Impaired Oocyte Maturation Research Articles

Oral antioxidants supplementation for women with unexplained infertility undergoing ICSI/IVF: Randomized controlled trial

Objective: Good oocyte quality and maturity are important prerequisites for high fertilization and implantation rates in IVF/ICSI treatment cycles. Reactive oxygen species (ROS) are produced within ovarian follicles, especially during the ovulation process, and increased ROS activity may be a cause of impaired oocyte maturation and higher rate of failure of IVF/ICSI cycles. Study design: RCT evaluating the effect of antioxidant supplementation on ICSI/IVF outcomes. Two hundred and eighteen women with unexplained subfertility undergoing IVF/ICSI were randomized into two groups. The study group (n = 112) received daily oral antioxidants in the form of multivitamins and minerals (amino acid chelated) while the control group (n = 106) did not. Main outcomes were number of mature metaphase II (MII) oocytes and clinical pregnancy rate. Results: There were no significant changes between the groups as regards age, BMI, basal FSH, number of mature (MII) oocytes (12.7 ± 9.4 vs. 13.2 ± 8.6, P = 0.7) and clinical pregnancy rate per woman randomized (38% vs. 34%; [OR = 1.2; 95% CI, 0.70–2.11]. Conclusion: Oral antioxidants in the form of a combination of multivitamins and minerals (amino acid chelated) did not improve oocyte quality and pregnancy rates in women with unexplained infertility undergoing IVF/ICSI treatment.

Lipids and oocyte developmental competence: the role of fatty acids and β-oxidation.

Metabolism and ATP levels within the oocyte and adjacent cumulus cells are associated with quality of oocyte and optimal development of a healthy embryo. Lipid metabolism provides a potent source of energy and its importance during oocyte maturation is being increasingly recognised. The triglyceride and fatty acid composition of ovarian follicular fluid has been characterised for many species and is influenced by nutritional status (i.e. dietary fat, fasting, obesity and season) as well as lactation in cows. Lipid in oocytes is a primarily triglyceride of specific fatty acids which differ by species, stored in distinct droplet organelles that re-localise during oocyte maturation. The presence of lipids, particularly saturated vs unsaturated fatty acids, in in vitro maturation systems affects oocyte lipid content as well as developmental competence. Triglycerides are metabolised by lipases that have been localised to cumulus cells as well as oocytes. Fatty acids generated by lipolysis are further metabolised by β-oxidation in mitochondria for the production of ATP. β-oxidation is induced in cumulus-oocyte complexes (COCs) by the LH surge, and pharmacological inhibition of β-oxidation impairs oocyte maturation and embryo development. Promoting β-oxidation with l-carnitine improves embryo development in many species. Thus, fatty acid metabolism in the mammalian COC is regulated by maternal physiological and in vitro environmental conditions; and is important for oocyte developmental competence.

Alteration of energy metabolism gene expression in cumulus cells affects oocyte maturation via MOS–mitogen-activated protein kinase pathway in dairy cows with an unfavorable “Fertil−” haplotype of one female fertility quantitative trait locus

Prim'Holstein heifers selected for the “Fertil−” homozygous haplotype of QTL-Female-Fert ility-BTA3 showed a greater rate of early pregnancy failure and slower embryo development after IVM suggesting lower oocyte quality than those selected for “Fertile+”. We aimed to ascertain intrafollicular factors related to lower oocyte quality in “Fertil−” cows. Analysis of individual oocytes showed meiotic progression delay in “Fertil−” compared with “Fertil+” dairy cows after in vivo maturation and IVM (P < 0.05). Expression of several genes localized to QTL-F-Fert-BTA3 or related to meiosis and mitogen-activated protein kinase pathway was analyzed in individual metaphase-II oocytes using reverse transcription- real-time polymerase chain reaction. Energy metabolism, apoptosis, extracellular matrix, and QTL-F-Fert-BTA3 genes were analyzed in surrounding cumulus cells (CC). In vivo, a significant decrease in prostaglandin synthase PTGES1 and PTGS2 expression coupled with lower PTGS2 protein abundance in CC and reduced expression of MOS in enclosed metaphase-II oocytes from “Fertil−” cows was observed. IVM strongly deregulated gene expression in CC and in oocytes compared with in vivo; nevertheless, differential expression of several genes including PEX19, NAMPT and MOS was observed between the two haplotypes. During IVM, PTGS2 activity inhibitor NS398 (50 μM) led to lower expression of fatty acid synthase (FASN) in CC and of MOS in treated metaphase-II oocytes. Using immunofluorescence, MOS protein was localized to a midbody-like contractile ring separating the polar body from the ooplasm, suggesting a role in the terminal stage of oocyte maturation. Our results suggest that factors involved in prostaglandin synthesis and lipid metabolism in CC could impair oocyte maturation, and might be involved in the reduced fertility of “Fertil−” cows.

