) peak. The maximal diameter of the DF ranged from 3 to 7 mm. Laparoscopic examinations to determine the site of the DF confirmed ultrasonic findings in 10 of 14 cycles (P < 0.1). There was no significant difference in the size of the dominant and contralateral ovaries; however, more follicles with a diameter of 2 to 7 mm were found on the dominant ovary (P < 0.05). Two animals stimulated with exogenous gonadotropins showed a linear increase in ovarian size for 6 d prior to oocyte recovery (P < 0.05), reflecting an increase in the number of developing follicles. Ultrasonography can be used to identify the DF during spontaneous cycles in rhesus monkeys and to monitor the response of monkeys to exogenous gonadotropins.     

Characterization of ovarian follicular wave dynamics in women

A wave phenomenon of ovarian follicular development in women has recently been documented in our laboratory. The objective of the present study was to characterize follicular waves to determine whether women exhibit major and minor wave patterns of follicle development during the interovulatory interval (IOI). The ovaries of 50 women with clinically normal menstrual cycles were examined daily using transvaginal ultrasonography for one IOI. Profiles of the diameters of all follicles >or=4 mm and the numbers of follicles >or=5 mm were graphed during the IOI. Major waves were defined as those in which one follicle grew to >or=10 mm and exceeded all other follicles by >or=2 mm. Minor waves were defined as those in which follicles developed to a diameter of <10 mm and follicle dominance was not manifest. Blood samples were drawn to measure serum concentrations of estradiol-17beta, LH, and FSH. Women exhibited major and minor patterns of follicular wave dynamics during the IOI. Of the 50 women evaluated, 29/34 women with two follicle waves (85.3%) exhibited a minor-major wave pattern of follicle development and 5 women (14.7%) exhibited a major-major wave pattern. Ten of the 16 women with three follicle waves (62.5%) exhibited a minor-minor-major wave pattern, 3 women (18.8%) exhibited a minor-major-major wave pattern, and 3 women (18.8%) exhibited a major-major-major wave pattern. Documentation of major and minor follicular waves during the menstrual cycle challenges the traditional theory that a single cohort of antral follicles grows only during the follicular phase of the menstrual cycle.     

Ovarian follicular dynamics in the llama

Ovarian follicular dynamics were determined in adult llamas by ultrasonography and palpation per rectum and hormone analysis (estradiol-17 beta and estrogen conjugates) of plasma and urine. The relationship of gonadotropin secretion to follicular development was determined by the analysis of plasma FSH and LH concentrations. Progesterone analysis of plasma was used to verify or deny the presence of CL. Final follicular development (from 3 mm) averaged 4.8 days, while the duration of the mature follicle (8-12 mm) averaged 5.0 days; regression of the follicle occurred over about 4 days. The development of a subsequent dominant follicle usually began within 2-3 days after onset of regression of the dominant follicle. While several follicles were present at the time of the demise of the dominant follicle, only one follicle continued to develop. The interval between ovarian follicle waves averaged 11.1 days. Dominant follicle activity alternated between ovaries in 81% of the cycles. The occurrence of dominant follicles was evenly distributed between ovaries. While plasma estradiol and estrogen conjugate concentrations were positively associated (p less than 0.05) with follicular activity, urinary estrogen conjugate concentrations best reflected ovarian follicular dynamics (p less than 0.001). Daily FSH concentrations in plasma were not correlated with follicular activity. LH concentrations in plasma were low in all animals throughout the study, indicating estrogen from developing ovarian follicles does not induce the release of LH. Progesterone values were low during the study, indicating that the llama does not spontaneously ovulate, at least under the conditions of this study. In summary, llamas have overlapping ovarian follicle waves that occur at about 11-day intervals.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ultrasonographic study of the effects of the corpus luteum on antral follicular development in unilaterally ovulating western white-faced ewes

