GnRH action on luteal steroidogenesis during pregnancy

Expression of GnRH receptor in the canine corpus luteum, and luteal function following deslorelin acetate-induced puberty delay

The goals of this study were as follows: (Experiment 1) to examine the basic capability of canine corpora lutea (CL) to respond to GnRH by assessing expression of gonadotropin-releasing hormone receptor (GnRH-R) in luteal samples collected throughout the luteal lifespan from non-pregnant dogs, and (Experiment 2) to investigate the effects of pre-pubertal application of the GnRH agonist deslorelin acetate on luteal function following the first oestrus. Mature CL were collected during the mid-luteal phase (days 30-45) from treated and control bitches. Transcript levels of several factors were determined: estrogen receptors (ESR1/ERα, ESR2/ERβ), progesterone (P4)-receptor (PGR), prolactin receptor (PRLR), PGE2-synthase (PTGES) and PGE2 receptors (PTGER2/EP2, PTGER4/EP4), vascular endothelial growth factor (VEGFA) and VEGF receptors (VEGFR1 and VEGFR2), cyclooxygenase 2 (COX2/PTGS2), steroidogenic acute regulatory protein (STAR) and 3β-hydroxysteroid dehydrogenase (3βHSD). Additionally, levels of Kisspeptin 1 (Kiss1) and its receptor (KISS1-R) were evaluated. Although generally low, GnRH-R expression was time dependent and was elevated during early dioestrus, with a significant decrease towards luteal regression. In deslorelin-treated and control dogs, its expression was either low or frequently below the detection limit. EP2 and VEGFR1 were higher in the treated group, which could be caused by a feedback mechanism after long-term suppression of reproductive activity. Despite large individual variations, 3βHSD was higher in the deslorelin-treated group. This, along with unchanged STAR expression, was apparently not mirrored in increased luteal functionality, because similar P4 levels were detected in both groups. Finally, the deslorelin-mediated long-term delay of puberty does not have negative carry-over effects on subsequent ovarian functionality in bitches.

Leuprolide acetate reduces both in vivo and in vitro ovarian steroidogenesis in infertile women undergoing assisted reproduction

Despite the probable inhibitory effects of GnRH analogues on ovarian steroidogenesis in vitro, their association with assisted reproduction protocols shows favorable results. This suggests that there are important differences in the behaviors of these drugs when administered in vivo versus in vitro. To clarify these differences, this study was designed to analyze the effect of leuprolide acetate (LA) on ovarian steroidogenesis in women undergoing In Vitro Fertilization (IVF). A prospective, randomized open label study was conducted on 14 women (26-35 years): seven receiving only gonadotrophins (Group 1) and seven receiving gonadotrophin plus LA at 1mg/day (Group 2). The LA in vivo effect was determined with serum and follicular fluid (FF) samples and via luteinized granulosa cell cultivation (GCC), where cells were obtained during oocyte retrieval after ovarian hyperstimulation. In vitro analysis was performed via addition of LA to GCC only for Group 1 (without LA) at progressively higher concentrations (0, 10(-12), 10(-9) and 10(-6)M). In vivo, the main observation was a reduction in androgen production in Group 2, represented by lower androstenedione production in FF (G1=6479+/-3458; G2=3021+/-1119 ng/ml; p=0.04) and a lower testosterone peak in GC at 96h (G1=0.64+/-0.12 ng/ml; G2=0.50+/-0.19 ng/ml; P=0.02), but a higher fertilization rate (G1=67%; G2=83%; p=0.009). In vitro, testosterone, estradiol and progesterone were also reduced by LA, even though this reduction occurred for progesterone only at the highest LA dosage (10(-6)M; 606.0+/-114.3 ng/ml versus 1524.0+/-246.5 ng/ml; p=0.02). Results show that LA reduces ovarian steroidogenesis in vivo by essentially inhibiting androgen synthesis; whereas, in vitro, ovarian steroidogenesis is reduced overall.

