An analytical model for ovarian follicle dynamics

Nonlinear compartmental modeling to monitor ovarian follicle population dynamics on the whole lifespan

In this work, we introduce a compartmental model of ovarian follicle development all along lifespan, based on ordinary differential equations. The model predicts the changes in the follicle numbers in different maturation stages with aging. Ovarian follicles may either move forward to the next compartment (unidirectional migration) or degenerate and disappear (death). The migration from the first follicle compartment corresponds to the activation of quiescent follicles, which is responsible for the progressive exhaustion of the follicle reserve (ovarian aging) until cessation of reproductive activity. The model consists of a data-driven layer embedded into a more comprehensive, knowledge-driven layer encompassing the earliest events in follicle development. The data-driven layer is designed according to the most densely sampled experimental dataset available on follicle numbers in the mouse. Its salient feature is the nonlinear formulation of the activation rate, whose formulation includes a feedback term from growing follicles. The knowledge-based, coating layer accounts for cutting-edge studies on the initiation of follicle development around birth. Its salient feature is the co-existence of two follicle subpopulations of different embryonic origins. We then setup a complete estimation strategy, including the study of structural identifiability, the elaboration of a relevant optimization criterion combining different sources of data (the initial dataset on follicle numbers, together with data in conditions of perturbed activation, and data discriminating the subpopulations) with appropriate error models, and a model selection step. We finally illustrate the model potential for experimental design (suggestion of targeted new data acquisition) and in silico experiments.

Mathematical recapitulation of the end stages of human ovarian aging

Ovarian aging in women can be described as highly unpredictable within individuals but predictable across large populations. We showed previously that modeling an individual woman's ovarian reserve of primordial follicles using mathematical random walks replicates the natural pattern of growing follicles exiting the reserve. Compiling many simulations yields the observed population distribution of the age at natural menopause (ANM). Here, we have probed how stochastic control of primordial follicle loss might relate to the distribution of the preceding menopausal transition (MT), when women begin to experience menstrual cycle irregularity. We show that identical random walk model conditions produce both the reported MT distribution and the ANM distribution when thresholds are set for growing follicle availability. The MT and ANM are shown to correspond to gaps when primordial follicles fail to grow for 7 and 12 days, respectively. Modeling growing follicle supply is shown to precisely recapitulate epidemiological data and provides quantitative criteria for the MT and ANM in humans.

Slowest first passage times, redundancy, and menopause timing

Biological events are often initiated when a random "searcher" finds a "target," which is called a first passage time (FPT). In some biological systems involving multiple searchers, an important timescale is the time it takes the slowest searcher(s) to find a target. For example, of the hundreds of thousands of primordial follicles in a woman's ovarian reserve, it is the slowest to leave that trigger the onset of menopause. Such slowest FPTs may also contribute to the reliability of cell signaling pathways and influence the ability of a cell to locate an external stimulus. In this paper, we use extreme value theory and asymptotic analysis to obtain rigorous approximations to the full probability distribution and moments of slowest FPTs. Though the results are proven in the limit of many searchers, numerical simulations reveal that the approximations are accurate for any number of searchers in typical scenarios of interest. We apply these general mathematical results to models of ovarian aging and menopause timing, which reveals the role of slowest FPTs for understanding redundancy in biological systems. We also apply the theory to several popular models of stochastic search, including search by diffusive, subdiffusive, and mortal searchers.

Regenerative Medicine Approaches in Bioengineering Female Reproductive Tissues

Diseases, disorders, and dysfunctions of the female reproductive tract tissues can result in either infertility and/or hormonal imbalance. Current treatment options are limited and often do not result in tissue function restoration, requiring alternative therapeutic approaches. Regenerative medicine offers potential new therapies through the bioengineering of female reproductive tissues. This review focuses on some of the current technologies that could address the restoration of functional female reproductive tissues, including the use of stem cells, biomaterial scaffolds, bio-printing, and bio-fabrication of tissues or organoids. The use of these approaches could also be used to address issues in infertility. Strategies such as cell-based hormone replacement therapy could provide a more natural means of restoring normal ovarian physiology. Engineering of reproductive tissues and organs could serve as a powerful tool for correcting developmental anomalies. Organ-on-a-chip technologies could be used to perform drug screening for personalized medicine approaches and scientific investigations of the complex physiological interactions between the female reproductive tissues and other organ systems. While some of these technologies have already been developed, others have not been translated for clinical application. The continuous evolution of biomaterials and techniques, advances in bioprinting, along with emerging ideas for new approaches, shows a promising future for treating female reproductive tract-related disorders and dysfunctions.