The objective of this study was to examine the local effects of the corpus luteum (CL) on ovarian antral follicle development by looking at follicle populations and dynamics in ovaries with or without CL, in unilaterally ovulating ewes, using a retrospective analysis of daily ultrasonographic records. The present report summarises the data from the first luteal phase of the breeding season (August-October; n = 4), a luteal phase in the mid-breeding season (November-December; n = 5), the last luteal phase of the breeding season (January-March; n = 5), and the luteal phase after GnRH-induced ovulations in mid-anoestrus (May-June; n = 4) of western white-faced ewes. Mean daily numbers of 3mm follicles that did not grow any larger were significantly reduced in the CL-containing ovaries of ewes at all periods of study except for the transition to anoestrus. With all scanning periods combined, daily numbers of 3mm follicles not growing further increased (P<0.05) between day 6 and 15 after ovulation in the CL-containing ovaries. Based on mean data for the whole periods of observation, the non-CL-bearing ovaries of ewes in the transition to anoestrus had fewer (P<0.05) follicles growing from 3 to > or =5mm in size before regression compared with the mid-breeding season and mid-anoestrus. The lifespan of follicles reaching > or =5mm in diameter was shorter (P < 0.05) in the CL- compared with non-CL-containing ovaries of anoestrous ewes induced to ovulate with GnRH ((6.5+/- 1.3) and (9.0+/- 1.0) days, respectively). Circulating concentrations of progesterone were lower during both transitional periods (into and out of anoestrus) and mid-anoestrus than during the mid-breeding season (P < 0.001), and were less during anoestrus than during both transitional periods (P < 0.05). It was concluded that CL/luteal structures locally suppressed the growth of ovarian antral follicles to the 3mm size-range except during the transition to anoestrus, but that there was no inhibitory effect of the CL on the growth of ovarian follicles to larger diameters. The presence of CL/luteal structures did not affect the length of the lifespan of follicles reaching > or =5mm in diameter nor the number of ovulations per ovary in cyclic ewes, but shortened large follicle lifespan in anoestrous ewes. Variations in peripheral concentrations of progesterone across the breeding season and between the breeding season and anoestrus did not alter the lifespan of large antral follicles. In the transition to anoestrus and during mid-anoestrus, the presence of the CL in an ovary appeared to maintain follicle development to ovulatory sizes and to increase the rate of turnover of large antral follicles, respectively.     

Localization of an activin/activin receptor system in the porcine ovary.

The aim of this study was to locate a possible activin/activin receptor system within porcine ovaries containing functional corpora lutea. In situ hybridization was used to assess the gene expression of beta(A)- and beta(B)-activin subunits, and immunohistochemical studies were done to detect activin-A protein and activin receptor type II. mRNA expression of the beta(A)- and beta(B)-activin subunits was found in the granulosa from the unilaminar follicle stage onward, in the developing thecal layer of multilaminar and small antral follicles, in the theca interna of mid-sized antral follicles, in corpora lutea, and in the ovarian surface epithelium. Immunoreactive activin A protein could be detected at the same ovarian sites, but in thecal tissue of small antral follicles only. This protein was also demonstrated at the peripheral zone of oocytes from multilaminar and antral follicles. A positive immunoreaction for activin receptor was found in granulosa cells from multilaminar and older follicles and in oocytes from the earliest stages of follicular development onward. In late multilaminar follicles and in antral follicles, the oolemma was stained. Except for small antral follicles, a positive activin receptor immunoreaction was absent in the follicular theca. Activin receptor immunoreaction was furthermore present in corpora lutea and in the ovarian surface epithelium. It is concluded that, within porcine ovaries containing functional corpora lutea, an activin/activin receptor system is present in all intact follicles, the corpora lutea and the surface epithelium. Within follicles, granulosa and theca cells are the main sites of activin synthesis, while oocytes and granulosa cells are the main activin binding sites.     

