Histomorphometry of dominant and subordinate bovine ovarian follicles

A Mathematical Model of Estradiol Production from Ultrasound Data for Bovine Ovarian Follicles

In this paper, we present a new way to assess the concentration of estradiol (E2) and Insulin Growth Factor-1 (IGF) based on the results from ultrasound scans combined with mathematical models. The IGF1 model is based on the progesterone (P4) concentration, which can be estimated with models calculating P4 level based on the size/volume of corpus luteum (CL) measured during ultrasound scans. At this moment little is known about the underlying reasons for double ovulation and silent heat occurrences. Both of these are linked to the level of IGF1: double ovulations are linked to higher IGF1 levels and and silent heat is linked to lower E2 to P4 ratio. These models can help to improve understanding of the related concentrations of E2 and IGF1. Currently, it is known that diet and genetic factors have an impact on ovulation rates and silent heat. In this study, we also examine the decline of the production of E2 in vivo by atretic follicles throughout the process of atresia. This is the first recorded quantitative description of this decline.

The dynamics of trkA expression in the bovine ovary are associated with a luteotrophic effect of ovulation-inducing factor/nerve growth factor (OIF/NGF)

BACKGROUND

Ovulation-inducing factor in semen (OIF/NGF) influences ovulation and CL form and function in camelids and, remarkably, in cows. To test the hypothesis that the luteotrophic effect of OIF/NGF is mediated by an increase in trkA receptors in the ovulatory follicle and early CL, a study was designed to characterize the spatial and temporal distribution of trkA in ovarian follicles and CL at known stages of the bovine estrous cycle.

METHODS

Sexually mature cattle (n = 14) were examined daily by transrectal ultrasonography to determine the day of ovulation (Day 0), and assigned randomly to be unilaterally ovariectomized on Day 2, 4, 6 or in the pre-ovulatory period just before or after exogenous LH treatment. After a complete interovulatory interval, the cows were re-assigned to a different day-group on which the remaining ovary was removed. Sections of ovarian tissue representing the dominant follicle, largest subordinate follicle, and the CL were processed for immunofluorescent detection and quantification of trkA receptor.

RESULTS

TrkA immuno-fluorescence in ovarian tissues was restricted to follicles and the CL (no reaction in stroma or vessels), and was restricted to the cytoplasm (no nuclear staining). The trkA staining intensity, area of staining, and proportion of cells stained was greater in both theca and granulosa layers of dominant follicles than in that of subordinate follicles (P ≤ 0.05) in all day-groups except the Pre-LH group. Among dominant follicles, a progressive reduction in the immuno-positive reaction was detected from Day 2 to Day 6. Among subordinate follicles, immuno-reactivity remained low and unchanged except a rise in the Pre-LH group. The number of immuno-positive cells was greater in early developing CL (Days 2 and 4 combined) than in mature or regressing stage CL (Day 6, Pre- and Post-LH combined; P = 0.01). The intracellular distribution of trkA was more diffuse and widespread in dominant than subordinate follicles, particularly on Day 2 and Post-LH (P < 0.05).

CONCLUSIONS

Distinct differences in trkA expression between dominant and subordinate follicles, particularly when circulating progesterone is minimal (early luteal development and after luteolysis) is consistent with a local role of OIF/NGF in follicle selection and early luteogenesis.

Organelle reorganization in bovine oocytes during dominant follicle growth and regression

BACKGROUND

We tested the hypothesis that organelles in bovine oocytes undergo changes in number and spatial distribution in a manner specific for phase of follicle development.

METHODS

Cumulus-oocyte-complexes were collected from Hereford heifers by ultrasound-guided follicle aspiration from dominant follicles in the growing phase (n = 5; Day 0 = ovulation), static phase (n = 5), regressing phase (n = 7) of Wave 1 and from preovulatory follicles (n = 5). Oocytes were processed and transmission electron micrographs of ooplasm representing peripheral, perinuclear and central regions were evaluated using standard stereological methods.

RESULTS

The number of mitochondria and volume occupied by lipid droplets was higher (P < 0.03) in oocytes from regressing follicles (193.0 ± 10.4/1000 μm(3) and 3.5 ± 0.7 %) than growing and preovulatory stages (118.7 ± 14.4/1000 μm(3) and 1.1 ± 0.3 %; 150.5 ± 28.7/1000 μm(3) and 1.6 ± 0.2 %, respectively). Oocytes from growing, static and preovulatory follicles had >70 % mitochondria in the peripheral regions whereas oocytes from regressing follicles had an even distribution. Oocytes from growing follicles had more lipid droplets in peripheral region than in central region (86.9 vs. 13.1 %). Percent surface area of mitochondria in contact with lipid droplets increased from growing (2.3 %) to static, regressing or preovulatory follicle stage (8.9, 6.1 and 6.2 %). The amount, size and distribution of other organelles did not differ among phases (P > 0.11).

