Is there any physiological role for gonadotrophin oligosaccharide heterogeneity in humans? I. Gondatrophins are synthesized and released in multiple molecular forms. A matter of fact

Effectiveness of recombinant human FSH: recombinant human LH combination treatment versus recombinant human FSH alone for assisted reproductive technology in women aged 35-40 years

RESEARCH QUESTION

According to real-world data, is recombinant human FSH (r-hFSH) combined with recombinant human LH (r-hLH) or r-hFSH alone more effective for women of advanced maternal age (AMA) in terms of live birth?

DESIGN

Non-interventional study comparing the effectiveness of r-hFSH and recombinant r-hLH (2:1 ratio) versus r-hFSH alone for ovarian stimulation during ART treatment in women aged 35-40 years, using real-world data from the Deutsches IVF-Register.

RESULTS

Overall clinical pregnancy (29.8%, 95% CI 28.2 to 31.6 versus 27.8%, 95% CI 26.5 to 29.2) and live birth (20.3%, 95% CI 18.7 to 21.8 versus 18.0%, 95% CI 16.6 to 19.4) rates were not significantly different between the combined r-hFSH and r-hLH group and the r-hFSH alone group (P = 0.269 and P = 0.092, respectively). Treatment effect was significantly higher for combined r-hFSH and r-hLH compared with r-hFSH alone for clinical pregnancy (33.1%, 95% CI 31.0 to 35.0 versus 28.5%, 95% CI 26.6 to 30.4; P = 0.001, not adjusted for multiplicity) and live birth (22.5%, 95% CI 20.5 to 24.2 versus 19.4%, 95% CI 17.6 to 20.9; P = 0.014, not adjusted for multiplicity) in a post-hoc analysis of women with five to 14 oocytes retrieved (used as a surrogate for normal ovarian reserve), highlighting the potential benefits of combined r-hFSH and r-hLH for ovarian stimulation in women aged 35-40 years with normal ovarian reserve.

CONCLUSIONS

Women of AMA with normal ovarian response benefit from treatment with combined r-hFSH and r-hLH in a 2:1 ratio versus r-hFSH alone in terms of live birth rate. The effectiveness of treatments is best assessed by RCTs; however, real-world data are valuable for examining the effectiveness of fertility treatment, especially among patient groups that are not well represented in clinical trials.

New insights into the role of LH in early ovarian follicular growth: a possible tool to optimize follicular recruitment

Evidence shows that LH participates in enhancing transition from the early stage to the antral stage of folliculogenesis. It has been demonstrated that functional LH receptors are expressed, albeit at a very low level and even in smaller follicles, during the phase that was traditionally considered to be gonadotrophin independent, suggesting a role for LH in accelerating the rate of progression of non-growing and primary follicles to the preantral/antral stage. Hypogonadotropic hypogonadism, together with other clinical conditions of pituitary suppression, has been associated with reduced functional ovarian reserve. The reduction in LH serum concentration is associated with a low concentration of anti-Müllerian hormone. This is the case in hypothalamic amenorrhoea, pregnancy, long-term GnRH-analogue therapy and hormonal contraception. The effect seems to be reversible, such that after pregnancy and after discontinuation of drugs, the functional ovarian reserve returns to the baseline level. Evidence suggests that women with similar primordial follicle reserves could present with different numbers of antral follicles, and that gonadotrophins may play a fundamental role in permitting a normal rate of progression of follicles through non-cyclic folliculogenesis. The precise role of gonadotrophins in early folliculogenesis, as well as their use to modify the functional ovarian reserve, must be investigated.