The temporal relationship between patterns of LH and FSH secretion, and development of ovulatory-sized follicles during the mid- to late-luteal phase of sheep

The aim of the present study was to investigate the temporal relationship between the secretory pattern of serum LH and FSH concentrations and waves of ovarian antral follicles during the luteal phase of the estrous cycle in sheep. The growth pattern of ovarian antral follicles and CL were monitored by transrectal ultrasonography and gonadotropin concentrations were measured in blood samples collected every 12 min for 6 h/d from 7 to 14 d after ovulation. There were two follicular waves (penultimate and final waves of the cycle) emerging and growing during the period of intensive blood sampling. Mean and basal LH concentrations and LH pulse frequency increased (P < 0.001) with decreasing progesterone concentration at the end of the cycle. Mean and basal FSH concentrations reached a peak (P < 0.01) on the day of follicular wave emergence before declining to a nadir by 2 d after emergence. None of the parameters of pulsatile LH secretion varied significantly with either the emergence of the final follicular wave or with the end of the growth phase of the largest follicle of the penultimate wave of the cycle. However, mean and basal LH concentrations did increase (P < 0.05) after the end of the growth phase of the largest follicle of the final follicular wave of the cycle. Furthermore, the end of the growth phase of the largest follicle of the final wave coincided with functional luteolysis. In summary, there was no abrupt or short-term change in pulsatile LH secretion in association with the emergence or growth of the largest follicle of a wave. We concluded that the emergence and growth of ovarian antral follicles in follicular waves do not require changes in LH secretion, but may involve changes in sensitivity of ovarian follicles to serum LH concentrations.     

Transition to the ovulatory season in mares: An investigation of antral follicle receptor gene expression in vivo

The inability to obtain in vivo samples of antral follicle wall layers without removing the ovaries or sacrificing the animals has limited more in‐depth studies on folliculogenesis. In this study, a novel ultrasound‐guided follicle wall biopsy (FWB) technique was used to obtain in vivo follicle wall layers and follicular fluid samples of growing antral follicles. The expression of proliferative, hormonal, angiogenic, and pro‐/antiapoptotic receptors and proteins in the follicular wall among three follicle classes were compared during the spring transitional anovulatory (SAN) and spring ovulatory (SOV) seasons in mares. The main findings observed in the granulosa, theca interna, and/or all follicle layers during the SOV season compared with the SAN season were (a) small‐sized follicles (10–14 mm) had greater epidermal growth factor receptor (EGFR) and Bcl‐2 expression; (b) medium‐sized follicles during the expected deviation/selection diameter (20–24 mm) had greater expression of EGFR, Ki‐67, luteinizing hormone receptor (LHR), and Bcl‐2; and (c) dominant follicles (30–34 mm) had greater EGFR, Ki‐67, vascular endothelial growth factor, LHR, and Bcl‐2 expression. Estradiol related receptor alpha expression and intrafollicular estradiol concentration increased, along with an increase in follicle diameter in both seasons. In this study, the application of the FWB technique allowed a direct comparison of different receptors’ expression among follicles in different stages of development and between two seasons using the same individuals, without jeopardizing their ovarian function. The successful utilization of the FWB technique and the mare as an experimental animal offer a great combination for future folliculogenesis studies on mechanisms of follicle selection, development, and ovulation in different species, including women.     