Mathematical modeling approaches of cellular endocrinology within the hypothalamo-pituitary-gonadal axis

The reproductive neuroendocrine axis, or hypothalamo-pituitary-gonadal (HPG) axis, is a paragon of complex biological system involving numerous cell types, spread over several anatomical levels communicating through entangled endocrine feedback loops. The HPG axis exhibits remarkable dynamic behaviors on multiple time and space scales, which are an inexhaustible source of studies for mathematical and computational biology. In this review, we will describe a variety of modeling approaches of the HPG axis from a cellular endocrinology viewpoint. We will in particular investigate the questions raised by some of the most striking features of the HPG axis: (i) the pulsatile secretion of hypothalamic and pituitary hormones, and its counterpart, the cell signaling induced by frequency-encoded hormonal signals, and (ii) the dual, gametogenic and glandular function of the gonads, which relies on the tight control of the somatic cell populations ensuring the proper maturation and timely release of the germ cells.

Cadherin 22 participates in the self-renewal of mouse female germ line stem cells via interaction with JAK2 and β-catenin

The self-renewal capacity of the stem cell pool determines tissue function and health. Cadherin-22 (Cdh22), a member of the cadherin superfamily, has two splicing patterns in rats, and the short type that lacks a catenin binding domain is closely related to spermatogonial stem cell self-renewal. Previously, we reported that CDH22 was highly expressed in mouse ovary germ cells, especially in female germ line stem cells (FGSCs). However, its underlying function in FGSCs is still not clear. Here, we found that Cdh22 encodes only one type of protein product in mice and demonstrated that CDH22 was required for FGSC self-renewal. In addition, JAK2 and β-catenin were found to interact with CDH22 and be involved in CDH22 signaling in mouse FGSCs. Moreover, extrinsic CDH22 was identified as a potential molecule that participates in FGSC adhesion and is pivotal for FGSC maintenance and self-renewal. These results reveal that CDH22 functions as an essential molecule in FGSC maintenance and self-renewal via different mechanisms, including interaction with the JAK-STAT signaling pathway and β-catenin.

Putative germline and pluripotent stem cells in adult mouse ovary and their in vitro differentiation potential into oocyte-like and somatic cells

According to classical knowledge of reproductive biology, in the ovary of female mammals there is a limited number of oocytes and there is no possibility of renewal if the oocytes are lost due to disease or injury. However, in recent years, the results of some studies on renewal and formation of oocytes and follicles in the adult mammalian ovary have led to the questioning of this opinion. The aim of our study is to demonstrate the presence of putative germline and pluripotent stem cells in the adult mouse ovary and their differentiation potential into germ and somatic cells. In ovary tissues and cells harvested from pre-differentiation step, the expression of pluripotent and germline stem cell markers was analysed by reverse transcription-polymerase chain reaction (RT-PCR), immunofluorescence staining and western blotting. Embryoid bodies that formed in this step were analysed using immunofluorescence staining and transmission electron microscopy. Ovarian stem cells were induced to differentiate into oocyte, osteoblast, chondrocyte and neural cells. Besides morphological observation, differentiated cells were analysed by RT-PCR, histochemical and immunofluorescence staining. Expression of germline and pluripotent stem cell markers both in mRNA and at the protein level were detected in the pre-differentiated cells and ovary tissues. As a result of the differentiation process, the formation of oocyte-like cells, osteoblasts, chondrocytes and neural cells was observed and characteristics of differentiated cells were confirmed using the methods mentioned above. Our study results revealed that the adult mouse ovary contains germline and pluripotent stem cells with the capacity to differentiate into oocyte-like cells, osteoblasts, chondrocytes and neural cells.

