[Molecular mechanisms selected by evolution m primates for self-protection against human chorionic gonadotropin]

The constitutive activation of the follitropin receptor (FSHR) could lead to promiscuous toxic activation by placental chorionic gonadotropin (CG) during human pregnancy. This study demonstrated that the evolution of the transmembrane region of the simian FSHR parallels the progressive accumulation of CG copies in the primate genomes. We assist to a purifying selection to keep the FSHR constitutively inactive and thus insensitive to CG.

The role of chorionic gonadotropin and Notch1 in implantation

PURPOSE

Failed implantation is a major limiting factor in infertility and early pregnancy loss. In primates, human chorionic gonadotropin mediated inhibition of stromal cell apoptosis and their subsequent differentiation into decidual cells is critical for successful embryo implantation. A major regulator of cell survival and differentiation is the Notch receptor, which transduces extracellular signals responsible for cell fate determination during development. Proteolytic cleavage of full-length Notch1 releases an active intracellular peptide, which later translocates to the nucleus and activates gene transcription. Induction of Notch1 during the window of uterine receptivity in stromal fibroblasts in response to chorionic gonadotropin upregulates anti- apoptotic genes and induces alpha-smooth muscle actin, enabling stromal cells to proliferate and differentiate into a decidualized phenotype. As such, prior to implantation the embryonic signal, chorionic gonadotropin, rescues stromal fibroblasts from normal regression at the end of each ovarian cycle.

CONCLUSION

We are suggesting that chorionic gonadotropin and Notch1 coordinately regulate decidualization by preventing apoptosis of endometrial stromal fibroblasts, averting uterine sloughing, and promoting cell survival and differentiation into the decidualized phenotype, which is critical for the maintenance of pregnancy.

[Oocytes in-vitro maturation--a new technique for reproductive endocrinologist practitioners]

In vitro maturation is a new and promising technique in the field of artificial reproductive technology. This method provides an alternative treatment to the known treatments and a solution for one of the most common and disturbing problems of infertility treatment, the hyperstimulation syndrome. The method is particularly useful in cases of patients with polycystic ovarian syndrome. The physiological process of oocyte maturation requires maturation of the nucleus and maturation of the oocyte cytoplasm. In the process of in vitro maturation of the oocyte, oocytes in their late stages of maturation are aspirated from the follicles and transferred to specific culture conditions to achieve complete maturation. The process of oocyte retrieval from small and undeveloped follicles needs proper equipment and experience. Therefore, this process requires deep understanding of the physiological process of oocyte and follicles growth and maturation, proper equipment and especially good experienced laboratory support. This review aims to describe the physiological basis for the process, the recommended protocols and to report the experience published so far on success rates and treatment safety, both maternal and fetal.

Human placental development is impaired by abnormal human chorionic gonadotropin signaling in trisomy 21 pregnancies

Placental development is markedly abnormal in women bearing a fetus with trisomy 21, with defective syncytiotrophoblast (ST) formation and function. The ST occurs from cytotrophoblast (CT) fusion and plays an essential role by secreting human chorionic gonadotropin (hCG), which is essential to placental development. In trisomy of chromosome 21 (T21) pregnancies, CTs do not fuse and differentiate properly into STs, leading to the secretion of an abnormal and weakly bioactive hCG. In this study we report for the first time, a marked decrease in the number of mature hCG receptor (LH/CG-R) molecules expressed at the surface of T21-affected CTs. The LH/CG-R seems to be functional based on sequencing that revealed no mutations or deletions and binding of recombinant hCG as well as endogenous hCG. We hypothesize that weakly bioactive hCG and lower LH/CG-R expression may be involved in the defect of ST formation. Interestingly, the defective ST formation is mimicked in normal CT cultures by using LH/CG-R small interfering RNA, which result in a lower hCG secretion. Furthermore, treatment of T21-affected CTs with recombinant hCG overcomes in vitro the T21 phenotype, allowing CTs to fuse and form a large ST. These results illustrate for the first time in trisomy 21 pathology, how abnormal endogenous hCG signaling impairs human placental development.