CONCLUSIONS

Our hypothesis was supported in that mitochondrial number increased and translocation occurred from a peripheral to an even distribution as follicles entered the regressing phase. In addition, lipid droplets underwent spatial reorganization from a peripheral to an even distribution during the growing phase and mitochondria-lipid contact area increased with follicle maturation.

Macroscopic and histological characteristics of fluid-filled ovarian structures in dairy cows

The primary objective of this study was to use macroscopic and histological features of corpora lutea with a cavity and anovulatory cystic ovarian structures, present in 90 pairs of abattoir-derived dairy cow ovaries, as the basis to clarify the nomenclature of ovarian structures. Excluding morphologically normal ovarian fol-licles (antrum < 2 cm, wall < 1 mm), there were 27 fluid-filled ovarian structures. Ovulatory structures > 16 mm in diameter were designated as Group A (cavity ≤ 10 mm and wall > 10 mm) or Group B (cavity > 10 mm and wall < 10 mm). The volume of luteal tissue was less (P < 0.05) in Group B than in Group A, whereas that of a solid corpus luteum (CL) was intermediate (least square means ± SEM: 72 ± 1.92, 11.22 ± 1.57 and 5.84 ± 1.92 cm3, respectively). There was a greater proportion (P < 0.05) of small luteal cells in Group B compared to a solid CL, whereas Group A was intermediate (58.6 ± 5.3, 37.4 ± 5.3 and 44.0 ± 4.4%, respectively). Connective tissue was thicker (P < 0.05) in Group B than in Group A (295.4 ± 46.9 vs. 153.9 ± 38.2 μm). Based on the above-mentioned characteristics and differences, Groups A and B were designated as a CL with a cavity and a cystic CL, respectively. Furthermore, there were three groups of anovulatory ovarian structures. Structures in Group C were termed persistent/anovulatory follicles (overall diameter and wall thickness ≤ 20 and 1-3 mm, respectively). Finally, Groups D and E were designated as a follicle-fibrous cyst and a follicle-luteinised cyst (based on histological structure) for anovulatory structures with an overall diameter and wall thickness of ≥ 20 and ≤ 3 mm, and ≥ 20 and ≥ 3 mm, respectively.

Computational modelling of bovine ovarian follicle development

Background

The development of ovarian follicles hinges on the timely exposure to the appropriate combination of hormones. Follicle stimulating hormone (FSH) and luteinizing hormone (LH) are both produced in the pituitary gland and are transported via the blood circulation to the thecal layer surrounding the follicle. From there both hormones are transported into the follicle by diffusion. FSH-receptors are expressed mainly in the granulosa while LH-receptors are expressed in a gradient with highest expression in the theca. How this spatial organization is achieved is not known. Equally it is not understood whether LH and FSH trigger distinct signalling programs or whether the distinct spatial localization of their G-protein coupled receptors is sufficient to convey their distinct biological function.

Results

We have developed a data-based computational model of the spatio-temporal signalling processes within the follicle and (i) predict that FSH and LH form a gradient inside the follicle, (ii) show that the spatial distribution of FSH- and LH-receptors can arise from the well known regulatory interactions, and (iii) find that the differential activity of FSH and LH may well result from the distinct spatial localisation of their receptors, even when both receptors respond with the same intracellular signalling cascade to their ligand.

Conclusion

The model integrates the large amount of published data into a consistent framework that can now be used to better understand how observed defects translate into failed follicle maturation.

Ultrastructural and cytochemical characterization of follicular cell types in bovine (Bos taurus) cumulus-oocyte complexes aspirated from small and medium antral follicles during the estrus cycle

Stereological quantitative methods have revealed the presence of three distinct follicular cell populations (C1-C3) in bovine cumulus-oocyte complexes. Type C3 cells became largely predominant from metestrous to proestrous, with a simultaneously large decrease in the other two cell types. To further characterize these cumulus cell types, cumulus-oocyte complexes from small (1-4mm) and medium (4-8mm) antral follicles (category 1: with a compact multilayered cumulus and a homogeneous ooplasm) were aspirated from ovaries of Holstein-Friesian cows and processed for electron microscopy, ultrastructural cytochemical detection of glycogen and glycoproteins, and immunogold localization of chondroitin sulfate. Each follicular cell type displayed the same ultrastructural characteristics independently of the size of the follicle and the stage of the estrous cycle. Type C1 cells showed morphological characteristics of undifferentiated cells and progressively transformed into type C2 cells. Type C2 cells were characterized by cell extensions, polarized nuclei with evident nucleolar fibrilar centers, steroidogenic characteristics (numerous large lipid droplets, large endoplasmic reticulum vesicles and vacuoles), and synthesis of glycoproteins and chondroitin sulfate by the Golgi apparatus and endoplasmic reticulum. Type C3 cells presented morphologic features of fully differentiated and luteinized cumulus cells. They were characterized by an increase in cytoskeleton filaments, loss of cell extensions and of intercellular junctions, depletion of lipid and glycogen stores, and initiation of glycoprotein and chondroitin sulfate exocytosis. In conclusion, the present study suggests that bovine cumulus cells from small and medium antral follicles follow a complete dynamic functional differentiation process, in which the three cell types seem to correspond to a functional continuum. We identified undifferentiated cells, cells strongly engaged in glycoprotein and proteoglycan synthesis, and cells fully differentiated and secreting.

