Oxygen Tension and Medium Supplements for In Vitro Maturation of Bovine Oocytes Cultured Individually in a Chemically Defined Medium

An Overview of Reactive Oxygen Species Damage Occurring during In Vitro Bovine Oocyte and Embryo Development and the Efficacy of Antioxidant Use to Limit These Adverse Effects

The in vitro production (IVP) of bovine embryos has gained popularity worldwide and in recent years and its use for producing embryos from genetically elite heifers and cows has surpassed the use of conventional superovulation-based embryo production schemes. There are, however, several issues with the IVP of embryos that remain unresolved. One limitation of special concern is the low efficiency of the IVP of embryos. Exposure to reactive oxygen species (ROS) is one reason why the production of embryos with IVP is diminished. These highly reactive molecules are generated in small amounts through normal cellular metabolism, but their abundances increase in embryo culture because of oocyte and embryo exposure to temperature fluctuations, light exposure, pH changes, atmospheric oxygen tension, suboptimal culture media formulations, and cryopreservation. When uncontrolled, ROS produce detrimental effects on the structure and function of genomic and mitochondrial DNA, alter DNA methylation, increase lipid membrane damage, and modify protein activity. Several intrinsic enzymatic pathways control ROS abundance and damage, and antioxidants react with and reduce the reactive potential of ROS. This review will focus on exploring the efficiency of supplementing several of these antioxidant molecules on oocyte maturation, sperm viability, fertilization, and embryo culture.

Cysteamine Supplementation In Vitro Remarkably Promoted Rumen Fermentation Efficiency towards Propionate Production via Prevotella Enrichment and Enhancing Antioxidant Capacity

Cysteamine (CS) is a vital antioxidant product and nutritional regulator that improves the productive performance of animals. A 2 × 4 factorial in vitro experiment was performed to determine the effect of the CS supplementation levels of 0, 20, 40, and 60 mg/g, based on substrate weight, on the ruminal fermentation, antioxidant capacity, and microorganisms of a high-forage substrate (HF, forage:corn meal = 7:3) in the Statistical Analysis System Institute. After 48 h of incubation, the in vitro dry matter disappearance and gas production in the LF group were higher when compared with a low-forage substrate (LF, forge hay:corn meal = 3:7), which was analyzed via the use of the MIXED procedure of the HF group, and these increased linearly with the increasing CS supplementation (p < 0.01). With regard to rumen fermentation, the pH and acetate were lower in the LF group compared to the HF group (p < 0.01). However, the ammonia N, microbial crude protein, total volatile fatty acids (VFA), and propionate in the LF group were greater than those in the HF group (p < 0.05). With the CS supplementation increasing, the pH, ammonia N, acetate, and A:P decreased linearly, while the microbial crude protein, total VFA, and propionate increased linearly (p < 0.01). Greater antioxidant capacity was observed in the LF group, and the increasing CS supplementation linearly increased the superoxide dismutase, catalase, glutathione peroxidase, total antioxidant capacity, glutathione, and glutathione reductase, while it decreased the malondialdehyde (p < 0.05). No difference occurred in the ruminal bacteria alpha diversity with the increasing CS supplementation, but it was higher in the LF group than in the HF group (p < 0.01). Based on the rumen bacterial community, a higher proportion of Bacteroidota, instead of Firmicutes, was in the LF group than in the HF group. Furthermore, increasing the CS supplementation linearly increased the relative abundance of Prevotella, norank_f_F082, and Prevotellaceae_UCG-001 under the two substrates (p < 0.05). Prevotella, norank_f_F082, and Prevotellaceae_UCG-001 were positively correlated with gas production, rumen fermentation, and antioxidant capacity in a Spearman correlation analysis (r > 0.31, p < 0.05). Overall, a CS supplementation of not less than 20 mg/g based on substrate weight enhanced the rumen fermentation and rumen antioxidant capacity of the fermentation system, and it guided the rumen fermentation towards glucogenic propionate by enriching the Prevotella in Bacteroidetes.

Transcriptional regulation of HIF1α-mediated STAR expression in murine KK1 granulosa cell line involves cJUN, CREB and CBP-dependent pathways

Gonadal function is connected to hypoxia, with hypoxia-inducible factor (HIF) 1α, as a component of HIF1-complexes, regulating cellular adaptation to hypoxic conditions. In the ovary, it regulates follicular maturation, ovulation and luteal development. At the cellular level, HIF1-complexes coordinate the expression of steroidogenic acute regulatory protein (STAR), and thereby ovarian steroidogenesis. The functionality of STAR is associated with the cAMP/PKA-dependent pathways. In vitro, HIF1α is required for basal and cAMP-induced STAR expression, under ambient and reduced oxygen (O₂) tension. Lowering O₂ increases the responsiveness of the Star promoter towards cAMP and PKA mediates activation/phosphorylation (P) of several transcriptional factors, including cJUN and cAMP response element-binding protein (CREB), whose functionality is linked to HIF1 through utilization of CREB-binding protein (CBP). Since the mechanisms underlying HIF1α-dependent expression of STAR remain unknown, we investigated the involvement of HIF1α in CREB-, cJUN- and CBP-mediated expression of STAR using a well-characterized steroidogenic model, murine KK1 granulosa cells; ambient and lowered (10%) O₂ were applied. Our main findings were that while functional suppression of the α-subunit of HIF1 lowered STAR/P-STAR and steroidogenic output from granulosa cells, surprisingly the levels of P-CREB and its transcriptional activity were strongly induced. However, its association with the Star promoter was decreased, indicating dissociation of P-CREB from the promoter. Further, suppression of HIF1 activity ultimately diminished the expression of cJUN/P-cJUN and CBP. Finally, the study suggests that HIF1-complex: (1) regulates cJUN expression in granulosa cells, (2) is involved in regulating the recruitment of P-CREB to the Star promoter in (3) a mechanism which possibly involves the HIF1-dependent regulation of CBP expression.