Human chorionic gonadotropin produced by the invasive trophoblast but not the villous trophoblast promotes cell invasion and is down-regulated by peroxisome proliferator-activated receptor-gamma

A critical step in the establishment of human pregnancy is the invasion of the uterus wall by extravillous cytotrophoblasts (EVCTs) during the first trimester. It is well established that human chorionic gonadotropin hormone (hCG) is secreted by the endocrine syncytiotrophoblast (ST) into the maternal compartment. We recently reported that invasive EVCTs also produce hCG, suggesting an autocrine role in the modulation of trophoblast invasion. Here we analyzed the role of hCG secreted in vitro by primary cultures of invasive EVCT and noninvasive ST. We first demonstrated that LH/CG receptor was present in EVCTs in situ and in vitro as well as in an EVCT cell line (HIPEC65). We next showed that hCG secreted by EVCTs stimulated progesterone secretion by MA10 cells in a concentration-dependent manner. Incubation of HIPEC65 with EVCT supernatants induced a 10-fold increase in cell invasion, whereas ST supernatants had no effect. This stimulating effect was strongly decreased when hCG was depleted from EVCT supernatants containing a large amount of the hyperglycosylated form of hCG, which is almost undetectable in ST supernatants. Finally, we investigated the regulation of hCG expression by peroxisome proliferator-activated receptor (PPAR)-gamma, a nuclear receptor shown to inhibit trophoblast invasion. Activation of PPARgamma decreased alpha- and beta-subunit transcript levels and total hCG secretion in primary EVCTs. Our results offer the first evidence that hCG secreted by the invasive trophoblast, likely the hyperglycosylated form of hCG, but not by the syncytiotrophoblast, promotes trophoblast invasion and may be a PPARgamma target gene in trophoblast invasion process.

Negative Effect of Estradiol on Luteinizing Hormone Throughout the Ovulatory Luteinizing Hormone Surge in Mares1

The negative effect of estradiol-17beta (E2) on LH, based on exogenous E2 treatments, and the reciprocal effect of LH on endogenous E2, based on hCG treatments, were studied throughout the ovulatory follicular wave during a total of 103 equine estrous cycles in seven experiments. An initial study developed E2 treatment protocols that approximated physiologic E2 concentrations during the estrous cycle. On Day 13 (ovulation = Day 0), when basal concentrations of E2 and LH precede the ovulatory surges, exogenous E2 significantly depressed LH concentrations to below basal levels. Ablation of all follicles > or = 10 mm when the largest was > or =20 mm resulted in an increase in percentage change in LH concentration within 8 h that was greater (P < 0.03) than for controls or E2-treated/follicle-ablated mares. Significant decreases in LH occurred when E2 was given when the largest follicle was either > or =25 mm, > or =28 mm, > or =35 mm, or near ovulation. Treatment with 200 or 2000 IU of hCG did not affect E2 concentrations during the initial portion of the LH surge (largest follicle, > or =25 mm), but 2000 IU significantly depressed E2 concentrations before ovulation (largest follicle, > or =35 mm). Results indicated a continuous negative effect of E2 on LH throughout the ovulatory follicular wave and may be related to the long LH surge and the long follicular phase in mares. Results also indicated that a reciprocal negative effect of LH on E2 does not develop until the E2 surge reaches a peak.

Comparison of human chorionic gonadotropin and gonadotropin-releasing hormone agonist for final oocyte maturation in oocyte donor cycles

In this retrospective study of 74 oocyte-donor IVF cycles, the rates of fertilization, implantation, clinical pregnancy, ongoing pregnancy, and early pregnancy loss were similar after an agonist or hCG trigger. These findings suggest that the agonist trigger is a viable alternative for oocyte donors with significant risk factors for ovarian hyperstimulation syndrome.