Effectiveness of recombinant human follicle-stimulating hormone (r-hFSH): recombinant human luteinizing hormone versus r-hFSH alone in assisted reproductive technology treatment cycles among women aged 35-40 years: A German database study

This non-interventional study compared the effectiveness of recombinant human follicle-stimulating hormone (r-hFSH) and recombinant human luteinizing hormone (r-hLH) (2:1 ratio) versus r-hFSH alone for ovarian stimulation (OS) during assisted reproductive technology treatment in women aged 35-40 years, using real-world data from the Deutsches IVF-Register (D·I·R). Numerically higher clinical pregnancy (29.8% [95% CI 28.2, 31.6] vs. 27.8% [26.5, 29.2]) and live birth (20.3% [18.7, 21.8] vs. 18.0% [16.6, 19.4]) rates were observed with r-hFSH:r-hLH versus r-hFSH alone. The treatment effect was consistently higher for r-hFSH:r-hLH compared with r-hFSH alone in terms of clinical pregnancy (relative risk [RR] 1.16 [1.05, 1.26]) and live birth (RR 1.16 [1.02, 1.31]) in a post-hoc analysis of women with 5-14 oocytes retrieved (used as a surrogate for normal ovarian reserve), highlighting the potential benefits of r-hFSH:r-hLH for OS in women aged 35-40 years with normal ovarian reserve.

Comparative Assessment of the Structural Features of Originator Recombinant Human Follitropin Alfa Versus Recombinant Human Follitropin Alfa Biosimilar Preparations Approved in Non-European Regions

Although the full primary structures of the alfa and beta subunits of reference r-hFSH-alfa and its biosimilars are identical, cell context-dependent differences in the expressing cell lines and manufacturing process can lead to variations in glycosylation profiles. In the present study, we compared the structural features of reference r-hFSH-alfa with those of five biosimilar preparations approved in different global regions outside Europe (Primapur^®, Jin Sai Heng^®, Follitrope^®, Folisurge^®, and Corneumon^®) with respect to glycosylation, macro- and microheterogeneity, and other post-translational modifications and higher order structure. The mean proportion of N-glycosylation-site occupancy was highest in reference r-hFSH-alfa, decreasing sequentially in Primapur, Jin Sai Heng, Corneumon, Follisurge and Follitrope, respectively. The level of antennarity showed slightly higher complexity in Corneumon, Primapur and Follitrope versus reference r-hFSH-alfa, whereas Jin Sai Heng and Folisurge were aligned with reference r-hFSH-alfa across all N-glycosylation sites. Sialylation level was higher in Corneumon and Follitrope, but small differences were detected in other biosimilar preparations compared with reference r-hFSH-alfa. Jin Sai Heng showed higher levels of N-glyconeuramic acid than the other preparations. Minor differences in oxidation levels were seen among the different products. Therefore, in summary, we identified var ious differences in N-glycosylation occupancy, antennarity, sialylation and oxidation between reference r-hFSH-alfa and the biosimilar preparations analyzed.

Reduced FSH and LH action: implications for medically assisted reproduction

Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) play complementary roles in follicle development and ovulation via a complex interaction in the hypothalamus, anterior pituitary gland, reproductive organs, and oocytes. Impairment of the production or action of gonadotropins causes relative or absolute LH and FSH deficiency that compromises gametogenesis and gonadal steroid production, thereby reducing fertility. In women, LH and FSH deficiency is a spectrum of conditions with different functional or organic causes that are characterized by low or normal gonadotropin levels and low oestradiol levels. While the causes and effects of reduced LH and FSH production are very well known, the notion of reduced action has received less attention by researchers. Recent evidence shows that molecular characteristics, signalling as well as ageing, and some polymorphisms negatively affect gonadotropin action. These findings have important clinical implications, in particular for medically assisted reproduction in which diminished action determined by the afore-mentioned factors, combined with reduced endogenous gonadotropin production caused by GnRH analogue protocols, may lead to resistance to gonadotropins and, thus, to an unexpected hypo-response to ovarian stimulation. Indeed, the importance of LH and FSH action has been highlighted by the International Committee for Monitoring Assisted Reproduction Technologies (ICMART) in their definition of hypogonadotropic hypogonadism as gonadal failure associated with reduced gametogenesis and gonadal steroid production due to reduced gonadotropin production or action. The aim of this review is to provide an overview of determinants of reduced FSH and LH action that are associated with a reduced response to ovarian stimulation.

