Gonadotropin Surge-Attenuating Factor: A Nonsteroidal Ovarian Hormone Controlling GnRH-Induced LH Secretion in the Normal Menstrual Cycle.

Gonadotropin surge-attenuating factor (GnSAF) is a nonsteroidal ovarian substance, which attenuates the endogenous LH surge in superovulated women. Different molecular sequences have been found, but only one of them has shown substantial homology to a known substance of the human genome. A molecular mass of 12.5kDa showing identity to the carboxyl-terminal fragment of human serum albumin and expressing GnSAF bioactivity in vitro has been identified. It has been suggested that in the normal menstrual cycle the in vivo bioactivity of GnSAF increases under the influence of the intercycle rise of FSH. GnSAF is considered the "missing link" between the ovaries and the hypothalamo-pituitary system, maintaining the pituitary in a state of low responsiveness to GnRH in the early- to midfollicular phase of the cycle. A marked decline in GnSAF bioactivity in the late follicular phase facilitates the onset and the full expression of the midcycle LH surge.

Submaximal doses of ghrelin do not inhibit gonadotrophin levels but stimulate prolactin secretion in postmenopausal women.

OBJECTIVE: An inhibitory effect of ghrelin on gonadotrophin secretion has been reported in normally menstruating women possibly modulated by endogenous oestrogen. The aim of this study was to examine the effect of ghrelin on gonadotrophin and prolactin (PRL) secretion in oestrogen-deprived postmenopausal women. DESIGN: Prospective intervention study. PATIENTS AND MEASUREMENTS: Ten healthy postmenopausal volunteer women were studied during two 15-days periods of oestrogen treatment (A and B) a month apart. Four experiments (Exp) were performed in total, two on day 1 (Exp 1A and Exp 1B) and two on day 15 (Exp 15A and Exp 15B) of the two periods. The women received in Exp 1A and in Exp 15A two iv injections of ghrelin (0.15 µg/kg at time 0 minute and 0.30 µg/kg at time 90 minutes) and in Exp1B and in Exp 15B normal saline (2 mL), respectively. Blood samples were taken at -15, 0, 30, 60, 90, 120, 150 and 180 minutes. RESULTS: After oestrogen treatment, late follicular phase serum oestradiol levels were attained on day 15 of periods A and B. Ghrelin administration did not affect serum levels of follicle-stimulating hormone (FSH) and luteinizing hormone (LH), whereas it increased significantly those of growth hormone (GH) and PRL. In Exp 15A, serum PRL increment in response to ghrelin (area under the curve, net increment) was significantly greater than in Exp 1A (P<.05). CONCLUSIONS: This study demonstrates for the first time that in oestrogen-deprived postmenopausal women, ghrelin administration affects neither FSH nor LH levels but stimulates PRL secretion, that is amplified by exogenous oestrogen administration.

Gonadotropin-inhibitory hormone (GnIH) in the amphibian brain and its relationship with the gonadotropin releasing hormone (GnRH) system: An overview.

It is well known that the hypothalamic neuropeptide gonadotropin-releasing hormone (GnRH) plays an important role as a primary factor regulating gonadotropin secretion in reproductive processes in vertebrates. The discovery of the presence of a gonadotropin-inhibitory hormone (GnIH) in the brains of birds has further contributed to our understanding of the reproduction control by the brain. GnIH plays a key role in inhibition of reproduction and acts on the pituitary gland and GnRH neurons via a novel G protein-coupled receptor (GPR147). GnIH decreases gonadotropin synthesis and release, thus inhibiting gonadal development and maintenance. The GnRH and GnIH neuronal peptidergic systems are well reported in mammals and birds, but limited information is available regarding their presence and localization in the brains of other vertebrate species, such as reptiles, amphibians and fishes. The aim of this review is to compile and update information on the localization of GnRH and GnIH neuronal systems, with a particular focus on amphibians, summarizing the neuroanatomical distribution of GnIH and GnRH and emphasizing the discovery of GnIH based on RFamide peptides and GnIH orthologous peptides found in other vertebrates and their functional significance.

[Spontaneous ovulation in in vitro fertilization-embryo transfer cycles using gonadotropin-releasing hormone antagonist: a large-sample retrospective study].