Thyroid hormone concentrations in systemic circulation and ovarian follicular fluid of cows

The aim of this study was to determine and compare the concentrations of total (T) and free (F) fractions of thyroid hormones (T3-triiodithyronine and T4-thyroxin) in peripheral circulation and follicular fluid of cows in relation to ovarian follicular status in vivo (Experiment 1), and in the follicles from the slaughterhouse ovaries (Experiment 2). In Experiment 1, estrus was synchronized in 15 cows using two Estrumate® (cloprostenol sodium) injections (250 mg cloprostenol intramuscular), the time of ovulation (Day 0) was confirmed by ultrasonography, and ovarian antral follicles were ablated on Day 5. The ensuing superovulatory treatment consisted of eight Folltropin®-V injections (50 mg intramuscular) administered twice daily from Day 6 to Day 9, followed by two injections of Estrumate® (Day 10 am and pm) and a single dose of Lutropin Alfa® (Day 11; 750 IU intramuscular). On Day 5, both TT3 and FT3 concentrations were greater ( P < 0.05) in serum than follicular fluid from dominant (DFs) or subordinate antral follicles (SFs), and TT4 concentrations were greater ( P < 0.05) in DFs compared with SFs. Serum concentrations of FT4 were greater ( P < 0.05) on Day 12 than on Day 5, and TT4 concentrations in follicular fluid collected on Day 12 were higher than those in DFs and SFs on Day 5. In Experiment 2, there were no differences ( P > 0.05) in thyroid hormone concentrations between the largest and all remaining antral follicles visible on the surface of the ovary ( n = 20 ovaries). We concluded that: (i) physiological status of bovine antral follicles (i.e. dominant versus subordinate) may impinge on the accumulation of TT4 in follicular fluid; and (ii) hormonal ovarian superstimulation increases circulating levels of FT4 and follicular fluid content of TT4.

Evaluation of the ultrasound image attributes of developing ovarian follicles in the four follicular waves of the interovulatory interval in ewes

Computer-assisted quantitative echotextural analysis was applied to ultrasound images of antral follicles in the follicular waves of an interovulatory interval in sheep. The ewe has three or four waves per cycle. Seven healthy, cyclic Western White Face ewes (Ovis aris) underwent daily, transrectal, ovarian ultrasonography for an interovulatory interval. Follicles in the third wave of the ovulatory interval had a longer static phase than that of those in Waves 1 and 2 (P<0.05). The numeric pixel value for the wall of anovulatory follicles emerging in the third wave of the cycle was significantly higher than that for Waves 1 and 2 at the time of emergence (156.7+/-8.09, 101.6+/-3.72, and 116.5+/-13.93, respectively), and it decreased as follicles in Wave 3 reached maximum follicular diameter (P<0.05). The numeric pixel value of the antrum in the ovulatory follicles decreased as follicular diameter increased to > or =5mm in diameter (P<0.05). The pixel heterogeneity of the follicular antrum in Wave 1 increased from the end of the growth phase to the end of the regression phase for follicles in that wave (P<0.05). The total area for the wall and antrum of the follicles studied were correlated with follicular diameter in all follicular waves (r=0.938, P<0.01 and r=0.941, P<0.01 for the wall and antrum, respectively). Changes in image attributes of the follicular wall and antrum indicate potential morphologic and functional differences among antral follicles emerging at different stages of the interovulatory interval in cyclic ewes.

Relationships of changes in ultrasonographic image attributes to ovulatory and steroidogenic capacity of large antral follicles in sheep