Exposure to lipid-rich follicular fluid is associated with endoplasmic reticulum stress and impaired oocyte maturation in cumulus-oocyte complexes

To determine whether the high lipid content of human follicular fluid influences oocyte maturation. Mouse oocytes as substitutes for human oocytes were exposed to follicular fluids of differing lipid content with outcome monitoring. Private infertility clinic and university laboratory. Seventy-four women seeking assisted reproduction, and gonadotropin-stimulated mice. Assay of follicular fluids for triglyceride and free fatty acids, and stimulation of mouse cumulus-oocyte complexes (COCs) to maturity in vitro in the presence of lipid-rich or lipid-poor follicular fluid. Oocyte lipid content, expression of endoplasmic reticulum stress marker genes, and oocyte maturation assessed in mouse COCs exposed to lipid-rich follicular fluid were compared with complexes exposed to lipid-poor follicular fluid and complexes matured in vivo. Follicular fluids were obtained from women of known body mass index undergoing oocyte aspiration at a private infertility clinic, and the follicular fluids were assayed for triglyceride and free fatty acids; those with the highest and lowest levels of these lipids were selected. The mouse COCs exposed to lipid-rich follicular fluid during their maturation had increased oocyte lipid content, induction of endoplasmic reticulum stress markers, and impaired oocyte nuclear maturation. Increased body mass index is associated with elevated triglycerides and free fatty acids in ovarian follicular fluid. Maturation within this lipid-rich environment is detrimental to oocytes.

Loss of embryonic poly(A) binding protein (ePAB) in mouse results in female infertility due impaired oocyte maturation and ovulation

Gene expression during oocyte maturation and early embryogenesis until zygotic genome activation is mainly regulated by translational activation of maternally-derived mRNAs. Embryonic poly(A) binding protein (ePAB) is the predominant poly(A) binding protein during this period in frog, mouse, and human; it stabilizes maternal mRNAs and promotes their translation. We hypothesized that ePAB is required for female fertility.

Endometrial Indian hedgehog expression is decreased in women with endometriosis

Nuclear and cytoplasmic endometrial expression of Indian hedgehog increased from the late proliferative to mid and late secretory phases in 26 healthy volunteers compared with 30 women with endometriosis. The abnormal expression of Indian hedgehog protein in women with endometriosis suggests a resistance to P action.

Micronutrients in Parenteral Nutrition: Boron, Silicon, and Fluoride

Boron may be beneficial for bone growth and maintenance, central nervous system function, and the inflammatory response, and silicon may be beneficial for bone maintenance and wound healing. Fluoride is not an essential element but amounts provided by contamination may be beneficial for bone strength. Fluoride toxicity may be a concern in parenteral nutrition. Further studies are warranted to determine whether there are optimal amounts of boron and silicon that should be delivered to typical and special population patients receiving parenteral nutrition. In addition, further studies are needed to determine whether providing the dietary guideline of adequate intake amounts of fluoride parenterally would prevent or treat parenteral nutrition osteopenia.

Embryonic Poly-A-Binding Protein (Epab) Is Necessary for Mammalian Oogenesis.