Hormonal Stimulation of Human Ovarian Xenografts in Mice: Studying Folliculogenesis, Activation, and Oocyte Maturation

Ovarian tissue cryopreservation and banking provides a fertility preservation option for patients who cannot undergo oocyte retrieval; it is quickly becoming a critical component of assisted reproductive technology programs across the world. While the transplantation of cryopreserved ovarian tissue has resulted in over 130 live births, the field has ample room for technological improvements. Specifically, the functional timeline of grafted tissue and each patient's probability of achieving pregnancy is largely unpredictable due to patient-to-patient variability in ovarian reserve, lack of a reliable method for quantifying follicle numbers within tissue fragments, potential risk of reintroduction of cancer cells harbored in ovarian tissues, and an inability to control follicle activation rates. This review focuses on one of the most common physiological techniques used to study human ovarian tissue transplantation, xenotransplantation of human ovarian tissue to mice and endeavors to inform future studies by discussing the elements of the xenotransplantation model, challenges unique to the use of human ovarian tissue, and novel tissue engineering techniques currently under investigation.

In-vivo biological activity and glycosylation analysis of a biosimilar recombinant human follicle-stimulating hormone product (Bemfola) compared with its reference medicinal product (GONAL-f)

Recombinant human follicle-stimulating hormone (r-hFSH) is widely used in fertility treatment. Although biosimilar versions of r-hFSH (follitropin alfa) are currently on the market, given their structural complexity and manufacturing process, it is important to thoroughly evaluate them in comparison with the reference product. This evaluation should focus on how they differ (e.g., active component molecular characteristics, impurities and potency), as this could be associated with clinical outcome. This study compared the site-specific glycosylation profile and batch-to-batch variability of the in-vivo bioactivity of Bemfola, a biosimilar follitropin alfa, with its reference medicinal product GONAL-f. The focus of this analysis was the site-specific glycosylation at asparagine (Asn) 52 of the α-subunit of FSH, owing to the pivotal role of Asn52 glycosylation in FSH receptor (FSHR) activation/signalling. Overall, Bemfola had bulkier glycan structures and greater sialylation than GONAL-f. The nominal specific activity for both Bemfola and GONAL-f is 13,636 IU/mg. Taking into account both the determined potency and the nominal amount the average specific activity of Bemfola was 14,522 IU/mg (105.6% of the nominal value), which was greater than the average specific activity observed for GONAL-f (13,159 IU/mg; 97.3% of the nominal value; p = 0.0048), although this was within the range stated in the product label. A higher batch-to-batch variability was also observed for Bemfola versus GONAL-f (coefficient of variation: 8.3% vs 5.8%). A different glycan profile was observed at Asn52 in Bemfola compared with GONAL-f (a lower proportion of bi-antennary structures [~53% vs ~77%], and a higher proportion of tri-antennary [~41% vs ~23%] and tetra-antennary structures [~5% vs <1%]). These differences in the Asn52 glycan profile might potentially lead to differences in FSHR activation. This, together with the greater bioactivity and higher batch-to-batch variability of Bemfola, could partly explain the reported differences in clinical outcomes. The clinical relevance of the differences observed between GONAL-f and Bemfola should be further investigated.

Novel pathways in gonadotropin receptor signaling and biased agonism

Gonadotropins play a central role in the control of male and female reproduction. Selective agonists and antagonists of gonadotropin receptors would be of great interest for the treatment of infertility or as non steroidal contraceptive. However, to date, only native hormones are being used in assisted reproduction technologies as there is no pharmacological agent available to manipulate gonadotropin receptors. Over the last decade, there has been a growing perception of the complexity associated with gonadotropin receptors' cellular signaling. It is now clear that the Gs/cAMP/PKA pathway is not the sole mechanism that must be taken into account in order to understand these hormones' biological actions. In parallel, consistent with the emerging paradigm of biased agonism, several examples of ligand-mediated selective signaling pathway activation by gonadotropin receptors have been reported. Small molecule ligands, modulating antibodies interacting with the hormones and glycosylation variants of the native glycoproteins have all demonstrated their potential to trigger such selective signaling. Altogether, the available data and emerging concepts give rise to intriguing opportunities towards a more efficient control of reproductive function and associated disorders.