Expression of mRNA and proteins for GnRH I and II and their receptors in primate corpus luteum during menstrual cycle

The differential expression of mRNA and protein of GnRH I, II and their receptors (RI and RII) in the monkey corpus luteum (CL) were measured during different stages of the luteal phase of the menstrual cycle as an initial step towards considering the role and regulation of GnRH (I and II) system during luteinization and luteolysis in primates. RT-PCR confirmed the sequence identity of PCR products and real time PCR quantified specific mRNA expressions. Proteins were localized by immunohistochemistry (IHC). Changes in mRNA expression patterns of GnRH I and II (increased) and GnRH RII (decreased) were maximal at mid-late to late stages, that is, at CL regression, where as GnRH RI was low during the entire luteal phase. However, RT-PCR and IHC studies confirmed the presence of GnRH RI at both mRNA and protein levels, respectively. IHC results showed the presence of GnRH I, II and their receptors in steroidogenic cells (granulose-luteal cells and thecal-luteal cells) across the luteal phase. Hence, GnRH I and II systems may have a role on both luteinization (from early to mid stages of CL) and luteolysis (from mid-late to very-late stages of CL). These novel findings suggest that monkey luteal GnRH system may have a role in fertility regulation in paracrine and/or autocrine manner.

Presence of immunoreactive gonadotropin releasing hormone (GnRH) and its receptor (GnRHR) in rat ovary during pregnancy

The present study aims at quantification of gonadotropin releasing hormone (GnRH) by radioimmunoassay, relative expression of its mRNA by real-time PCR accompanied by its cellular localization in the rat ovary by immunonohistochemistry (IHC) during different time points of pregnancy. To determine the involvement of endogenous ovarian GnRH in receptor mediated local autocrine/paracrine functions within the ovary, the cell specific localization of the classical receptor for GnRH (GnRHR) in the ovary by IHC and expression pattern of its mRNA were studied during pregnancy. Receptor expression during each time point within the ovary was reconfirmed by Western blot analysis accompanied by densitometric analysis of the signal intensity. Results reveal that the content of ovarian GnRH reaches its maximum on Day 20. The densitometric analysis of GnRHR receptor expression from Western blot study exhibits a decreasing trend by Day 20. Presence of GnRH and GnRHR mRNA in the ovary indicates the local synthesis of both ligand and receptor in the rat ovary. Differential expression of GnRH/GnRHR in the corpus luteum throughout pregnancy strengthens the hypothesis of the involvement of ovarian GnRH in local ovarian functions by receptor-mediated mechanisms. The expression of GnRH and GnRHR in the atretic antral follicles is indicative of the possible involvement of this decapeptide in processes like follicular atresia. The expression of GnRH/GnRHR in the nonatretic antral follicles and their oocytes requires further in-depth investigation. Collectively, this study for the first time reveals the presence of endogenous ovarian GnRH/GnRHR supporting their possible involvement in local autocrine/paracrine functions during pregnancy.

Regulation of ovarian angiogenesis and apoptosis by GnRH-I analogs

An adequate vascular supply is important to provide endocrine and paracrine signals during follicular development. We evaluated the direct in vivo effects of both the GnRH-agonist Leuprolide acetate (LA) and the GnRH-antagonist Antide (Ant) on the expression of VEGF-A and ANPT-1 and their receptors in ovarian follicles from prepubertal eCG-treated rats. We also examined whether the changes observed in apoptosis by GnRH-I analogs have an effect on the caspase cascade. LA significantly decreased the levels of VEGF-A, its receptor Flk-1, and ANPT-1 when compared to controls, while the co-injection of Ant interfered with this effect. No changes were observed in the levels of Tie-2 after treatment with these analogs. When we measured the follicular content of caspase-3 protein, we observed that LA significantly increased the level of the active form. The co-injection of Ant interfered with this effect and Ant alone significantly decreased caspase-3 cleavage. IHC analyses corroborated these data. Notably, while LA increased caspase-3 activity levels, Ant decreased them when compared to controls. In follicles obtained from LA-treated rats, cleavage of PARP (a substrate of caspase-3) from the intact 113-kDa protein showed a significant enhancement in an 85-kDa fragment. The co-injection of Ant interfered with this effect. Ant alone significantly decreased PARP cleavage as compared to controls. We conclude that the decrease in VEGF-A, its receptor Flk-1/KDR, and ANPT-1 produced by the administration of GnRH-I agonist is one of the mechanisms involved in ovarian cell apoptosis. This suggests an intraovarian role of an endogenous GnRH-like peptide in gonadotropin-induced follicular development.

