Embryo transfer and related techniques in domestic animals, and their implications for human medicine

The ‘Note added in proof’ to the above paper wasincorrect. It should read as follows: Note added in proof Early embryos are capable of producing, have receptors for,and can respond to, a number of growth factors, suggesting thatautocrine or paracrine mechanisms are involved in early development(see Schultz and Heyner, 1993). A notable example is the reportthat platelet-derived growth factor promotes development ofcattle embryos through the 8-cell block in culture, and transforminggrowth factor alpha, or fibroblast growth factor, promotes subsequentblastulation (Larson et al., 1992a). Larson et al. (1992b) havealso shown that fibronectin, a glycoprotein component of theextracellular matrix, can significantly improve the developmentof 2-cell cattle embryos through the 8-cell block. These reportshave significant implications for the understanding of controlof early embryonic development, and for the improvement of cultureof domestic animal, and perhaps human, embryos.     

A background to nuclear transfer and its applications in agriculture and human therapeutic medicine

The development of a single celled fertilized zygote to an animal capable of reproduction involves not only cell division but the differentiation or specialization to numerous cell types forming each tissue and organ of the adult animal. The technique of nuclear transfer allows the reconstruction of an embryo by the transfer of genetic material from a single donor cell, to an unfertilized egg from which the genetic material has been removed. Successful development of live offspring from such embryos demonstrates that the differentiated state of the donor nucleus is not fixed and can be reprogrammed by the egg cytoplasm to control embryo and fetal development. Nuclear transfer has many applications in agriculture and human medicine. This article will review some of the factors associated with the success of embryo development following nuclear transfer and outline the potential uses of the technology.     

Metabolism of human embryos following cryopreservation: implications for the safety and selection of embryos for transfer in clinical IVF

BACKGROUND: Cryopreservation of supernumerary embryos is routinely performed in human-assisted reproduction, providing a source of embryos which can be thawed for use in subsequent treatment cycles. However, the viability of cryopreserved embryos has traditionally relied on morphological assessment, which is a poor predictor of embryo health since freezing leads to a significant overall reduction in implantation potential, and its long-term efficacy is unknown. This study describes how the post-thaw metabolism of human embryos can be used to predict future development to the blastocyst stage. METHODS: HPLC was used to analyse the post-thaw amino acid metabolism of human embryos from day 2 to day 3 of development. RESULTS: It was possible to predict with 87% accuracy which frozen-thawed embryo would develop to the blastocyst stage. Developmentally competent embryos were more metabolically quiescent than their arresting counterparts. Amino acid turnover was also capable of distinguishing between the developmental potential of the best, Grade I embryos P < 0.05. CONCLUSIONS: The data suggests that cryopreservation in IVF is a safe procedure and that amino acid turnover can be used to select which cryopreserved embryo will develop to the blastocyst stage, irrespective of their post-thaw grade.     

Morphology and biochemistry of in-vitro produced bovine embryos: implications for their cryopreservation

Examination of some ultrastructural and physiological characteristicsof in-vitro produced bovine embryos may help to explain whysuch embryos are more sensitive to freezing than their in-vivoderived counterparts. Improvement of embryo survival after freezingcan be achieved by changing the conditions of their culture,selection of embryos based on the kinetics of their development,and changing ‘standard’ freezing procedures. Cryopreservationof embryos by vitrification, in particular, seems to yield highersurvival than conventional slow freezing. Further developmentof protocols requires additional embryo transfer studies toensure that the ability of thawed embryos to develop normallyin vivo correlates strongly with in-vitro survival assays.     

Relationship between human oocyte maturity, fertilization and follicular fluid growth factors

Follicular fluid concentrations of growth hormone (GH), insulin-likegrowth factor-I (IGF-I), epidermal growth factor (EGF) and oestradiolwere related to diversities in oocyte maturation and fertilizationamong oocytes obtained for invitro fertilization (IVF). Follicularfluid GH, IGF-I and oestradiol concentrations were significantlycorrelated with increasing follicular size. Follicles with immatureoocytes had concentrations of oestradiol that were significantlylower when compared to follicles with intermediate and matureoocytes. Follicular fluid EGF concentration was similar forall oocyte maturational stages. In follicular fluids with matureoocytes we found IGF-I and GH concentrations were significantlyhigher compared to those of follicular fluid with atretic oocytes.Follicular fluids with Immature and intermediate oocytes hadsimilar concentrations of GH and IGF-I to follicular fluid containingmature oocytes and higher concentrations than follicular fluidwith atretic oocytes. No statistically significant differencewas found between fertilized and unfertilized oocytes. We concludethat maturation of oocytes Is associated with higher concentrationsof GH, IGF-I and oestradiol, but follicular fluid IGF-I andGH concentrations cannot serve as a predictor for IVF.     

