Heightened response of eosinophilic asthmatic patients to the CRTH2 antagonist OC000459.

BACKGROUND: The CRTH2 antagonist OC000459 has previously been demonstrated to reduce airway inflammation and improve lung function in moderate persistent asthma. A study was conducted to determine the effect of lower once daily doses of OC000459 and to define the phenotype of subjects most responsive to treatment. METHODS: Adult subjects (percentage of predicted forced expiratory volume in 1 s (FEV1 ) 60-85%) were randomized to OC000459 at three dose levels (25 mg once daily, 200 mg once daily or 100 mg twice daily) or placebo for 12 weeks (n = 117-125 per group, full analysis set). The primary endpoint was the change from baseline in prebronchodilator FEV1 , and secondary endpoints included Asthma Control Questionnaire (ACQ) and Standardised Asthma Quality of Life Questionnaire [AQLQ(S)], and incidence of exacerbations and respiratory tract infections. RESULTS: OC459 caused a significant improvement in FEV1 compared with placebo at a dose of 25 mg once daily (P = 0.028). A similar increase was observed in the other dose groups, and the mean change in FEV1 in the pooled dose groups at endpoint was 95 ml greater than placebo (P = 0.024). In a post hoc analysis of atopic eosinophilic subjects with uncontrolled asthma, a mean increase in FEV1 of 220 ml was observed compared with placebo (P = 0.005). The mean increase in FEV1 was more marked in younger subjects in this group: for subjects aged ≤40 years, there was a mean increase of 355 ml compared with placebo (P = 0.007). Improvements in ACQ and AQLQ(S) were observed in both the full analysis set and the atopic eosinophilic subgroup. There was a lower incidence of exacerbations and respiratory infections in subjects treated with OC000459. There were no drug-related serious adverse events. CONCLUSIONS: OC000459 is a safe and effective oral anti-inflammatory agent, which achieved clinically meaningful improvements in lung function and asthma control in allergic asthmatics with an eosinophil-dominant form of the disease. A dose of 25 mg given once daily was as effective as the higher doses studied.

The CRTH2 antagonist OC000459 reduces nasal and ocular symptoms in allergic subjects exposed to grass pollen, a randomised, placebo-controlled, double-blind trial.

BACKGROUND: CRTH2 mediates activation of Th2 cells, eosinophils and basophils in response to prostaglandin D(2). The CRTH2 antagonist OC000459 has previously been demonstrated to reduce airway inflammation and improve lung function in moderate persistent asthma. The objective of the present study was to determine the involvement of CRTH2 in promoting nasal and ocular symptoms in allergic subjects exposed to grass pollen. METHODS: A single centre, randomised, double-blind, placebo-controlled, two-way crossover study was conducted in 35 male subjects allergic to grass pollen comparing OC000459 200 mg bid with placebo for 8 days. Subjects were exposed to grass pollen (≥ 1400 grains/m(3)) for 6 h on the 2nd and 8th days of treatment and assessed for nasal symptoms, ocular symptoms, other symptoms, nasal secretion weight and rhinomanometry over the 6-h period. After a washout period of 3 weeks, subjects were switched to the alternative treatment for a further 8 days. The trial was registered on the clinical trials.gov database (Identifier NCT01448902). RESULTS: During the first treatment period, treatment with OC000459 significantly reduced both nasal and ocular symptoms in allergic subjects compared with placebo after challenge with grass pollen. A significant effect was observed on the 2nd day of dosing which was increased on the 8th day of dosing. The therapeutic effects of OC000459 persisted into the second treatment period despite a 3-week washout phase. The safety profile of OC000459 was similar to that of placebo. CONCLUSION: Treatment with OC000459 was well tolerated and led to a significant and persistent reduction in the symptoms of rhinoconjunctivitis.

The ontogeny of components of the renin-angiotensin system in the porcine fetal ovary.

