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.

Amino acid turnover by human oocytes is influenced by gamete developmental competence, patient characteristics and gonadotrophin treatment.

STUDY QUESTION: Can amino acid profiling differentiate between human oocytes with differing competence to mature to metaphase II (MII) in vitro? SUMMARY ANSWER: Oocytes which remained arrested at the germinal vesicle (GV) stage after 24 h of in vitro maturation (IVM) displayed differences in the depletion/appearance of amino acids compared with oocytes which progressed to MII and patient age, infertile diagnosis and ovarian stimulation regime significantly affected oocyte amino acid turnover during IVM. WHAT IS KNOWN ALREADY: Amino acid profiling has been proposed as a technique which can distinguish between human pronucleate zygotes and cleavage stage embryos with the potential to develop to the blastocyst stage and implant to produce a pregnancy and those that arrest. Most recently, the amino acid turnover by individual bovine oocytes has been shown to be predictive of oocyte developmental competence as indicated by the gamete's capacity to undergo fertilization and early cleavage divisions in vitro. STUDY DESIGN, SIZE, DURATION: The study was conducted between March 2005 and March 2010. A total of 216 oocytes which were at the GV or metaphase I (MI) stages at the time of ICSI were donated by 67 patients. PARTICIPANTS/MATERIALS, SETTINGS, METHODS: The research was conducted in university research laboratories affiliated to a hospital-based infertility clinic. Oocytes were cultured for 24 h and the depletion/appearance of amino acids was measured during the final 6 h of IVM. Amino acid turnover was analysed in relation to oocyte meiotic progression, patient age, disease aetiology and controlled ovarian stimulation regime. MAIN RESULTS AND THE ROLE OF CHANCE: The depletion/appearance of key amino acids was linked to the maturation potential of human oocytes in vitro. Oocytes which arrested at the GV stage (n = 9) depleted significantly more valine and isoleucine than those which progressed to MI (n = 32) or MII (n = 107) (P < 0.05). Glutamate, glutamine, arginine and valine depletion or appearance differed in MII versus degenerating oocytes (n = 20) (P < 0.05). Glutamine, arginine, methionine, phenylalanine, total depletion and total turnover all differed in oocytes from patients aged < 35 years versus patients ≥35 years (P < 0.05). MII oocytes obtained following ovarian stimulation with recombinant FSH depleted more isoleucine (P < 0.05) and more alanine and lysine (P < 0.05) appeared than oocytes from hMG-stimulated cycles. MII oocytes from patients with a polycystic ovary (PCO) morphology (n = 33) depleted more serine (P < 0.05) than oocytes from women with normal ovaries (n = 61). LIMITATIONS, REASONS FOR CAUTION: Immature oocytes collected at the time of ICSI were used as the model for human oocyte maturation. These oocytes have therefore failed to respond to the ovulatory hCG trigger in vivo (they are meiotically incompetent), and have limited capacity to support embryo development in vitro. The lack of cumulus cells and stress of the conditions in vitro may have influenced turnover of amino acids, and owing to the small sample sizes further studies are required to confirm these findings. WIDER IMPLICATIONS OF THE FINDINGS: The findings provide support for the hypothesis that oocyte metabolism reflects oocyte quality. Longitudinal studies are required to link these functional metabolic indices of human oocyte quality with embryo developmental competence. Oocyte amino acid profiling may be a useful tool to quantify the impact of new assisted reproduction technologies (ART) on oocyte quality. STUDY FUNDING/COMPETING INTERESTS: This project was funded by the UK Biology and Biotechnology Research Council (BB/C007395/1) and the Medical Research Council (G 0800250). K.E.H was in receipt of a British Fertility Society/Merck Serono studentship. H.J.L. is a shareholder in Novocellus Ltd, a company which seeks to devise a non-invasive biochemical test of embryo health.

Oocyte developmental failure in response to elevated nonesterified fatty acid concentrations: mechanistic insights.