OBJECTIVE: To investigate the premature spontaneous ovulation rates in in vitro fertilization-embryo transfer (IVF-ET) cycles using gonadotropin-releasing hormone antagonist (GnRH-ant) and gonadotropin-releasing hormone agonist (GnRH-a), as well as the risk factors for premature spontaneous ovulation. METHODS: The rates of premature spontaneous ovulation in a total of 10 612 cycles using GnRH-ant or GnRH-a were compared. Matched case-controlled study and binary logistic regression model were conducted to analyze the risk factors for premature spontaneous ovulation. RESULTS: The spontaneous ovulation rate in the whole for GnRH-a cycles was 0.15% (13/8 514), compared with a 1.62% (34/2 098) in GnRH-ant cycles (P<0.01). Further matched controlled study and regression analyze found out that higher basal FSH level was a predominant risk and prediction factor for spontaneous ovulation (OR=1.20, P=0.009). CONCLUSIONS: In GnRH-ant cycles, spontaneous ovulation rate is about 10 times than which in GnRH-a cycles. Diminished ovarian function is a predominate risk factor for premature spontaneous ovulation.

Differential expression of RFamide-related peptide, a mammalian gonadotrophin-inhibitory hormone orthologue, and kisspeptin in the hypothalamus of Abadeh ecotype does during breeding and anoestrous seasons.

Gonadotrophin-inhibitory hormone (GnIH) is a novel hypothalamic neuropeptide that was discovered in birds as an inhibitory factor for gonadotrophin release. RFamide-related peptide (RFRP) is a mammalian GnIH orthologue that inhibits gonadotrophin synthesis and release in mammals through actions on gonadotrophin-releasing hormone (GnRH) neurones and gonadotrophs, mediated via the GnIH receptor (GnIH-R), GPR147. On the other hand, hypothalamic kisspeptin provokes the release of GnRH from the hypothalamus. The present study aimed to compare the expression of RFRP in the dorsomedial hypothalamus and paraventricular nucleus (DMH/PVN) and that of kisspeptin in the arcuate nucleus (ARC) of the female goat hypothalamus during anoestrous and breeding seasons. Mature female Abadeh does were used during anoestrus, as well as the follicular and luteal phases of the cycle. The number of RFRP-immunoreactive (-IR) neurones in the follicular phase was lower than in the luteal and anoestrous stages. Irrespective of the ovarian stage, the number of RFRP-IR neurones in the rostral and middle regions of the DMH/PVN was higher than in the caudal region. By contrast, the number of kisspeptin-IR neurones in the follicular stage was greater than in the luteal stage and during the anoestrous stage. Irrespective of the stage of the ovarian cycle, the number of kisspeptin-IR neurones in the caudal region of the ARC was greater than in the middle and rostral regions. In conclusion, RFRP-IR cells were more abundant in the rostral region of the DMH/PVN nuclei of the hypothalamus, with a greater number being found during the luteal and anoestrous stages compared to the follicular stage. On the other hand, kisspeptin-IR neurones were more abundant in the caudal part of the ARC, with a greater number recorded in the follicular stage compared to the luteal and anoestrous stages.

Cholesterol homeostasis in the ovaries of neonatally diethylstilbestrol-treated mice.

In the ovary of neonatally DES-treated mice, lipid droplets accumulation was observed in the hypertrophied interstitial tissues. Our previous results demonstrated that the impaired steroidogenesis in the ovary of neonatally DES-treated mice was caused by altered gonadotropins levels, and resulted in the hypertrophy of ovarian interstitial cells. We speculated that lipid droplets in the ovary mainly consisted of cholesterol. This study was aimed to examine the effects of neonatal DES on cholesterol homeostasis in the ovary. The serum and ovarian total cholesterol concentrations in 3-month-old neonatally DES-treated mice were significantly higher than those in the neonatally oil-treated mice, but triglyceride concentrations were not altered. In the ovary of neonatally DES-treated mice, expression of Hmgcr, a rate-limiting enzyme in de novo cholesterol biosynthesis, was reduced but expression of Ldlr and Scarb1, involved in cholesterol uptake, was not changed. These results suggest that cholesterol uptake is not altered in the ovary of 3-month-old neonatally DES-treated mice. However, the expression of Acat1, the microsomal acyl coenzyme A cholesterol acyltransferase which is involved in cholesterol esterification and storing was increased compared with that in the ovary of neonatally oil-treated mice. Since ovarian steroidogenesis in neonatally DES-treated mice was impaired, synthesized and/or obtained cholesterol from the blood may not be used sufficiently. Thus, in the ovary of neonatally DES-treated mice, cholesterol is esterified by ACAT1 and stored in the interstitial cells.