Mathematical modeling of the female reproductive system: from oocyte to delivery

From ovulation to delivery, and through the menstrual cycle, the female reproductive system undergoes many dynamic changes to provide an optimal environment for the embryo to implant, and to develop successfully. It is difficult ethically and practically to observe the system over the timescales involved in growth and development (often hours to days). Even in carefully monitored conditions clinicians and biologists can only see snapshots of the development process. Mathematical models are emerging as a key means to supplement our knowledge of the reproductive process, and to tease apart complexity in the reproductive system. These models have been used successfully to test existing hypotheses regarding the mechanisms of female infertility and pathological fetal development, and also to provide new experimentally testable hypotheses regarding the process of development. This new knowledge has allowed for improvements in assisted reproductive technologies and is moving toward translation to clinical practice via multiscale assessments of the dynamics of ovulation, development in pregnancy, and the timing and mechanics of delivery. WIREs Syst Biol Med 2017, 9:e1353. doi: 10.1002/wsbm.1353 For further resources related to this article, please visit the WIREs website.

Non-linear compartmental models

The linear compartmental model arises when ‘particles’ move independently between (or out of) a system of compartments in a stochastically similar way. With a given ‘initial’ particle count, the subsequent compartmental particle counts follow multinomial probability distributions (Faddy (1976)) for Markov or semi-Markov movement processes. One immediate consequence of this is that the variance of the compartmental particle count is always less than the mean, with the result that the coefficient of variation is very small for large mean counts. In applications (e.g, Faddy, Jones and Edwards (1976)) this underestimation of the variation can be a shortcoming of a compartmental analysis. Clustering, introduced by Matis and Wehrly (1981), where ‘clusters’ of particles may move together, is a way in which increased variability may be attained. Increased variability in general will result from relaxing the main assumption that gives rise to a linear model: independent behaviour of the particles. Such nonlinear compartmental models can be generally difficult to handle; in this paper some particular cases are discussed and illustrated with reference to one- and twocompartment systems.

The Oldham Notebooks: an analysis of the development of IVF 1969-1978. VI. Sources of support and patterns of expenditure

Three major sources of financial support for the research undertaken by Edwards, Steptoe and Purdy between 1969 and 1978 are identified: the Ford Foundation, Oldham and District General Hospital (ODGH) Management Committee, and Miss Lillian Lincoln Howell via the American Friends of Cambridge University. Significant possible financial support from the World Health Organization was also identified. In addition, evidence of support in kind from GD Searle and Co. plus staff at ODGH was found. Expenditure on salaries of staff at Oldham was negligible, as most volunteered their time outside of their official paid duties. Work in Cambridge was evidently funded largely from Ford Foundation grants, as was Edwards' salary and probably that of Purdy. Clinical costs seem to have been largely borne by ODGH. The funds from Lillian Lincoln Howell supported travel and accommodation costs plus office costs. Overall, Edwards, Steptoe and Purdy achieved reasonable support for the programme of research, despite the initial rejection of funding by the Medical Research Council. However, this was at the expense of considerable inconvenience to Purdy and Edwards, and depended upon the good will of staff led by Muriel Harris in Oldham, who donated their time and expertise. As a result of our research, we conclude that, to Edwards, Steptoe and Purdy, should be added the names of two other hitherto neglected people who were essential to the success of this pioneering research: namely Muriel Harris and Lillian Lincoln Howell.

Post-natal oogenesis: a concept for controversy that intensified during the last decade

For decades, scientists have considered that female mammals are born with a lifetime reserve of oocytes in the ovary, irrevocably fated to decline after birth. However, controversy in the matter of the possible presence of oocytes and granulosa cells that originate from stem cells in the adult mammalian ovaries has been expanded. The restricted supply of oocytes in adult female mammals has been disputed in recent years by supporters of neo-oogenesis, who claim that germline stem cells (GSCs) exist in the ovarian surface epithelium (OSE) or the bone marrow (BM). Differentiation of ovarian stem cells (OSCs) into oocytes, fibroblast-like cells, granulosa phenotype, neural and mesenchymal type cells and generation of germ cells from OSCs under the contribution of an OSC niche that consists of immune system-related cells and hormonal signalling has been claimed. Although these arguments have met with intense suspicion, their confirmation would necessitate the revision of the current classic knowledge of female reproductive biology.