Fertilization and development of the human oocyte following exposure to cryoprotectants, low temperatures and cryopreservation: a comparison of two techniques.

Both glycerol and dimethyl sulphoxide (DMSO) equilibration prior to cryopreservation produced adequate rates of survival and development to the hatching blastocyst stage for mouse oocytes using the two chosen cooling and warming regimes. Successful fertilization of human oocytes and further development of the embryos produced, was achieved following equilibration with DMSO at 0 degrees C. Although fertilization of fresh human ova previously exposed to glycerol was recorded, all oocytes with two pronuclei failed to continue to undergo cell division by 48 h in culture. Following cryopreservation, human oocytes were successfully inseminated after equilibration with both glycerol and DMSO. However, cell division to the 2-cell stage was recorded in only one oocyte which had undergone exposure to DMSO, freezing and thawing. No cell divisions were recorded after glycerol cryopreservation, or even after simple exposure to glycerol. Therefore it appears that DMSO and slow cooling may be the best protocol, although further evaluation will be necessary.     

Developmental competence of human in vitro aged oocytes as host cells for nuclear transfer

BACKGROUND: Improving human nuclear transfer (NT) efficiencies is paramount for the development of patient-specific stem cell lines, although the opportunities remain limited owing to difficulties in obtaining fresh mature oocytes. METHODS: Therefore, the developmental competence of aged, failed-to-fertilize human oocytes as an alternate cytoplasmic source for NT was assessed and compared with use of fresh, ovulation-induced oocytes. To further characterize the developmental potential of aged oocytes, parthenogenetic activation, immunocytochemical analysis of essential microtubule proteins involved in meiotic and mitotic division, and RT-PCR in single oocytes (n = 6) was performed to determine expression of oocyte-specific genes [oocyte-specific histone 1 (H1FOO), growth differentiation factor 9 (GDF9), bone morphogenetic protein 15 (BMP15), zygote arrest 1 (ZAR1)] and microtubule markers [nuclear mitotic arrest (NuMA), minus-end directed motor protein HSET and the microtubule kinesin motor protein EG5]. RESULTS: For NT, enucleation and fusion rates of aged oocytes were significantly lower compared with fresh oocytes (P < 0.05). Cleavage rates and subsequent development were poor. In addition, parthenote cleavage was low. Immunocytochemical analysis revealed that many oocytes displayed aberrant expression of NuMA and EG5, had disrupted meiotic spindles and tetrapolar spindles. One of the six oocytes misexpressed GDF9, BMP15 and ZAR1. Two oocytes expressed EG5 messenger RNA (mRNA), and HSET and NuMA were not detectable. RT-PCR of mRNA for oocyte specific genes and microtubule markers in single aged oocytes. CONCLUSIONS: Thus, aneuploidy and spindle defects may contribute to poor parthenogenetic development and developmental outcomes following NT.     

Embryo development after successful somatic cell nuclear transfer to in vitro matured human germinal vesicle oocytes

BACKGROUND: Somatic cell nuclear transfer (SCNT) involves the transfer of somatic cell nuclei into enucleated oocytes. Because human in vivo matured oocytes are scarcely available, we investigated whether in vitro matured (IVM) germinal vesicle (GV) oocytes could also support preimplantation development of human cloned embryos. METHODS: Three groups were used for SCNT: in vitro matured GV oocytes (IVM oocytes), 'in vivo' matured oocytes (in vivo oocytes) and 'failed fertilized' oocytes after routine-ICSI (FF oocytes). After removal of the chromosome-spindle complex, cumulus cell nuclei were injected, and oocytes were artificially activated and cultured. RESULTS: In total 61, 54 and 45 metaphase II oocytes were used for SCNT in the three groups, respectively. Survival and pronuclear rates were 59, 78 and 58% and 61, 64 and 50%, respectively. Of the 22 activated IVM oocytes, 13 cleaved to the 2-cell stage, whereby 2 morulae were formed. For the in vivo oocytes, 17 of 27 activated oocytes cleaved to the 2-cell stage and 1 morula was observed. Cleavage to the 2-cell stage in the group of FF oocytes was compromised. CONCLUSIONS: To our knowledge, this is the first report describing development of cloned human embryos using IVM oocytes and non-autologous transfer using a conventional method of SCNT.     