Ribonucleic acid binding protein-mediated regulation of luteinizing hormone receptor expression in granulosa cells: relationship to sterol metabolism

Posttranscriptional mechanism plays a crucial role in regulating LH receptor (LHR) expression in the ovary. We have identified a novel trans-factor, LHR mRNA binding protein (LRBP), which binds to a polypyrimidine-rich bipartite sequence of the coding region of LHR mRNA, and its identity was established as mevalonate kinase (Mvk). Although an inverse relation between LHR mRNA expression and RNA binding activity of LRBP has been established, its intermediary role in LHR mRNA expression has not been demonstrated. The present study examined the direct role of Mvk in regulating LHR expression by using primary cultures of human granulosa cells as a model system. A marked decrease in LHR mRNA stability and an increase in Mvk expression were seen when cultured granulosa cells were treated with human chorionic gonadotropin (hCG) in vitro. This treatment also resulted in an increase in LHR mRNA binding activity in the cytosolic fractions prepared from hCG-treated cells compared with the control. Because Mvk expression is regulated by sterol response element-binding protein-1, which is sensitive to the cellular concentration of 25-hydroxycholesterol (25-OHC), cultured granulosa cells were treated with this oxysterol, and the expression of Mvk gene was examined. As expected, treatment with 25-OHC inhibited the Mvk (LRBP) expression, as well as the LHR mRNA binding activity of LRBP. To determine the role of Mvk in ligand-mediated down-regulation of LHR mRNA, cells were additionally treated with 25-OHC when treated with hCG. The results showed that the decrease in Mvk expression by oxysterol treatment abrogated ligand-induced down-regulation of LHR mRNA. These results therefore establish a direct participation of Mvk in regulating LHR expression and suggest a novel relationship between cholesterol metabolism and LHR expression in the ovary.

Effects of gonadotropin-releasing hormone agonists and antagonists on luteal function

PURPOSE OF REVIEW

This review addresses the effects of gonadotropin-releasing hormone agonists and antagonists on various aspects of the luteal phase.

RECENT FINDINGS

Recent studies have shown that use of both gonadotropin-releasing hormone agonists and antagonists during in-vitro fertilization cycles leads to alterations in the hormonal profiles of the luteal phase as well as changes in endometrial histology. Gonadotropin-releasing hormone agonists are effective in triggering final oocyte maturation and reducing the incidence of ovarian hyperstimulation syndrome. Ongoing pregnancy rates are excellent after gonadotropin-releasing hormone agonist trigger when luteal phase and early pregnancy supplementation with estradiol and progesterone is provided. Gonadotropin-releasing hormone agonists have recently been used for luteal phase support in in-vitro fertilization cycles.

SUMMARY

Although gonadotropin-releasing hormone agonists and antagonists are clinically useful, they may have adverse effects on luteal function. Luteal phase supplementation significantly improves clinical outcomes in in-vitro fertilization cycles because it may correct some of these detrimental effects. Use of gonadotropin-releasing hormone agonist to induce oocyte maturation is beneficial to patients who are at increased risk for ovarian hyperstimulation syndrome. The key factor in achieving favorable ongoing pregnancy rates with use of gonadotropin-releasing hormone agonist to induce oocyte maturation appears to be adequate luteal phase support.