There is an autonomous renin-angiotensin system (RAS) in the adult ovary. Renin is present in the primitive kidney, and the fetal ovary develops from the nephrogenic ridge. We hypothesised that components of the ovarian RAS would be present from early gestation, with potential roles in ovarian development. We studied fetal pig ovaries from approximately day 45 (approximately 0.39 gestation) to term and measured mRNA (RT-PCR) for prorenin, angiotensinogen and the angiotensin II (AngII) Type 1 and 2 receptors (AT(1) and AT(2)), and protein expression (Western blot) and localization (immunohistochemistry) of the AT(1) and AT(2) receptors. mRNA for prorenin was present in relatively low abundance from at least day 45 and rose to approximately day 75 of gestation, whilst mRNA for angiotensinogen rose steadily. mRNA for the AT(1) receptor was present from approximately day 45 and did not alter significantly with increasing gestation but AT(2) receptor mRNA was initially high, falling sharply through pregnancy. The AT(1) receptor protein abundance fell steadily to term, whereas the AT(2) receptor protein did not change during gestation. Both receptors were localised in the surface epithelium and egg nests, the granulosa cells of primordial, primary and secondary follicles, and the oocytes of all except the secondary follicles. Collectively, our results support the hypothesis that there is a functional RAS in the fetal ovary from at least approximately day 45 of gestation until term and that it may have a paracrine role in ovarian growth and development.

Intra-follicular regulatory mechanisms in the porcine ovary.

The mechanisms controlling the follicular growth continuum in the pig involve the interaction between local growth factors which are expressed throughout development and extra-follicular factors such as gonadotrophins. A large number of follicular growth factors, many belonging to the transforming growth factor-beta (TGF-beta) superfamily, have been identified in the somatic cells and in the oocyte. The relative importance of these intra-follicular factors varies with stage of development. The initiation of follicular growth and early preantral development is controlled locally (by factors including c-kit-kit ligand, members of the bone morphogenetic family (e.g BMP-15) and growth differentiation factor-9 (GDF-9)) and gonadotrophins are not thought to be involved until later. During antral follicle development, the oocyte secretes factors that stimulate porcine granulosa cell proliferation and differentiation, modulate apoptosis and suppress progesterone production, thereby preventing premature luteinisation. Likely candidates for mediating these effects include BMP-6, -15 and GDF-9 that are critical for fertility and ovulation rate in several mammals. There are also paracrine interactions between the somatic cells, with theca derived transforming growth factor beta (TGF-beta) playing a key role in regulating antral follicle maturation. Finally, during the periovulatory period, members of the EGF family from the granulosa cells stimulate cumulus expansion and oocyte maturation. Evidence indicates that some of these local factors may also influence oocyte developmental potential, emphasizing further the complexity, and importance, of these intra-follicular interactions.

Angiogenesis and vascular function in the ovary.

Ovarian function is dependent on the establishment and continual remodelling of a complex vascular system. This enables the follicle and/or corpus luteum (CL) to receive the required supply of nutrients, oxygen and hormonal support as well as facilitating the release of steroids. Moreover, the inhibition of angiogenesis results in the attenuation of follicular growth, disruption of ovulation and drastic effects on the development and function of the CL. It appears that the production and action of vascular endothelial growth factor A (VEGFA) is necessary at all these stages of development. However, the expression of fibroblast growth factor 2 (FGF2) in the cow is more dynamic than that of VEGFA with a dramatic upregulation during the follicular-luteal transition. This upregulation is then likely to initiate intense angiogenesis in the presence of high VEGFA levels. Recently, we have developed a novel ovarian physiological angiogenesis culture system in which highly organised and intricate endothelial cell networks are formed. This system will enable us to elucidate the complex inter-play between FGF2 and VEGFA as well as other angiogenic factors in the regulation of luteal angiogenesis. Furthermore, recent evidence indicates that pericytes might play an active role in driving angiogenesis and highlights the importance of pericyte-endothelial interactions in this process. Finally, the targeted promotion of angiogenesis may lead to the development of novel strategies to alleviate luteal inadequacy and infertility.