Elevated plasma nonesterified fatty acid (NEFA) concentrations are associated with negative energy balance and metabolic disorders such as obesity and type II diabetes. Such increased plasma NEFA concentrations induce changes in the microenvironment of the ovarian follicle, which can compromise oocyte competence. Exposing oocytes to elevated NEFA concentrations during maturation affects the gene expression and phenotype of the subsequent embryo, notably prompting a disrupted oxidative metabolism. We hypothesized that these changes in the embryo are a consequence of modified energy metabolism in the oocyte. To investigate this, bovine cumulus oocyte complexes were matured under elevated NEFA conditions, and energy metabolism-related gene expression, mitochondrial function, and ultrastructure evaluated. It was found that expression of genes related to REDOX maintenance was modified in NEFA-exposed oocytes, cumulus cells, and resultant blastocysts. Moreover, the expression of genes related to fatty acid synthesis in embryos that developed from NEFA-exposed oocytes was upregulated. From a functional perspective, inhibition of fatty acid ß-oxidation in maturing oocytes exposed to elevated NEFA concentrations restored developmental competence. There were no clear differences in mitochondrial morphology or oxygen consumption between treatments, although there was a trend for a higher mitochondrial membrane potential in zygotes derived from NEFA-exposed oocytes. These data show that the degree of mitochondrial fatty acid ß-oxidation has a decisive impact on the development of NEFA-exposed oocytes. Furthermore, the gene expression data suggest that the resulting embryos adapt through altered metabolic strategies, which might explain the aberrant energy metabolism previously observed in these embryos originating from NEFA-exposed maturing oocytes.

Effects of changes in the concentration of systemic progesterone on ions, amino acids and energy substrates in cattle oviduct and uterine fluid and blood.

Early embryo loss is a major factor affecting the conception rate in cattle. Up to 40% of cattle embryos die within 3 weeks of fertilisation while they are nutritionally dependent on oviduct and uterine fluids for their survival. Inadequate systemic progesterone is one of the factors contributing to this loss. We have characterised the effects of changes in systemic progesterone on amino acid, ion and energy substrate composition of oviduct and uterine fluids on Days 3 and 6, respectively, of the oestrus cycle in cattle. Oviduct and uterine fluids were collected in situ following infusion of progesterone. There was no effect of progesterone on oviduct fluid secretion rate; however, uterine fluid secretion rate was lowered. Progesterone increased uterine glucose, decreased oviduct sulfate and, to a lesser degree, oviduct sodium, but had no effect on any of the ions in the uterus. The most marked effect of progesterone was on oviducal amino acid concentrations, with a twofold increase in glycine, whereas in the uterus only valine was increased. These results provide novel information on the maternal environment of the early cattle embryo and provide further evidence of progesterone regulation of oviduct amino acid concentrations in cattle.

Amino acid metabolism of bovine blastocysts: a biomarker of sex and viability.

The ratio of male/female embryos may be modified by environmental factors such as maternal diet in vivo and the composition of embryo culture media in vitro. We have used amino acid profiling, a noninvasive marker of developmental potential to compare the effect of sex on the metabolism of bovine blastocysts conceived in vivo and in vitro. Blastocysts were incubated individually for 24 hr in a close-to-physiological mixture of amino acids and the depletion or appearance of 18 amino acids measured using HPLC. Blastocysts were then sexed by PCR. Amino acid depletion by in vitro-produced blastocysts and expanded blastocysts was higher than in embryos conceived in vivo (P = 0.02). When cultured in vitro, female embryos exhibited increased depletion of arginine, glutamate, and methionine and appearance of glycine, while male embryos displayed increased depletion of phenylalanine, tyrosine, and valine. Overall, in vitro-produced blastocysts exhibited sex-specific differences in metabolic profiles of 7 out of 18 amino acids; in vivo-produced, in 2 out of 18. These differences had disappeared by the expanded blastocyst stages. We have also shown that amino acid metabolism can predict the ability of bovine zygotes to develop to the blastocyst stage, providing "proof of principle" for the use of this technology in clinical IVF to select single embryos for transfer and thereby avoid the problem of multiple births.

Role of fatty acids in energy provision during oocyte maturation and early embryo development.