Ovarian morphometrics in TP53-deficient mice

The objective of these investigations was to characterize ovarian responses to hormonal stimulation in TP53-deficient mice. TP53-deficient (KO) and wild-type (WT) mice were induced to ovulate with pregnant mare serum gonadotropin followed by human chorionic gonadotropin. Effect of estradiol on ovarian morphology was determined in induced and control mice implanted with estradiol-containing or placebo pellets. Blood was collected and mice were killed 7 days following implantation. Preserved ovaries were serially sectioned and stained. Numbers of follicles (all classifications) decreased with ovulation induction, but did not differ between WT and KO mice. Numbers of corpora lutea (CL) were less in ovulation-induced KO mice treated with estradiol compared to WT mice. Area of individual CL and serum concentrations of progesterone were greater in ovulation-induced KO mice given estradiol compared to WT mice. Ovulation-induced KO mice had more, larger hemorrhagic follicles than similarly treated WT mice, but hemorrhagic follicles were not influenced by estradiol. Proliferation of ovarian surface epithelial cells did not differ between KO and WT mice induced to ovulate and given estradiol. Ovaries from TP53 gene knockout mice (n = 4) induced to ovulate and given a 21-day estradiol implant three times over 58 days were observed for precursor lesions. There was no indication of precursor lesions in any TP53 KO or WT mouse. TP53 status did not influence recruitment of follicles, but TP53 deficiency hindered the ability of human chorionic gonadotropin to cause ovulation.

LH/hCG action and development of ovarian cancer--a short review on biological and clinical/epidemiological aspects

A link between infertility therapy, especially ovulation induction therapy using gonadotropins, and the development of ovarian cancer has long been an issue of debate since an epidemiological report supporting the possibility appeared in 1992. A number of clinical/epidemiological and biological studies, including a few that we conducted, have revealed various facts regarding this issue. The aim of this short review was to summarize the last 10 years findings and to address the implications of the debates on this issue.

Human adrenal cortex hyperfunction due to LH/hCG

Adrenal cortex hyperfunction may occasionally be due to stimulation of steroid hormone production by LH/hCG. The recent demonstration of the LH/hCG receptor in a variety of normal and abnormal human adrenal tissues has provided a novel explanation for these clinical observations and offers the possibility of spontaneous remission (as in pregnancy-related hyperfunction) or effective treatment with GnRH-agonists (to down-regulate LH secretion in menopausal patients). Involvement of adrenal LH/hCG receptors should be considered in pregnant or post-menopausal patients with ACTH-independent Cushing's syndrome or androgen excess. Additional investigations are needed to better define the role of the LH/hCG receptor in the normal adult and fetal human adrenal and to understand how this system is excessively activated in rare cases of human disease.

Is human chorionic gonadotropin directly involved in the regulation of human implantation?

The regulation of human implantation is not fully understood. hCG as one of the earliest embryonal signals may be a major regulator in the parakrine embryo-endometrial communication. The expression of full-length hCG/LH-receptor mRNA could be demonstrated in human endometrium throughout the follicular and secretory phase of the menstrual cycle. In contrast, in early pregnancy decidua only truncated variants could be detected. To investigate direct effects of hCG on the human endometrium, an intrauterine microdialysis device was developed to measure parakrine mediators within the uterine cavity in vivo. Using this system, hCG was applied in the secretory phase and the endometrial response was evaluated. The administration of hCG (500 IU/ml) provoked a significant inhibition of intrauterine IGFBP-1 and M-CSF, while LIF, VEGF and MMP-9 were significantly stimulated. Taken together there appear to be multiple direct effects of hCG on the endometrium that precede the classical endocrine role of the hormone.

Luteinizing hormone in testicular descent

A proper hypothalamus-pituitary-testis axis with normal androgen synthesis and action is a prerequisite for normal testicular descent. Various defects in this axis may result in cryptorchidism but endocrine abnormalities are rarely detected. Androgens regulate testicular descent but androgen action alone is not sufficient for normal testicular descent. The regulation of androgen production is influenced both by placental human chorionic gonadotropin (hCG) and pituitary luteinizing hormone (LH). There is evidence that the longer pregnancy continues, the more important role pituitary LH may have. Insulin-like hormone-3 (INSL3) is suggested to be the main regulator of gubernacular development and therefore an apparent regulator of testicular descent. INSL3 production is also related to LH, and reduced INSL3 action is a possible cause for cryptorchidism. Cryptorchid boys have normal testosterone levels with slightly but significantly elevated LH levels as compared to healthy boys. This high gonadotropin drive may compensate for mild Leydig cell dysfunction in cryptorchidism.