Intermittent hypoxia suppresses adiponectin secretion by adipocytes.

Obstructive sleep apnea (OSA), characterized by cyclic intermittent hypoxia (IH) during sleep, is an independent risk factor for cardiovascular disease. Adiponectin (APN), an adipocytokine secreted exclusively by adipocytes, possesses antiatherogenic properties. Low levels of APN, particularly the high-molecular-weight (HMW) form, are associated with an increased risk of cardiovascular disease. Here, we hypothesized that IH would result in the dysregulation of APN expression and secretion. 3T3-L1 adipocytes were exposed to IH at 12 cycles/h for 6 h/d to simulate the IH condition similar to that encountered in OSA. Control adipocytes were exposed to 21% O(2) under identical conditions. After 48 h of incubation, IH caused a decrease in the secretion of total and HMW APN in spite of a significant upregulation of APN mRNA expression by adipocytes. This study suggested a novel mechanism of how the cyclic hypoxemia in OSA predisposes OSA patients to cardiovascular disease through the dysregulation of secretion of APN by adipocytes. Further studies are needed to determine the exact molecular mechanism how IH reduces the release of APN by adipocytes.

MicroRNA-126 inhibits invasion in non-small cell lung carcinoma cell lines.

Crk is a member of a family of adaptor proteins that are involved in intracellular signal pathways altering cell adhesion, proliferation, and migration. Increased expression of Crk has been described in lung cancer and associated with increased tumor invasiveness. MicroRNAs (miRNAs) are a family of small non-coding RNAs (approximately 21-25 nt long) that are capable of targeting genes for either degradation of mRNA or inhibition of translation. Crk is a predicted putative target gene for miR-126. Over-expression of miR126 in a lung cancer cell line resulted in a decrease in Crk protein without any alteration in the associated mRNA. These lung cancer cells exhibit a decrease in adhesion, migration, and invasion. Decreased cancer cell invasion was also evident following targeted knockdown of Crk. MiR-126 alters lung cancer cell phenotype by inhibiting adhesion, migration, and invasion and the effects on invasion may be partially mediated through Crk regulation.

Corpus luteum-endometrium-embryo interactions in the dairy cow: underlying mechanisms and clinical relevance.

Conception rates of dairy cows are currently declining at an estimated 1% every year. Approximately, 35% of embryos fail to prevent luteolysis during the first three weeks of gestation. Interactions between the corpus luteum, endometrium and embryo are critical to the successful establishment of pregnancy and inadequacies will result in the mortality of the embryo. For example, as little as a one day delay in the post-ovulatory rise of progesterone has serious consequences for embryo development and survival. Recently, we found that LH support, degree of vascularization and luteal cell steroidogenic capacity were not the major factors responsible for this luteal inadequacy, but are nevertheless essential for luteal development and function. Progesterone acting on its receptor in the endometrium stimulates the production of endometrial secretions on which the free-living embryo is dependent. However, their exact composition and effects of inadequate progesterone remains to be determined. The embryo is recognized through its secretion of interferon tau (IFNT), which suppresses luteolytic pulses of prostaglandin F(2 alpha). In the cow, it is most likely that IFNT inhibits oxytocin receptor up-regulation directly and does not require the prior inhibition of oestrogen receptor alpha (ESR1). Unravelling the precise luteal-endometrium and embryo interactions is essential for us to understand pregnancy establishment and development of strategies to reverse the declining fertility of dairy cows.

A novel physiological culture system that mimics luteal angiogenesis.

