The effects of IVF aspiration on the temperature, dissolved oxygen levels, and pH of follicular fluid

Enhancing oxygen delivery to ovarian follicles by three different methods markedly improves growth in serum-containing culture medium

Invitro ovarian follicle culture systems are routinely used to study folliculogenesis and may provide solutions for infertility. Mouse follicles are typically cultured in standard gas-impermeable culture plates under gas phase oxygen concentrations of 5% or 20% (v/v). There is evidence that these conditions may not provide adequate oxygenation for follicles cultured as non-attached intact units in medium supplemented with serum and high levels of FSH. Three different methods of enhancing follicle oxygenation were investigated in this study: increasing the gas phase oxygen concentration, inverting the culture plates and using gas-permeable culture plates. Follicles cultured under 40% O2 were significantly larger (P P P 2 . These effects were associated with reduced secretion of vascular endothelial growth factor (P P P invivo -matured follicles (~500μm in diameter). Such follicular development is not possible under hypoxic conditions.

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.

Limitations of ultrasound guided follicular aspiration for analysis of ovarian follicular fluid in dairy cattle

The aim of this study was to evaluate the applicability of ovum pick-up equipment for follicular fluid collection from various follicular structures (experiment 1) and for recovery of follicular fluid for acid-base balance analysis (experiment 2). An ultrasound scanner equipped with a 5-MHz convex transducer was used for transvaginal ultrasound-guided follicular aspiration. A 17-gauge, 60-cm aspiration needle was connected with a shortened aspiration line. The fluid was aspirated manually into a 2 ml plastic syringe at a speed of approximately 0.2 ml/s. The success of aspiration was higher in ovarian cysts (100%) and single follicles larger than 13 mm (76.7%) compared to single follicles smaller than 12 mm (20%,p< 0.001). The success of aspiration of multiple follicles on day 4 (diameter of 7–9 mm) was higher (90.9%) compared to follicles on day 2 (diameter of 4-6 mm) (66.7%,p< 0.05) in experiment 1. The fluid from ovarian cysts > 25 mm in diameter was aspirated in a two-step procedure (samples 1 and 2) for the determination of pH, HCO3,BE, pCO2and pO2(experiment 2). The indicators were compared between samples 1 and 2. Higher pO2as well as pH and lower pCO2in sample 1 compared to sample 2 showed insufficient anaerobic conditions during the first phase of the puncture in experiment 2. Our study brings for the first time the finding that the ovum pick-up equipment used in our experiments is suitable for the collection of follicular fluid only from larger follicular structures. The sampling of follicular fluid for acid-base balance assays requires the development of a special new device to prevent samples from coming into contact with air during aspiration.

Epigenetic profile of developmentally important genes in bovine oocytes

Assisted reproductive technologies are associated with an increased incidence of epigenetic aberrations, specifically in imprinted genes. Here, we used the bovine oocyte as a model to determine putative epigenetic mutations at three imprinted gene loci caused by the type of maturation, either in vitro maturation (IVM) in Tissue Culture Medium 199 (TCM) or modified synthetic oviduct fluid (mSOF) medium, or in vivo maturation. We applied a limiting dilution approach and direct bisulfite sequencing to analyze the methylation profiles of individual alleles (DNA molecules) for H19/IGF2, PEG3, and SNRPN, which are each associated with imprinting defects in humans and/or the mouse model, and are known to be differentially methylated in bovine embryos. Altogether, we obtained the methylation patterns of 203 alleles containing 4,512 CpG sites from immature oocytes, 213 alleles with 4,779 CpG sites from TCM-matured oocytes, 215 alleles/4,725 CpGs in mSOF-matured oocytes, and 78 alleles/1,672 CpGs from in vivo-matured oocytes. The total rate of individual CpGs and entire allele methylation errors did not differ significantly between the two IVM and the in vivo group, indicating that current IVM protocols have no or only marginal effects on these critical epigenetic marks. Furthermore, the mRNA expression profiles of the three imprinted genes and a panel of eight other genes indicative of oocyte competence were determined by quantitative real-time PCR. We found different mRNA expression profiles between in vivo-matured oocytes versus their in vitro-matured counterparts, suggesting an influence on regulatory mechanisms other than DNA methylation.