hCG in the Regulation of Placental Angiogenesis. Results of an In Vitro Study

Placental vascular development is essential for fetal growth and development. Inadequate placental vascular development is associated with early pregnancy losses and other pregnancy related pathologies. In addition to the ubiquitous, well-characterized angiogenic factors like vascular endothelial growth factor (VEGF) or basic fibroblast growth factor (bFGF), some pregnancy-specific factors (e.g. human chorionic gonadotropin (hCG), insulin-like growth factor-II (IGF-II) or alpha fetoprotein (AFP) were recently described to play a possible regulatory role in this process. In the present study we described an improved separation method for human placental microvascular endothelial cells (HPMVEC) and their functional characterization. Using the combination of enzymatic digestion and multistep immunomagnetic sorting with CD31 antibodies a model for villous vascularization was established. Isolated cells took up ac-dil-LDL, spontaneously formed capillary-like structures, and expressed common endothelial markers such as vascular endothelial growth factor receptor-2 (VEGFR-2), angiopoetin-1 and -2, Tie-2, CD144, thrombomodulin, and von Willebrand factor (vWF) as shown by RT-PCR, flow cytometry and Western blot analysis. The expression of the hCG/LH receptor in the placental vascular tree was verified both in vitro and in vivo. hCG stimulated proliferation of HPMVEC in a dose specific manner. While hCG alone had no significant effect on endothelial cell apoptosis, the combination of VEGF-A and hCG protected HPMVEC from staurosporine-induced apoptosis. hCG significantly stimulated sprout formation when compared to controls in a spheroid angiogenesis assay. Our results demonstrate a modified and reproducible method allowing studies of placental vascular development and provide new insights into the possible role of trophoblastic factors in this process.

Hyperglycosylated hCG

Hyperglycosylated hCG (hCG-H) is a glycosylation variant of the hormone hCG. Here we review all that is known about this independently functioning molecule. As discussed, it is a very different molecule to the hormone hCG. First, hCG-H is produced by cytotrophoblast cells while regular hCG is made in syncytiotrophoblast cell. Second, it is an autocrine acting directly on the cells which produce it, while regular hCG is an endocrine acting on maternal corpus luteal cells. Third, hCG-H has minimal biological activity in promoting progesterone production compared to regular hCG. Fourth, hCG-H functions unlike regular hCG as an invasion promoter, whether invasion as in choriocarcinoma and testicular germ cell malignancies, or as in implantation of pregnancy. These functions seemingly occur through action on cytotrophoblast cell TGFbeta receptors. Fifth, hCG-H is an essential component for successful human implantation to prevent early pregnancy loss and spontaneous abortion. Sixth, hCG-H is critical for promoting the midtrimester hemochorial implantation, and for preventing preeclampsia. Seventh, measurements of hCG-H have advantages over measurements of regular hCG or total hCG, in detecting pregnancy, pregnancy outcome (failing or term pregnancy), predicting preeclampsia in pregnancy, or as a tumor marker for gestational trophoblastic diseases.

[Role of natural killer cells in normal pregnancy and recurrent pregnancy loss]

Pregnancy is an immunological mystery. The conceptus survives and develops despite being an allogenic transplant, in terms of classical immunology. Natural killer cells are the predominant immune-cell population in the early human placenta. The role of these cells in human pregnancy is not fully established, yet it presumed they are required for placental development and local immunomodulation at the maternal-fetal interface. The purpose of this review is to examine recent progress in characterizing natural killer cells, the quantitative and qualitative changes that occur in these cells through pregnancy. We will also point out the possible role of these cells in the maintenance of normal pregnancy and the pathogenesis of recurrent pregnancy loss.