Luteal inadequacy is a major cause of poor embryo development and infertility. Angiogenesis, the formation of new blood vessels, is an essential process underpinning corpus luteum (CL) development and progesterone production. Thus, understanding the factors that regulate angiogenesis during this critical time is essential for the development of novel strategies to alleviate luteal inadequacy and infertility. This study demonstrates the development of a physiologically relevant primary culture system that mimics luteal angiogenesis. This system incorporates all luteal cell types (e.g. endothelial, steroidogenic cells, fibroblasts and pericytes). Using this approach, endothelial cells, identified by the specific marker von Willebrand factor (VWF), start to form clusters on day 2, which then proliferate and develop thread-like structures. After 9 days in culture, these tubule-like structures lengthen, thicken and form highly organized intricate networks resembling a capillary bed. Development of the vasculature was promoted by coating wells with fibronectin, as determined by image analysis (P<0.001). Progesterone production increased with time and was stimulated by LH re-enforcing the physiological relevance of the model in mimicking in vivo luteal function. LH also increased the area stained positively for VWF by twofold (P<0.05). Development of this endothelial cell network was stimulated by fibroblast growth factor 2 and vascular endothelial growth factor A, which increased total area of VWF positive staining on day 9, both independently (three- to fourfold; P<0.01) and in combination (tenfold; P<0.001). In conclusion, the successful development of endothelial cell networks in vitro provides a new opportunity to elucidate the physiological control of the angiogenic process in the developing CL.

Luteal characteristics and progesterone production on day 5 of the bovine oestrous cycle.

In this study we have examined luteal function in non-lactating and late lactation dairy cows on day 5 of the cycle, during the period of the post-ovulatory progesterone rise. Comparison of luteal progesterone content and in vitro synthetic capacity with circulating plasma progesterone demonstrated that circulating progesterone concentration is a function of total luteal activity rather than the activity of individual units of tissue. Incubation of luteal tissue in vitro demonstrated stimulatory activity of LH and IGF-I, and to a greater degree IGF-II, on luteal progesterone synthesis. Finally the study showed no effect of double ovulation on luteal function. Occurrence of double ovulation in 35% of animals was not associated with any difference in luteal function or plasma progesterone concentrations.

Physiological temperature variants and culture media modify meiotic progression and developmental potential of pig oocytes in vitro.

Ovarian follicles in vivo are cooler than surrounding abdominal and ovarian tissues. This study investigated whether typical follicular temperatures influence the maturation and developmental potential of pig oocytes in vitro. Oocytes were synchronised at the germinal vesicle (GV) stage and incubated at 39, 37 or 35.5 degrees C. When compared with 39 degrees C, which is often used for in vitro studies, lower temperatures delayed spontaneous progression to the metaphase I and II (MI and MII) stages of meiosis. The MII was delayed by about 12 h per degrees C. All oocytes had normal morphology. Oocytes reaching GV breakdown (GVBD) at 39 degrees C were subsequently unaffected by cooling, demonstrating thermal sensitivity during the pre-GVBD stage only. Simultaneous assay of maturation-controlling kinases (maturation promoting factor (MPF) and MAPK) showed that cooling delayed kinase activation, provided it was applied prior to GVBD. Activity profiles remained coupled to the stage of meiosis. Neither enzyme was directly thermally sensitive over this temperature range. Following in vitro fertilisation, fewer blastocysts developed from embryos derived from 35.5 or 37 degrees C oocytes as compared with those from 39 degrees C oocytes. Manipulation of fertilisation timings to allow for delayed maturation showed that over-maturing or aging at lower temperatures compromises subsequent embryo development, despite normal nuclear maturation; the GV stage was again the thermally sensitive period. Cleavage rates were improved by the culture of oocytes with follicle-stimulating hormone (FSH) at 37 but not at 35.5 degrees C. Inclusion of 20% follicular fluid in the oocyte medium restored the blastocyst rate to that seen at higher temperatures. Thus, FSH and follicular fluid may allow oocytes to achieve normal developmental potential at in vivo temperatures.

Intra-ovarian regulation of follicular development and oocyte competence in farm animals.