Diagnosis and preventing inherited disease: Allelic drop-out and preferential amplification in single cells and human blastomeres: implications for preimplantation diagnosis of sex and cystic fibrosis

Previously the diagnosis of sex and cystic fibrosis status hasbeen studied on single cells using the polymerase chain reaction(PCR). It has been suggested that allelic drop-out (PCR failureof one allele) and/or preferential amplification (hypo-amplificationof one allele) may contribute to poor reliability and misdiagnosis,although this remains controversial as some reports suggestthat allelic drop-out does not occur. We investigated an improvedmethod of diagnosing sex and cystic fibrosis in single cellsusing a new technology (fluorescent PCR) to determine the baselevel of PCR artefacts (allelic drop-out and preferential amplification)which, in combination with improved sensitivity, should improvePCR reliability and accuracy. Fluorescent PCR gives high reliability(97%) and accuracy rates (97%) in somatic cells for both sexand cystic fibrosis diagnosis and its lower detection thresholdallows allelic drop-out and preferential amplification to beeasily distinguished. We also achieved high reliability andaccuracy in diagnosing cystic fibrosis in human blastomeres.This study confirms earlier reports of both allelic drop-outand preferential amplification in single cell analysis. We demonstratethat both allelic drop-out and preferential amplification occurin somatic cells and suggest these are separate phenomena. Preferentialamplification appeared common in single cell PCR while allelicdropout apparently occurred at random in each allele. Preferentialamplification was mainly amplification of the larger allele.We suggest that some inaccuracy/misdiagnosis may be due to bothpreferential amplification as well as allelic drop-out. Otherfindings were variability in drop-out between PCR and that amplificationof signals from human blastomeres may be linked to embryo quality.We suggest that allelic drop-out is dependent on the numberof cells within the sample.     

Zona pellucida damage to human embryos after cryopreservation and the consequences for their blastomere survival and in-vitro viability

The study objective was to quantify zona pellucida (ZP) damage in cryopreserved human embryos. The influence of two different freezing containers was investigated, and the influence of freezing damage on the survival and viability of the embryos evaluated. ZP damage did not differ according to whether embryos originated from in-vitro fertilization (IVF) cycles or from IVF cycles in association with intracytoplasmic sperm injection (ICSI). The freezing container, however, significantly influenced the occurrence of ZP damage after cryopreservation. More damage was observed when the embryos were frozen-thawed using plastic cryovials than using plastic mini-straws (16.6% versus 2.3%; P < 0.0001). A clear association was found between blastomere survival and ZP intactness. Consequently, the percentage of embryos with 100% blastomere survival was higher when embryos were frozen-thawed using plastic mini-straws. The further cleavage of frozen-thawed embryos suitable for transfer was not different whether there was ZP damage or not; however, it was higher when there was 100% blastomere survival as compared with when some blastomeres were damaged (79.0% versus 43.7%; P < 0.0001). Consequently, more embryos suitable for transfer cleaved further when they were frozen-thawed using plastic mini-straws. In conclusion, the aim of a cryopreservation programme should be to have as many fully intact embryos as possible after thawing. Increased ZP damage might indicate a suboptimal cryopreservation procedure.     

Transplantation in reproductive medicine: previous experience, present knowledge and future prospects

The use of transplantation in reproductive medicine has beenconsidered by physicians and scientists alike for many years.Despite being side-tracked into futile pursuits of rejuvenationin the early days, the possibility of usefulness remains, particularlyfor preserving fertility in patients undergoing ablative chemo-or radiotherapy. These aims have been enhanced by advances intissue cryopreservation. When isolated primordial folliclesare transferred in the mouse, or ovarian tissue slices are graftedinto sheep, it is possible to obtain follicular survival withsubsequent maturation and oestrogen secretion and even restorefertility to sterilized hosts. For preservation of fertility,autografts avoid both the immunological problems of allograftsand the ethical dilemmas when using donor tissue. In the male,the concept of spermatogonial cell transfer after isolationand frozen storage of cells recovered from a testicular biopsyis most attractive, since it may provide another option forrescuing fertility in cancer patients, and provide a much neededone in children. Recent results demonstrate that gonocytes fromimmature mice injected into the tubules of sterilized hostsrestore spermatogenesis and produce fertile spermatozoa. Furthermore,the gonocytes can be stored frozen prior to transfer and stillproduce fertile tubules. This review presents a broad historyof transplantation in the male and female genital tracts aswell as attempts to anticipate possible future developments.     