Effects of 17beta-oestradiol and norethisterone acetate on sulfonation and sialylation of gonadotrophins in post-menopausal women

BACKGROUND

The number of terminal sialic acid and sulfonated N-acetylgalactosamine (SO(3)-GalNAc) on gonadotrophins in serum varies during the menstrual cycle and changes at menopause, suggesting that gonadal steroids modify their oligosaccharide synthesis. Our objective was to determine the effects of 17beta-oestradiol (E(2)) and a progestogen, norethisterone acetate (NETA), on the sulfonation and sialylation of gonadotrophins in post-menopausal women.

METHODS

Serum samples were obtained from eight post-menopausal women treated with 20 mg E(2) implants every 6 months, from four women who in addition were treated daily with 5 mg NETA orally for a 2-week period, and from four women who got this NETA treatment during a 4-week period. Sera from 11 non-treated post-menopausal women served as a reference group. The gonadotrophin serum concentrations, the number of SO(3)-GalNAc and sialic acid residues per serum luteinizing hormone (LH) and follicle-stimulating hormone (FSH) molecule, and the distributions of molecules with 0-1-2-3-4 sulfonated residues were measured.

RESULTS

The E(2)-treated post-menopausal women had considerably less (P < 0.001) sialic acid and slightly more (P < 0.01) SO(3)-GalNAc per serum LH and FSH molecule than the non-treated. Two weeks of NETA treatment increased the sulfonation of LH (P < 0.01) and FSH (P < 0.05) concomitantly with decreased (P < 0.05) sialylation of LH.

CONCLUSION

The primary effect of E(2) treatment was a decrease in sialylation and, due to competition for the same substrate, a secondary and consequentially minor increase in sulfonation of LH and FSH. The primary effect of the NETA therapy was an increase in the sulfonation of LH and FSH concomitantly with secondary and consequentially decreases in sialylation of LH.

Reproductive axis function and gonadotropin microheterogeneity in a male rat model of diet-induced obesity

Obesity causes complex metabolic and endocrine changes that may lead to adverse outcomes, including hypogonadism. We herein studied the reproductive axis function in male rats under a high-fat diet and analyzed the impact of changes in glycosylation of pituitary LH on the bioactivity of this gonadotropin. Rats were fed with a diet enriched in saturated fat (20% of total calories) and euthanized on days 90 or 180 of diet. Long-term (180 days), high-fat feeding rats exhibited a metabolic profile compatible with insulin resistance and metabolic syndrome; they concomitantly showed decreased intrapituitary and serum LH concentrations, low serum testosterone levels, and elevated serum 17beta-estradiol concentrations. A fall in biological to immunological ratio of intrapituitary LH was detected in 180 days control diet-treated rats but not in high-fat-fed animals, as assessed by a homologous in vitro bioassay. Chromatofocusing of pituitary extracts yielded multiple LH charge isoforms; a trend towards decreased abundance of more basic isoforms (pH 9.99-9.0) was apparent in rats fed with the control diet for 180 days but not in those that were fed the diet enriched in saturated fat. It is concluded that long-term high-fat feeding alters the function of the pituitary-testicular axis, resulting in hypogonadotropic hypogonadism. The alterations in LH function found in these animals might be subserved by changes in hypothalamic GnRH output and/or sustained gonadotrope exposure to an altered sex steroid hormone milieu, representing a distinctly different regulatory mechanism whereby the pituitary attempts to counterbalance the effects of long-term obesity on reproductive function.