In most metazoa, oocytes become arrested at the prophase of the first meiotic division. This arrest may last a few years in Xenopus and several decades in humans, and is characterized by synthesis and storage of dormant mRNA. The resumption of meiosis marks the onset of oocyte maturation and is associated with suppression of transcription, which persists until embryonic genome activation. Consequently, gene expression during oocyte maturation, fertilization and early embryogenesis depends on translational activation of maternally-derived mRNAs stored in the oocyte during the first meiotic arrest. Embryonic poly(A) binding protein (ePAB), identified in Xenopus oocytes, is the predominant poly(A) binding protein during early Xenopus development until zygotic genome activation (ZGA). In Xenopus oocytes, ePAB stabilizes maternal mRNAs and promotes their translation, and therefore seems to play a central role in the translational regulation of maternally derived transcripts during a critical period of early development when transcription is suppressed. Mouse and human Epab's have been identified and demonstrate an expression pattern similar to that of Xenopus ePAB. We hypothesized that Epab plays a key role in mammalian early development. To test our hypothesis, we generated Epab-null mice by targeted deletion of Epab exon 2 which resulted in a translational frame shift and generated a premature stop codon. Male and female ePAB -/- mice were viable and appeared phenotypically normal. However, ePAB-/- female mice were infertile, while ePAB-/- males and ePAB+/- of both sexes demonstrated normal fertility. Superovulation and mating with wild type males showed that ePAB-/- female mice could not generate embryos. In addition, ePAB-/- females exhibited a marked reduction in the number of Graafian follicules in their ovaries, and produced a significantly decreased number of oocytes with impaired maturation in response to superovulation. Here, we report that Epab-null phenotype is associated with infertility and impaired oocyte maturation. Our findings indicate that Epab is necessary for oogenesis and reproduction in mammals. Molecular mechanisms of Epab-mediated translational activation during mammalian early development, and their implications for human reproduction remain to be elucidated. This research was supported by NIH HD046581-01 (ES). (platform)

Autoimmune response to Chlamydia trachomatis infection and in vitro fertilization outcome

This observational study was conducted in 235 patients undergoing IVF who had a cervical swab positive for Chlamydia trachomatis and who underwent antibiotic treatment until a negative cervical swab before IVF attempt. After oocyte retrieval, follicular fluids of 109 patients out of 228 still showed the presence of IgA antichlamydia antibodies and a significantly lower pregnancy and implantation rate; therefore we conclude that patients should undergo IVF procedure after serum antichlamydia IgA tests negative.

Influence of serum from pregnant women and selected pregnancy hormones on in-vitro maturation of murine oocytes

Maturation medium for in-vitro maturation (IVM) is usually supplemented with serum. The objective of this study was to investigate whether serum from pregnant women had any adverse effects on IVM, and if so, whether the hormonal changes in pregnancy played a role. Serum was obtained from 40 pregnant women and was analysed for oestradiol, prolactin, β-human chorionic gonadotrophin (β-HCG), progesterone and testosterone. In the first part of the study, immature murine oocytes were cultured in maturation media supplemented with various sera. The control group was supplemented with 10% serum from fertile women, and groups 2–5 were respectively supplemented with 10, 20, 40 and 80% serum from pregnant women. In the second part of the study, immature murine oocytes were matured in the medium with the addition of different hormones according to the concentrations found in the serum of pregnant women. Compared with the control group, the maturation and fertilization rates were significantly lower in medium supplemented with 10% serum from pregnant women (59.7 versus 71.5% and 60.1 versus 77.0% respectively, both P < 0.05). There was a trend of decreasing maturation and fertilization rates with increasing concentrations of serum from pregnant women. Addition of prolactin, β-HCG, progesterone and testosterone also impaired oocyte maturation.

Rauchen alteriert die Sekretion angiogenetischer Substanzen während der Eizellreifung des Menschen

Objective: An adequate vascularization in the ovary is important for optimal oocyte maturation. By secreting vascular endothelial growth factor (VEGF) granulosa cells promote blood vessel growth. In addition, they paracrinely reduce the production of VEGF antagonist sVEGFR-1 (soluble VEGF receptor 1) in endothelial cells. In the present study we examined the influence of smoking on the sVEGFR-1 concentration in human follicular fluid and on the paracrine activity of granulosa cells. Material and Methods: Follicular fluid samples were obtained during oocyte retrieval from 50 smoking and 50 non-smoking women undergoing in-vitro fertilization treatment. Follicular fluids were used either directly for sVEGFR-1 quantification or added to endothelial cell cultures to determine the soluble receptor concentration in culture supernatant after four days' incubation. Results: In this study we were able to show that smokers have a distinctly higher concentration of soluble VEGF receptor 1 in follicular fluid than non-smokers (499.6±77.7 pg/ml versus 159.2±29.8 pg/ ml). Also, follicular fluid of smoking women shows a significantly less inhibiting effect on endothelial sVEGFR-1 production than of non-smoking women (1174.1 ± 93.8pg/ml compared to 794.2 ± 70.1 pg/ml). Conclusion: A higher concentration of sVEGFR-1 indicates decreased angiogenic activity in follicles of smokers which may result in reduced blood circulation during follicular growth and thus impaired oocyte maturation by malnutrition.