Theoretical investigation into the dissolved oxygen levels in follicular fluid of the developing human follicle using mathematical modelling

Oxygen levels in the follicle are likely to be critical to follicle development. However, a quantitative description of oxygen levels in the follicle is lacking. Mathematical modelling was used to predict the dissolved oxygen levels in the follicular fluid of the developing human follicle. The model predictions showed that follicular fluid dissolved oxygen levels are highly variable among follicles, due to the unique geometry of individual follicles. More generally, predictions showed that oxygen levels in follicular fluid increase rapidly during the initial early antral stages of follicle growth before peaking in the later early antral phase. Follicular fluid dissolved oxygen levels then decline through to the beginning of the pre-ovulatory phase, from which they increase through to ovulation. Based on the best available parameter estimates, the model predictions suggest that the mean dissolved oxygen levels in human follicular fluid during the late antral and pre-ovulatory phases range between 11 and 51 mmHg (~1.5–6.7 vol%). These predictions suggest that the human ovarian follicle is a low-oxygen environment that is often challenged by hypoxia, and are in agreement with only some published data on follicular fluid oxygen levels. Predictions are discussed in relation to follicle health and oocyte culture.

Interactions between oxygen tension and glucose concentration that modulate actions of heat shock on bovine oocytes during in vitro maturation

Exposure of oocytes to elevated temperature (i.e. heat shock) during maturation can reduce fertilization rate and development of the resultant embryos. Given the possible role of free radicals in actions of heat shock on cellular function, we tested the hypothesis that a high oxygen environment exacerbates the magnitude of deleterious effects of heat shock on in vitro maturation of bovine oocytes. A preliminary experiment was performed to establish conditions for oocyte maturation that would be independent of oxygen concentration. Oocytes were matured in a modified tissue culture medium-199 (mTCM-199) or modified synthetic oviduct fluid (mSOF) containing 5.6 or 20 mM glucose and under either high (atmospheric oxygen, approximately 21%, v/v) or low oxygen (5%, a value approximating oxygen content of the follicle). For oocytes matured in mTCM-199, development was greater in high oxygen than in low oxygen, whereas development was unaffected by oxygen using mSOF (mediumxoxygen, P<0.05). Accordingly, mSOF was used as the maturation medium in a second study to test the effect of oxygen concentration on the magnitude of actions of heat shock during maturation. Maturation was at 38.5 degrees C for 22 h (control) or 41 degrees C for 12h and 38.5 degrees C for 10h (heat shock). Heat shock slightly decreased cleavage rate, regardless of the maturation conditions, and decreased blastocyst development under all maturation conditions except for the group matured under high oxygen and high glucose (temperature x glucose for oocytes under low oxygen, P<0.05). The percentage of oocytes becoming blastocysts for control and heat shocked oocytes was 25.9% versus 22.5% (low oxygen -- 5.6 mM glucose), 41.6% versus 34.9% (low -- 20 mM), 41.7% versus 35.0% (high -- 5.6 mM), and 37.6% versus 37.5% (high -- 20 mM). In conclusion, under an oxygen tension that approached physiological conditions, heat shock during in vitro maturation reduced oocyte competence for fertilization and subsequent development.

Mathematical modelling of oxygen transport-limited follicle growth

Mathematical modelling was used to investigate oxygen transport in the developing ovarian follicle. In contrast to previous findings, the results show that oxygen can reach the oocyte in large preantral follicles. This is largely due to the inclusion of fluid voidage in the model and improved estimates of oxygen diffusion coefficients through the granulosa. The results also demonstrate that preantral follicles will eventually reach a size beyond which further growth will result in the follicle becoming increasingly anoxic. The predicted size range at which this occurs is consistent with the size range at which antrum formation is observed in many mammals. This suggests that the antrum formation stage of follicular growth may be pivotal to the further development and ultimate fate of the follicle, and that antrum formation itself may represent a mechanism by which the follicle can overcome oxygen limitations. This was supported through extension of the model to the antral follicle, which showed that antrum formation can provide a way in which the follicle can continue to grow and yet avoid becoming hypoxic. The results of the model were consistent with observed follicle development.