In both mono-ovulatory species, such as cattle, and poly-ovulatory species, such as pigs, the interactions among extra-ovarian gonadotropins, metabolic hormones and intra-ovarian growth factors determine the continued development of follicles, the number of follicles that ovulate and the developmental competence of the ovulated oocyte. FSH and then subsequently LH are the main hormones regulating antral follicle growth in both mono- and poly-ovular species. However, a range of intra-ovarian growth factors, such as insulin-like growth factors (IGFs) and bone morphogenetic proteins (BMPs), are expressed throughout follicle and oocyte development and interact with gonadotropins to control follicle maturation. In addition, environmental factors such as nutrition, including both the amount and composition of the diet consumed prior to ovulation, can influence follicle development and the quality of the oocyte. Recent progress in our understanding has resulted in the development of diets that enhance oocyte quality and improve pregnancy rate in both pigs and cattle. In conclusion, despite some species-specific differences, similar interacting mechanisms control follicular development and influence oocyte quality.

Corpus luteum size and function following single and double ovulations in non-lactating dairy cows.

Data was collated from a number of studies on various aspects of luteal function in non-lactating dairy cows to allow comparisons to be made between single and double ovulating animals. In these studies, estrous cycles had been synchronized and animals slaughtered on day 5 or 8. The overall incidence of double ovulations was 28.3%. Double ovulation was associated with smaller individual corpora lutea but no difference in total weight of luteal tissue or any aspect of luteal tissue function or plasma concentrations of progesterone. Furthermore, in a sub set of animals, there was no difference in preovulatory follicle characteristics or plasma concentrations of estradiol around ovulation. These results demonstrated a high incidence of double ovulation in non-lactating cows that had no influence on circulating progesterone concentrations.

Fibroblast growth factor 2 is more dynamic than vascular endothelial growth factor A during the follicle-luteal transition in the cow.

Luteal inadequacy is a major cause of infertility in a number of species. During the early luteal phase, progesterone production requires the rapid growth of the corpus luteum (CL), which is in turn dependent on angiogenesis. In the present study, we examined the temporal changes in vascular endothelial growth factor A (VEGFA), fibroblast growth factor 2 (FGF2) and secreted protein, acidic, cysteine-rich (osteonectin) (SPARC) during the follicular-luteal transition and CL development in the cow. Luteal VEGFA concentrations increased as the CL developed but were lower in the regressing CL. Conversely, luteal FGF2 concentrations were highest immediately postovulation in the collapsed follicle and declined as the CL developed. Furthermore, three FGF2 isoforms were present in the collapsed follicle, but only one isoform was detected in older CL. Interestingly, FGF2 concentrations increased in the regressing CL. Western blot analysis for SPARC showed the presence of two isoforms, which were constitutively expressed throughout CL development. Further studies investigated the regulation of FGF2 by LH, which showed that FGF2 concentrations in preovulatory follicular fluid were higher in those animals that had experienced an LH surge. Moreover, LH stimulated FGF2 production in dispersed luteal cells. Conversely, the LH surge had no effect on follicular fluid VEGFA concentrations. In conclusion, FGF2 was more dynamic than VEGFA and SPARC during the follicular-luteal transition, which suggests that FGF2 plays a key role in the initiation of angiogenesis at this time. Furthermore, it is likely that this is stimulated by the LH surge. The results also suggest that VEGFA and SPARC have a more constitutive, but essential, role in the development of the CL vasculature.

Beneficial effects of a high fibre diet on oocyte maturity and embryo survival in gilts.

The present study examined the effects of feeding gilts a high fibre diet from the third post-pubertal oestrus until either day 19 of the same cycle or insemination at the following oestrus on oocyte maturity, embryo survival and associated changes in reproductive hormone concentrations. Gilts fed with the high fibre diet had lower circulating oestradiol concentrations on days 17, 18 and 19 of the cycle and increased LH pulse frequency on day 18. More oocytes recovered on day 19 from gilts receiving the high fibre diet were at metaphase II after 46-h culture in medium containing 10% of their own follicular fluid, despite fewer large (>7 mm) follicles in these gilts when compared with control animals. There was no effect of diet on ovulation rate, corpora lutea size or progesterone concentrations on days 10-12 after insemination, but embryo survival on days 27-29 after insemination was higher in gilts that received the high fibre diet. This study demonstrates that a high fibre diet that increases embryo survival also improves oocyte maturity and provides information on endocrine correlates that may shed light on underlying mechanisms.