While much is known about the metabolism of exogenous nutrients such as glucose, lactate, pyruvate, amino acids by oocytes and pre-implantation mammalian embryos, the role of endogenous stores, particularly lipid, has been largely overlooked. The presence of lipid within oocytes and early embryos has been long known, and comparisons between species indicate that the amounts and types of lipid present vary considerably. Large amounts of intracellular lipid can compromise the success of cryopreservation and the removal of such lipid has been the subject of considerable effort. In this review, we present evidence that strongly suggests a metabolic role for lipid, specifically with regard to energy provision, in the late-stage oocyte and the pre-implantation embryo. We focus initially on oxygen consumption as a global indicator of metabolic activity, before reviewing different approaches that either have been designed to investigate directly, or have revealed indirectly the role of endogenous lipid in energy generation. These fall under five headings: (i) fatty acid oxidation; (ii) inhibition of triglyceride oxidation; (iii) culture in the absence of exogenous substrates; (iv) cytoplasmic organization; and (v) delipidation. On the basis of the data derived from these studies, we conclude that there is strong evidence for the utilization of endogenous lipid as an energy substrate by oocytes and early embryos.

Expression of genes involved in early cell fate decisions in human embryos and their regulation by growth factors.

Little is understood about the regulation of gene expression in human preimplantation embryos. We set out to examine the expression in human preimplantation embryos of a number of genes known to be critical for early development of the murine embryo. The expression profile of these genes was analysed throughout preimplantation development and in response to growth factor (GF) stimulation. Developmental expression of a number of genes was similar to that seen in murine embryos (OCT3B/4, CDX2, NANOG). However, GATA6 is expressed throughout preimplantation development in the human. Embryos were cultured in IGF-I, leukaemia inhibitory factor (LIF) or heparin-binding EGF-like growth factor (HBEGF), all of which are known to stimulate the development of human embryos. Our data show that culture in HBEGF and LIF appears to facilitate human embryo expression of a number of genes: ERBB4 (LIF) and LIFR and DSC2 (HBEGF) while in the presence of HBEGF no blastocysts expressed EOMES and when cultured with LIF only two out of nine blastocysts expressed TBN. These data improve our knowledge of the similarities between human and murine embryos and the influence of GFs on human embryo gene expression. Results from this study will improve the understanding of cell fate decisions in early human embryos, which has important implications for both IVF treatment and the derivation of human embryonic stem cells.

Energy substrates in bovine oviduct and uterine fluid and blood plasma during the oestrous cycle.

Up to 40 percent of cattle embryos die within 3 weeks of fertilization but there is little or no published information on the composition of the oviduct and uterine fluids essential for their survival during this time. We have measured the concentrations of the energy substrates, glucose, lactate, and pyruvate in cattle oviduct fluid on Days 0, 2, 4, and 6 and uterine fluid on Days 6, 8, and 14 of the oestrous cycle and corresponding blood samples. Oviduct and uterine fluids were collected in situ. Glucose concentrations in oviduct and uterine fluids were similar on all days and lower than in plasma (P < 0.05). Oviduct lactate concentration was up to eightfold higher than uterine or plasma concentration (P < 0.01). Oviduct pyruvate concentrations were similar on all days and lower than plasma concentrations on Days 0 and 2 (P < 0.005). Pyruvate concentrations were similar in the uterus and in plasma except on Day 14 when the concentration in plasma was higher (P < 0.05). There were no associations between systemic progesterone or oestradiol and glucose, lactate or pyruvate. There was a linear positive relationship (P < 0.001) between oviduct fluid secretion rate and oviduct glucose concentration and a linear negative relationship (P < 0.001) between oviduct fluid secretion rate and oviduct lactate, but no association between uterine fluid secretion rate and energy substrates. The different concentrations and associations between the energy substrates in oviduct and uterine fluids and blood plasma indicate a differential regulation of the secretion of these energy substrates by the oviduct and uterine epithelium.

The delivery of PEBBLE nanosensors to measure the intracellular environment.

Cellular introduction of PEBBLEs (photonic explorers for bioanalysis with biologically localized embedding) has been investigated by a wide variety of methods in a range of cell types. These methods include surface functionalization with CPPs (cell-penetrating peptides), pinocytosis, commercial lipid transfection agents, cytochalasin D, picoinjection, and Gene gun bombardment. This paper will overview several of the most popular methods used for the introduction of PEBBLE nanosensors to the cellular environment and discuss the efficacy of the techniques.