A prospective, randomized study comparing day 2 and day 3 embryo transfer in human IVF

It is believed that delayed transfer of embryos after IVF allows for a better selection of good quality embryos. Hence, the number of embryos and all other prognostic factors being equal, transfer of day 3 embryos should be associated with higher implantation and pregnancy rates than transfer of day 2 embryos. To investigate this hypothesis, a prospective randomized study was carried out to compare implantation and pregnancy rates between day 2 and day 3 transfers. The relationship between the embryo quality score of day 2 and day 3 embryos and their respective implantation rates was also analysed. In a 2 year period all patients undergoing infertility treatment and in whom at least seven normally fertilized oocytes were obtained were included in the study. A minimization procedure was performed taking into account the patient's age and the method of fertilization (IVF or intracytoplasmic sperm injection). By using a uniform policy of embryo transfer, the number of embryos transferred was similar in both groups. The outcome parameters were embryo quality, implantation and pregnancy rates. No difference was observed in implantation and pregnancy rates between transfers on day 2 versus day 3 (23.8 versus 23.8% and 47.9 versus 46.8% respectively). The incidence of embryos of moderate to poor quality was higher in embryos cultured for 3 days compared with those cultured for 2 days. It is concluded that the outcomes of embryo transfer in terms of implantation and pregnancy rates are comparable for day 2 and day 3 embryos, although the overall embryo quality score decreases when embryos are kept in culture till day 3.     

多药耐药相关基因 HV126的电子克隆及在化疗前后白血病细胞中的表达

目的探讨白血病细胞多药耐药发生的分子机理，寻找新的多药耐药相关基因。方法以HL-60细胞为“驱动方”，以多药耐药细胞系HL-60／VCR为“实验方”，建立人白血病多药耐药细胞系HL-60／VCR抑制消减杂交文库，利用基因芯片技术从中筛选出一条在野生型HL-60细胞中基本不表达，而在HL-60／VCR耐药细胞中呈低丰度差异表达的新表达序列标记序列。用表达序列标记拼接的同源基因克隆法得到人类新基因HV126序列，再利用生物信息学数据库和软件对其进行功能的预测和分析。最后针对推导序列开放阅读框设计引物，逆转录-聚合酶链反应检测推导HV126基因序列在临床白血病患者化疗前后白血病细胞中的表达。结果HV1126的cDNA序列长1991bp，编码365个氨基酸，其编码蛋白序列局部与新近发现的在细胞凋亡与炎症反应中起重要作用的蛋白基序“PYRIN”存在约43％的相似性。逆转录-聚合酶链反应结果提示该基因与白血病细胞受化疗药物的作用和耐药存在联系。结论HV126可能是与白血病细胞耐药相关的一条新基因，有必要对该基因进行进一步的实验室克隆与功能研究。     

Oocyte maturation,follicle rupture and luteinization in human cryopreserved ovarian tissue following xenografting

BACKGROUND: Previous studies have demonstrated development of antral follicles in cryopreserved human ovarian tissue after autografting and xenografting, thus indicating successful preservation of follicular function. The study aim was to assess whether these follicles could also undergo periovulatory changes in response to hCG. METHODS: Ovarian tissue from three patients were dehydrated in propanediol (PROH)/sucrose and cryopreserved using the slow cooling/rapid thaw procedure. Thawed tissue was placed under the kidney capsule in immunodeficient mice. Following growth (>20 weeks) in the presence of gonadotrophin, hCG was administered and ovarian tissue examined histologically. RESULTS: Thirty-two antral follicles (diameter range 0.6 to 5 mm) were examined. Histological evidence of a response to hCG was evident in all follicles. Disruption of the concentric layers of mural granulosa and theca cells was apparent in all antral cavities. In 17 (53%) follicles the exterior follicular wall had reduced to a few cells thick, and in eight (25%) the wall had ruptured. Mucified oocyte-cumulus cell complexes were present in 32 follicles, 17 of which had begun to detach from the pedicle. Resumption of meiosis had occurred in over half the oocytes (five metaphase II and seven metaphase I oocytes, eight germinal vesicle breakdown). Two corpora lutea were also detected. CONCLUSIONS: Follicles cryopreserved within human ovarian tissue using the PROH procedure, can develop to the antral stage and undergo periovulatory changes following xenografting and exposure to a luteinizing stimulus.     