Molecular impact of propiconazole on Daphnia magna using a reproduction-related cDNA array

We have developed a first version cDNA microarray of the cladoceran Daphnia magna. Through Suppression Subtractive Hybridisation PCR (SSH–PCR) 855 life stage-specific cDNAs were collected and used to document the toxicological mode of action of the pesticide propiconazole. DNA sequencing analysis revealed gene fragments related to important functional classes such as embryo development, energy metabolism, molting and cell cycle. Major changes in transcription were observed in organisms exposed for 4 and 8 days to 1 μg/mL. After 4 days a 3-fold down-regulation of the gene encoding the yolk protein, vitellogenin, was observed indicating impaired oocyte maturation. Moreover, genes such as a larval-specific gene and chaperonin were repressed, whereas the heat shock 90 protein and ATP synthase were induced. Organismal effects clearly confirmed the major molecular findings: at the highest concentration (1 μg/mL) adult growth was significantly ( p < 0.05) impaired and increased developmental effects in the offspring could be noted. We have demonstrated the potential of microarray analysis in toxicity screening with D. magna. The use of vitellogenin mRNA as a rapid biomarker of reproductive effects in chronic toxicity studies with cladocerans is suggested.

Predictive value of cumulus cell apoptosis with regard to blastocyst development of corresponding gametes

To test if a high degree of apoptosis in cumulus cells could indicate diminished oocyte quality and developmental competence. Prospective analysis. Public hospital and university. Thirty seven women who gave written consent to participate in this study. Cumulus-oocyte complexes were denuded separately and the resulting cumulus cell suspensions were analyzed for presence of apoptosis using a terminal deoxynucleotidyl transferase-mediated digoxigenin-dUTP nick-end labeling (TUNEL) assay detection kit. Percentage of apoptotic cumulus cells and blastocyst formation rate. Younger patients (< or = 35 years) showed significantly fewer apoptotic cumulus cells than older ones. In all patients gamete maturity was shown to be highly correlated to the rate of apoptosis in cumulus cells. At zygote and cleavage stages (days 1 to 4) no morphologic features were related to the degree of programmed cell death. However, blastocyst development was predictable taking into account the percentage of apoptosis in associated somatic cells. In addition, there was a trend toward better quality blastocysts from follicles with a lower rate of apoptotic cells. No influence on pregnancy and implantation rate was observed. Apoptotic processes within follicles seem to impair oocyte maturation. Though not manifested in the morphologic appearance, gametes and embryos derived from cumulus complexes with no or minor apoptosis have an increased chance of giving rise to optimal blastocysts.

A successful model to assess embryo development after transplantation of prophase nuclei.

Germinal vesicle transplantation (GVT) provides a means of investigating interactions between karyoplasts and cytoplasts isolated from different cells. Technically, GVT can be accomplished with a high degree of efficiency without compromising the maturation of either the human or mouse oocyte nucleus. Although maturation, fertilization and preimplantation development have been established using GVT, full-term development has been reported only after supplementation with fresh mature ooplasm. In this study, we assess the ability of immature oocytes collected from gonadotrophin-primed ovaries to mature in vitro after GVT and develop to full-term. GV oocytes were retrieved from either non-stimulated or pregnant mare's serum gonadotrophin (PMSG)-primed female mice. Microsurgically isolated GV karyoplasts were transplanted into previously enucleated oocytes. Oocytes successfully reconstituted by electrofusion were cultured for 14 h to allow nuclear maturation. Metaphase II oocytes were subjected to Piezo-ICSI, and those fertilized normally were cultured to the blastocyst stage. Some such embryos were transferred to pseudopregnant female mice to examine their potential for normal development. Cumulus-denuded non-manipulated oocytes that were matured in vitro served as controls. The reconstitution and maturation rates were comparable in oocytes isolated from PMSG-primed and from unstimulated ovaries. The rate of normal fertilization in oocytes from primed ovaries was significantly higher than that of their non-primed counterparts (63.5 versus 39.6%; P < 0.01). This difference was also confirmed in terms of blastocyst development (31.8 versus 7.9%; P < 0.01). Of a total of 70 embryos transferred to the oviduct of five recipient mice, 21.4% developed to normal live offspring. All developed as normal adults and proved to be fertile. The live birth rate was comparable to that obtained using non-manipulated control oocytes (22.3%). Higher rates of fertilization and blastocyst formation were obtained after GVT of mouse oocytes isolated from PMSG-primed ovaries compared with their non-primed counterparts. These represent the first mouse offspring derived from in vitro matured, cumulus-denuded oocytes treated by allo-GVT and fertilized by ICSI. Thus, GVT appears not to impair oocyte maturation, fertilization and pre- and post-implantation development and, after gonadotrophin priming, allows generation of healthy mouse offspring without mature ooplasm supplementation.