Stem cells and the reproductive system: historical perspective and future directions

Recent findings in stem cell biology have presented new perspectives and opportunities for the treatment of reproductive disease. In a departure from the long held dogma of embryologically fixed numbers of oocytes, current literature suggests that human ovaries contain stem cells which form new oocytes even in adulthood and that these stem cells can be cultured in vitro to develop into mature oocytes. These findings have provided new hope and broader options for fertility preservation. Evidence of endometrial regeneration by bone marrow stem cells in endometrial tissue of women who received bone marrow transplant highlight potential for the novel treatments of uterine disorders and supports new theories for the etiology of endometriosis - ectopic transdifferentiation of stem cells. Further, endometrial derived stem cells have been demonstrated to be useful in the treatment of several chronic and often debilitating diseases, including Parkinson's Disease and Diabetes. Other cells that may present future therapeutic benefits for a myriad of disease states include placental and fetal cells which enter maternal circulation during pregnancy and can later promote parenchymal regeneration in maternal tissue. These findings highlight novel functions of the uterus and ovaries. They demonstrate that the uterus is a dynamic organ permeable to fetal stem cells capable of transdifferentiation as well as a renewable source of multipotent stem cells. While we still have much to understand about stem cells, their potential applications in reproductive biology and medicine are countless.

Hormone-controlled culture of secondary follicles of domestic cats

Ovaries were obtained from domestic cats during ovariohysterectomy. Large, preantral follicles were freed by dissection and mechanical crushing, and were cultured in TCM 199 + 10% FCS medium in the presence or absence of hormones (FSH, hydrocortisone and Insulin-Transferrin-Selenite) as well as in hypoxanthine. A decline in growth potential along with increasing follicle size were observed after one week, with no FSH added. Hormone-supplemented medium was found to induce growth to 2 or 3 times the original volume in more than 80% of follicles of all sizes. Oocyte diameters were continuously increasing, depending on follicle size, and reached 90 mum (80 %) at the point of antrum formation. Nuclear configuration of oocytes from follicles which had been cultured without addition of hormones up to the antral stage indicated a high rate of degeneration which, however, could be reduced by gonadotrophic stimulation. Meiosis at the germinal vesicle stage was found to be inhibited by hypoxanthine. For some oocytes, evidence was provided to meiotic maturation up to extrusion of the first polar body.

Prepubertal primordial follicle loss in mice is not due to classical apoptotic pathways

More than half of the primordial follicles that are formed by Day 6 of postnatal life in the mouse will be eliminated from the ovary by the time of puberty. Apoptosis, a form of programmed cell death, is one mechanism by which these follicles could be actively lost. To investigate whether apoptosis is responsible for the loss of primordial follicles, follicular atresia was examined during the prepubertal period, when follicles die and are cleared from the ovary at an extremely high rate. Four hallmarks of classical apoptosis were measured in follicles present in prepubertal ovaries. The primordial follicle cohort was not positively associated with nuclear condensation or cell shrinkage, activation of caspase 3, cleavage of poly(ADP ribose) polymerase 1 (PARP1), or fragmentation of DNA. These data are consistent with a nonapoptotic pathway that is responsible for small follicle death.

Stem cells and female reproduction

Several recent findings in stem cell biology have resulted in new opportunities for the treatment of reproductive disease. Endometrial regeneration can be driven by bone marrow derived stem cells. This finding has potential implications for the treatment of uterine disorders. It also supports a new theory for the etiology of endometriosis. The ovaries have been shown to contain stem cells that form oocytes in adults and can be cultured in vitro to develop mature oocytes. Stem cells from the fetus have been demonstrated to lead to microchimerism in the mother and implicated in several maternal diseases. Additionally the placenta may be another source of hematopoietic stem cell. Finally endometrial derived stem cells have been demonstrated to differentiate into non-reproductive tissues. While we are just beginning to understand stem cells and many key questions remain, the potential advantages of stem cells in reproductive biology and medicine are apparent.