Seasonal effect of gonadotrophin inhibitory hormone on gonadotrophin-releasing hormone-induced gonadotroph functions in the goldfish pituitary.

We have shown that native goldfish gonadotrophin inhibitory hormone (gGnIH) differentially regulates luteinsing hormone (LH)-ß and follicle-stimulating hormone (FSH)-ß expression. To further understand the functions of gGnIH, we examined its interactions with two native goldfish gonadotrophin-releasing hormones, salmon gonadotrophin-releasing hormone (sGnRH) and chicken (c)GnRH-II in vivo and in vitro. Intraperitoneal injections of gGnIH alone reduced serum LH levels in fish in early and mid gonadal recrudescence; this inhibition was also seen in fish co-injected with either sGnRH or cGnRH-II during early recrudescence. Injection of gGnIH alone elevated pituitary LH-ß and FSH-ß mRNA levels at early and mid recrudescence, and FSH-ß mRNA at late recrudescence. Co-injection of gGnIH attenuated the stimulatory influences of sGnRH on LH-ß in early recrudescence, and LH-ß and FSH-ß mRNA levels in mid and late recrudescence, as well as the cGnRH-II-elicited increase in LH-ß, but not FSH-ß, mRNA expression at mid and late recrudescence. sGnRH and cGnRH-II injection increased pituitary gGnIH-R mRNA expression in mid and late recrudescence but gGnIH reduced gGnIH-R mRNA levels in late recrudescence. gGnIH did not affect basal LH release from perifused pituitary cells and continual exposure to gGnIH did not alter the LH responses to acute applications of GnRH. However, a short 5-min GnIH treatment in the middle of a 60-min GnRH perifusion selectively reduced the cGnRH-II-induced release of LH. These novel results indicate that, in goldfish, gGnIH and GnRH modulate pituitary GnIH-R expression and gGnIH differentially affects sGnRH and cGnRH-II regulation of LH secretion and gonadotrophin subunit mRNA levels. Furthermore, these actions are manifested in a reproductive stage-dependent manner.

The clinical ramifications of polycystic ovarian morphology in oocyte donors.

OBJECTIVE: To determine the relationship between Polycystic Ovary (PCO) morphology and In Vitro Fertilization (IVF) outcome in oocyte donation cycles. DESIGN: Cross sectional study SETTING: Private IVF clinic PATIENTS: 164 consecutive ovum donors and their recipients were reviewed, 149 were included in the study where 113 patients had normal ovarian morphology and 36 patients had PCO morphology. INTERVENTIONS: All donors underwent ovarian stimulation in conjunction with GnRH agonist or antagonist in standard fashion. MAIN OUTCOME MEASURES: Baseline donor characteristics were recorded, as well as details of IVF stimulation and embryo data. Recipient data on pregnancy and miscarriage were also collected. RESULTS: Patients with PCO ovaries had significantly higher peak estradiol levels and required less gonadotropins during IVF stimulation. In addition, the baseline characteristics between donor groups did not differ except for ovarian morphology. The number of oocytes retrieved and indicators of embryo quality did not differ between the two groups, and there was no significant difference between pregnancy and miscarriage rates in the recipients. CONCLUSIONS: Oocyte donors with PCO morphology have equivalent pregnancy rates and do not need to be excluded as potential donors.

Gonadatrophin suppression to prevent chemotherapy-induced ovarian damage: a randomized controlled trial.