Leptin infusion during the early luteal phase in ewes does not affect progesterone production.

Infusion of leptin during the ovine follicular phase has been shown to increase progesterone secretion during the subsequent luteal phase. In this study, we have assessed the effects of infusing leptin during the early luteal phase. Infusion of leptin (2.5 microg/h) into the ovarian artery of ewes with ovarian autotransplants (n=5) on day 3 of the luteal phase for 12h did not affect progesterone estradiol or LH concentrations compared to control ewes (n=5). These results suggest no direct effect of leptin on ovarian function at this stage of the estrous cycle.

Leptin in the bovine corpus luteum: receptor expression and effects on progesterone production.

In cattle, leptin has been implicated in the control of ovarian function and has been shown to modulate steroid production by theca and granulosa cells in a number of species. However, a direct effect of leptin on bovine luteal function has not been demonstrated. This study was conducted to determine if the leptin receptor (OB-R) is expressed in the bovine corpus luteum (CL), and to examine the effects of leptin on progesterone production by dispersed luteal cells in vitro. RT-PCR was used to detect the presence of OB-R and, more specifically, the long, biologically active isoform (OB-Rb), in CL, collected on days 2-18 of the oestrous cycle (n=18). The effects of leptin on progesterone production were investigated in dispersed luteal cells prepared from CL collected on days 5 and 8 (n=14) of the cycle. The dispersed luteal cells were cultured for 24 hr with recombinant human leptin and/or LR3-IGF-1 and/or LH. OB-Rs, in particular, OB-Rb, were expressed in the CL at all stages of development. Progesterone production by luteal cells was increased (P<0.001) by treatment with LH (10 ng/ml) but treatment with leptin alone had no effect. However, in the presence of IGF-1 (100 ng/ml), leptin (10 ng/ml) caused a significant (P<0.005) increase in progesterone production. In conclusion, we have shown that the leptin receptor is expressed in the bovine CL and have demonstrated a modulatory effect of leptin on luteal progesterone production in vitro.

Effect of alterations in the quantity and composition of the pre-mating diet on embryo survival and foetal growth in the pig.

This trial examined the effects of feeding six diets, which varied in either amount or composition, during the oestrous cycle prior to insemination on embryo survival and foetal development on day 27+/-2 of pregnancy in gilts. Ten or 11 gilts per group received either a maintenance (M) diet, 1.8 x M, 2.6 x M or nutritionally balanced diets in which the content of fibre, protein or starch was increased. Of the six diets tested, only the high fibre diet significantly increased embryo survival when compared to its 1.8 x M isoenergetic control (88.20+/-1.96% versus 81.25+/-2.67%; P<0.05). More litters from gilts fed the 1.8 x M and the starch diets had foetuses defined as intra-uterine growth retarded (IUGR; 50% and 62.5 of litters, respectively), compared to the other four groups in which 0-12.5% of litters contained IUGR foetuses (P<0.05). There was no effect of dietary treatment on foetal or placental size or on the within-litter variability in foetal and placental size. Plasma concentrations of oestradiol and progesterone on days 4-8 of the oestrous cycle and on day 27+/-2 of pregnancy were unaffected by treatment. Feed intake was positively related to mean plasma IGF-1 concentrations on days 4-8 of the cycle (P<0.01) and to mean leptin concentrations on days 4 and 5 (P<0.001). Leptin concentrations were unaffected by alterations in the composition of the diet, whereas IGF-1 concentrations were higher in gilts fed the starch diet compared to the M control (159+/-9.52 versus 127+/-7.65 ng/ml; P<0.05). These data demonstrate that alteration to the composition of the feed consumed during the cycle before insemination can affect both embryo survival and the distribution of foetal size within the litter. The underlying mechanism(s) remain to be determined, but probably involve dietary-induced changes in concentrations of reproductive hormones and/or intermediary metabolites that in turn affect ovarian follicular and oocyte development.