Chronic low-dose antiprogestin impairs preimplantation embryogenesis, but not oocyte nuclear maturation or fertilization in rhesus monkeys

Continual administration of low doses of the antiprogestin ZK 137 316 permits ovarian/menstrual cyclicity, but prevents pregnancy in female rhesus monkeys. The sites of contraceptive action remain unknown. This study determined whether chronic, low-dose antiprogestin exposure during follicular development impairs oocyte maturation in vivo, as well as fertilization and preimplantation embryogenesis in vitro. Adult, female rhesus monkeys exhibiting normal menstrual cycles received vehicle ( n=9) or 0.03 mg ZK 137 316 ( n=8)/kg body weight i.m. daily for 3 months. Controlled ovarian stimulation with recombinant gonadotropins was initiated in the 3rd month. Oocytes collected from preovulatory follicles were evaluated for nuclear maturity and inseminated in vitro. Preimplantation embryonic development was monitored in vitro. The total number of oocytes and percentage collected at each nuclear stage were similar in both groups. More ( P<0.05) atretic oocytes were recovered following antiprogestin relative to vehicle treatment. Fertilization rates and percentages of embryos that progressed to the morula stage were similar between groups, but antiprogestin-treated females exhibited less ( P<0.05) normal cleavage. Embryonic development was accelerated by 1 day ( P<0.05) from the 16-cell to the morula stage in the antiprogestin group relative to vehicle. Despite this, the majority of embryos became blastocysts within 6 days in vitro in the antiprogestin group, but fewer expanded ( P=0.09) and hatched ( P<0.05) compared to vehicle. During in vivo treatment with chronic, low-dose antiprogestin, oocytes retained their ability to resume and complete meiosis as well as fertilize following insemination in vitro. However, preimplantation embryogenesis in vitro was impaired, particularly during the later stages of blastocyst development. Thus, antiprogestin exposure during follicular development altered oocyte functions that are critical for normal preimplantation embryogenesis; this may contribute to pregnancy prevention.

Superovulation treatment with recombinant human FSH results in impaired bovine follicular function and oocyte maturation

Superovulation treatment with recombinant human FSH results in impaired bovine follicular function and oocyte maturation

Molecular biology of the female reproductive system

Suprabasal progesterone concentrations around oestrus have induced disturbances in oestrous behaviour and ovulation. To determine whether fertility in such an altered oestrus can be maintained at normal levels with additional inseminations (AI) until ovulation, fertility was compared in heifers (n = 11) inseminated in normal oestrous cycles and thereafter in cycles in which the animals were treated with progesterone in order to create suprabasal concentrations after luteolysis. The treatment consisted of silicone implants containing 10.6 mg kg−1 of progesterone inserted subcutaneously on Day 8 of the oestrous cycle (day of ovulation designated Day 0) and removed on Day 25. Both in control oestrous cycles and oestrous cycles under progesterone treatment, growth of the ovulatory follicle and ovulation were determined by frequent ultrasound scanning. Blood was collected frequently for further analysis of progesterone, oestradiol-17β and luteinising hormone (LH). Insemination was performed 12 h after onset of standing oestrus. if ovulation did not occur 24 h after AI, heifers were inseminated again until ovulation. Pregnancy was diagnosed by ultrasound 25 days after ovulation.In control oestrous cycles, plasma progesterone decreased to 0.3 ± 0.3 nmol 1−1. Duration of oestrus was 22.9 ± 2.0 h, the interval from onset of oestrus to ovulation was 32.4 ± 2.3 h and the interval from LH peak to ovulation was 28.6 ± 1.4 h. The interovulatory interval was 20.7 ± 0.6 days. In oestrous cycles in treated heifers, progesterone decreased to 1.0 ± 0.3 nmol l−1 (P > 0.10) and the interovulatory interval was prolonged to 23.5 ± 1.0 days (P < 0.05). Standing oestrus lasted 47.2 ± 12.0 h (P = 0.09, n = 7). The interval from the onset of oestrus to ovulation was 59.4 ± 13.0 h (P = 0.08) and the interval from LH peak to ovulation 25.8 ± 1.3 h (P > 0.10). The prolonged oestrus was associated with increased (P < 0.05) growth of the ovulatory follicle and higher (P < 0.05) release of oestradiol-17β. Conception rates were 90% and 46% (P < 0.05), and the numbers of AI per heifer were 1.1 ± 0.1 and 3.4 ± 0.6 (P < 0.01) for control oestrous cycles and after treatment, respectively.The induction of suprabasal concentrations of progesterone caused asynchronies similar to those observed in cases of repeat breeding. The repeated AI did not maintain fertility at normal levels. It is suggested that the extended growth of the ovulatory follicle may cause impaired oocyte maturation or it may alter the maternal milieu owing to the prolonged release of oestradiol.