Ovarian steroidogenesis and antral follicular development in ewes, following the treatment with medroxyprogesterone acetate (MAP) and equine chorionic gonadotrophin (eCG), are affected by the reproductive season. The objective of this study was to compare the ultrasonographic attributes of large antral follicles between cyclic (December) and seasonally anovular (June-July) ewes, after a 12-day treatment with MAP-soaked intravaginal sponges, with or without the administration of 500IU of eCG at sponge removal, and to determine whether there is a correlation between the ultrasonographic attributes of the follicular wall and serum concentrations of oestradiol. Digital images of ovulatory follicles from cyclic ewes and eCG-treated anoestrous ewes (n=34 follicles), and of anovulatory follicles attaining > or =5mm in control anoestrous ewes (n=8 follicles), were analysed using the spot and line techniques designed to determine the echotextural characteristics of the follicular antrum (central and peripheral), follicular wall and perifollicular ovarian stroma. The mean diameter of ovulatory follicles was greater (P<0.001) in cyclic than anoestrous ewes, with or without the eCG treatment. The mean pixel heterogeneity (SD of numerical pixel values) of the follicular antrum (P<0.05), as well as mean pixel intensity and heterogeneity of the peripheral antrum, follicular wall proper and perifollicular ovarian stroma (P<0.05), were consistently greater in anoestrous than cyclic ewes at the time of sponge removal and 24h after the treatment with MAP sponges or MAP/eCG. Mean oestradiol concentrations were greater (P<0.05) in cyclic compared to anoestrous ewes in both MAP- and MAP/eCG-treated animals, from 1 to 2 days after sponge withdrawal. There was a moderate negative correlation (r(2)=0.12, P<0.05; Pearson's Product Moment and r(2)=0.23, P<0.05; ANCOVA) between mean pixel heterogeneity (standard deviation of mean pixel values) of the follicular wall proper (all follicles > or =5mm in diameter) and serum concentrations of oestradiol after sponge withdrawal. Our results indicate that large antral follicles from cyclic and seasonally anovular ewes exhibit distinctive ultrasonographic characteristics. The differences in follicular echotexture appear to be related mainly to seasonal variations in ovarian follicular morphology and oestradiol production.

Comparative histomorphological study of ovary and ovarian follicles in Iranian Lori-Bakhtiari sheep and native goat

In this project, for measuring and comparing dimensions of ovary and ovarian follicles between Lori-Bakthiari sheep and native goat, eighty ovaries of sheep and goat, aged 1-2 years, from Shahrekord abattoir were collected. After weighing the ovaries, some factors such as: length, width and thickness of left and right ovaries by caliper device were measured. For histological studies, after tissue preparation and staining with H and E, diameter of follicles, thickness of follicular layers (granulosa, theca interna and theca externa) by micrometry methods were measured. By analyzing data with t-test and comparing them between sheep and goat we concluded that, there were significant difference between weight and dimensions of ovaries in sheep and goat. These parameters in goats were larger than sheep. Microscopical studies revealed that, the mean thickness of theca externa of graafian follicle in left ovary of sheep was more than right. The mean diameter of oocyte in secondary follicle of goat in left ovary was more than right. Also in goat, the number of layers of cumulus oophorus around corona radiata was more than sheep.

Phenotypes of the ovarian follicular basal lamina predict developmental competence of oocytes

BACKGROUND

The ovarian follicular basal lamina underlies the epithelial membrana granulosa and maintains the avascular intra-follicular compartment. Additional layers of basal lamina occur in a number of pathologies, including pili annulati and diabetes. We previously found additional layers of follicular basal lamina in a significant percentage of healthy bovine follicles. We wished to determine if this phenomenon existed in humans, and if it was related to oocyte function in the bovine.

METHODS AND RESULTS

We examined follicles from human ovaries (n = 18) by electron microscopy and found that many follicles had additional layers of basal lamina. Oocytes (n = 222) from bovine follicles with normal or unusual basal laminas were isolated and their ability to undergo in vitro maturation, fertilization and culture to blastocyst was compared. Healthy bovine follicles with a single layer of basal lamina had oocytes with significantly (P < 0.01) greater developmental competence than healthy follicles with additional layers of follicular basal lamina (65% versus 28%).

CONCLUSIONS

These findings provide direct evidence that the phenotype of the follicular basal lamina is related to oocyte competence.

Relationships between ultrasonographic image attributes, histomorphology and proliferating cell nuclear antigen expression of bovine antral follicles and corpora lutea ex situ

The aim of this study was to examine the relationships between quantitative ultrasonographic image characteristics, histological attributes and cell proliferating ability of bovine antral follicles and corpora lutea (CL) ex situ. Bovine ovaries (n = 30) from animals at various reproductive states (metoestrus-early dioestrus, n = 8; mid-dioestrus, n = 12; oestrous phase of peripubertal heifers, n = 6; and pregnancy, n = 4) were collected at the slaughterhouse. High-resolution ultrasonographic images of the ovaries were obtained in the water bath, digitized and subjected to computerized image analyses. The analyses utilized line and spot techniques designed to determine pixel values of the follicular wall (the largest follicles >2 mm in diameter in each ovary) and CL, respectively. Individual ovarian structures were dissected and processed for histology and immunohistochemical detection of proliferating cell nuclear antigen (PCNA). The mean follicular diameter was negatively correlated with total cell density (r = -0.45, p < 0.05), granulosa layer thickness (r = -0.67, p < 0.001) and the percentage of PCNA-positive cells (r = -0.57, p < 0.001). Numerical pixel values and heterogeneity of the follicular wall were positively correlated with total cell density (r = 0.42, p < 0.05 and r = 0.62, p < 0.05; respectively), granulosa layer thickness (both r = 0.39, p < 0.05), and the percentage of PCNA-positive cells (r = 0.54, p < 0.01 and r = 0.69, p < 0.001, respectively). Estimates of cell density and proliferating cell index were not correlated with the ultrasonographic image attributes of CL. We conclude that follicular size and echotextural variables, as determined by computer-assisted image analysis of ovaries ex situ, are reliable markers of the histophysiological properties of bovine antral follicles, but the ultrasonographic characteristics are not indicative of cell density and proliferation in the bovine CL.