Identification of novel genes regulated by chorionic gonadotropin in baboon endometrium during the window of implantation

Chorionic gonadotropin (CG) is an early embryo-derived signal that is known to support the corpus luteum. An in vivo baboon model was used to study the direct actions of human CG (hCG) on the endometrium, during the periimplantation period. Endometrial gene expression was analyzed using microarrays. The endometrial biopsies were taken from hCG-treated (n = 5) and control (n = 6) animals on d 10 after ovulation. Class comparison identified 61 genes whose transcript levels differed between control and hCG-treated samples (48 increased, 13 decreased in mean expression level more than 2.5-fold; P < 0.01). Real-time PCR of transcript abundance confirmed up-regulation of several of these, including SerpinA3, matrix metalloproteinase 7, leukemia inhibitory factor (LIF), IL-6, and Complement 3 (P </= 0.05). Analysis of protein abundance in endometrial flushings showed increased LIF and IL-6 protein in uterine flushings from hCG-treated animals compared with controls. Complement C3 and Superoxide dismutase 2 that were also up-regulated, were further evaluated by immunocytochemistry. Complement C3 showed a marked increase in stromal staining in response to hCG, whereas and superoxide dismutase 2 localization was most markedly increased in the glandular epithelial cells. Expression of Soluble Frizzled Related Protein 4, the most highly down-regulated gene, was also validated by PCR. Our experiments have shown that hCG induces alterations in the endometrial expression of genes that regulate embryo attachment, extracellular matrix remodeling and the modulation of the immune response around the implanting blastocyst. Several of these genes, including LIF and gp130, have been shown to be essential for implantation in other species. This study provides strong evidence that the preimplantation embryo itself influences the development of the receptive endometrium via secreted paracrine signals.

Mosaic tetrasomy 9p case with the phenotype mimicking Klinefelter syndrome and hyporesponse of gonadotropin-stimulated testosterone production

Tetrasomy 9p is a rare clinical syndrome and about 30% of known cases exhibit chromosome mosaicism. The cases with tetrasomy 9p mosaicism have been reported to show the various phenotypes. On the other hand, Klinefelter syndrome is well recognized chromosomal abnormality caused by an additional X chromosome in males (47,XXY), and the characteristic clinical findings include tall stature, immaturity of external genitalia, testicular dysfunction. Here, we report a 10-year-old male with tetrasomy of 9p mosaicism, whose phenotypic feature is mimicking Klinefelter syndrome. He was referred to our hospital for inconspicuous penis. He showed tall height (+2.5 SD). Endocrinological examination revealed the poor testosterone response to human chorionic gonadotropin administration, which indicated the testicular hypofunction, whereas MRI revealed concealed penis as a cause of inconspicuous penis. Because of the phenotype mimicking Klinefelter syndrome, karyotype of his blood lymphocytes was analyzed, and an additional marker chromosome was detected in 6% of the investigated metaphases. Fluorescence in situ hybridization analysis revealed that the marker chromosome was an isochromosome 9p, which resulted in tetrasomy 9p. Chromosome analysis of buccal smear also showed mosaicism for two karyotypes: 5% of cells had the isochromosome of 9p, and the other cells showed normal. This case is the second case with tetrasomy 9p mosaicism mimicking Klinefelter syndrome phenotype in the world. Our case, together with previously reported cases with the same association, indicates the possibility of testicular hypofunction and urogenital anomalies induced by overexpression of some genes on chromosome 9p.

Hyperglycosylated hCG in gestational implantation and in choriocarcinoma and testicular germ cell malignancy tumorigenesis

OBJECTIVE

Hyperglycosylated human chorionic gonadotropin (hCG-H) is a carbohydrate variant of hCG with double-sized oligosaccharide side chains. While hCG-H is produced exclusively by stem cytotrophoblast cells in gestational choriocarcinoma, by pregnancy cytotrophoblast at implantation and by the cytotrophoblast produced in testicular malignancies, regular hCG is produced only by differentiated syncytiotrophoblast cells.