Ovarian structure in mice lines selected for weight

Selection for body weight at 49 day of age (s and h, downward selected lines; s' and h', upward selected lines) affected reproductive traits in CF1 mice lines. The objective of this study was to compare ovarian structures in females of these lines, as well as in unselected controls (Line t). The number of ovarian follicles (N), follicle diameter (FD), number of corpora lutea (CL), litter size (LS), and body weight (W), were recorded. There were significant differences among lines for N, FD, CL, LS and W; means values for the lines with the greatest difference for post-pubertal females were: N(s) = 19.3 and N(s') = 32.7; FD(h') = 161.7 and FD(s') = 178.2; CL(h) = 10.3 and CL(s') = 21.9; LS(s) = 6.0 and LS(h') = 11.1; W(h) = 18.9 and W(s') = 32.4. There were also differences between positive lines; Line s' had a higher proportion of large follicles in pre-pubertal females, a greater capacity to convert these follicles into CL, but a lower capacity to maintain embryos until term than Line h'. For negative lines, Line h apparently had a reduced incidence of embryonic loss when compared with Line s. In conclusion, selection for body weight modified ovarian structure, as well as reproductive efficiency.

Quantification of healthy follicles in the neonatal and adult mouse ovary: evidence for maintenance of primordial follicle supply

Proliferation and partial meiotic maturation of germ cells in fetal ovaries is believed to establish a finite, non-renewable pool of primordial follicles at birth. The supply of primordial follicles in postnatal life should be depleted during folliculogenesis, either undergoing atresia or surviving to ovulation. Recent studies of mouse ovaries propose that intra- and extraovarian germline stem cells replenish oocytes and form new primordial follicles. We quantified all healthy follicles in C57BL/6 mouse ovaries from day 1 to 200 using unbiased stereological methods, immunolabelling of oocyte meiosis (germ cell nuclear antigen (GCNA)) and ovarian cell proliferation (proliferating cell nuclear antigen (PCNA)) and electronmicroscopy. Day 1 ovaries contained 7924+/-1564 (s.e.m.) oocytes or primordial follicles, declining on day 7 to 1987+/-203, with 200-800 oocytes ejected from individual ovaries on that day and day 12. Discarded oocytes and those subjacent to the surface epithelium were GCNA-positive indicating their incomplete meiotic maturation. From day 7 to 100 mean numbers of primordial follicles per ovary were not significantly depleted but declined at 200 days to 254+/-71. Mean numbers of all healthy follicles per ovary were not significantly different from day 7 to 100 (range 2332+/-349-3007+/-322). Primordial follicle oocytes were PCNA-negative. Occasional unidentified cells were PCNA-positive with mitotic figures observed in the cortex of day 1 and 12 ovaries. Although we found no evidence for ovarian germline stem cells, our data support the hypothesis of postnatal follicle renewal in postnatal and adult ovaries of C57BL/6 mice.

Tumor necrosis factor (TNF) receptor type 2 is an important mediator of TNF alpha function in the mouse ovary

It is believed that a finite pool of primordial follicles is established during embryonic and neonatal life. At birth, the mouse ovary consists of clusters of interconnected oocytes surrounded by pregranulosa cells. Shortly after birth these structures, termed germ cell cysts or nests (GCN), break down to facilitate primordial follicle formation. Tumor necrosis factor alpha (TNF) is a widely expressed protein with myriad functions. TNF is expressed in the ovary and may regulate GCN breakdown in rats. We investigated whether it participates in GCN breakdown and follicle formation in mice by using an in vitro ovary culture system as well as mutant animal models. We found that TNF and both receptors (TNFRSF1A and TNFRSF1B) are expressed in neonatal mouse ovaries and that TNF promotes oocyte death in neonatal ovaries in vitro. However, deletion of either receptor did not affect follicle endowment, suggesting that TNF does not regulate GCN breakdown in vivo. Tnfrsf1b deletion led to an apparent acceleration of follicular growth and a concomitant expansion of the primordial follicle population. This expansion of the primordial follicle population does not appear to be due to decreased primordial follicle atresia, although this cannot be ruled out completely. This study demonstrates that mouse oocytes express both TNF receptors and are sensitive to TNF-induced death. Additionally, TNFRSF1B is demonstrated to be an important mediator of TNF function in the mouse ovary and an important regulator of folliculogenesis.