OBJECTIVE: To estimate the effectiveness of gonadotropin-releasing hormone (GnRH) analogues cotreatment in preventing chemotherapy-induced amenorrhea in young breast cancer patients undergoing cyclophosphamide-based chemotherapy. METHODS: One hundred hormone-insensitive breast cancer participants (aged 18-40 years) were recruited from two university-affiliated oncology centers in Egypt. Opting for type of cotreatment was based on available timeframe until start of chemotherapy. Fifty women ready for early chemotherapy were randomized to receive either chemotherapy alone (arm I) or chemotherapy after downregulation (estradiol less than 50 pg/mL) by GnRH antagonist and agonist (arm II). Then, GnRH antagonist was discontinued and agonist was continued until the end of chemotherapy. When chemotherapy was to start later than 10 days after study inclusion, 50 women were randomized to receive either chemotherapy alone (arm III) or chemotherapy after downregulation with GnRH agonist (arm IV). Resumption of menstruation at 12 months after end of chemotherapy was the primary outcome. Postchemotherapy hormonal and ultrasound changes were secondary outcomes. RESULTS: Twelve months after termination of chemotherapy, there were no differences in menstruation resumption rates between GnRH-treated patients and control group individuals in either early (80% in arms I and II, risk ratio 1, 95% confidence interval 0.7-.32; P=1.00) or delayed chemotherapy groups (80% and 84% in arms III and IV, risk ratio 0.95, 95% confidence interval 0.73-1.235; P=.71). There were no differences in hormonal and ultrasound markers between GnRH analogue users and control group individuals. The use of GnRH analogue cotreatment did not predict independently the odds of menstruating at 12 months. CONCLUSION: GnRH analogue cotreatment does not offer a significant protective effect on ovarian function in patients treated by cyclophosphamide-based chemotherapy. CLINICAL TRIAL REGISTRATION: Australian New Zealand Clinical Trials Registry. www.anzctr.org.au, ACTRN12609001059257. LEVEL OF EVIDENCE: I.

Discovery and evolutionary history of gonadotrophin-inhibitory hormone and kisspeptin: new key neuropeptides controlling reproduction.

Gonadotrophin-releasing hormone (GnRH) is the primary hypothalamic factor responsible for the control of gonadotrophin secretion in vertebrates. However, within the last decade, two other hypothalamic neuropeptides have been found to play key roles in the control of reproductive functions: gonadotrophin-inhibitory hormone (GnIH) and kisspeptin. In 2000, we discovered GnIH in the quail hypothalamus. GnIH inhibits gonadotrophin synthesis and release in birds through actions on GnRH neurones and gonadotrophs, mediated via GPR147. Subsequently, GnIH orthologues were identified in other vertebrate species from fish to humans. As in birds, mammalian and fish GnIH orthologues inhibit gonadotrophin release, indicating a conserved role for this neuropeptide in the control of the hypothalamic-pituitary-gonadal axis across species. Subsequent to the discovery of GnIH, kisspeptin, encoded by the KiSS-1 gene, was discovered in mammals. By contrast to GnIH, kisspeptin has a direct stimulatory effect on GnRH neurones via GPR54. GPR54 is also expressed in pituitary cells, but whether gonadotrophs are targets for kisspeptin remains unresolved. The KiSS-1 gene is also highly conserved and has been identified in mammals, amphibians and fish. We have recently found a second isoform of KiSS-1, designated KiSS-2, in several vertebrates, but not birds, rodents or primates. In this review, we highlight the discovery, mechanisms of action, and functional significance of these two chief regulators of the reproductive axis.

The relationship between the production and the anti-gonadotrophic action of prostaglandin F 2 alpha in luteal cells from the marmoset monkey (Callithrix jacchus) in the early and mid-luteal phase.

To address the potential luteolytic role for prostaglandin F(2 alpha) (PGF(2 alpha)) in the corpus luteum of the common marmoset monkey (Callithrix jacchus), the ability of marmoset luteal cells, maintained in monolayer culture, to produce PGF(2 alpha) was determined in vitro in the presence and absence of human chorionic gonadotrophin (hCG) and other established pharmacological modulators of PGF(2 alpha) synthesis. We also assessed the effects of the PGF(2 alpha) analogue, cloprostenol, on progesterone output from luteal cells isolated in the early luteal phase versus the mid-luteal phase (days 3 and 14 post ovulation, respectively). Cloprostenol had no effect on progesterone output from luteal cells isolated on day 3 of the luteal phase, whereas it significantly inhibited both basal and hCG-stimulated progesterone synthesis by day 14 luteal cells during the culture period 48-72 h (P<0.001). Intra-luteal PGF(2 alpha) concentrations were 5-fold higher in luteal cells isolated in the early luteal phase than in mid-luteal phase cells (16.5+/-3.5 versus 3.5+/-0.6 pmol/10(5) cells). While PGF(2 alpha) production was unaffected by hCG in vitro, it was decreased by indomethacin (1000 ng/ml) (P<0.05) and stimulated by the calcium ionophore A23187 (10 micromol/l) (P<0.05) in luteal cells from both stages of the luteal phase. Phospholipase A(2) did not influence PGF(2 alpha) production by day 3 luteal cells whereas at 10 IU/ml, it significantly stimulated PGF(2 alpha) production by day 14 luteal cells (P<0.05). Hence, the timing of luteolysis in the common marmoset monkey appears to involve changes in both the luteal cell response to and production of PGF(2 alpha).