Cellular and molecular alterations of buffalo oocytes cultured under two different levels of oxygen tension during in vitro maturation

This study was conducted to monitor the cellular and molecular changes of buffalo cumulus-oocytes complexes (COCs) cultured under high or low oxygen levels. Morphologically good quality COCs (n = 1627) were screened using brilliant cresyl blue (BCB) staining and placed into three groups (BCB+, BCB- and control). All groups of COCs were cultured under low (5%) or high (20%) oxygen tensions. Intracellular and molecular changes including oocyte ultrastructure, lipid contents, mitochondrial activity and transcript abundance of genes regulating different pathways were analyzed in the matured oocyte groups. The results revealed that oxygen tension did not affect cumulus expansion rates, however the BCB+ group had a higher (P ≤ 0.05) expansion rate compared with the BCB- group. BCB- oocytes recorded the lowest meiotic progression rate (P ≤ 0.05) under high oxygen levels that was linked with an increased level of reactive oxygen species (ROS) compared with the BCB+ oocytes. Ultrastructure examination indicated that BCB+ oocytes had a higher rate of cortical granules migration compared with BCB- under low oxygen tension. In parallel, our results indicated the upregulation of NFE2L2 in groups of oocytes cultured under high oxygen tension that was coupled with reduced mitochondrial activity. In contrast, the expression levels of MAPK14 and CPT2 genes were increased (P ≤ 0.05) in groups of oocytes cultured under low compared with high oxygen tension that was subsequently associated with increased mitochondrial activity. In conclusion, data from the present investigation indicated that low oxygen tension is a favourable condition for maintaining the mitochondrial activity required for nuclear maturation of buffalo oocytes. However, low-quality oocytes (BCB-) responded negatively to high oxygen tension by reducing the expression of gene-regulating metabolic activity (CPT2). This action was an attempt by BCB- oocytes to reduce the increased levels of endogenously produced ROS that was coupled with decreased expression of the gene controlling meiotic progression (MAPK14) in addition to nuclear maturation rate.

Hypoxia-inducible factor (HIF1alpha) inhibition modulates cumulus cell function and affects bovine oocyte maturation in vitro†

Various metabolic and hormonal factors expressed in cumulus cells are positively correlated with the in vitro maturation (IVM) of oocytes. However, the role of hypoxia sensing both during maturation of cumulus–oocyte complexes (COCs) as well as during the resumption of meiosis remains uncertain. HIF1alpha plays major roles in cellular responses to hypoxia, and here we investigated its role during bovine COC maturation by assessing the expression of related genes in cumulus cells. COCs were divided into the following groups: immature (control), in vitro matured (IVM/control), or matured in the presence of a blocker of HIF1alpha activity (echinomycin, IVM/E). We found an inhibition of cumulus cell expansion in IVM/E, compared with the IVM/control. Transcript levels of several factors (n = 13) were assessed in cumulus cells. Decreased expression of HAS2, TNFAIP6, TMSB4, TMSB10, GATM, GLUT1, CX43, COX2, PTGES, and STAR was found in IVM/E (P < 0.05). Additionally, decreased protein levels were detected for STAR, HAS2, and PCNA (P < 0.05), while activated-Caspase 3 remained unaffected in IVM/E. Progesterone output decreased in IVM/E. The application of PX-478, another blocker of HIF1alpha expression, yielded identical results. Negative effects of HIF1alpha suppression were further observed in the significantly decreased oocyte maturation and blastocyst rates from COCs matured with echinomycin (P < 0.05) or PX-478 (P < 0.05). These results support the importance of HIF1alpha for COC maturation and subsequent embryo development. HIF1alpha is a multidirectional factor controlling intercellular communication within COCs, steroidogenic activity, and oocyte development rates, and exerting effects on blastocyst rates.

Energy metabolism of the equine cumulus oocyte complex during in vitro maturation

Horses are one of the few species, beside humans, in which assisted reproductive technology has important clinical applications. Furthermore, the horse can serve as a valuable model for the study of comparative reproductive biology. Here we present the first comprehensive characterisation of energy metabolism and mitochondrial efficiency in equine cumulus-oocyte complexes (COCs) during in vitro maturation (IVM), as determined using a combination of non-invasive consumption and release assays and mitochondrial function analysis. These data reveal notable species-specific differences in the rate and kinetics of glucose consumption and glycolysis throughout IVM. Approximately 95% of glucose consumed was accounted for by lactate production; however, high concurrent oxygen consumption indicated a comparatively increased role for non-glycolytic oxidative phosphorylation. Up to 38% of equine COC oxygen consumption could be attributed to non-mitochondrial activities and there was a significant loss of spare respiratory capacity over the course of IVM. Notably, our data also revealed that current IVM protocols may be failing to satisfy the metabolic demands of the equine COC. Our findings constitute the first report on mitochondrial efficiency in the equine COC and provide new insight into comparative gamete biology as well as metabolism of the COC during in vitro maturation.

Transcriptome profiling of in vitro-matured oocytes from a korean native cow (hanwoo) after cysteamine supplementation

This study elucidated the molecular markers that decrease oocyte quality during in vitro culture, restricting optimal developmental potential. Here, we evaluated the transcriptomic differences between cysteamine-treated and non-treated bovine cumulus oocyte complexes (COCs) after 22 h of co-culture in the maturation media using RNA sequencing. In total, 39,014 transcripts were sequenced between cysteamine-treated and non-treated mature COCs. We evaluated the relative expression of 21,472 genes, with 59 genes showing differential expression between the two COC groups. The cysteamine-treated group had 36 up-regulated gene transcripts and 23 down-regulated gene transcripts. Moreover, gene ontology (GO) enrichment analysis revealed that multiple biological processes were significantly enriched after cysteamine supplementation. Differentially expressed genes appeared to maintain normal oocyte physiology, regulation of apoptosis, differentiation, ossification or bone formation, cardiac and muscle physiology, hormonal secretion, and membrane construction for further embryonic development. In conclusion, cysteamine affects the mRNA level of COCs during oocyte maturation by upregulating potential molecular markers and downregulating genes that affect further embryonic development.