Reproductive performance of heifers induced to oestrous asynchrony by suprabasal plasma progesterone levels

Suprabasal progesterone concentrations around oestrus have induced disturbances in oestrous behaviour and ovulation. To determine whether fertility in such an altered oestrus can be maintained at normal levels with additional inseminations (AI) until ovulation, fertility was compared in heifers (n = 11) inseminated in normal oestrous cycles and thereafter in cycles in which the animals were treated with progesterone in order to create suprabasal concentrations after luteolysis. The treatment consisted of silicone implants containing 10.6 mg kg−1 of progesterone inserted subcutaneously on Day 8 of the oestrous cycle (day of ovulation designated Day 0) and removed on Day 25. Both in control oestrous cycles and oestrous cycles under progesterone treatment, growth of the ovulatory follicle and ovulation were determined by frequent ultrasound scanning. Blood was collected frequently for further analysis of progesterone, oestradiol-17β and luteinising hormone (LH). Insemination was performed 12 h after onset of standing oestrus. if ovulation did not occur 24 h after AI, heifers were inseminated again until ovulation. Pregnancy was diagnosed by ultrasound 25 days after ovulation. In control oestrous cycles, plasma progesterone decreased to 0.3 ± 0.3 nmol 1−1. Duration of oestrus was 22.9 ± 2.0 h, the interval from onset of oestrus to ovulation was 32.4 ± 2.3 h and the interval from LH peak to ovulation was 28.6 ± 1.4 h. The interovulatory interval was 20.7 ± 0.6 days. In oestrous cycles in treated heifers, progesterone decreased to 1.0 ± 0.3 nmol l−1 (P > 0.10) and the interovulatory interval was prolonged to 23.5 ± 1.0 days (P 0.10). The prolonged oestrus was associated with increased (P < 0.05) growth of the ovulatory follicle and higher (P < 0.05) release of oestradiol-17β. Conception rates were 90% and 46% (P < 0.05), and the numbers of AI per heifer were 1.1 ± 0.1 and 3.4 ± 0.6 (P < 0.01) for control oestrous cycles and after treatment, respectively. The induction of suprabasal concentrations of progesterone caused asynchronies similar to those observed in cases of repeat breeding. The repeated AI did not maintain fertility at normal levels. It is suggested that the extended growth of the ovulatory follicle may cause impaired oocyte maturation or it may alter the maternal milieu owing to the prolonged release of oestradiol.

Progression of Oocyte Maturation From Metaphase I to Metaphase II is disturbed by previous immunological interference with cumulus cell function

The effects of an antibody preparation reacting with preovulatory mouse cumuli oophori (anticumulus Ig) on oocyte maturation in vivo and in vitro were studied. Continuous presence of anticumulus Ig in culture medium did not impair oocyte maturation in vitro. Similarly, no effect on oocyte maturation in vivo was observed when anticumulus Ig was given to females superovulated with pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin (hCG) at the time of hCG treatment. However, when administered earlier, anticumulus Ig brought about serious disturbances of oocyte meiotic competence, since only immature oocytes were ovulated after anticumulus Ig injection at the time of PMSG treatment and as much as 70% of the ovulated oocytes were immature when the antibody was applied 24 hr later. Previous absorption of anticumulus Ig with isolated cumulus cells removed the inhibitory effect of this preparation on oocyte meiotic competence to the same extent as absorption with whole cumuli oophori, despite the persistence of a strong reactivity of the cumulus cell-absorbed antibody preparations with the cumulus intercellular matrix. The ability of oocytes obtained from antibody-injected animals to mature in vitro was also considerably impaired when the injection was made at the time of PMSG treatment. In all cases the maturation defect concerned the progression of meiosis from metaphase I to metaphase II, while the ability of oocytes to undergo germinal vesicle breakdown (GVBD) was unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)