[Ovarian gonadotropic inhibition and endometriosis. About fighting false dogmas...]. / Inhibition gonadotrope et endométriose. Comment lutter contre les dogmes s'ils sont erronés ?

Ovarian gonadotropic inhibition is today an efficacious tool in the treatment of endometriosis mainly when associated with surgery and sometimes by itself. However, to be useful, this inhibition must be stable - without any cyclical looseness - of long duration, sometimes during years and sufficiently powerful. Depending on the severity of symptoms and that of the disease, the choice will be among GnRH agonists, gestagens and combined OCs. The recent development of continuous oral contraception with protracted amenorrhoea makes treatment by continuous hormonal administration easier for the patients with endometriosis.

Oestrogen-induced androgen insufficiency results in a reduction of proliferation and differentiation of spermatogonia in the zebrafish testis.

Androgens can induce complete spermatogenesis in immature or prepubertal teleost fish. However, many aspects of the role of androgens in adult teleost spermatogenesis have remained elusive. Since oestrogens inhibit androgen synthesis, we used an oestrogen-induced androgen depletion model to identify androgen-dependent stages during adult zebrafish spermatogenesis. Exposure to 10 nM 17beta-oestradiol (E(2)) in vivo at least halved the mass of differentiating germ cells (from type B spermatogonia to spermatids), while type A spermatogonia accumulated. Studies on the cellular dynamics revealed that a reduction of spermatogonial proliferation together with an inhibition of their differentiation to type B spermatogonia were the basis for the oestrogen-mediated disturbance of spermatogenesis. The capacity of the zebrafish testis to produce 11-ketotestosterone as well as the expression of steroidogenesis-related genes was markedly decreased after in vivo oestrogen exposure. Moreover, the androgen-release response to recombinant zebrafish Lh was lost after oestrogen exposure. We conclude that oestrogen exposure caused a state of androgen insufficiency in adult male zebrafish. Since the downregulation of the steroidogenic system as well as the disturbance of spermatogenesis in testicular explants exposed to E(2) ex vivo was much less severe than after in vivo exposure, the main inhibitory effect appears to be exerted via feedback inhibition of gonadotropin release. This experimental set-up helped to identify spermatogonial proliferation and their differentiation as androgen targets in adult zebrafish spermatogenesis.

Impact of ovarian stimulation on mid-luteal endometrial tissue and secretion markers of receptivity.

The objective of this study was to investigate the effect of ovarian stimulation for IVF on endometrial secretion and tissue markers of receptivity in the mid-luteal phase. In 10 oocyte donors, endometrial secretions and biopsies were sampled 5 days after spontaneous ovulation and oocyte retrieval in consecutive cycles. Four subjects received progesterone in the luteal phase of the stimulated cycles. Mid-luteal endometrial maturation in the stimulated cycle was compared with the spontaneous cycle, by histological dating, Ki-67, oestrogen receptor (ER) and progesterone receptor (PR) expression, secretion levels of leukaemia inhibitory factor (LIF), glycodelin A (GdA) and progesterone, and protein profile. No significant differences in histological markers, expression of Ki-67, PR, ER, secretion protein profiles or concentrations of LIF, GdA, or progesterone were observed when comparing natural with stimulated cycles. Progesterone supplementation of stimulated cycles was associated with significantly lower Ki-67 (P = 0.03) and ER (P = 0.04) expression compared with the non-supplemented stimulated cycle. In this pilot study, ovarian stimulation was not demonstrated to alter the studied markers of endometrial maturation in the mid-luteal phase.

Activin receptor subunits in normal and dysfunctional adult human testis.