Effects of gaseous atmosphere and antioxidants on the development and cryotolerance of bovine embryos at different periods of in vitro culture

This study examined the effects of antioxidant supplementation and O2 tension on embryo development, cryotolerance and intracellular reactive oxygen species (ROS) levels. The antioxidant supplementation consisted of 0.6 mM cysteine (CYST); 0.6 mM cysteine + 100 μM cysteamine (C+C); 100 IU catalase (CAT) or 100 μM β-mercaptoethanol (β-ME) for 3 or 7 days of in vitro culture (IVC). Two O2 tensions (20% O2 [5% CO2 in air] or 7% O2, 5% CO2 and 88% N2 [gaseous mixture]) were examined. After 7 days of antioxidant supplementation, the blastocyst frequencies were adversely affected (P < 0.05) by CYST (11.2%) and C+C (1.44%), as well as by low O2 tension (17.2% and 11.11% for 20% and 7% O2, respectively) compared with the control (26.6%). The blastocyst re-expansion rates were not affected (P > 0.05) by the treatments (range, 66-100%). After 3 days of antioxidant supplementation, the blastocyst frequencies were not affected (P > 0.05) by any of the antioxidants (range, 43.6-48.5%), but they were reduced by low O2 tension (P < 0.05) (52.1% and 38.4% for 20% and 7% O2, respectively). The intracellular ROS levels, demonstrated as arbitrary fluorescence units, were not affected (P > 0.05) by antioxidant treatment (range, 0.78 to 0.95) or by O2 tension (0.86 and 0.88 for 20% and 7% O2, respectively). The re-expansion rates were not affected (P > 0.05) by any of the treatments (range, 63.6-93.3%). In conclusion, intracellular antioxidant supplementation and low O2 tension throughout the entire IVC period were deleterious to embryo development. However, antioxidant supplementation up to day 3 of IVC did not affect the blastocyst frequencies or intracellular ROS levels.

Cysteamine supplementation during in vitro maturation (IVM) of rabbit oocyte improves the developmental capacity after intracytoplasmic sperm injection

Purpose

Current approaches to in vitro maturation (IVM) may result in low efficiency and inadequate quality of the oocytes due to insufficient cytoplasmic maturation. Although positive effects of the cysteamine supplementation in IVM medium for oocyte nuclear maturation or male pronuclear formation have been confirmed, it is still controversial whether the cysteamine addition affects embryo development after IVM. We aimed here to confirm the effect of cysteamine addition into IVM medium for subsequent embryo development in vitro.

Methods

We administered the cysteamine to the IVM culture of rabbit immature oocytes at various concentrations and observed the developmental rate, speed to reach blastocyst stage and cell numbers at the blastocyst stage.

Results

Cysteamine supplementation improved developmental rate to blastocyst stage of the IVM oocytes. On the other hand, addition of glutathione (GSH) inhibitor buthionine sulfoximine inhibited GSH accumulation in the oocytes and subsequent embryo development to the blastocyst stage.

Conclusions

Controlling the GSH quantity of IVM oocytes may be an important factor for success of embryo development, and it is quite probable that a cysteamine supplementation can contribute to an increase of GSH content in oocyte.

Beneficial effect of two culture systems with small groups of embryos on the development and quality of in vitro-produced bovine embryos

Currently, in vitro-produced embryos derived by ovum pick up (OPU) and in vitro fertilization (IVF) technologies represent approximately one-third of the embryos worldwide in cattle. Nevertheless, the culture of small groups of embryos from an individual egg donor is an issue that OPU-IVF laboratories have to face. In this work, we tested whether the development and quality of the preimplantation embryos in vitro cultured in low numbers (five embryos) could be improved by the addition of epidermal growth factor, insulin, transferrin and selenium (EGF-ITS) or by the WOW system. With this aim, immature oocytes recovered from slaughtered heifers were in vitro matured and in vitro fertilized. Presumptive zygotes were then randomly cultured in four culture conditions: one large group (LG) (50 embryos/500 μl medium) and three smaller groups [five embryos/50 μl medium without (control) or with EGF-ITS (EGF-ITS) and five embryos per microwell in the WOW system (WOW)]. Embryos cultured in LG showed a greater ability to develop to blastocyst stage than embryos cultured in smaller groups, while the blastocyst rate of WOW group was significantly higher than in control. The number of cells/blastocyst in LG was higher than control or WOW, whereas the apoptosis rate per blastocyst was lower. On the other hand, the addition of EGF-ITS significantly improved both parameters compared to the control and resulted in similar embryo quality to LG. In conclusion, the WOW system improved embryo development, while the addition of EGF-ITS improved the embryo quality when smaller groups of embryos were cultured.

Influence of selected (pre-)maturational parameters on in vitro development and sex distribution of bovine embryos

The objectives of this research were to study the influence of a reduced oxygen concentration during in vitro maturation (IVM) and examine the effect of follicular glucose concentration on bovine in vitro development and sex distribution. In the first experiment, abattoir-derived cumulus-oocyte complexes (COC) were matured under 5% O2 or 20% O2. Secondly, COC were isolated and the glucose (G) concentration of each follicle was determined. COC were pooled in groups (G (< 1.1 mMol) or G (≥ 1.1 mMol)) according to the glucose content before being subjected to in vitro production (IVP). Cleavage and development rates were assessed on days 3, 7 and 8 post insemination. Blastocysts of each group were sexed by polymerase chain reaction (PCR). Expanded blastocysts were stained to assess total cell numbers and live-dead cell ratio. Cleavage and development rates stayed similar after reducing the O2 concentration during IVM. The sex ratio of embryos generated from oocytes matured under 5% O2 was shifted in favour of the female (♀: 61.9%), whereas the sex ratio of embryos belonging to the IVM 20% O2 group did not differ significantly from the expected 50:50 ratio. Neither a 'higher' nor a 'lower' intrafollicular glucose concentration influenced cleavage and development rates, cell numbers or live-dead cell ratio. Eighty five per cent (G (<1.1)) and 63.6% (G (≥ 1.1)) of the analysed embryos were female. In summary, neither a reduced O2 concentration during IVM nor selection based on follicular glucose concentrations affected the morphological quality of embryos. Although the sex distribution was shifted in favour of female embryos in all three experimental groups, more male embryos could be seen in the G (≥ 1.1) group compared with the G(<1.1) group.

Culture systems: low-oxygen culture

The tension of oxygen measured in the oviducts of several mammals was 5-8.7 %, but this drops in the uterine milieu to <2 % in cows and primates. For embryo culture in human in vitro fertilization (IVF), a non-physiologic level of 20 % oxygen has been used for the past 30 years. However, several animal studies have shown that low levels of oxygen plays an important physiological role in reducing the high levels of detrimental reactive oxygen species within cells, influences the embryonic gene expression, helps with embryo metabolism of glucose, and enhances embryo development to blastocysts. However, clinical studies have given contradictory results. Nevertheless, in nearly all reports, some kind of improvement has been observed, either in embryo development or in implantation and no detriments have been reported. For these reasons, more and more IVF laboratories utilize low oxygen during embryo culture.