Ultrasonographic characteristics of ovulatory follicles and associated endocrine changes in cyclic ewes treated with medroxyprogesterone acetate (MAP)-releasing intravaginal sponges and equine chorionic gonadotropin (eCG)

The aim of this study was to assess the ultrasonographic characteristics of ovulatory follicles in cyclic Western White Face ewes (December) that had received intravaginal sponges containing medroxyprogesterone acetate (MAP; 60 mg) for 12 days, with or without an injection of 500 IU of equine chorionic gonadotropin (eCG) at sponge removal. We hypothesized that quantitative echotextural attributes of the follicles in ewes treated only with MAP would differ from those in MAP/eCG-treated ewes, reflecting the increased antral follicular growth and secretory function under eCG influence. Digital images of ovulatory follicles obtained at 0 and 24 h after MAP sponge removal and at 24 h before ovulation in the eCG-treated (five ewes, 13 follicles) and control (six ewes, 9 follicles) animals, were subjected to computerized analyses. The mean diameter of ovulatory follicles increased (p < 0.001) 24 h after eCG treatment. The mean pixel intensity and heterogeneity of the follicular antrum (p < 0.001), as well as mean pixel intensity of the follicular wall and perifollicular ovarian stroma (p < 0.05), were greater in eCG-treated animals compared with control ewes 24 h after sponge removal and at 24 h before ovulation. Mean serum concentrations of oestradiol-17beta tended to increase (p = 0.06) 24 h after eCG treatment and the eCG-treated ewes exceeded (p < 0.05) control animals in progesterone concentrations from days 9-15 after ovulation. Our results support the hypothesis that large antral follicles in eCG-treated ewes exhibit distinctive echotextural characteristics. Follicular image attributes in eCG-treated ewes appear to be indicative of the changes in follicular morphology and secretory activity caused by the administration of the exogenous gonadotropin, which has both FSH- and LH-like activities.

Ultrasonographic image attributes of non-ovulatory follicles and follicles with different luteal outcomes in gonadotropin-releasing hormone (GnRH)-treated anestrous ewes

Ultrasonographic images are composed of multiple square picture elements called pixels. Quantitative changes in numerical pixel values (echotexture) determined by computer-assisted analysis of digital images reflect discrete changes in the microscopic structure and physiological status of ovarian antral follicles. The objective of the present study was to determine and compare the ultrasonographic attributes of non-ovulatory antral follicles that grew to an ostensibly ovulatory diameter (> or =5mm) and follicles with different luteal outcomes in response to gonadotropin-releasing hormone (GnRH) in anestrous Western White Face ewes (n=34). All animals received GnRH injections (250ng i.v. every 2h for 24h) followed by a bolus injection of 125microg of GnRH i.v. Ovarian images obtained by repeated transrectal ultrasonography were digitized and subjected to computerized analyses to determine the changes in follicular size and echotexture of the follicular antrum and wall. At the beginning of GnRH treatment, follicles that formed inadequate corpora lutea following ovulation (ICL; n=22) had higher (P<0.001) pixel intensity of the central and peripheral antrum compared with non-ovulatory follicles (n=40). Pixel intensity of the central follicular antrum was greater (P<0.01) in follicles that formed ICL compared with follicles that formed normal (full-lifespan) CL post-treatment (NCL; n=20) and mean pixel heterogeneity of the follicular wall was greater (P<0.05) in non-ovulatory follicles compared with follicles that gave rise to NCL. At the time of GnRH bolus injection (i.e., induction of a synchronous LH surge), the mean diameter of non-ovulatory follicles was greater (P<0.01) than that of all ovulating follicles, and pixel heterogeneity of the central follicular antrum was lowest (P<0.05) in non-ovulatory follicles. The mean diameter of luteinized unovulated follicles (n=9) tended to be greater (P<0.10) at 2.5 and 3 days after emergence, and pixel intensity of the follicular wall was lower (P<0.05) compared with non-luteinized follicles (n=8) at 1.5 and 2.5 days after emergence (beginning of the growth from approximately 3mm onwards). In conclusion, ovarian antral follicles with different outcomes after GnRH treatment (in seasonally anestrous ewes) had distinctive ultrasonographic characteristics.