Methods for quantifying follicular numbers within the mouse ovary

Accurate estimation of the number of ovarian follicles at various stages of development is an important indicator of the process of folliculogenesis in relation to the endocrine signals and paracrine/autocrine mechanisms that control the growth and maturation of the oocytes and their supporting follicular cells. There are 10-fold or greater differences in follicular numbers per ovary at similar ages and/or strains reported in earlier studies using various methods, leading to difficulties with interpretation of ovarian function in control vs experimental conditions. This study describes unbiased, assumption-free stereological methods for quantification of early and growing follicular numbers in the mouse ovary. A fractionator approach was used to sample a defined fraction of histological sections of adult wild-type ovaries. Primordial and primary follicles were counted independently with the optical and physical disector methods. The fractionator/disector methods, which are independent of follicular size or shape, gave estimations of 1930 ± 286 (S.E.M.) and 2227 ± 101 primordial follicles, and 137 ± 25 and 265 ± 32 primary follicles per ovary at 70 and 100 days of age respectively. From exact counts on serial sections, secondary and later follicular numbers at 100 days of age were estimated at 135 per ovary. Remnants of zona pellucidae (a marker of previous follicular atresia) were estimated using a fractionator/physical disector approach and were approximately 500 per ovary. The application of the quantitative methods described will facilitate an improved understanding of follicular dynamics and the factors that mediate their growth and maturation and allow for a better comparison between different studies.

Germline stem cells and follicular renewal in the postnatal mammalian ovary

A basic doctrine of reproductive biology is that most mammalian females lose the capacity for germ-cell renewal during fetal life, such that a fixed reserve of germ cells (oocytes) enclosed within follicles is endowed at birth. Here we show that juvenile and adult mouse ovaries possess mitotically active germ cells that, based on rates of oocyte degeneration (atresia) and clearance, are needed to continuously replenish the follicle pool. Consistent with this, treatment of prepubertal female mice with the mitotic germ-cell toxicant busulphan eliminates the primordial follicle reserve by early adulthood without inducing atresia. Furthermore, we demonstrate cells expressing the meiotic entry marker synaptonemal complex protein 3 in juvenile and adult mouse ovaries. Wild-type ovaries grafted into transgenic female mice with ubiquitous expression of green fluorescent protein (GFP) become infiltrated with GFP-positive germ cells that form follicles. Collectively, these data establish the existence of proliferative germ cells that sustain oocyte and follicle production in the postnatal mammalian ovary.

Is follicular atresia biphasic?

OBJECTIVE

To examine the rate of human follicular depletion and the interpretation of curved scatters on log-linear plots.

DESIGN

Four mathematical models were tested with use of data drawn from published autopsy studies and histologic analyses of ovaries.

SETTING

None.

PATIENT(S)

None.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

None.

RESULT(S)

Human oocyte depletion data do not support the inference of a biphasic follicular atresia. On original measurement scales there is no perturbation in the data between ages 37 and 40, and the instantaneous rate of follicle loss is lower after age 40 than ever before.

CONCLUSION(S)

There is no abrupt increase in the "rate" of follicular atresia that corresponds with a drop in fecundability or an increase in risk of chromosomal abnormalities at approximately age 38. The apparent abrupt increase in rate of follicular depletion is an artifact of log-linear transformation.

Influence of sampling on the reproducibility of ovarian follicle counts in mouse toxicity studies

Different ovarian follicle counting procedures were investigated to reduce labor while retaining statistical power. Intact ovaries of untreated CD-1 mice (20/group) from National Toxicology Program Reproductive Assessment by Continuous Breeding (RACB) studies were serially sectioned at 6 microm. Mean numbers of small and growing follicles were used to assess sampling efficiency. In 10 mice per group, comparisons were made between 10% nonrandom samples from every 10th section starting at either the first or sixth section having follicles (approximately 40 sections per ovary). These 10% counts were compared with 5% (20 sections) and 20% (80 sections) nonrandom samples and with 1% (4 sections), 5%, or 10% random samples from the same 10 animals. For two studies, a 10% nonrandom sample was analyzed from 20 mice per group. Follicle counts for each group were comparable regardless of the sampling paradigm. Four to 10 animals provided 90% confidence that a 20% difference in mean counts would be detected. The 1% sample had a larger error term and, thus, slightly reduced statistical power. These data suggest that follicle counts from 1% or 5% random samples may provide a suitable screen for ovarian toxicity.