Chemically and mechanically induced membrane fusion: non-activating methods for nuclear transfer in mature human oocytes

Most current studies of nuclear transfer in mammalian oocytes have used electrofusion to incorporate donor cell nuclei into enucleated oocyte cytoplasts. However, the application of electrofusion to human oocytes is hampered by the relative ease with which this procedure induces oocyte activation. Here we tested a previously described chemical fusion technique and an original mechanical fusion procedure in this application. Enucleated metaphase II oocytes were first agglutinated with karyoplasts originating from other metaphase II oocytes and then induced to fuse with the use of polyethylene glycol or by micromanipulation with an intracytoplasmic sperm injection (ICSI) micropipette. Both techniques yielded a high frequency of fusion and did not cause oocyte activation. Moreover, the reconstructed oocytes were easily activated by subsequent treatment with ionophore A23187 and 6-dimethylaminopurine. These techniques may be used in attempts to alleviate female infertility due to insufficiency of ooplasmic factors by nuclear transfer from patients' oocytes to enucleated donor oocyte cytoplasts. For eventual future use in human cloning, they would ensure prolonged exposure of transferred nuclei to metaphase promoting factor, which appears to be required for optimal nuclear reprogramming.     

Comparison of follicular fluid IGF-I, IGF-II, IGFBP-3, IGFBP-4 and PAPP-A concentrations and their ratios between GnRH agonist and GnRH antagonist protocols for controlled ovarian stimulation in IVF-embryo transfer patients

BACKGROUND: Insulin-like growth factors (IGF) and their binding proteins (IGFBP) play a major role in the autocrine and paracrine regulation of folliculogenesis. This is the first study that has compared follicular fluid (FF) IGF-I, IGF-II, IGFBP-3, IGFBP-4 and pregnancy-associated plasma protein (PAPP)-A concentrations, and their ratios, to investigate whether there was any difference in the intrafollicular microenvironment between the GnRH agonist (GnRHa) and antagonist (GnRHant) protocols for controlled ovarian stimulation (COS). METHODS: A total of 68 IVF cycles were included in this study; two groups were studied: GnRHa long protocol group (n = 36) and the flexible GnRHant multiple-dose protocol group (n = 32). FF was obtained from dominant follicles during oocyte retrieval and stored at -70 degrees C until assayed. IGF-I, IGF-II and IGFBP-3 concentrations were measured by radioimmunoassay and IGFBP-4 and PAPP-A by enzyme-linked immunosorbent assay. RESULTS: The duration of COS was significantly longer, and total dose of gonadotrophins used, serum estradiol (E(2)) levels on hCG day and the number of oocytes retrieved were significantly higher in the GnRHa long protocol group. The concentrations of FF IGF-II and IGFBP-4 were significantly higher, and the ratio of IGF-I/IGFBP-4 was significantly lower in the GnRHa long protocol group. Serum E(2) levels per mature follicle were not different between the two groups. CONCLUSIONS: Our data may indicate a difference of intrafollicular microenvironment between cycles using GnRHa long protocols and those using GnRHant protocols. However, the difference in microenvironment does not appear to result in a difference in clinical outcome.     

Trends in embryo transfer practices and multiple gestation for IVF procedures in the USA, 1996-2002

BACKGROUND: Increasing use of IVF in the USA has been a major contributor to the rising national multiple birth rate. Many have advocated that reducing the number of embryos transferred is essential for addressing the IVF-associated multiple birth problem. METHODS: A population-based sample of 506 072 IVF transfers performed in the USA in 1996-2002 was used to investigate trends in embryo transfer practices and to determine whether any changes in practice patterns have impacted the multiple gestation risk associated with IVF. RESULTS: The proportion of procedures in which >or=3 embryos were transferred declined significantly for most patient groups between 1996 and 2002. However, declines for some groups were not sizeable (from 79 to 73% and from 76 to 71% for fresh, non-donor procedures among women aged 38-40 and 41-42 years respectively) and transferring >or=3 embryos remained the norm for all groups. As of 2002, single embryo transfer had not increased for most groups and remained uncommon. Some declines in overall multiple gestation rates were observed, although multiple gestation risk associated with 2 embryos transferred increased significantly for all groups. CONCLUSIONS: Despite changes in embryo transfer practices, multiple gestation risk remains high, in part due to increased multiple gestation rates associated with the transfer of two embryos.     

The yield, motility and performance in the hamster egg test of human spermatozoa prepared from cryopreserved semen by four different methods.