Ovarian function in ewes at the onset of the breeding season

Transrectal ultrasonography of ovaries was performed each day, during the expected transition from anoestrus to the breeding season (mid-August to early October), in six Western white-faced cross-bred ewes, to record ovarian antral follicles > or = 3 mm in size and luteal structures. Jugular blood samples were collected daily for radioimmunoassay (RIA) of follicle-stimulating hormone (FSH), oestradiol and progesterone. The first ovulation of the breeding season was followed by the full-length oestrous cycle in all ewes studied. Prior to the ovulation, all ewes exhibited a distinct increase in circulating concentrations of progesterone, yet no corpora lutea (CL) were detected and luteinized unovulated follicles were detected in only three ewes. Secretion of FSH was not affected by the cessation of anoestrus and peaks of episodic FSH fluctuations were associated with the emergence of ovarian follicular waves (follicles growing from 3 to > or = 5 mm). During the 17 days prior to the first ovulation of the breeding season, there were no apparent changes in the pattern of emergence of follicular waves. Mean daily numbers of small antral follicles (not growing beyond 3 mm in diameter) declined (P < 0.05) after the first ovulation. The ovulation rate, maximal total and mean luteal volumes and maximal serum progesterone concentrations, but not mean diameters of ovulatory follicles, were ostensibly lower during the first oestrous cycle of the breeding season compared with the mid-breeding season of Western white-faced ewes. Oestradiol secretion by ovarian follicles appeared to be fully restored, compared with anoestrous ewes, but it was not synchronized with the growth of the largest antral follicles of waves until after the beginning of the first oestrous cycle. An increase in progesterone secretion preceding the first ovulation of the breeding season does not result, as previously suggested, from the ovulation of immature ovarian follicles and short-lived CL, but progesterone may be produced by luteinized unovulated follicles and/or interstitial tissue of unknown origin. This increase in serum concentrations of progesterone does not alter the pattern of follicular wave development, hence it seems to be important mainly for inducing oestrous behaviour, synchronizing it with the preovulatory surge of luteinizing hormone (LH), and preventing premature luteolysis during the ensuing luteal phase. Progesterone may also enhance ovarian follicular responsiveness to circulating gonadotropins through a local mechanism.     

Localization of androgen receptor in the follicle and corpus luteum of the primate ovary during the menstrual cycle

Ovarian androgens may act locally to modulate follicular and luteal function in various species. This study examined the distribution of androgen receptors within the primate ovary throughout the menstrual cycle. Ovaries were collected from rhesus and cynomolgus monkeys during the early, mid-, and late (n = 3-5 per stage) follicular and luteal phases of the cycle. The tissues were processed for indirect immunocytochemical localization of androgen receptors with a specific monoclonal antibody against human androgen receptor (AN1-15). In addition, ovaries (n = 3) were collected from rhesus monkeys for biochemical detection of androgen receptor using 3H-androgen and AN1-15. Specific immunocytochemical staining, as determined by comparing adjacent tissue sections incubated with either AN1-15 or a nonspecific control antibody, was exclusively nuclear. Androgen receptor was detected in the germinal epithelium and ovarian stroma at all stages of the cycle. The thecal and granulosa cells of growing follicles, and of many but not all atretic follicles, contained androgen receptors. Luteinizing granulosa cells of the periovulatory follicle and luteal cells from the early and midluteal phase stained intensely for androgen receptor. Regressing corpora lutea of the late luteal phase also stained for androgen receptor; however, fully regressed corpora lutea in the early follicular phase of the next cycle did not exhibit receptor staining. Luteal cells that were androgen receptor-positive also stained histochemically for the presence of 3 beta-hydroxysteroid dehydrogenase. Sucrose gradient analysis with radiolabeled androgen demonstrated a shift in the androgen receptor peak in monkey ovarian tissue upon addition of AN1-15, confirming the presence of androgen receptor.(ABSTRACT TRUNCATED AT 250 WORDS)     

Animal and temporal effects on ovarian follicular dynamics in Brahman heifers

The aims of the current study were to determine if the pattern of ovarian follicular growth and development in Bos indicus heifers is different to that reported in Bos taurus breeds, and to examine the factors that determine which dominant follicle will ovulate. In addition, the extent to which variation in follicular dynamics is attributable to variation between animals and over time was evaluated. The ovaries of 17 Brahman heifers were examined daily by transrectal ultrasonography using a 7.5 MHz transducer for a total of 117 interovulatory intervals over a period of 10 months. Size and position of individual follicles ⪖5 mm in diameter, and size of corpora lutea (CL) were recorded. Circulating progesterone concentrations were determined from plasma samples obtained twice weekly. Although size of dominant follicles and CL within the ovaries of Bos indicus heifers were smaller than reported for Bos taurus breeds, the overall patterns of dominant follicle growth were similar. There were significant correlations between number of dominant follicles occurring prior to ovulation and time of appearance of the second dominant follicle, duration of detection of CL and size of the ovulatory follicle in the preceding oestrous cycle (P < 0.05). There were significant animal effects on a number of ovarian characteristics including number of dominant follicles per oestrous cycle (P < 0.001), with one heifer having four dominant follicles in more than a third of oestrous cycles observed. In addition, changes in daylength over the 10 month period were related to changes in duration of the interovulatory interval, persistence and maximum diameter of CL and size of ovulatory follicles. Liveweight change over the same period was related to changes in maximum diameter of the first dominant follicle.     