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.

On-chip single embryo coculture with microporous-membrane-supported endometrial cells

In vitro culture (IVC) of the mammalian embryo is an essential technique in reproductive technology and other related life science disciplines. Although embryos are usually cultured in groups, a single embryo culture has been highly desired for IVC to investigate developmental processes. In this study, we proposed and developed the first single embryo coculture device, which allows making an array of a single embryo coculture with endometrial cells by controlling the culture environment in a microfluidic device. To realize this concept, we investigated three key issues: selection of a culture medium for the embryo coculture with endometrial cells using a mouse embryo and endometrial cells, evaluation of an on-microporous-membrane coculture of endometrial cells and an embryo to control the polarization of endometrial cells on the membrane, and evaluation of the coculture of endometrial cells and the embryo in the microfluidic device. We successfully obtained an array of a single coculture of embryo with endometrial cells in a microfluidic device. This concept will open and enhance the management of an individual embryo for assisted reproductive technology, livestock breeding, and fundamental stage research by further development.

Low oxygen tension during IVM improves bovine oocyte competence and enhances anaerobic glycolysis

This study evaluated the effect of two oxygen concentrations (20 and 5%) on bovine embryo development (kinetics of first cleavage and blastocyst development) during maturation (M) and fertilization (F) and analysed differences in gene expression between cumulus-oocyte complexes (COC) matured at 5 or 20% oxygen and the resulting blastocysts. A total of 1179 COC were divided into four groups according to the oxygen tension used (M5F5, M5F20, M20F5 and M20F20). Relative poly(A) mRNA abundance of GLUT1, GAPDH, LDHA, G6PD, MNSOD, GPX1, IGFR2, BAX, CCNB1, PTGS2 and GREM1 was analysed in COC, whereas 10 quality-related genes were analysed in blastocysts. M20F5 group developmental rates were significantly lower than all other groups (one-way ANOVA, P < or = 0.05). Two-way ANOVA showed a beneficial effect of low oxygen tension during in-vitro maturation on developmental rates, whereas the opposite situation was obtained in fertilization (P < or = 0.05). GAPDH, IGFR2, CCNB1, and GREM1 were up-regulated in the oocytes matured in low oxygen, whereas GLUT1, GAPDH, LDHA and GREM1 were up-regulated and PTGS2 down-regulated in the cumulus cells from the M5 group (P < or = 0.05). No differences were observed in blastocysts. Low oxygen tension during maturation alters the expression of genes related to oocyte competence and glucose metabolism and significantly (P < or = 0.05) improves embryo development, but not blastocyst quality.

The effect of interaction between macromolecule supplement and oxygen tension on bovine oocytes and embryos culturedin vitro

Aiming to improvein vitroproduction of bovine embryos and to obtain supplements to replace serum forin vitromaturation (IVM), this study evaluated the effects of macromolecular supplementation of IMV medium (bovine serum albumin – BSA, polyvinyl alcohol – PVA, polyvinyl pyrrolidone – PVP, Ficoll, KnockoutSR, or fetal calf serum – FCS) and oxygen tension [5% CO2in air (20% O2) or 5% CO2, 5% O2and 90% N2(5% O2)] on oocyte maturation and embryo development. Nuclear progression to germinal vesicle breakdown, metaphase I and metaphase II stages were evaluated and overall results revealed that undefined (FCS) and semi-defined (BSA) media gave better results at 20% O2and defined media (PVA, PVP and Ficoll) at 5% O2. Independent of macromolecule supplement, IVM at 20% O2was considered optimal for nuclear maturation. To evaluate embryo development, oocytes matured in the previously described conditions were fertilized and cultured at the same oxygen tension used for IVM and assessed for cleavage (43.0 to 74.8%) and development to morulae (16.4 to 33.8%), blastocyst (7.7 to 52.9%) and hatched blastocyst (9.6 to 48.1%). Apart from oxygen tension, all treatments, except Knockout (22.7%), gave similar results for blastocyst development (26.5 to 38.7%). Independently of macromolecule supplement, higher development rates were obtained in an oxygen tension of 20% O2(67.4% cleavage, 29.2% morulae, 40.8% blastocyst and 34.0% hatched blastocyst) when compared with 5% O2(52.5, 21.8, 18.2 and 15.6%, respectively). This study indicates that BSA, PVA, PVP and Ficoll can replace serum during IVM and that the optimal atmospheric condition forin vitroproduction of bovine embryos is 5% CO2and 20% O2.

Developmental competence of porcine oocytes selected by brilliant cresyl blue and matured individually in a chemically defined culture medium

The objective of this study was to investigate the effects of oocyte selection using brilliant cresyl blue (BCB) and culture density during individual in vitro maturation (IVM) on porcine oocyte maturity and subsequent embryo development using a chemically defined medium. Cumulus-oocyte complexes (COCs) were classified as BCB-positive or BCB-negative after exposure to a BCB solution for 90 min. The classified COCs were matured in a group (15 COCs per 100-microL droplet) or individually (1 COC per 1-, 2.5-, 5-, or 10-microL droplet). Meiotic competence, intraoocyte glutathione concentration, and developmental competence after intracytoplasmic sperm injection were monitored. The BCB selected oocytes competent for nuclear and cytoplasmic maturation. Furthermore, meiotic competence for oocytes matured individually in a 5-microL droplet was superior (P<0.05) to that of oocytes matured in a 1-microL droplet. Also, the culture density in a 5-microL droplet during IVM resulted in a higher (P<0.05) rate of cleaved embryos than that in a 1-microL droplet and produced a similar rate of blastocysts compared with that of a group culture system. Conversely, BCB selection did not improve cleavage and blastocyst formation. In conclusion, it was possible to predict porcine oocytes competent for maturation using oocyte selection with BCB. Moreover, a 5-microL droplet during the individual IVM culture was most suitable for oocyte maturation and subsequent embryo development, although every culture density used in this study supported development up to the blastocyst stage.