STUDY DESIGN

hCG-H was measured using the Nichols Advantage hCG-H assay (Nichols Institute Diagnostics, San Clemente, California).

RESULTS

hCG-H has a function separate from regular hCG. hCG-H, but not regular hCG, acts in vivo and in vitro to promote invasion, whether invasion through membranes or tumor formation. Invasion or tumorigenesis is completely blocked by administration of specific antibody to hCG-H. The same hCG-H-modulated invasion mechanisms are observed in early pregnancy, gestational choriocarcinoma and testicular cancers.

CONCLUSION

hCG-H is a cytokinelike molecule, produced by cells different from those that make regular hCG and having a completely separate function. It appears to be the modulator of invasion as in implantation of pregnancy, gestational choriocarcinoma and testicular cancer malignancy.

The empty follicle syndrome

The empty follicle syndrome (EFS) is a rare complication of in vitro fertilization (IVF) treatment, leading to cycle cancellation. Low human chorionic gonadotropin (hCG) bioavailability and ovarian dysfunction have been implicated with this condition. This case report illustrates a typical case of EFS and several strategies suggested to overcome this problem.

[What's new at the maternal-foetal interface: role of the hCG/LH-hCG receptor couple during embryo implantation]

Implantation of the embryo into the maternal endometrium represents a unique biological process, combining an immunological (tolerance of an allograft) and biological (adhesion of two epitheliums) paradox. The success of implantation depends on a receptive endometrium, a functionally normal blastocyst and a synchronized cross-talk between embryonic and maternal tissues. Though sexual steroids control the process, a cascade of growth factors or cytokines are the prime paracrine mediators of the dialogue at the maternal-embryonic interface. HCG is one of the molecules most precociously produced by the embryo and is the most specific marker of its presence. HCG is a luteotropic factor which relays the inadequate support provided by the reduced rates of LH, but also influences the pregnancy on a paracrine mode by a local action on implantation process, probably by interacting with its receptor, the LH/hCG-R that we have evidenced on endometrial epithelium. We demonstrate that embryo actively participate into its implantation, tolerance and placentation.

The classification, functions and clinical use of different isoforms of HCG

HCG is composed of two subunits, HCGalpha and HCGbeta. During early pregnancy, HCG stimulates progesterone production in the corpus luteum, and injection of HCG is widely used to induce ovulation in assisted reproduction treatment (ART). Under experimental conditions, the free subunits have been shown to exert functions other than those of HCG, but the relevance of these remains to be determined. Intact HCG, free subunits and degraded forms of these occur in biological fluids, and determinations of these are important for diagnosis and monitoring of pregnancy, pregnancy-related disorders and several types of cancer. Development of optimal methods for the various forms has been hampered by lack of appropriate standards and expression of the concentrations of the various forms in units that are not comparable. Furthermore, the nomenclature for HCG assays is confusing and in some cases misleading. These problems can now be solved; a uniform nomenclature has been established, and new standards are available for HCG, its subunits HCGalpha and HCGbeta, the partially degraded or nicked forms of HCG and HCGbeta, and the beta-core fragment. This review describes the biochemical and biological background for the clinical use of determinations of various forms of HCG. The clinical use of HCG and studies on HCG vaccines are briefly reviewed.

Hormonal and cytokine regulation of early implantation

Implantation of the blastocyst into the endometrium is a delicately controlled process and a prerequisite for the furtherance of the mammalian species. A complex network of molecules is involved in preparing both the endometrium and blastocyst for a successful interaction. However, the exact molecular steps are poorly understood. Studies so far have shown that disruption of certain pathways results in fertility defects. Impaired implantation is currently considered to be the most important limiting factor for the establishment of viable pregnancies in assisted reproduction. It is expected that elucidating the molecular background of the process will enable accurate diagnosis and effective treatment of infertility.