Ovarian and endocrine responses to prostaglandin F2α (PGF2α) given at the expected time of the endogenous FSH peak at mid-cycle in ewes

In the ewe, a rise in circulating concentrations of FSH preceding follicular wave emergence begins in the presence of growing follicles from a previous wave. We hypothesized that prostaglandin F(2alpha) (PGF(2alpha)) given at the time of an endogenous FSH peak in cyclic ewes would result in synchronous ovulation of follicles from two consecutive waves, increasing ovulation rate. Twelve Western White Face (WWF) ewes received a single i.m. injection of PGF(2alpha) (15 mg/ewe) at the expected time of a peak in FSH secretion, from Days 9 to 12 after ovulation. The mean ovulation rate after PGF(2alpha) treatment (2.3+/-0.3) did not differ (P>0.05) from the pre-treatment ovulation rate (1.7+/-0.1). Five ewes ovulated follicles from follicular waves emerging before and after PGF(2alpha) injection (3.0+/-0.6 ovulations/ewe) and seven ewes ovulated follicles only from a wave(s) emerging before PGF(2alpha) treatment (2.0+/-0.3 ovulations/ewe; P>0.05). The mean interval from PGF(2alpha) to emergence of the next follicular wave (1.0+/-0.4 and 4.0+/-0.0 d, respectively; P<0.001) and the interval from PGF(2alpha) treatment to the next FSH peak (0 and 3.5+/-0.4d, respectively; P<0.05) differed between the two groups. Six ewes ovulated after the onset of behavioral estrus, with a mean ovulation rate of 1.7+/-0.2, and six ewes ovulated both before and after the onset of estrus (3.0+/-0.5 ovulations/ewe; P<0.05). None of the ovulations that occurred before estrus resulted in corpora lutea (CL) with a full life span. At 24h before ovulation, follicles ovulating before or after the onset of estrus differed in size (4.1+/-0.3 or 5.5+/-0.4mm, respectively; P<0.05) and had distinctive echotextural characteristics. In conclusion, the administration of PGF(2alpha) at the expected time of an FSH peak at mid-cycle in ewes may alter the endogenous rhythm of FSH secretion and was not consistently followed by ovulation of follicles from two follicular waves. In non-prolific WWF ewes, PGF(2alpha)-induced luteolysis disrupted the normal distribution of the source of ovulatory follicles and may be associated with untimely follicular rupture and luteal inadequacy.

Bovine model for the study of reproductive aging in women: follicular, luteal, and endocrine characteristics

At present, there is no well-characterized animal model to study the effects of aging on fertility in women. The objectives of the study were to characterize age-related changes in ovarian and endocrine functions in old cows and to investigate the validity of a bovine model for the study of human reproductive aging. We tested the hypotheses that aging in cattle is associated with 1) elevated concentrations of gonadotropins and reduced concentrations of steroid hormones in systemic circulation and 2) increased recruitment of ovarian follicles during wave emergence. Daily ultrasonography was performed in 13- to 14-yr-old cows (n = 10) and their 1- to 4-yr-old daughters (n = 9) for one interovulatory interval to study ovarian function. Plasma samples were obtained every 12 h for determination of FSH, LH, progesterone, and estradiol concentrations. Circulating FSH concentrations were higher (P = 0.009) during follicular waves in old cows than in their daughters, but the number of 4- to 5-mm follicles recruited into a wave was lower (P = 0.04) in old cows. Plasma LH concentrations did not differ between groups (P = 0.4), but the ovulatory follicle in two-wave cycles was smaller in old cows (P = 0.04). Plasma estradiol concentrations were higher (P = 0.01) in old cows, and luteal phase progesterone tended to be lower (P = 0.1). We conclude that these changes are consistent with those reported for women approaching menopause transition. Therefore, our results validate the use of the bovine model to study reproductive aging in women.

Patterns of Antral Follicular Wave Dynamics and Accompanying Endocrine Changes in Cyclic and Seasonally Anestrous Ewes Treated with Exogenous Ovine Follicle-Stimulating Hormone During the Inter-Wave Interval1

In the ewe, ovarian follicular waves emerge every 4 to 5 days and are preceded by a peak in FSH secretion. It is unclear whether large antral follicle(s) in a wave suppress the growth of other smaller follicles during the inter-wave interval, as is seen in cattle. In this study, anestrous (n = 6; experiment 1) and cyclic (n = 5; experiment 2) Western white face ewes were given ovine FSH (oFSH) (0.5 microg/kg; two s.c. injections, 8 h apart) during the growth phase (based on ultrasonography) of a follicular wave (wave 1). Control ewes (n = 5 and 6, respectively) received vehicle. In oFSH-treated ewes, serum FSH concentrations reached a peak (P < 0.05) by 12 h after oFSH treatment, and this induced FSH peak did not differ (P > 0.05) from the endogenous FSH peaks. In all ewes, emergence of follicular waves 1 and 2 was seen (P > 0.05). However, in oFSH-treated ewes, an additional follicular wave emerged approximately 0.5 days after treatment: during the interwave interval of waves 1 and 2 without delaying the emergence of wave 2. The growth characteristics and serum estradiol concentrations did not differ (P > 0.05) between oFSH-induced waves and waves induced by endogenous FSH peaks. We concluded that, unlike in cattle, the largest follicle of a wave in sheep has limited direct effect on the growth of other follicles induced by exogenous oFSH. In addition, the largest follicle of a wave may possibly not influence the rhythmicity of follicular wave emergence, as it does in cattle.