Ovarian aging, follicular depletion, and steroidogenesis

The follicular population. Menopause occurs as a consequence of the continuous utilization of a fixed store of primordial follicles leading to almost total depletion at mid-life or sometimes earlier. The great majority of follicles that disappear are lost by atresia rather than by ovulation, and the rate of loss accelerates in the last decade of menstrual life. The numbers of growing follicles at a given age are correlated with those of the primordial stages, but there are always more being recruited than required for a single ovulation each month. The extent to which a dwindling number is responsible for the character of cycles of the menopausal transition remains unclear. Ovarian secretion. While menstrual cycles remain regular, circulating concentrations of estradiol and progesterone are relatively independent of age. On the other hand, serum levels of inhibin are substantially lower in women approaching menopausal age, probably reflecting smaller numbers of growing follicles at the beginning of the cycle. Alleviation of negative feedback on the pituitary gland results in a greater output of follicle-stimulating hormone (FSH), but the effects of chronic superstimulation on the aging ovary are not known. Follicular aging. Aging of long-lived oocytes could affect the developmental potential of the follicle unit as well as compromising the chances of late pregnancy. Another important field of investigation is therefore to determine the balance of responsibility between cumulated damage to molecules by toxins, on the one hand, and the effects of physiological aging and such epiphenomena as the changing hormonal or paracrine environments, on the other.

Morphometric study of the human neonatal ovary

A morphometric analysis, based on mathematical evaluations and stereological methods, has been used to study five left neonatal ovaries, removed from full-term neonates with a 46,XX karyotype free from malformations of the genital apparatus. Each ovary was completely cut obtaining serial sections and one 1-micron-thick section every 1,000 microns was examined. Ovarian length ranged from 9 to 17 mm (mean 13 mm), width from 3.5 to 7 mm (mean 5.7 mm), thickness from 2.5 to 5 mm (mean 4 mm), and volume from 82.23 to 198.3 mm3 (mean 125.88 mm3). In the ovarian cortex, primitive cortical tissue accounted for 10-20% of the total volume, follicles for 10-25% and interstitium for 35-45%; 10-30% of the organ consisted of inner medulla. The total follicle number ranged from 130,000 to 385,000 per ovary, with an average of 266,000 with 95% being represented by primordial follicles. In all ovaries examined follicular growth was still in process, with follicles at different stages of development.

An analysis of factors influencing the establishment of a clinical pregnancy in an ultrasound-based ambulatory in vitro fertilization program

In the study period (June 1984 to December 1986), 2232 cycles were stimulated in 1294 patients. Ultrasound-directed oocyte recovery (UDOR) was performed as an ambulatory procedure in 1737 (77.8%) cycles, resulting in 1375 embryos transfers (ET). Age, etiology, menstrual cycle length, number of oocytes collected, and number of embryos transferred were important determinants of the outcome. The number of attempts at in vitro fertilization did not affect the clinical pregnancy rate (CPR). In patients receiving four embryos, the CPR appeared to be highest when up to seven embryos were available for transfer. The fertilization rate in an individual cycle had a good prognostic value, the implantation rate being highest when 7 to 9 oocytes were retrieved and greater than 60% of these were fertilized. When 10 or more oocytes were collected, the implantation rate showed a progressive decline, regardless of the fertilization rate. Furthermore, multiple pregnancies failed to occur when greater than 12 oocytes were retrieved or more than eight embryos were available for transfer. These data suggest that, in excessively stimulated cycles, the quality of oocytes and embryos or uterine receptiveness may be suboptimal, and the transfer of more than four embryos is unlikely to increase the success rate.