Comparison of the total ovarian follicular populations at day 140 of pregnancy and at day 5 postpartum in ewes

The total ovarian follicular populations were determined in ewes at Day 140 of pregnancy and at Day 5 postpartum. The right and left ovaries of five pregnant and five non-suckling ewes of the Préalpes-du-Sud breed were used in this study. All the ovaries were serially sectioned at a thickness of 7 μm, and every section was examined microscopically.The mean numbers of preantral follicles per ovary increased (P<0.005) at Day 5 postapartum as compared to Day 140 of pregnancy. The distribution of preantral non-atretic follicles into different size classes clearly showed a sharp increase in the mean number of follicles per size class at Day 5 postpartum, especially those leaving the reserve of primordial follicles.No difference was detected between both groups of ewes in the mean number of antral follicles. The diameter of the largest antral follicle at Day 140 of pregnancy does not exceed 1.5 mm. However, at Day 5 postpartum, a population of large follicles ≥ 1.5 mm was observed, reaching 2–4 mm in diameter.We conclude that although the pattern of normal follicular development is inhibited during late pregnancy, the ovary at this time is not quiescent, and ovarian follicular development starts well before parturition. The increasing number of preantral follicles, as well as the enlargement of antral follicle diameter observed at Day 5 postpartum, may be correlated with increasing secretion of FSH after lambing.     

Antral follicle growth and endocrine changes in prepubertal cattle,sheep and goats

In the growing heifer calve, there is an early post-natal, gonadotrophin driven increase in ovarian antral follicle growth. The endocrine regulation of and reason for this initial stimulation of ovarian follicular development are not fully understood. This initial endocrine activity appears to be later held in check by negative feedback suppression mechanisms until the heifer is of a sufficient body size to initiate oestrous cycles and to reproduce. There is increasing evidence from recent ultrasonographic studies, performed in the same groups of prepubertal heifer calves, that the development of ovarian antral follicles and tubular genitalia occur in parallel. There appear to be two distinct periods of enhanced development of the reproductive organs, from 2 to 14 weeks of age and again from 34 to 60 weeks of age, or just prior to puberty. First ovulation in heifers is preceded by a gradual increase in pulsed LH secretion, which results in enhanced antral follicle development and oestrogen production. It was demonstrated that prepubertal heifers produced recurrent antral follicular waves; maximum sizes and life span of the dominant follicles of waves, as well as periodicity and FSH dependency of wave emergence were similar to those in adult cattle. In does, no Graafian follicles are seen at birth and total follicle numbers increase to 2 months of age, and then decline to 5 months of age. In ewe lambs, studies using transrectal ovarian ultrasonography showed that antral follicle recruitment and growth increased after the first 2 months of age and just before puberty. This bi-phasic pattern of changes in ovarian follicle recruitment and growth is strikingly similar to that in heifer calves, but it contrasts with earlier post-mortem examinations of ovaries in ewe lambs. Unlike in cattle and adult ewes, the rhythmic pattern of follicular wave emergence was not established in pre- and peripubertal ewe lambs. The early increase in antral follicle numbers and size in ewe lambs may be, at least in part, due to changes in FSH release and potency, and enhanced follicle production prior to first ovulation is probably caused by an increase in the frequency of LH pulses.     