Effects of N, N-dimethylglycine on the development of in vitro produced bovine embryos

This study investigated the effects of N, N-Dimethylglycine (DMG) on the development of in vitro produced (IVP) bovine embryos. IVP embryos were obtained by in vitro fertilization of in vitro matured oocytes for 6 h. In Experiment 1, IVP embryos were cultured in mSOFaa supplemented with bovine serum albumin but without glucose (SOF1) for 4 days, transferred to mSOFaa (with 5% fetal bovine serum and 1.5 mM glucose; SOF2) supplemented with 0 (control), 0.1,1 or 10 microM DMG and cultured for an additional 7 days (11 days in total) to assess their development in vitro. When cultured in the medium with 0.1 microM DMG, a significantly higher number of IVP embryos developed to the blastocyst and hatched blastocyst stages (40.3 and 40.8%, respectively) compared with the other groups (18.7-31.0% and 15.0-28.7%, respectively; P<0.05, analysis of variance). In Experiment 2, IVP embryos were cultured in SOF1 with or without 0.1 microM DMG for 4 days, transferred to SOF2 with or without 0.1 microM DMG and further cultured as in Experiment 1; DMG was added to either SOF1 or SOF2 and to both of them to assess its exposure effects on embryo development. When cultured continuously with DMG for 11 days, significantly higher rates of IVP embryos developed into blastocyst and hatched blastocyst stages (39.0 and 47.7%, respectively) compared with the other groups (31.0-32.2% and 29.5-31.0%, respectively; P<0.05). In Experiment 3, we examined developmental speed of IVP embryos cultured with or without addition of 0.1 microM DMG to IVC medium after 7 days of IVC. When DMG was added to IVC medium, the ratio of embryos developed to advanced developmental stages (No. of embryos developed to the blastocyst and expanded blastocyst stages/No. of embryos developed to the morula stage) was 28.7% (86/3) and 7 times higher than that of those cultured without DMG, 4.0% (52/13). These results suggest that addition of 0.1 microM DMG to mSOFaa during IVC of IVP bovine embryos has a promoting effect on their development.

Effect of including growth factors and antioxidants in maturation medium used for in vitro culture of buffalo oocytes recovered in vivo

This study examined the effect of including one of two growth factors (100 ng/ml IGF-1 or 20 ng/ml EGF) in combination with one of two antioxidants (50 microM cysteamine or 50 microM beta-mercaptoethanol) in maturation, fertilization and subsequent development of buffalo oocytes. The oocytes were recovered by in vivo ovum pick-up technique from six Murrah buffalo heifers twice a week over a period of 16 weeks. Immediately after ovum pick-up oocytes recovered from six donors were allocated randomly to five different maturation treatments. The control treatment was the basic maturation medium (MM; TCM-199 supplemented with 10% FBS, 10 IU/ml LH, 0.5 microg/ml FSH, 1 microg/ml estradiol-17beta and 50 microg/ml gentamicin). The other four treatments consisted of the control maturation medium (MM) plus one combination of a growth factor and an antioxidant viz. IGF-1+cysteamine; IGF-1+beta-ME; EGF+cysteamine or EGF+beta-ME. The total number of oocytes assigned to each maturation treatment ranged from 31 to 66. After maturation in different maturation medium, media used for in vitro fertilization and subsequent development of embryo was same for all groups. Data were analysed using Chi-square test. The maturation rate observed for the growth factor plus antioxidant treatments was similar to that for the control (90.4%). The highest cleavage rate recorded in the IGF-1+cysteamine treatment (71.9%) which was significantly higher (P<0.05) than the IGF-1+beta-ME (45.2%) and EGF+beta-ME (46.4%) treatments, but not significantly differ from the control (63.8%) and EGF+cysteamine treatment (60.7%). The proportion of cleaved oocytes those developed to blastocyst stage was significantly higher in the IGF-1+cysteamine treatment (52.2%; P<0.05) than in the control (23.3%), the EGF+cysteamine (13.5%) or the EGF+beta-ME (7.7%) treatments, but did not differ significantly from the IGF-1+beta-ME (28.6%) treatment. Following non-surgical transfer of 15 embryos to 14 synchronized recipients, four became pregnant and only one recipient sustained the pregnancy as long as 4.5 months when spontaneous abortion occurred. It was concluded that supplementing the maturation medium with IGF-1+cysteamine improved the production of buffalo embryos significantly in vitro culture.

Bovine in vitro oocyte maturation as a model for manipulation of the γ-glutamyl cycle and intraoocyte glutathione

Glutathione (GSH) is the main non-enzymatic defence against oxidative stress and is a critical intracellular component required for oocyte maturation. In the present study, several modulators of intracellular GSH were assessed for their effect on the in vitro maturation (IVM) and intracellular GSH content of bovine metaphase (MII) oocytes. Of the five GSH modulators tested, only the cell-permeable GSH donor glutathione ethyl ester (GSH-OEt) significantly increased the GSH content of IVM MII oocytes in a concentration-dependent manner without adversely affecting oocyte maturation rate. The GSH level in IVM MII oocytes was greatly influenced by the presence or absence of cumulus cells and severely restricted when oocytes were cultured in the presence of buthionine sulfoximine (BSO), an inhibitor of GSH synthesis. The addition of GSH-OEt to cumulus-denuded or BSO-treated oocytes increased the GSH content of bovine MII oocytes. Supplementation of the maturation medium with bovine serum albumin (BSA) or fetal calf serum (FCS) affected the GSH content of IVM MII oocytes, with greater levels attained under BSA culture conditions. The addition of GSH-OEt to the maturation medium increased the GSH content of IVM MII oocytes, irrespective of protein source. Spindle morphology, as assessed by immunocytochemistry and confocal microscopy, displayed distinct alterations in response to changes in oocyte GSH levels. GSH depletion caused by BSO treatment tended to widen spindle poles and significantly increased spindle area. Supplementation of the IVM medium with GSH-OEt increased spindle length, but did not significantly alter spindle area or spindle morphology. GSH-OEt represents a novel oocyte-permeable and cumulus cell-independent approach for effective elevation of mammalian oocyte GSH levels.

Validation of antifreeze properties of glutathione based on its thermodynamic characteristics and protection of baker's yeast during cryopreservation

The antifreeze ability of glutathione was evaluated on the basis of its thermodynamic characteristics and protection of baker's yeast during cryopreservation at -30 degrees C. The thermodynamic characteristics and protection of baker's yeast of glutathione were similar to those of known antifreeze proteins, such as carrot antifreeze protein and holly antifreeze protein. These properties included lowering the freezing point at about 0.20 degrees C non-colligatively, decreasing freezable water content, controlling the movement of free water for its strong hydrophilicity, and improving baker's yeast survival during the simulated processing of frozen dough. Therefore, glutathione was viewed to be an antifreeze protein like substance on the basis of its unique thermodynamic characteristics and protection of baker's yeast. The method combining thermodynamic characteristic analysis and protection evaluation is a new and simple way to screen new antifreeze proteins.