Fluorescence resonance energy transfer analysis of mitochondrial:lipid association in the porcine oocyte.

The role of endogenous lipid in the provision of energy during in vitro maturation of immature porcine oocytes has been studied. Fluorescence resonance energy transfer (FRET) acceptor bleaching methods have been used to examine mitochondrial:lipid droplet co-localisation in live oocytes. FRET experiments demonstrate whether organelles are within the FRET-distance (i.e. 6-10 nm), thus showing true association on a molecular scale. Immature and in vitro-matured porcine oocytes were stained with Mitotracker Green (MTG; mitochondria) and Nile Red (NR; lipid droplets). The data indicated sufficient overlap between MTG emission and NR excitation to support a FRET reaction and that mitochondria and lipid droplets were sufficiently co-localised for a FRET reaction to occur. When NR-stained lipid droplets were specifically bleached, a significant increase in the MTG signal in stained mitochondria was observed (FRET efficiency, E=22.2 +/- 3.18%). These results strongly suggest a metabolic role for lipid metabolism during oocyte maturation. This conclusion was reinforced by the use of inhibitors of fatty acid beta-oxidation, methyl palmoxirate or mercaptoacetate, exposure to which during oocyte maturation led to developmental failure post-fertilisation. These data provide strong evidence that MTG and NR can act as a FRET pair and that in porcine oocytes, mitochondria and lipid droplets lie within 6-10 nm of each other, indicating association on a molecular scale. The findings also suggest that endogenous triglycerides play an important role in energy metabolism during porcine in vitro maturation.

Amino acid metabolism of the porcine blastocyst.

The pattern of depletion and appearance of a mixture of amino acids by single porcine blastocysts incubated in two different media has been determined non-invasively using high performance liquid chromatography. Zygotes were produced by the in vitro fertilisation of in vitro-matured, abattoir-derived immature oocytes and cultured in medium NCSU 23 with or without amino acids. Embryos grown in the absence of amino acids up to the blastocyst stage were transferred to amino acid-containing culture medium for measurement of turnover (Experiment 1). Blastocysts grown in NCSU 23+amino acids were transferred into fresh droplets of the same medium (Experiment 2). Although the specific pattern of amino acid production and depletion varied between experiments, a general pattern emerged, with arginine being significantly depleted (p<0.001) and alanine consistently appearing in the media, in quantities that varied depending with culture conditions. The data suggest that arginine is important during porcine blastocyst development, most likely contributing to the formation of nitric oxide and polyamines and that alanine is produced as a means of disposing of excess amino groups. A model for the interactions of amino acids during porcine early embryo development is proposed. The profile of amino acid metabolism by porcine blastocysts is qualitatively and quantitatively similar to that given by human embryos during the morula:blastocyst transition suggesting that the porcine blastocyst is a good model for the human.

A biomimetic tissue from cultured normal human urothelial cells: analysis of physiological function.

The urinary bladder and associated tract is lined by the urothelium. Once considered as just an impermeable epithelium, it is becoming evident that the urothelium not only functions as a volume-accommodating urinary barrier but has additional roles, including sensory signaling. Lack of access to normal human urothelium has hampered physiological investigation, and although cell culture systems have been developed, there has been a failure to demonstrate that normal human urothelial (NHU) cells grown in vitro retain the capacity to form a functional differentiated urothelium. The aim of this study was to develop a biomimetic human urothelium from NHU cell cultures. Urothelial cells isolated from normal human urothelium and serially propagated as monolayers in serum-free culture were homogeneous and adopted a proliferative, nondifferentiated phenotype. In the presence of serum and physiological concentrations of calcium, these cells could be reproducibly induced to form stratified urothelia consisting of basal, intermediate, and superficial cells, with differential expression of cytokeratins and superficial tight junctions. Functionally, the neotissues showed characteristics of native urothelium, including high transepithelial electrical resistance of >3,000 Omega.cm(2), apical membrane-restricted amiloride-sensitive sodium ion channels, basal expression of Na(+)-K(+)-ATPase, and low diffusive permeability to urea, water, and dextran. This model represents major progress in developing a biomimetic human urothelial culture model to explore molecular and functional relationships in normal and dysfunctional bladder physiology.