Gene expression of endothelin-1 in the porcine ovary: follicular development

We have investigated which follicular compartment and stage of follicular development are associated with endothelin-1 (ET-1) gene expression in the porcine ovary. The localization of mature ET-1 peptide and of its mRNA was determined by immunohistochemistry and by in situ hybridization. Stage of follicular development associated with ET-1 expression was investigated in terms of follicular class and occurrence of atresia. The latter was investigated by determining the occurrence of DNA fragmentation in apoptotic cells on adjacent sections to those used for ET-1 gene expression. Fifteen ovaries from 10 prepubertal pigs stimulated with gonadotropin were collected; a total of 1050 follicles were examined. Specific ET-1 immunoreactivity was restricted to the ovarian vasculature and to the granulosa cell compartment of antral follicles. The pattern of ET-1 mRNA expression was similar to that found for ET-1 immunoreactivity. Primordial, primary, and most secondary follicles did not express ET-1. The theca cell layer did not express ET-1 regardless of follicle developmental stage. ET-1 expression occurred with a significantly greater probability (P < 0.001 by the likelihood ratio test) in the granulosa cell compartment of antral follicles than in any other follicle class. Furthermore, in antral follicles, ET-1 expression occurred with a greater likelihood in large antral follicles than in small antral follicles (P < 0.001 by the likelihood ratio test). In small antral follicles, only 16.8% expressed ET-1; in contrast, 66.7% of large antral follicles exhibited ET-1 expression. It is interesting that in follicles in which ovulation had already occurred, intense ET-1 expression was found only in the prominent developing vasculature, the other cells present in the luteinized follicle did not display any ET-1 expression. The pattern of ET-1 gene expression observed in this study would be in agreement with our previous suggestion of a plausible physiological role for ET-1 in preventing premature progesterone production by granulosa cells of an antral follicle. The occurrence of atresia and expression of ET-1 in the same follicle was rare. Small and large antral follicles constituted 5.1% and 5.6%, respectively, of the examined follicles in this category. The majority of atretic follicles did not express ET-1 and, conversely, follicles that expressed ET-1 were not atretic. To the best of our knowledge, this is the first report in which large, nonatretic follicles are clearly identified as the population of follicles expressing ET-1. The results of this study delineate the follicular developmental stage and the compartment of when and where ET-1 may be physiologically meaningful.     

Effects of ovarian tissue reduction on the menstrual cycle: persistent normalcy after near-total oophorectomy

These experiments were designed to evaluate whether removal of approximately 95% visible ovarian tissue would interrupt the short- or long-term regulation of cyclic ovarian function. On cycle Days 2 4 (onset of menses = Day 1), the entire left ovary and approximately 90% of the right ovary were removed from three cycling cynomolgus monkeys. After approximately 95% ovariectomy, there was an acute elevation of follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which lasted 11 +/- 2 days. A midcycle-like gonadotropin surge occurred 20 +/- 3 days following approximately 95% ovariectomy; the next menses occurred 19 +/- 1 days later. Follicular phase patterns of estradiol preceded the midcycle gonadotropin surge, and luteal phase progesterone levels indicated subsequent ovulation. Two of three monkeys resumed normal menstrual cyclicity in the following cycle with follicular phase, luteal phase, and menstrual cycle lengths similar to pretreatment levels. Histological examination of the ovarian remnant removed on Day 21 of the next cycle revealed a morphologically normal corpus luteum and many small follicles. A second group of 6 rhesus monkeys also underwent approximately 95% ovariectomy for long-term evaluation of menstrual cyclicity; typical 28-day menstrual cycle patterns were observed in 4 of the 6 monkeys for 5 mo, with 2 of these 3 animals maintaining regular menstrual cycles for 1 yr. In summary, our data suggest that normal ovarian function, i.e. recruitment, selection, and dominance of the ovulatory follicle, ovulation, and subsequent corpus luteum function, is maintained with only approximately 5% of functional ovarian tissue remaining.(ABSTRACT TRUNCATED AT 250 WORDS)