Expression pattern of oxygen and stress-responsive gene transcripts at various developmental stages of in vitro and in vivo preimplantation bovine embryos

The present study examined the expression pattern of oxygen (O(2)) and stress-responsive gene transcripts at various preimplantation developmental stages of in vitro produced (IVP) and in vivo derived (IVD) bovine embryos. Embryos were produced in vitro from oocytes matured, fertilized and cultured in synthetic oviductal fluid (SOF) medium under low (5%) and high (20%) O(2) concentrations. In vivo embryos were derived from 18 superovulated and artificially inseminated cows. In IVP and IVD groups, embryos were collected at 2-, 4-, 8-, 16-cell morula and blastocyst stages at specific time points for gene expression analysis. The cleavage rates (69.8+/-4.8%) did not differ significantly, but blastocyst rates were significantly higher (28.5+/-3.7%) in low O(2) than those in high O(2) group (18.7+/-3.9%). Mean cell number in low O(2) (145+/-12) and high O(2) (121+/-73) IVP blastocyst were lower (P<0.05) than those of IVD blastocyst (223+/-25). The ICM ratio of IVD blastocyst (26+/-4) was lower (P<0.05) than that of IVP embryos under 5% O(2) (33+/-5) and 20% O(2) (34+/-4) concentrations, respectively. Using real time PCR, for the set of target transcripts (Glut1, Glut5, Sox, G6PD, MnSOD, PRDX5, NADH and Hsp 70.1) analyzed, there were differences in the mRNA expression pattern at 2-, 4-, 8-, 16-cell morula and Day 7 blastocyst stages between the two embryo sources. It can be concluded that, although in vitro bovine embryo culture in SOF medium under low (5%) O(2) concentration provided a more conducive environment in terms of blastocyst formation; differences in the total cell number and gene expression pattern between the IVP and IVD embryos reflected the effect of O(2) concentration.

Blastocyst production by in vitro maturation and development of porcine oocytes in defined media following intracytoplasmic sperm injection

The present study was carried out to establish porcine defined IVP. In Experiments 1 and 2, we investigated the efficacy of additional 0.6 mM cystine and/or 100 µM cysteamine (Cys) to a defined TCM199 maturation medium with regard to the intracellular glutathione (GSH) concentration and the developmental competence of in vitro matured porcine oocytes following intracytoplasmic sperm injection (ICSI). The control medium was a modified TCM199 containing 0.05% (w/v) polyvinyl alcohol (PVA). Cys and/or cystine were added to the control medium. The control group and immature oocytes (presumptive germinal vesicle oocytes; GV) were prepared for GSH assay. In Experiment 3, the efficacy of epidermal growth factor (EGF) addition to a modified porcine zygote medium (mPZM) for in vitro culture (IVC) medium was investigated on embryonic development and the mean cell number of blastocysts following ICSI. As a positive or negative control, 0.3% BSA (mPZM-3) or 0.3% PVA (mPZM-4), respectively, was added to the base medium. The defined IVC medium was supplemented with 5 or 10 ng/ml EGF. In Experiment 1, no significant difference was found in the rates of cleavage (31.4–64.3%) and blastocyst formation (6.5–22.9%) among the treatment and control groups. The mean cell numbers per blastocyst ranged from 30 to 48 among the groups without significant differences. However, in Experiment 2, the intracellular GSH concentrations in the oocytes cultured in the medium supplemented with 100 µM Cys (9.6 pmol/oocyte) or Cys + cystine (9.9 pmol/oocyte) were significantly (p < 0.05) higher than the control (2.5 pmol/oocyte) and 0.6 mM cystine (6.5 pmol/oocyte) groups, but not different from the GV group (9.0 pmol/oocyte). The GSH concentration in the cystine group was also significantly (p < 0.05) higher than that in the control group, but not different from the GV group. In Experiment 3, the rates of cleavage and blastocyst formation and the mean cell numbers of blastocysts were not significantly different among the groups. However, the addition of 5 ng/ml EGF into the mPZM-4 resulted in a significantly (p < 0.05) higher blastocyst rate per cleaved embryo than the other two defined groups (mPZM-4 + 5 ng/ml: 48.6%, mPZM-4 and mPZM-4 +10 ng/ml: 23.4% and 23.1%, respectively).

The present results indicate that the addition of Cys to a defined medium for in vitro maturation (IVM) of porcine oocytes increases intracellular GSH concentration. Further addition of cystine into the IVM medium containing 100 µM Cys is not necessary and TCM199 plus Cys (100 µM) could be used as a defined IVM medium for porcine oocytes. The addition of 5 ng/ml EGF to a defined IVC medium has enhanced subsequent development after ICSI. This study shows that porcine blastocysts can be produced by defined media throughout the steps of IVP (IVM, ICSI and IVC).

Effect of cysteamine supplementation of in vitro matured bovine oocytes on chilling sensitivity and development of embryos

In vitro techniques for production of bovine embryos including in vitro oocyte maturation (IVM), fertilization (IVF) and culture (IVC) are becoming increasingly employed for a variety of research purposes. However, decreased viability following cryopreservation by conventional methods has limited commercial applications of these technologies. A practical alternative to facilitate transport would be to arrest development by chilling without freezing. The present research was undertaken to evaluate chilling sensitivity of IVM-IVF embryos at different stages of development, and to determine possible beneficial effects of cysteamine treatment during IVM, previously shown to enhance embryo development in culture, on survival following chilling at different stages. Embryos produced by standard IVM-IVF-IVC methods were chilled to 0 degrees C for 30 min at 2-cell (30-34 h post-insemination, hpi), 8-cell (48-52 hpi) or blastocyst (166-170 hpi) stages. Viability after chilling was assessed by IVC with development to expanded blastocyst stage determined on days 7 and 8 post-insemination (pi) and hatching blastocyst stage determined on days 9 and 10 pi. Control embryos at the same stages were handled similarly, but without chilling, and development during culture similarly assessed. The effect of cysteamine supplementation (100 microM) of the IVM medium was determined for both chilled and non-chilled (control) embryos. Cysteamine supplementation during IVM had no significant effect on oocyte maturation or fertilization, but increased the proportions of oocytes developing to blastocyst stage by day 7 (13.7+/-0.9% versus 7.2+/-0.9%; P<0.05), total blastocysts (20.5+/-0.9% versus 15.3+/-1.3%; P<0.05), and hatching blastocysts (16.8+/-1.6% versus 12.0+/-1.5%; P<0.05). The greater survival in terms of hatching (78.6+/-7.0) following chilling of blastocysts produced by IVM-IVF of oocytes matured in media supplemented with cysteamine offers promise for applications requiring short-term storage to facilitate transport of in vitro produced bovine embryos.