Sulfation of LH does not affect intracellular trafficking

LH and FSH are produced by the same gonadotrope cells of the anterior pituitary but differ in their mode of secretion. LH secretion is primarily episodic, or regulated, while FSH secretion is primarily basal, or constitutive. The asparagine (N)-linked oligosaccharides of LH and FSH terminate with sulfate and sialic acid, respectively. TSH also contains sulfated N-linked oligosaccharides and is secreted through the regulated pathway. It has been hypothesized that sulfate plays a role in segregating LH to the regulated pathway. Using a mouse pituitary model, we tested this hypothesis by examining the secretory fate of LH from pituitaries treated with sodium chlorate, a known inhibitor of sulfation. Here we show that mouse LH is sulfated and secreted through the regulated pathway, while FSH is secreted constitutively. LH secretion from chlorate-treated pituitaries, which showed complete inhibition of sulfation, was similar to untreated pituitaries. These data suggest that the metabolic role for sulfated N-linked oligosaccharides is not for intracellular trafficking but for the extracellular bioactivity of LH.

In vitro biological-to-immunological ratio of serum gonadotropins throughout male puberty in children with insulin-dependent diabetes mellitus

Information on the impact of prolonged deficient glycemic control in the quality of the gonadotropin signal delivered by the pituitary gland during puberty in children with insulin-dependent diabetes mellitus (IDDM) is scarce. In the present study, we examined the impact of deficient glycemic control on bioactive LH and FSH concentrations and their corresponding biological-to-immunological (B:I) ratio in boys with poorly controlled, but systemically uncomplicated IDDM. Dual control groups comprising patients with well-controlled IDDM and healthy boys of comparable age and body mass index were included for appropriate comparisons within and between each pubertal stage. Patients with poorly controlled and well-controlled IDDM exhibited serum bioactive FSH levels and B:I FSH ratio similar to those showed by the healthy control group. In contrast, in early and mid-pubertal boys with poorly controlled IDDM bioactive LH levels were normal, but its B:I LH relationship was significantly (P < 0.05) decreased. This attenuation in the quality of the LH signal did not affect total serum T concentrations, and apparently, progression of puberty. Long-standing uncontrolled diabetes and the consequent metabolic disturbances and/or complications may aggravate the reproductive axis dysfunction and eventually provoke pubertal arrest.

Effects of human pituitary FSH isoforms on mouse follicles in vitro

The effects of human FSH glycoforms on mouse follicle development and function in vitro were analysed, and an attempt was made to relate markers of follicular maturation to the expression of immunolocalized connexin (Cx) 43 and Cx26-based gap junctions. Three FSH fractions comprising discrete pI ranges [7.10-5.99 (pool I), pI 5.62-4.95 (pool II) and <3.75 (pool III)] were studied. Pool I produced the strongest effect on preantral granulosa cell proliferation and oestradiol production, and was highly effective for stimulating antral formation; this isoform also evoked a peripheral distribution of Cx43-containing gap junctions. Pool II was effective in promoting preantral granulosa cell proliferation but required higher FSH doses. This particular isoform provoked a more central distribution of Cx43-containing gap junctions, which was associated with a lower oestradiol production and less effective antral formation. Pool III was the least active for all markers of follicle development, and this was associated with minimal induction of Cx43-based gap junctions. The effects of the three FSH isoform pools on Cx26 expression were similar. The pattern of differences strongly suggests that FSH isoforms have complementary and specific actions on developing follicles, and that a shifting stage specific balance of isoforms is required for optimal follicle development.