Follicular dynamics around the recruitment of the first follicular wave in the cow

The present study aimed to test the generally accepted view that a follicular wave starts with follicles newly recruited from the population smaller than 3 mm, which later compete for dominance. According to this view, subordinate follicles are expected to be too atretic to join the next follicular wave. Ten cows were ovariectomized shortly prior to the LH surge, thus around the start of the first follicular wave of the cycle. Per cow, on average, 14.4 follicles of >/=3 mm were dissected. Follicular health was determined on the basis of four parameters: 1) judgment of the degree of atresia by stereomicroscope, 2) incidence of apoptotic nuclei among the granulosa cells, 3) estradiol and progesterone concentrations, and 4) insulin-like growth factor-I (IGF-I) binding proteins (IGFBPs)-2, -4, and -5 concentrations in the follicular fluid. In addition to the preovulatory follicle, 3.1 other follicles, mainly sized 3-4.5 mm, were found to be healthy based on the proportion of apoptotic nuclei, and concentrations of estradiol/progesterone, and IGFBPs. The ability of these follicles to respond with growth on the preovulatory and periovulatory FSH surges was supported by a comparison to the follicular population of four cows 31-68 h after the LH surge. The present results point to an alteration of the view on the follicular wave. The larger follicles during the first days of the follicular wave are, in general, derived from follicles that also joined the previous wave. A portion of these growing follicles are estradiol active and compete for dominance. Other growing follicles lack estradiol production and are probably derived from rather atretic follicles. The first newly recruited follicles do not reach the size of 3 mm before 31 h after the preovulatory FSH surge. At that time, the larger follicles are already competing for dominance.

Promise of new imaging technologies for assessing ovarian function

Advancements in imaging technologies over the last two decades have ushered a quiet revolution in research approaches to the study of ovarian structure and function. The most significant changes in our understanding of the ovary have resulted from the use of ultrasonography which has enabled sequential analyses in live animals. Computer-assisted image analysis and mathematical modeling of the dynamic changes within the ovary has permitted exciting new avenues of research with readily quantifiable endpoints. Spectral, color-flow and power Doppler imaging now facilitate physiologic interpretations of vascular dynamics over time. Similarly, magnetic resonance imaging (MRI) is emerging as a research tool in ovarian imaging. New technologies, such as three-dimensional ultrasonography and MRI, ultrasound-based biomicroscopy and synchrotron-based techniques each have the potential to enhance our real-time picture of ovarian function to the near-cellular level. Collectively, information available in ultrasonography, MRI, computer-assisted image analysis and mathematical modeling heralds a new era in our understanding of the basic processes of female and male reproduction.

A stereological study of medium antral follicles during the bovine estrous cycle

Stereological methods were applied to bovine cumulus-oocyte complexes (COCs) in order to characterize them quantitatively during the estrous cycle. COCs from medium (4-8mm) antral follicles with a compact and complete cumulus mass, and with an uniform or a non-visible ooplasm were aspirated from ovaries of Holstein-Friesian cows, fixed in glutaraldehyde, randomly embedded in glycol-methacrylate, and sectioned at 20 microm. The unbiased nucleator principle was used for estimating the mean volumes of complexes, oocytes, cumulus cells, and nuclei of oocytes and cumulus cells. The thickness of the zona pellucida and the relative numerical percentages of the several morphological types (C1-C3) of cumulus cells were also evaluated. The optical disector procedure was used for cumulus cell sampling. Quantitative data show that COCs appear heterogeneous for all studied parameters. From metestrus to proestrus the volumes of COCs and oocytes remained constant, the volumes of oocytes and oocyte nuclei were correlated, the thickness of the outer zona pellucida decreased, and the relative numerical frequency of follicular type C3 cells increased. Results suggest that COCs from distinct estrus stages are structurally different, with type C3 follicular cells gradually differentiating from cell types C1 and C2.