BACKGROUND: The cellular sites of activin action and its regulation in the normal and dysfunctional adult human testis are unknown. METHODS: Activin type I (ALK2 and ALK4) and type II (ActRIIA and ActRIIB) receptors were detected using immunohistochemistry on Bouins fixed sections of normal, carcinoma in situ (CIS), seminoma, non-seminoma and gonadotropin-deprived human testis. ActRIIA mRNA was localized by in situ hybridization. RESULTS: ALK2, ALK4 and ActRIIB proteins were observed in Sertoli cells, spermatogonia and some spermatocytes within normal and gonadotropin-suppressed adult human testis; all three receptor subunits were also detected in CIS, seminoma and non-seminoma cells. ActRIIA immunoreactivity was faint to absent in the normal testis and in CIS and non-seminoma cells, whereas some seminoma cells displayed a strong signal. Also in contrast to the normal testis, a majority of spermatogonia and Sertoli cells in gonadotropin-deprived samples exhibited a strong ActRIIA immunohistochemical and in situ hybridization signal. CONCLUSIONS: Spermatogonia and Sertoli cells appear as the primary targets of activin action in the adult human testis. Changes in testicular function associated with altered hormone levels may enhance ActRIIA mRNA and protein synthesis, thus modifying signalling by activin or other TGFbeta ligands within specific cells of the seminiferous epithelium.

Serum 17-hydroxyprogesterone strongly correlates with intratesticular testosterone in gonadotropin-suppressed normal men receiving various dosages of human chorionic gonadotropin.

OBJECTIVE: To determine if serum concentrations of testosterone precursors would correlate with intratesticular testosterone (ITT) concentration measured directly by testicular aspiration and allow for a less invasive means of inferring ITT. DESIGN: Controlled clinical study. SETTING: Healthy volunteers in an academic research environment. PATIENT(S): Twenty-nine normal men. INTERVENTION(S): We determined ITT concentration by testicular aspiration before and after treatment in men receiving exogenous T to block endogenous gonadotropin production and randomly assigned to one of four doses of hCG (0, 125 IU, 250 IU, or 500 IU every other day) for 3 weeks. MAIN OUTCOME MEASURE(S): The association between serum 17-hydroxyprogesterone (17OH-P), androstenedione, and DHEA and ITT. RESULT(S): With T administration alone, serum 17OH-P decreased significantly and increased significantly when 500 IU hCG was administered. End-of-treatment ITT strongly correlated with serum 17OH-P. Moreover, serum 17OH-P, but not androstenedione or DHEA, was independently associated with end-of-treatment ITT by multivariate linear regression. CONCLUSION(S): Serum 17OH-P is highly correlated with ITT in gonadotropin-suppressed normal men receiving T and stimulated with hCG. Serum 17OH-P is a surrogate biomarker of ITT and may be useful in research and in men receiving gonadotropin therapy for infertility.

The effects of chemotherapy and long-term gonadotrophin suppression on the ovarian reserve in premenopausal women with breast cancer.

BACKGROUND: Reproductive function following cancer treatment is of increasing importance with improving survival rates. We therefore assessed the markers of the ovarian reserve in premenopausal women, to investigate and compare the effects of chemotherapy and long-term gonadotrophin withdrawal on ovarian function. METHODS: Fifty premenopausal (age range 28-52 years) women with early breast cancer were recruited. Serum hormone and ovarian ultrasound measurements were taken before treatment and at intervals up to 1 year during chemotherapy or gonadotrophin suppressive therapy. RESULTS: Pretreatment samples indicated a fall in anti-Müllerian hormone (AMH) concentration with age before changes in other hormone concentrations. AMH concentration showed a rapid and marked fall during chemotherapy, with undetectable concentrations in many women (P<0.0001). Inhibin B concentration showed a lesser fall (P<0.0001), whereas estradiol (E2) concentrations were maintained. Both antral follicle count (AFC) and ovarian volume fell (P<0.0001 and P<0.05 respectively). Regimens containing taxanes in addition to cyclophosphamide showed increased gonadotoxicity. Gonadotrophin suppression resulted in expected falls in E2 (P<0.05) and inhibin B (P<0.001) levels, but also resulted in a delayed fall in AMH level after 6 months (P<0.0001). CONCLUSIONS: These data confirm the value of AMH concentration as an early indicator of ovarian ageing including assessment of chemotherapy-induced ovarian follicle loss. FSH and AMH concentration measurements may be useful for the comparison of ovarian toxicity of different chemotherapy regimens.