The kinetics of pre-antral follicle development in ovaries of CBA/Ca mice during the first 14 weeks of life

The kinetics of ovarian follicle growth and death have been estimated in virgin inbred mice using a compartmental model and data obtained from differential follicle counts in histologically sectioned ovaries. The results showed that both growth and death rates are dependent on stage of development, defined by the compartments, and age, indicated in the model by step functions with transitions at 20 and 60 days of age. During the initial phase of postnatal ovarian development, large numbers of follicles disappeared from the non-growing reserve as a result of the combined effects of follicle death and recruitment into the growing population. The reduced death rate after 20 days led to a secondary peak in the numbers of follicles at intermediate stages. In contrast to these fluctuations, the number of large follicles, including pre-ovulatory types, were remarkably constant after this age and the rate of outflow stabilized at two to three follicles per day after an initially high value. This rate is sufficient for the normal ovulation rate in a 4-day oestrous cycle with a small surplus of follicles undergoing atresia. The rates of migration through successive stages of development decreased during ageing as large follicles began to emerge at the approach of puberty: this result may indicate that the recruitment of small growing follicles is influenced by a feedback effect.

Effect of oocyte number and rate of atresia on the age of menopause

Menopause occurs when oocyte number falls below the threshold required for ovarian function. The age of menopause is decreased by some drugs, some occupational exposures, and cigarette smoke (both active and passive). Using data collected by Block (Acta Anat (Basel) 1954; 14:208), we have constructed four, two parameter models to explore the effect of oocyte number and rate of atresia on age at menopause. The models used are: linear [O(A) = OB + R * A]; natural log [O(A) = R * In (A)]; exponential [O(A) = OB * exp(R * A)], and power [O(A) = OB * Age(R)]. OB = oocyte number at birth, ATR = rate of atresia, and O(A) = number of oocytes at age A. The parameters for the four models are: (formula; see text) Each model has different behavior with respect to alterations in oocyte number and rate of atresia on age at menopause. Animal studies suggest that ovarian failure is only weakly dependent on oocyte number, consistent with the power and exponential models. These suggest that the decrease in age at menopause following xenobiotic exposures results from an increase in the rate of atresia.

Scintigraphy of normal mouse ovaries with monoclonal antibodies to ZP-2, the major zona pellucida protein

The zona pellucida is an extracellular glycocalyx, made of three sulfated glycoproteins, that surrounds mammalian oocytes. Parenterally administered monoclonal antibodies specific for ZP-2, the most abundant zona protein, localize in the zona pellucida. When labeled with iodine-125, these monoclonal antibodies demonstrate a remarkably high target-to-nontarget tissue ratio and provide clear external radioimaging of ovarian tissue.

Follicular growth and kinetics during the estrous cycle, pregnancy and postpartum in the Indian mole rat (Bandicota bengalensis)

Follicular growth and kinetics were studied in detail in the ovaries of the Indian mole rat (Bandicota bengalensis) during various stages of the estrous cycle; days 7, 12, 15, 19, and 21 of pregnancy; and day 2 postpartum. The sizes of follicles, oocytes, nuclei, and nucleoli were measured. In all rats, regression coefficients, a, and intercepts, b, were calculated in oocyte/follicle, oocyte nucleus/follicle and oocyte nucleus/oocyte regressions. The oocyte reached its maximum size when the average follicle diameter was 117 microns in nonpregnant rats and 131 microns in pregnant rats. The oocyte nucleus attained maximum size when the follicle diameter was 110 microns during the estrous cycle and 111 microns during pregnancy and postpartum. Maximum values of the diameter of the largest antral follicle and average diameter of the four largest antral follicles were observed during proestrus (473 and 442 microns, respectively) and on day 21 of pregnancy (611 and 538 microns, respectively). Chi 2 analysis showed that distribution of various types of follicles was not independent of the stage of the estrous cycle and pregnancy. In estrus and metestrus most of the follicles were between stages I and V. However, by diestrus and proestrus, follicles of all size groups developed. The numbers of stage I and II follicles did not differ as pregnancy advanced. More stage V follicles were present on day 12 than on day 7 of pregnancy; however, their numbers decreased by day 15. Afterwards, progressive increase of stage V and (VI + VII) follicles was observed until day 21. This was accompanied by the shift of follicles from stage (III + IV) on days 19 and 21 of pregnancy and even of stage II on day 2 postpartum. Wherever possible, the results have been compared with previous observations in various rodent species.