Identification of viable embryos in IVF by non-invasive measurement of amino acid turnover.

BACKGROUND: IVF is limited by low success rates and an unacceptably high multiple pregnancy rate. These outcomes would be improved significantly if a single embryo of high viability could be replaced in each treatment cycle, but widespread acceptance of such a policy is hindered by the lack of predictive factors for embryo selection. We have conducted a retrospective clinical study of a novel non-invasive method of embryo selection based on the depletion/appearance of amino acids in the culture medium. METHODS: Fifty-three cycles of IVF treatment using ICSI were studied. Embryos were cultured for 24 h in 4 microl drops of medium containing a physiological mixture of 18 amino acids. The spent medium was analysed for amino acid content by high performance liquid chromatography. RESULTS: The turnover of three amino acids, Asn, Gly and Leu, was significantly correlated with a clinical pregnancy and live birth. These correlations were independent of known predictors, such as female age, basal levels of FSH, embryo cell number and embryo morphological grade. CONCLUSIONS: Non-invasive assay of amino acid turnover has the potential to improve significantly the prospective selection of the most viable embryos, or single embryo, for replacement in an IVF cycle.

Effect of inhibiting nitric oxide production on mouse preimplantation embryo development and metabolism.

Nitric oxide (NO) is a free radical that functions as a cell signaling molecule but at high concentrations can be toxic. It is formed from arginine, which is consumed by the mouse blastocyst, but its effect on early embryo development has been little studied. In this study, the role of NO in mouse preimplantation development has been examined in terms of developmental rate and oxidative metabolism. Zygotes were cultured in one of four media; potassium simplex optimization medium (KSOM), KSOM with amino acids (KSOMaa), KSOM without glutamine (KSOM-glut), or KSOM with 0.5 mM arginine (KSOMarg) +/- l-NAME (a specific inhibitor of NO production). End points were Day 4 blastocyst rates, cell counts determined using bisbenzimide and oxygen consumption. In KSOM and KSOM-glut, the blastocyst rate was decreased by 1 mM l-NAME from 50.2% +/- 3.1% and 37.4% +/- 4.5% to 6% +/- 3% and 0%, respectively. In KSOMaa, cavitation rates were unaltered but the blastocysts contained fewer cells (P < 0.001). Blastocysts cultured in KSOM and KSOM-glut consumed significantly more oxygen than those cultured in KSOMaa (P < 0.001 and P < 0.05, respectively). However, the addition of 0.1 mM or 1 mM l-NAME to KSOMaa significantly increased the amount of oxygen consumed (P < 0.05 and P < 0.001, respectively). The data suggest a physiological role for NO in mouse preimplantation metabolism and development. One possibility is that NO may limit oxygen consumption at the blastocyst stage at the level of mitochondrial cytochrome c oxidase.

Metabolic characterization of the bovine blastocyst, inner cell mass, trophectoderm and blastocoel fluid.

The formation of a viable blastocyst is dependent upon the establishment of a correct inner cell mass (ICM):trophectoderm cell ratio but little is known about the metabolism of the two cell populations or about the composition of blastocoel fluid. In this study, the metabolism of intact bovine blastocysts, isolated ICM and trophectoderm was examined in terms of glucose and pyruvate uptake, lactate production, and amino acid consumption or production. The concentration of these nutrients in blastocoel fluid was also determined. The metabolism of glucose, pyruvate and lactate differed significantly between the isolated ICM and trophectoderm. Isolated trophectoderm had a higher pyruvate (P<0.001) and lower glucose (P<0.05) consumption, and higher lactate production (P<0.05) than did ICM. The consumption or production of amino acids by ICM and trophectoderm also differed, with the trophectoderm displaying a higher turnover (the sum of production and consumption). The ICM and trophectoderm both depleted arginine, aspartate and leucine, whereas the production of alanine was consistent. Isolated ICM depleted a further six amino acids, which appeared during trophectoderm culture; the reverse trend was observed for the remaining amino acids. The concentration of lactate in blastocoel fluid was significantly higher than in synthetic oviductal fluid supplemented with amino acids and BSA (SOFaaBSA; P<0.05). However, glucose (P<0.05) and pyruvate (P<0.001) concentrations were both lower. Aspartate, glutamate, glycine, alanine and tryptophan were present at significantly higher concentrations in blastocoel fluid than in SOFaaBSA, whereas threonine and asparagine concentrations were significantly lower. The metabolism of composite blastocysts, obtained by summing the consumption and production profiles of the ICM and trophectoderm, and taking into account their respective number of cells, was higher than that of intact blastocysts, indicating that upon isolation of the two cell populations there may be disruption to paracrine interactions or the onset of culture-induced cellular stress or both.