The role of O-linked and N-linked oligosaccharides on the structure-function of glycoprotein hormones: development of agonists and antagonists.

Thyrotropin (TSH) and the gonadotropins; follitropin (FSH), lutropin (LH) and human chorionic gonadotropin (hCG) are a family of heterodimeric glycoprotein hormones. These hormones composed of two noncovalently linked subunits; a common alpha and a hormone specific beta subunits. Assembly of the subunits is vital to the function of these hormones. However, genetic fusion of the alpha and beta subunits of hFSH, hCG and hTSH resulted in active polypeptides. The glycoprotein hormone subunits contain one (TSH and LH) or two (alpha, FSHbeta and hCGbeta) asparagine-linked (N-linked) oligosaccharides. CGbeta subunit is distinguished among the beta subunits because of the presence of a carboxyl-terminal peptide (CTP) bearing four O-linked oligosaccharide chains. To examine the role of the oligosaccharide chains on the structure-function of glycoprotein hormones, chemical, enzymatic and site-directed mutagenesis were used. The results indicated that O-linked oligosaccharides play a minor role in receptor binding and signal transduction of the glycoprotein hormones. In contrast, the O-linked oligosaccharides are critical for in vivo half-life and bioactivity. Ligation of the CTP bearing four O-linked oligosaccharide sites to different proteins, resulted in enhancing the in vivo bioactivity and half-life of the proteins. The N-linked oligosaccharide chains have a minor role in receptor binding of glycoprotein hormones, but they are critical for bioactivity. Moreover, glycoprotein hormones lacking N-linked oligosaccharides behave as antagonists. In conclusion, the O-linked oligosaccharides are not important for in vitro bioactivity or receptor binding, but they play an important role in the in vivo bioactivity and half-life of the glycoprotein hormones. Addition of the O-linked oligosaccharide chains to the backbone of glycoprotein hormones could be an interesting strategy for designing long acting agonists of glycoprotein hormones. On the other hand, the N-linked oligosaccharides are not important for receptor binding, but they are critical for bioactivity of glycoprotein hormones. Deletion of the N-linked oligosaccharides resulted in the development of glycoprotein hormone antagonists. In the case of hTSH, development of an antagonist may offer a novel therapeutic strategy in the treatment of thyrotoxicosis caused by Graves' disease and TSH secreting pituitary adenoma.

Identification and characterization of a gonadotropin-inhibitory system in the brains of mammals.

Successful reproduction requires maintenance of the reproductive axis within fine operating limits through negative feedback actions of sex steroids. Despite the importance of this homeostatic process, our understanding of the neural loci, pathways, and neurochemicals responsible remain incomplete. Here, we reveal a neuropeptidergic pathway that directly links gonadal steroid actions to regulation of the reproductive system. An RFamide (Arg-Phe-NH2) peptide that inhibits gonadotropin release from quail pituitary was recently identified and named gonadotropin-inhibitory hormone (GnIH). Birds are known to have specialized adaptations associated with gonadotropin-releasing hormone (GnRH) regulation to optimize reproduction (e.g., encephalic photoreceptors), and the existence of a hypothalamic peptide inhibiting gonadotropins may or may not be another such specialization. To determine whether GnIH serves as a signaling pathway for sex steroid regulation of the reproductive axis, we used immunohistochemistry and in situ hybridization to characterize the distribution and functional role of this peptide in hamsters, rats, and mice. GnIH-immunoreactive (GnIH-ir) cell bodies are clustered in the mediobasal hypothalamus with pronounced projections and terminals throughout the CNS. In vivo GnIH administration rapidly inhibits luteinizing hormone secretion. Additionally, GnIH-ir neurons form close appositions with GnRH cells, suggesting a direct means of GnRH modulation. Finally, GnIH-ir cells express estrogen receptor-alpha and exhibit robust immediate early gene expression after gonadal hormone stimulation. Taken together, the distribution of GnIH efferents to neural sites regulating reproductive behavior and neuroendocrine secretions, expression of steroid receptors in GnIH-ir nuclei, and GnIH inhibition of luteinizing hormone secretion indicate the discovery of a system regulating the mammalian reproductive axis.