Influence of in vitro oxygen concentrations on preimplantation embryo development, gene expression and production of hanwoo calves following embryo transfer

This study evaluated the effects of two different oxygen (O2) concentrations on in vitro embryo development, embryo quality, and gene expression and the in vivo development following embryos transfer to recipients of natural and synchronized estrus in bovines. Cumulus oocyte complexes were in vitro matured in TCM199 supplemented with FSH (10 microg/ml), LH (10 microg/ml), and 10% (v/v) FBS. Presumptive zygotes were cultured in SOF medium either under 5% (low) or 20% (high) O2 in air. Cleavage rates did not differ between groups. Blastocyst and hatched blastocyst development in 5% O2 were significantly (P < 0.05) higher than in 20% O2. Total cell number of in vivo blastocyst was significantly (P < 0.05) higher than that of in vitro blastocyst. ICM ratio and apoptosis of in vivo blastocyst were significantly (P < 0.05) lower than that of in vitro blastocyst. Using real time PCR, we have found that for the set of genes (GLUT-1, MnSOD, VEGF, Bax, and Bcl-2) analyzed, there were differences in mRNA expression between in vitro produced (IVP) and in vivo produced embryos. Interestingly, the abundance of transcript for IFN-tau in IVP embryos produced under 5% O2 concentration was similar to in vivo counterparts. The pregnancy and twin rates of natural recipients were significantly (P < 0.05) higher than those of synchronized counterparts. No significant difference in the offspring sex was observed. In conclusion, low (5%) O2 concentration during IVC was beneficial for enhancing the embryo quality and recipients of natural estrus were more suitable than synchronized estrus for stable production of Hanwoo calves.

The role of oxygen in ruminant preimplantation embryo development and metabolism

The long-term effects of in vitro embryo culture on animal health are presently unknown, however, current knowledge directs investigations toward understanding the mechanisms involved in regulating embryo development. In vitro culture is known to have short-term effects, particularly on gene expression and metabolism at the blastocyst stage, while large offspring syndrome is commonly observed following transfer of in vitro produced bovine embryos. Indeed, it is likely that the environment surrounding the early embryo, prior to implantation, may program later development. Regulation of gene expression and metabolism, through gene activation, is mediated by transcription factors, which are themselves controlled by internal and external factors. Alterations in the surrounding environment during preimplantation embryo development, such as that which occurs with inadequate developmental 'support' during in vitro culture, may modify the activation, or inactivation, of several transcription factors, and may therefore have long-term consequences for the developing offspring. In vitro culture deviates from in vivo conditions in many respects, but one of the critical factors that is generally not considered is the oxygen tension under which embryos are cultured. Numerous studies have demonstrated that atmospheric oxygen conditions during culture have detrimental effects on embryo development. While it is generally believed that this arises from the production of reactive oxygen species, this presents an over-simplistic view of the role of oxygen during development. The hypoxia-inducible factor transcription factor family is involved in the responses of cells to alterations in external oxygen concentrations, regulating the expression of numerous genes. Alterations in expression of some of these genes have been highlighted by recent studies in the bovine embryo, implicating oxygen as a regulator of several cellular and metabolic pathways. While it is clear that oxygen plays a role during embryo development, further work to investigate interactions between oxygen and other signaling pathways such as pH and Ca(2+), mitochondria and metabolism is required, as well as exposure of embryos at different time points, to determine the mechanisms that control preimplantation development, the interactions of a range of stimuli and to establish culture procedures that support optimal development and minimize risks to health. This review focuses largely on work undertaken in ruminant models, with brief references to other species.

The role of free radicals and antioxidants in reproduction

PURPOSE OF REVIEW

This review summarizes the role of free radicals and oxidative stress in the pathophysiology of human reproduction.

RECENT FINDINGS

An extensive review of the literature on the role of oxidative stress in influencing assisted reproduction and its outcome is described in this article. Free radicals or reactive oxygen species mediate their action through many of the proinflammatory cytokines and this mechanism has been proposed as a common underlying factor for endometriosis, ovarian cancer, polycystic ovary disease, and various other pathologies affecting the female reproductive process, as highlighted in this review. Oxidative stress, sperm DNA damage, and apoptosis have been implicated in male infertility. Elevated reactive oxygen species levels correlate with the poor fertility outcomes seen in the assisted reproductive technology setting.

SUMMARY

Oxidative stress has been implicated in male and female infertility, including fetal dysmorphogenesis, abortions, and intrauterine growth restriction. Accurate evaluation of seminal oxidative stress by standardized assays may help in the diagnosis and management of male infertility. There is evidence in the literature on the beneficial effects of oral antioxidant supplementation in male infertility. Current ongoing trials will provide answers on the safety and effectiveness of antioxidants in improving maternal and fetal outcomes. Further studies need to be conducted to determine if antioxidant supplementation will prevent fetal developmental defects in high-risk pregnancy with diabetes.

Cysteamine or β-mercaptoethanol added to a defined maturation medium improves blastocyst formation of porcine oocytes after intracytoplasmic sperm injection

The present study was carried out to investigate the effect of adding 100 microM cysteamine (Cys) or 100 microM beta-mercaptoethanol (beta-ME) to a defined maturation medium on in vitro maturation (IVM), and fertilization and developmental competence of in vitro matured porcine oocytes following intracytoplasmic sperm injection (ICSI). The two control media for IVM culture were modified TCM199 containing 10% (v/v) porcine follicular fluid (pFF) or 0.05% (w/v) polyvinyl alcohol (PVA), and Cys or beta-ME was supplemented to the PVA-control medium. There was no significant difference in the proportions of in vitro matured oocytes among the four treatment groups (94.5-98.4%). The percentages of pronuclear formation (51.0-64.2%) after ICSI were also not significantly different among the four groups. The cleavage rate (72.8%) in the oocytes treated with Cys showed no significant difference compared with those of the two control media containing pFF (72.2%) or PVA (61.5%), but was higher (P<0.05) than that in the oocytes treated with beta-ME (56.3%). However, the rates of blastocyst formation of Cys (36.7%), beta-ME (27.1%) and pFF (31.4%) were higher (P<0.05) than that using the control medium containing PVA (15.6%). The mean cell number of blastocysts ranged from 42 to 52 among the four groups, without significant differences. In conclusion, the addition of Cys or beta-ME to a defined maturation medium enhanced blastocyst formation after ICSI, to a level similar to that achieved by adding pFF.