FSH and folliculogenesis: from physiology to ovarian stimulation

FSH is a glycoprotein hormone consisting of two peptide subunits. The role of FSH in folliculogenesis is well known: to stimulate the formation of a large pre-ovulatory follicle that, because of its FSH-dependent maturation, is capable of ovulation and forming a corpus luteum in response to the mid-cycle surge of LH. FSH is widely used in ovarian stimulation for assisted reproduction techniques. Ovarian stimulation protocols combine the use of human menopausal gonadotrophin, urinary FSH or recombinant FSH with gonadotrophin-releasing hormone (GnRH) agonists or antagonists in order to increase oocyte number and to avoid premature LH surge. Recently, the availability of recombinant LH has permitted new stimulation protocols, combining recombinant FSH, recombinant LH and GnRH antagonists. Due to the limitations of the new Italian law in terms of the number of oocytes that can be fertilized, protocols with a softer ovarian stimulation are now considered, reducing risk of ovarian hyperstimulation syndrome, multiple pregnancies and emotional and physical burdens on the patients. Long-acting FSH preparations are also under clinical study. Knowledge of the stereochemical three-dimensional structure of FSH and its receptor will allow the study of new non-peptide orally administered molecules that fit the FSH receptors.

Impact of carbohydrate heterogeneity in function of follicle-stimulating hormone: studies derived from in vitro and in vivo models

Carbohydrates attached to the protein core of glycoprotein hormones influence a number of intracellular and extracellular processes. As with other members of the glycoprotein hormone family, FSH is produced and released as an array of isoforms that differ from each other in the structure of their oligosaccharide attachments. In this review, we discuss how carbohydrate heterogeneity can impact on FSH action in different in vitro and in vivo systems. We present evidence for diverse effects of distinct charge isoforms at the target cell level, including differential and unique effects on various end responses, and discuss how the use of multiple cell-type assays has allowed identification of some specific effects of FSH isoforms on different cell populations and follicle compartments as well as oocyte maturation. Finally, we discuss recent information on the ability of naturally occurring and laboratory manufactured FSH isoforms to evoke particular effects on granulosa cell function and ovarian follicular maturation in vivo. Such studies have provided evidence that the type(s) of FSH signal delivered may in fact regulate distinct biological outcomes irrespective or in addition to outcomes dictated solely by clearance rate differences.

Effect of FSH and its different isoforms on maturation of oocytes from pre-ovulatory follicles

FSH exists as a family of isohormones exhibiting distinct oligosaccharide structures, and the released FSH isoform mixtures change during the follicular phase of the menstrual cycle. In addition, the pulsatile release of gonadotrophins seems to expose follicles to bursts of more less-acidic FSH isoforms and the follicle is likely to be exposed to an almost ever changing composition of FSH isoforms. The different isoforms causes a number of different and divergent biological effects. FSH promotes oocyte maturation, and 5-10 IU/l of less-acidic FSH isoforms are sufficient to induce oocyte maturation in vitro. Exposure of cumulus-oocyte complexes to less-acidic FSH isoforms in a pulse-like fashion results in a rapid pattern of cAMP accumulation exceeding that seen with acidic isoforms, which appear to sustain lower but more constant cAMP production. The presence of particularly less-acidic isoforms for a period exceeding 30 min causes an attenuated cAMP response. In conclusion, it appears that pulsatile and intermittent release of less-acidic/short-living FSH isoforms is sufficient to induce biological responses, while allowing the granulosa cells to regain responsiveness to further FSH stimulation. Together with the interpulse release of more acidic isoforms, overall FSH secretion seems to ensure proper follicular maturation resulting in the release of developmentally competent oocytes.