Stereological characterization of bovine (Bos taurus) cumulus-oocyte complexes aspirated from small antral follicles during the metestrous and proestrous phases

Bovine cumulus-oocyte complexes (COCs) aspirated from slaughterhouse ovaries are used for in vitro maturation and fertilization after selection on the basis of morphological appearance of the cumulus and ooplasm. In this context, a quantitative characterization of COCs could provide additional criteria for selecting the most competent complexes. Bovine COCs from small (1-4mm) antral follicles were aspirated from metestrous and proestrous stage ovaries of Holstein-Friesian cows, fixed in glutaraldehyde, randomly embedded in glycol-methacrylate, and sectioned at 20 microm. The unbiased nucleator principle of stereology was used for estimating the mean volumes of complexes, oocytes, cumulus cells, and nuclei of oocytes and cumulus cells. The thickness of the zona pellucida and the relative numerical percentages of the several morphological types (C1, C2 and C3) of cumulus cells were also evaluated. The optical dissector procedure was used for cumulus cell sampling. Quantitative data show that the variability among complexes is generally high, especially for the volume of COCs. There were no linear correlations between the studied parameters, except between the volume of the oocyte and nucleus at metestrus. At proestrus, the volumes of COCs, oocytes and nuclei of oocytes, the volume of follicular cells and the thickness of the inner zona pellucida, were significantly higher than at metestrus. The relative numerical frequency of follicular type C1 cells was lower whereas that of type C3 cells was higher at proestrus than at metestrus. In conclusion, small antral follicles had larger COCs and oocytes at proestrus compared to metestrus and the COCs also had a higher percentage of follicular type C3 cells. Results suggest that for the same type of follicle size there may exist different functional populations of COCs at distinct stages of the bovine ovarian cycle.

Ultrasound image characteristics of ovarian follicles in relation to oocyte competence and follicular status in cattle

Assessment of the quality of the female gamete has become paramount for in vitro procedures. There is a need to identify reliable indicators of oocyte competence and develop a simple, non-invasive method to assess competence. The aim of this study was to investigate the relationships among ultrasonographic attributes of a follicle, its stage of development and the competence of the oocyte that it contains. We tested the hypotheses that follicular echotexture characteristics are related to: (1) the phase of development of the follicle, (2) the presence of the corpus luteum (CL) and/or the dominant follicle in the ovary, and (3) developmental competence of cumulus oocyte complexes (COC) from the same ovary. Crossbred beef cows (n=143), age 4-14 years, were given a luteolytic dose of dinoprost to cause ovulation. Ultrasound-guided ablation of all follicles > or = 4mm was done 8 days later to induce new follicular wave emergence during a luteal phase. Ultrasonographic images of dominant follicles and the three largest subordinate follicles (n=402 follicles; 84 cows) were acquired on Days 2, 3, 5 or 7 of the follicular wave (Day 0: wave emergence), i.e. growing, early-static, late static, and regressing phases of subordinate follicle development, respectively. From a subset of these animals (n=33), ovaries were collected within 30 min of slaughter and COC from subordinate follicles > or = 3mm underwent in vitro maturation, fertilization and culture to the blastocyst stage.Image analysis revealed differences in echotexture between dominant and subordinate follicles among Days 2-7 of the follicular wave. Images of dominant and subordinate follicles at Day 7 of the wave displayed consistently lower grey-scale values (P<0.05) in the peripheral antrum, follicular wall and perifollicular stroma than all other days. Follicle images displayed a consistent pattern of variation in echotexture among follicular phases. Data did not support the hypothesis of a local effect of the CL or dominant follicle on follicular echotexture. Echotexture values of the perifollicular stroma were lower in ovaries that did not produce embryos compared to ovaries that produced embryos. Our results showed that the changes in follicular image attributes are consistent with changes in follicular status. The sensitivity of the technique is not yet sufficient for use in a diagnostic setting, but results provide rationale for further development of image analysis as a tool for evaluating oocyte competence in situ.

Extracellular matrix of the bovine ovarian membrana granulosa

Much is known about the control of the development of ovarian follicles by growth factors and hormones. The study of extracellular matrix in the ovary, though, is a relatively new area. To date much research has focused on identifying the matrix components present, and more recently, its production and the physiological roles. In this review we focus on the changes that occur in the follicular basal lamina from primordial follicles through to ovulation and formation of the corpus luteum, the changes that occur during follicular atresia, and we discuss our observations of a novel matrix which forms in the membrana granulosa. The follicular basal lamina changes considerably during follicular development in its expression pattern of type IV collagens. Of the laminin chains examined, there appears only to be an increase in amount, except for laminin alpha2. It is expressed only in a small proportion of healthy antral follicles and in the majority of atretic antral follicles. Call-Exner bodies have the same composition as the basal lamina, except they do not contain laminin alpha2, even when the follicular basal lamina does. The novel matrix that develops within the membrana granulosa is similar in composition to Call-Exner bodies which occur predominantly in preantral follicles, except that it is far more common in large antral follicles, does not induce polarization of the surrounding granulosa cells, and does not contain follicular fluid-like material as the Call-Exner bodies of some species do. The expression of this matrix occurs prior to and during the time when granulosa cells express steroidogenic enzymes. It does not exist in corpora lutea. In addition large luteal cells, derived from granulosa cells, do not appear to have a basal lamina. These findings suggest that the maturational changes in the membrana granulosa are accompanied by changes in the matrix.