Different procedures were investigated for the dilution of human cryopreserved semen and the preparation of an enriched population of motile spermatozoa for assisted reproduction. The dilution of a 0.25 ml straw of cryopreserved human semen by addition of 2.0 ml Ham's F-10 buffer in one step caused a large decrease in the proportion of motile spermatozoa. This was due to osmotic stress because many of the diluted spermatozoa exhibited swollen tails. To a large extent the damage could be avoided by adding the buffer in 0.10-ml aliquots at 30-s intervals. Spermatozoa obtained after such dilution of cryopreserved human semen were subjected to the swim-up procedure, to centrifugation on two-step gradients of Nycodenz or Percoll, or to filtration through glass fibre paper and compared with respect to yield, motility parameters and penetrating ability in the hamster egg test. The swim-up procedure yielded spermatozoa with excellent motility but only 12% of the available motile spermatozoa were recovered. On both Nycodenz and Percoll gradients, greater than 40% of the available motile spermatozoa were recovered and the average velocity of the spermatozoa was not significantly less than for the swim-up technique. When A23187 was used to promote acrosome reactions in the hamster egg test, Percoll-prepared spermatozoa achieved an average of 8.6 decondensed sperm heads/egg compared to 1.9 for Nycodenz and 1.3 for the swim-up procedure. The yield from glass fibre paper filtration was only 12% and the velocity of the spermatozoa and their performance in the hamster egg test was significantly poorer than in all the other methods.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of cooling rate and dehydration regimen on the histological appearance of human ovarian cortex following cryopreservation in 1, 2-propanediol.

Thin slices of human ovarian cortex were evaluated following cryopreservation in 1,2-propanediol (PROH)/sucrose under various conditions. Following rapid thawing, 1 microm sections were assessed by light microscopy and oocyte abnormalities were further examined by electron microscopy. Follicles (n = 503) were predominantly primordial (91%), with no follicles larger than the proliferating primary stage. Proportions of intact pre-granulosa cells and oocytes (expressed as percentages of the total numbers observed) were significantly reduced following cooling at three different rates with the highest levels of intactness (55 and 85% respectively) being achieved with slow cooling. The frequency of oocyte abnormalities [loss of organelles (mitochondria), organelle-free areas, and/or cytoplasmic vacuolation] was significantly increased at all cooling rates with slow cooling resulting in the highest proportion (56%) of normal oocytes. With slow cooling, increasing dehydration time increased the proportions of intact pre-granulosa cells and oocytes (maximum 74 and 91% respectively after 90 min dehydration). Under these conditions, the highest proportion of follicles with all pre-granulosa cells intact (44%) was observed, as was the highest proportion of 'normal' oocytes (85%). In this study, single step dehydration in PROH/sucrose for 90 min and slow cooling/rapid thawing results in the highest proportion of intact human primordial and primary follicles.     

Differential expression of angiopoietins 1 and 2 and their receptor Tie-2 in human endometrium

Angiogenesis, the growth of new capillaries from pre-existing blood vessels, is a physiological process involved in both normal menstrual cycling and implantation of the embryo. So far, very little is known about the expression of angiopoietins, growth factors involved in angiogenesis, in human endometrium. Both angiopoietin-1 (Ang-1) and angiopoietin-2 (Ang-2) are ligands for the endothelial cell-specific receptor tyrosine kinase Tie-2. In this study we determined the mRNA expression of Ang-1, Ang-2 and Tie-2 by quantitative competitive RT/(QC)-PCR (including specifically designed competitor cDNA) in biopsied human endometrium throughout the menstrual cycle. We detected the mRNA for the angiopoietins in 30 out of 32 endometrial biopsies (94%), covering early proliferative (n = 4), mid proliferative (n = 12), late proliferative (n = 3), early secretory (n = 3), mid secretory (n = 5) and late secretory (n = 3) phases. Analysis of the target/competitor ratios (QC-PCR) revealed that Ang-1 mRNA expression was significantly up-regulated (P = 0.027) during the secretory phase of the menstrual cycle. In contrast, the expression levels of both Ang-2 mRNA and Tie-2 mRNA showed only minor variations at different cycle stages. These findings were confirmed by the relative expression ratio of Ang-1 versus Ang-2 in a multiplex PCR. The expression of Ang-1, Ang-2 and Tie-2 mRNA was detected in both isolated endometrial epithelial and stromal cell fractions. Immunohistochemical localization of the proteins revealed qualitative differences in both cell type and cycle stage expression. In conclusion, the enhanced Ang-1 expression during the secretory phase might serve to stabilize the newly developed blood vessels.