Yvonne Stokes

Prematuration with Cyclic Adenosine Monophosphate Modulators Alters Cumulus Cell and Oocyte Metabolism and Enhances Developmental Competence of In Vitro-Matured Mouse Oocytes

ABSTRACT Oocyte in vitro maturation (IVM) is an important assisted reproductive technology and research tool. The adoption of IVM into routine clinical practice has been hindered by its significantly lower success rates compared to conventional in vitro fertilization. Cyclic AMP (cAMP) modulation and follicle-stimulating hormone (FSH), independently, have long been known to improve IVM oocyte developmental competence. This study comprehensively examined the effects of FSH and cAMP/cGMP modulation, alone and in combination, on IVM oocyte metabolism and developmental outcomes. Mouse cumulus-oocyte complexes (COCs) were subjected to a 1 h prematuration phase ± the cAMP modulator forskolin and cAMP/cGMP modulator 3-isobutyl-1-methylxanthine followed by IVM ± FSH. Prematuration with these cyclic nucleotide modulators or IVM with FSH significantly improved oocyte developmental competence and reduced spindle abnormalities compared to spontaneous IVM (no treatment); however, these two treatments in combination endowed even greater developmental competence (improved subsequent blastocyst rates and quality; P < 0.05), albeit blastocyst yield and quality remained significantly lower than that of oocytes matured in vivo. A significant additive effect of combined IVM treatments was evident as increased COC lactate production and oxygen consumption and enhanced oocyte oxidative metabolism, ATP production, ATP:ADP ratio, and glutathione levels (P < 0.05). Nevertheless, IVM increased reactive oxygen species production, particularly as a consequence of FSH addition, relative to in vivo matured oocytes. In conclusion, improvements in the embryo yield following IVM is associated with increased COC oxygen consumption and oocyte oxidative metabolism, but these remain metabolically and developmentally less competent relative to in vivo derived oocytes.

The role of inertia in extensional fall of a viscous drop

In flows of very viscous fluids, it is often justifiable to neglect inertia and solve the resulting creeping-flow or Stokes equations. For drops hanging beneath a fixed wall and extending under gravity from an initial rest state, an inevitable consequence of neglect of inertia and surface tension is that the drop formally becomes infinite in length at a finite crisis time, at which time the acceleration of the drop, which has been assumed small relative to gravity

On generalised penalty approaches for slip, free surface and related boundary conditions in viscous flow simulation

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Estimation of glucose uptake by ovarian follicular cells.

, formally also becomes infinite. This is a physical impossibility, and the acceleration must in fact approach the (finite) free-fall value

Follicle Structure Influences the Availability of Oxygen to the Oocyte in Antral Follicles

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Mathematical Modeling of Glucose Supply Toward Successful In Vitro Maturation of Mammalian Oocytes

. However, we verify here, by a full Navier–Stokes computation and also with a slender-drop approximation, that the crisis time is a good estimate of the time at which the bulk of the drop goes into free fall. We also show that the drop shape at the crisis time is a good approximation to the final shape of the freely falling drop, prior to smoothing by surface tension. Additionally, we verify that the drop has an initial acceleration of

Numerical design tools for thermal replication of optical-quality surfaces

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Behavior of a particle-laden flow in a spiral channel

, which quickly decreases as viscous forces in the drop become dominant during the early stages of fall.

Slow slumping of a very viscous liquid bridge

Purpose – The purpose of this paper is to extend the penalty concept to treat partial slip, free surface, contact and related boundary conditions in viscous flow simulation.Design/methodology/approach – The penalty partial‐slip formulation is analysed and related to the classical Navier slip condition. The same penalty scheme also allows partial penetration through a boundary, hence the implementation of porous wall boundaries. The finite element method is used for investigating and interpreting penalty approaches to boundary conditions.Findings – The generalised penalty approach is verified by means of a novel variant of the circular‐Couette flow problem, having partial slip on one of the cylindrical boundaries, for which an analytic solution is derived. Further verificationis provided by consideration of viscous flow over a sphere with partial slip on the surface, and comparison of numerical and classical solutions. Numerical studies illustrate the versatility of the approach.Research limitations/implic...

Quantifying oxygen diffusion in paraffin oil used in oocyte and embryo culture

In vitro maturation (IVM) of mammalian oocytes provides an alternative to traditional in vitro fertilization techniques for clinical treatment of infertility or animal breeding. IVM involves the collection of oocytes from the ovary prior to ovulation, with maturation occurring in a laboratory environment. The success of IVM is highly sensitive to the in vitro nutrient environment. The nurse cells surrounding the oocyte, known as cumulus cells, regulate this environment and removal of these cells reduces the ability of the oocyte to develop following insemination. Determining the nature of the interaction between the oocyte and cumulus cells, collectively called the cumulus–oocyte complex (COC), is a difficult task experimentally. Here we use a combination of experimental and mathematical techniques to investigate glucose transport within bovine COCs and find quantitative estimates of the glucose uptake rates of the oocyte and cumulus cells. Surprisingly, our modeling shows the rate of uptake of glucose by the oocyte to increase and then decrease with concentration, a result that needs further experimental investigation but which supports the expectation that high and low glucose concentrations are detrimental to oocyte development. The methodology described is suitable for use across species and for investigating the transport of other important nutrients within the COC.