Endocrine and cellular characteristics of corpora lutea from cows with a delayed post-ovulatory progesterone rise.

The timing of the post-ovulatory progesterone rise is critical to the embryonic development and survival. The aim of this study was to determine the underlying causes of delayed post-ovulatory progesterone rises. Two groups of non-lactating dairy cows with early (n = 11) or late (n = 9) post-ovulatory progesterone rises were created by inducing luteolysis in the presence of either a large (> 10 mm) or small (< 10 mm) follicle, respectively. LH pulses were measured on days 4 (all cows) and 7 (n = 7, early; n = 5, late) (day 1= ovulation). The cows were slaughtered on day 5 (n = 4 each group) or 8 (n = 7, early; n = 5, late). Immunohistochemical analysis for endothelial cells (von Willebrand Factor, VWF), steroidogenic cells (3beta-HSD) and proliferation marker (Ki67) were performed. The basal progesterone production and LH responsiveness (0.001-100 ng/ml) of dispersed luteal cells was investigated. The luteal concentrations of FGF-2 and VEGF were measured by ELISA and RIA, respectively. There were no differences in LH pulse characteristics, area of VWF staining, proliferation index, steroidogenic cell characteristics, basal or LH-stimulated progesterone production by luteal cells between cows with an early or late progesterone rise (P > 0.10). However, the area of VWF staining increased from days 5 to 8, while the proliferation index decreased (P < 0.05). Furthermore, the luteal cells were more responsive to LH on day 8 (P < 0.01). Luteal concentrations of FGF-2 were higher on day 5 (P = 0.05), while VEGF was greater on day 8 (P < 0.01). In conclusion, we have clearly shown that LH support, degree of vascularization or luteal cell steroidogenic capacity were not the major factors responsible for inadequate secretion of progesterone by the developing bovine CL.

Relationships between maternal hormone secretion and embryo development on day 5 of pregnancy in dairy cows.

In cattle, increasing early embryonic losses are associated with inadequate progesterone concentrations within the first three weeks of pregnancy. The aim of this study was to investigate the complex relationship between early maternal progesterone concentration and embryo development early within the first week of pregnancy, specifically, on day 5 post-oestrus in dairy cows. Twenty Holstein-Friesian cows at the end of lactation were inseminated at oestrus (day 0) and on day 5 post-oestrus cows were slaughtered and the reproductive tract flushed to determine the presence and stage of embryo development. Three cows that had failed to synchronise correctly were excluded from analysis while in the remaining 17 cows 11 (65%) were pregnant with embryos at the morula (n = 3), 9-16 (n = 3) and 8-cell (n = 5) stages of development. No differences in day 5 plasma progesterone concentrations or corpus luteum (CL) size or progesterone content were observed between pregnant (n = 11) and non-pregnant (n = 6) cows. In cows with embryos beyond the 8-cell stage of development (n = 6) plasma progesterone concentration (P < 0.001) and CL weight (P < 0.01) were higher and plasma insulin concentrations lower (P < 0.001) than in cows with 8-cell embryos (n = 5). In addition there was a negative relationship between plasma progesterone and plasma insulin in pregnant cows (R(2) = 0.65; P < 0.005). In cows with an embryo present in the oviduct, oviductal glucose concentrations were lower (P < 0.05) than in cows with no embryo present. These results confirm progesterone is not only directly associated with embryo development, but that it may indirectly modulate embryo development via changes in the oviductal environment. In summary, the association between maternal progesterone concentration and embryo development exists as early as day 5 of pregnancy in dairy cows.