Energy metabolism in pig oocytes and early embryos.

Pig oocytes and embryos differ from those of other species in having a large quantity of endogenous lipid, a potential role for which has yet to be identified. In the present study, the hypothesis that endogenous triglyceride acts as a metabolic substrate during in vitro maturation and early embryo development was tested. Embryos were produced by in vitro fertilization (IVF) of in vitro-matured, abattoir-derived immature oocytes, cultured in medium NCSU23 up to the blastocyst stage. The triglyceride content of single oocytes and embryos was measured throughout development. Oxygen and glucose consumption and the formation of lactate were measured non-invasively over the same period, enabling total ATP production to be calculated. The triglyceride content of oocytes before maturation (135+/-4.9 ng) decreased by 13 ng (P<0.05) during in vitro maturation, but there was no apparent change in triglyceride content during embryo development (117.68 ng). Oxygen consumption was low throughout embryo cleavage before reaching a peak at the blastocyst stage (P<0.01), a pattern similar to that seen in other mammals studied. Glucose consumption and lactate production were also at a maximum at the blastocyst stage (P<0.05). These data indicate that pig oocytes may use endogenous triglyceride as an energy source during in vitro maturation and that most (91-97%) of the ATP produced during embryo development comes from oxidative phosphorylation. The high exogenous glucose concentration in NCSU23 (5.5 mmol l(-1)) may be needed to form pyruvate, which in turn, produces oxaloacetate, which is required to prime the tricarboxylic acid cycle. However, the reason for the high lipid content in early pig embryos remains to be elucidated.

Amino acid turnover by elongating cattle blastocysts recovered on days 14-16 after insemination.

Blastocyst elongation from day 14 to day 16 after insemination coincides with a major phase of embryo loss in cattle. Protein synthesis, reflected in protein content, increases markedly over this period but little is known about the amino acid requirement of elongating blastocysts at this time. Cattle blastocysts produced in vivo were recovered on days 14-16 after insemination and cultured individually for up to 8 h in synthetic oviduct fluid containing a physiological mixture of amino acids plus 1 mmol glutamine l(-1) and 0.1% (w/v) polyvinyl alcohol (SOFaaPVA). After 1, 4 and 8 h in culture, an aliquot of culture medium was removed and the rate of amino acid depletion or production was calculated per unit of protein and per hour of culture. Amino acids were depleted or produced at different rates. Arginine was depleted from the medium at a significant rate (P < 0.05) during all culture periods. Alanine and glutamate were produced at a significant rate (P < 0.05) during all culture periods. The rate of alanine production was significantly greater (P < 0.05) in blastocysts recovered on day 14 compared with days 15 or 16 after insemination. Alanine production and arginine depletion tended to be greater in smaller embryos recovered on day 14 compared with larger and later stage embryos, indicating that earlier stage embryos may have higher metabolic activity than later stage embryos. Qualitatively, the pattern of amino acid consumption and production during elongation was similar to that shown from the zygote to early blastocyst stage.

Effect of timing of urea feeding on the yield and quality of embryos in lactating dairy cows.