In Vitro Culture Conditions Using Chemically Defined Media for In Vitro Matured and Intracytoplasmically Inseminated Porcine Oocytes

The present study investigated in vitro culture methods [droplet and Well of the Well (WOW)] using semi-defined and defined media [modified porcine zygote medium (mPZM)] and the additional effects of insulin on in vitro matured and intracytoplasmically inseminated porcine oocytes. In Experiment 1, in vitro matured and intracytoplasmically inseminated porcine oocytes were cultured for 6 days in the following four groups: 1) mPZM-3 (containing bovine serum albumin) + droplet (30 mul), 2) mPZM-3 + WOW, 3) mPZM-4 (containing polyvinyl alcohol) + droplet, and 4) mPZM-4+ WOW. The culture media (mPZM-3 and mPZM-4) and methods (droplet and WOW) did not significantly affect the cleavage rate, but the blastocyst rate of the oocytes cultured in mPZM-3 was significantly (P<0.01) higher than that of mPZM-4 (20.1 and 9.4%, respectively). The blastocyst rates as percentages of the cleaved oocytes (51.8 and 16.9%) and the hatched blastocyst rate as percentages of the number of blastocysts (12.3 and 2.2%) were also significantly (P<0.01) higher in mPZM-3 compared with those in mPZM-4. There was significant interaction (P<0.05) between the two main factors; the effects of the culture media and methods on the rate of hatched blasyocysts as percentages of the blastocysts produced and, the hatched blastocyst rate (20.3%) as percentages of the number of blastocysts produced in mPZM-3 were significantly (P<0.05) higher than in the other groups. In Experiment 2, the additional effects of insulin (100 ng/ml) in mPZM-3 and mPZM-4 media was investigated in the WOW culture system. Insulin addition did not improve cleavage, blastocyst formation, or the number of cells in blastocysts. However, as in Experiment 1, mPZM-3 resulted in a significantly higher blastocyst rate as percentages of the cleaved oocytes than mPZM-4 (33.9 and 18.4%). These results indicate that a chemically defined medium (mPZM-4) needs to be improved to provide more suitable culture conditions for in vitro development of in vitro matured and intracytoplasmically inseminated porcine oocytes. However, the WOW system may be a useful IVC method for blastocyst development of in vitro matured porcine oocytes following ICSI when a semi-defined medium (mPZM-3) is used.

Effects of culture media and energy sources on the inhibition of nuclear maturation in bovine oocytes

The influence of the culture medium and energy sources on spontaneous nuclear maturation and inhibition of maturation in bovine cumulus-enclosed oocytes (CEO) was examined. CEO were cultured in Medium 199, minimum essential medium, M16, or synthetic oviduct fluid (SOF), all containing 3 mg/mL bovine serum albumin (BSA), and SOF without BSA, alone or supplemented with hypoxanthine (HYPO, 4 mM) or forskolin (FSK, 100 microM) for 21 h. More CEO remained at the GV stage in M16 compared to other media (P < 0.05). Supplementation with HYPO increased and FSK reduced the percentage of CEO remaining at the GV stage (P < 0.05) only in M16. The effects of energy sources, in the absence or presence of HYPO or FSK, were examined in CEO cultured in M16 salts+PVA. Glucose (0.5 and 5.5 mM), pyruvate (0.32 and 3.2 mM), lactate (3.3 mM) and glutamine (1.3 mM) significantly reduced the percentage of CEO remaining at the GV stage compared to M16 salts alone; only glutamine significantly increased the percentage of CEO at the MII stage compared to M16 salts. In M16 salts+HYPO, glucose (0.5 mM), pyruvate (0.32 mM), lactate (3.3 mM) and glutamine (1.3 mM) significantly reduced the percentage of GV and degenerate oocytes and increased the percentage of CEO at the MI stage. In M16 salts+FSK, the energy sources significantly decreased the percentage of oocytes with condensed chromosomes and increased the percentage of CEO reaching metaphase I. In conclusion, meiotic inhibitors had different effects in different culture media and glucose, pyruvate, lactate and glutamine were stimulatory to nuclear maturation. It was noteworthy that some of the results obtained were contrary to previous findings in mouse oocytes.

Intracytoplasmic Glutathione Levels in Heifer Oocytes Cultured in different Maturation Media and its Effect on Embryo Development

The present study was carried out to study the effect of different maturation media on embryo development of heifer oocytes and on their glutathione (GSH) synthesis during in vitro maturation (IVM). Immature heifer oocytes were matured in parallel in one of four maturation media: (i) Tissue Culture Medium (TCM)-199 supplemented with 10 ng/ml of epidermal growth factor (EGF); (i) TCM-199 supplemented with 10 ng/ml of EGF plus 1 microg/ml of FSH; (iii) TCM-199 supplemented with 10% of foetal bovine serum (FBS) and (iv) TCM-199 supplemented with 10% of FBS plus 1 microg/ml of FSH. Cow oocytes were used as control and were matured in TCM-199 supplemented with 10 ng/ml of EGF. No differences were observed in blastocyst rate among the different heifer oocyte groups (8.8, 7.5. 8.4 and 6.8%, respectively) however, the percentage of blastocysts obtained from cow oocytes was significantly higher (30%; p < 0.01) than those obtained from heifer oocytes. De novo GSH synthesis during oocyte maturation of heifer and cow oocytes was detected. No significant differences in intracytoplasmic GSH levels were observed among the experimental heifer oocyte groups or between heifer and cow oocytes both before and after IVM. In conclusion, the blastocyst yield obtained from heifer oocytes was lower than that from cow oocytes and this fact could not be explained by significant differences in intracytoplasmic GSH contents of oocytes before or after IVM.