Distribution and function of FSH receptor genetic variants in normal men

Follicle stimulating hormone (FSH) plays a key role in the maintenance of qualitatively and quantitatively normal spermatogenesis. It controls gamete development through Sertoli cells, via binding to its receptor. The influence and importance of FSH receptor (FSHR) variants on Sertoli cell function is not completely understood and remains to be investigated. In this retrospective study, we explored the impact and action of two distinct FSHR isoforms, Thr307/Asn680 and Ala307/Ser680, in a large group of men. This investigation includes 288 normal healthy men, 86 of whom were proven fathers previously studied, and 202 were newly recruited subjects. The FSHR polymorphism at position 680 was analyzed in the whole group, while position 307 was investigated in 150 subjects, both of them by single-stranded conformation polymorphism (SSCP) gel electrophoresis. The distribution frequency for position 680 was 29% for the Asn/Asn, 52% for the Asn-Ser, 19% for the Ser-Ser variant, and for position 307, 27% for the Thr-Thr, 55% for the Ala-Thr, 18% for the Ala-Ala, respectively. Polymorphism combinations that were different from Thr307/Asn680 - Ala307/Ser680 were found in four subjects. When subjects were grouped according to genotype at position 680, no significant differences between basal FSH, testosterone, inhibin B levels and semen parameters were found. This clinical finding demonstrates that, differently from females, in whom a significant correlation between FSHR polymorphism and basal FSH levels was found, the FSHR genotype has no influence on clinical parameters in males.

Immunochemical measurement of early pregnancy isoforms of HCG: potential applications to fertility research, prenatal diagnosis, and cancer

Human chorionic gonadotropin, the glycoprotein hormone of pregnancy, is found naturally in blood and urine in a variety of isoforms. These variants are related to both peptide bond cleavages (such as the nicked forms of hCG) and the beta core fragment urinary metabolite, as well as the larger variety of species resulting from carbohydrate heterogeneity. We have recently developed immunoassay systems that can measure nicked forms of hCG (antibody B151) as well as particular high carbohydrate variants (hyperglycosylated forms) of hCG (B152), which are associated with cancers producing hCG. Using the assay system for nicked hCG, we found that nicked hCG does not appear to be present as a significant hCG isoform during normal pregnancies if the urine specimens are well preserved. Applying the assay for hyperglycosylated hCG isoforms, we discovered that these forms are prevalent during very early pregnancy and decline rapidly to low concentration after the first 6 weeks of pregnancy. Persistence of these early pregnancy forms does not bode well for the pregnancy. Other investigators report that measurement of such hCG isoforms may aid in diagnosis of Down syndrome pregnancies. In summary, measurement of the hyperglycosylated hCG isoforms are useful for evaluation of healthy progress of normal pregnancy, as an additional detection marker for Down syndrome pregnancies, and as a potential new marker of trophoblastic malignancy. New reference preparations will soon be available for the calibration of assay systems for measurement of many of these hCG variants and metabolites.

The role of chorionic gonadotropin (CG) in blastocyst implantation

Implantation is a complex spatio-temporal interaction between the genotypically different embryo and the mother. Success of this event requires the synchronization of development and effective biochemical communications from both sides. Chorionic gonadotropin (CG), which is a major embryonic signal in the primate, is a glycoprotein hormone synthesized and secreted by the trophoblast. Various isoforms exist in plasma, urine, and blastocyst culture medium, a result of posttranslational modifications. The exponential secretion of CG and its long circulatory half-life extends the life span of corpus luteum to maintain the supply of progesterone during the first 6-8 weeks of pregnancy. To study the direct effects of CG in the uterus, we used the baboon (Papio anubis) as a non-human primate model. In vivo stimulation with CG during the window of uterine receptivity results in further morphologic and biochemical modifications of the receptive endometrium. These are characterized by the plaque reaction in the luminal epithelium, an increase in glycodelin expression and secretion by the glandular epithelium, and the differentiation of subepithelial stromal fibroblasts characterized by expression of the alpha smooth muscle actin (alpha SMA). Pretreatment with progesterone receptor antagonist (PRa) completely or partially inhibits these effects. The signal transduction pathway activated by CG in primate endometrial epithelial cells involves the protein kinase A (PKA)-independent phosphorylation of extracellular signal regulated kinase (ERK 1/2). This alternate signal transduction pathway may prevent CG Receptor (R) downregulation at the implantation site and enhance epithelial cell proliferation and differentiation. Thus, our results suggest that CG plays an important role in implantation in addition to its luteotrophic role.