High protein diets, which lead to excess production of nonprotein nitrogen such as ammonia and urea, have been associated with reduced fertility in dairy cows. In this study we test the hypothesis that diets containing high levels of quickly degradable urea nitrogen (QDN) compromise embryo development. Lactating dairy cows were fed mixed silage and concentrates twice daily. At 60 days postpartum, a synchronized estrus was induced and the cows were subsequently superovulated and inseminated using a standard protocol. On Day 7 after insemination, the uteri were flushed and embryos retrieved. At the start of treatment, cows were randomly allocated into three nutritional groups: control (CONT, n = 8), long (L-) QDN (n = 8) and short (S-) QDN (n = 9). The L-QDN cows were fed a supplement of urea from 10 days before insemination, and the S-QDN cows were fed the supplement from insemination until embryo collection. Both L- and S-QDN diets produced significant increases in plasma ammonia and urea 3 h post-feeding. The S-QDN but not the L-QDN diet was associated with a significant reduction in embryo yield. Embryo quality was also significantly reduced in the S-QDN cows. This study indicates that there is no deleterious effect on the yield and quality of embryos recovered 7 days after breeding when QDN feeding is initiated during the previous midluteal phase. However, introduction of a similar diet 10 days later, at the time of insemination, was deleterious. We suggest that QDN is toxic to embryos but cows can adjust within 10 days.

Effect of platelet-activating factor on the electrophysiology of the human Fallopian tube: early mediation of embryo-maternal dialogue?

Platelet-activating factor (PAF) is produced by preimplantation embryos and may be involved in the earliest stages of embryo-maternal dialogue. This study explored the potential effects of PAF acting as a signalling agent on human Fallopian tubal epithelial cells grown as a polarized layer in primary culture. The response of the tubal epithelium was assessed in terms of the transepithelial potential difference and short-circuit current (I(scc)), which were recorded using a modified Ussing chamber. Resistance was calculated from the measurements of potential difference and I(scc). PAF (1.9 nmol to 1.9 micromol l(-1)) administered to the apical surface of the cells produced a marked, transient increase in both potential difference and I(scc) in a dose-dependent manner. The mode of action of PAF on the electrophysiological responses of human tubal epithelial cells was investigated. Blockers of Na(+), K(+) and voltage-operated Ca(2+) channels had little effect on PAF action. However, incubation of the epithelial cells in Cl(-)free medium or with a blocker of the Na(+)-K(+)-2Cl(-) cotransporter (Furosemide) reduced the effect of PAF. Blockade of chloride-bicarbonate channels with 4-acetamido-4'-iso-thiocyanostilbene-2.2'-disulphonic acid (SITS) reduced the effect of low doses of PAF only. These results indicate that PAF influences the movement of chloride ions across the tubal epithelial cell and is a candidate molecule for initial embryo-maternal dialogue.

Regulation of apoptosis in the bovine blastocyst by insulin and the insulin-like growth factor (IGF) superfamily.

Insulin and the insulin-like growth factors, IGF-I and IGF-II, have been reported to exert a mitogenic effect on the preimplantation mammalian embryo. Furthermore, it has been proposed that loss of imprinting of the insulin-like growth factor II receptor gene and the consequent over-production of IGF-II may be involved in the aetiology of the Enlarged Offspring Syndrome, which occurs as an artefact of in vitro embryo production. We have previously shown that apoptosis occurs in the preimplantation bovine embryo and is influenced by in vitro culture conditions. We have therefore sought to establish the effects of insulin, IGF-I and IGF-II on apoptosis and cell proliferation in bovine blastocysts in vitro. Zygotes, obtained by in vitro maturation and fertilization of follicular oocytes, were cultured to blastocysts, with or without exogenous growth factors. Embryos were stained with propidium iodide to label all nuclei and by TUNEL to label apoptotic nuclei and analyzed by epifluorescent and confocal microscopy. IGF-I and IGF-II, but not insulin, were found to increase the proportion of embryos which formed blastocysts. Insulin decreased the incidence of apoptosis without affecting blastocyst cell number. IGF-I acted to decrease apoptosis and increase total cell number and IGF-II increased cell number alone. These data suggest roles for insulin and the IGFs as mitogens and/or apoptotic survival factors during early bovine development. Perturbation of IGF-II regulated growth may be involved in fetal oversize.