Inhibition of cytochrome P-450 C17 enzyme by a GnRH agonist in ovarian follicles from gonadotropin-stimulated rats

Our objective was to study the direct action of a GnRH-I agonist, leuprolide acetate (LA), on ovarian steroidogenesis in preovulatory follicles obtained from equine chorionic gonadotropin (eCG)-treated rats. Previously, we have demonstrated an inhibitory effect of LA on steroidogenesis and follicular development. In this study, we tested the hypothesis that gonadotropin-releasing hormone (GnRH) exerts its negative effect on follicular development by inhibiting thecal cytochrome P-450 C17 (P450C17) alpha-hydroxylase expression and, consequently, androgen synthesis. Studies were carried out in prepubertal female rats injected with either eCG (control) or eCG plus LA (LA) and killed at different time points. Immunohistochemical studies indicated that LA induced steroidogenic acute regulatory protein (StAR) expression mainly in theca cells of preantral and antral follicles. In addition, serum progesterone levels increased significantly (P < 0.05), whereas those of androsterone decreased (P < 0.05) after 8 h of LA treatment. This inhibition caused by LA seemed to be a consequence of the decreased expression of follicular P450C17 alpha-hydroxylase, as demonstrated by Western blot and RT-PCR techniques. In vitro studies using follicles isolated from 48-h-eCG-treated rats and cultured with LA showed a significant (P < 0.05) inhibition of FSH-induced androsterone follicular content as well as P450C17 alpha-hydroxylase protein levels, as determined by Western analysis. However, LA increased StAR protein expression in these follicles without significant changes in P450scc enzyme levels. Taking all these findings into account, we suggest that GnRH-I exerts a direct inhibitory action on gonadotropin-induced follicular development by decreasing the temporal expression of the P450C17 enzyme and, consequently, androgen production, thus reducing the supply of estrogens available to developing follicles.

Localization of immunoreactive gonadotropin-releasing hormone and relative expression of its mRNA in the oviduct during pregnancy in rats

This study was designed to determine the cellular and ultrastructural distribution of the gonadotropin-releasing hormone (GnRH) and the relative expression of its mRNA in the oviduct of rats during different time points (days 7, 9, 16, and 20) of pregnancy. Immunofluorescent localization and confocal microscopic techniques were used to determine the cellular distribution of GnRH in the oviduct. Immunogold electron microscopy indicated its localization at the ultrastructural level, and real-time PCR was used to study the expression pattern of GnRH mRNA in the oviduct during pregnancy. In general, GnRH was localized within the epithelial cells lining the oviductal lumen at each selected time point. A strong correlation between the fluorescence intensity of GnRH-immunoreactive cells and the relative expression of GnRH mRNA was noted on days 7 and 16, followed by a plateau by day 20. At the ultrastructural level, uniform labeling of colloidal gold particles was observed in secretory vesicles and lamella of the luminal epithelium as well as the lumen of the oviduct. Collectively, these results demonstrate for the first time that the oviductal epithelium synthesizes and secretes the decapeptide GnRH during pregnancy in rats, which may have a possible role in postimplantation embryonic development and the maintenance of pregnancy.

The molecular control of corpus luteum formation, function, and regression

The corpus luteum (CL) is one of the few endocrine glands that forms from the remains of another organ and whose function and survival are limited in scope and time. The CL is the site of rapid remodeling, growth, differentiation, and death of cells originating from granulosa, theca, capillaries, and fibroblasts. The apparent raison d'etre of the CL is the production of progesterone, and all the structural and functional features of this gland are geared toward this end. Because of its unique importance for successful pregnancies, the mammals have evolved a complex series of checks and balances that maintains progesterone at appropriate levels throughout gestation. The formation, maintenance, regression, and steroidogenesis of the CL are among the most significant and closely regulated events in mammalian reproduction. During pregnancy, the fate of the CL depends on the interplay of ovarian, pituitary, and placental regulators. At the end of its life span, the CL undergoes a process of regression leading to its disappearance from the ovary and allowing the initiation of a new cycle. The generation of transgenic, knockout and knockin mice and the development of innovative technologies have revealed a novel role of several molecules in the reprogramming of granulosa cells into luteal cells and in the hormonal and molecular control of the function and demise of the CL. The current review highlights our knowledge on these key molecular events in rodents.

The celiac ganglion modulates LH-induced inhibition of androstenedione release in late pregnant rat ovaries

BACKGROUND

Although the control of ovarian production of steroid hormones is mainly of endocrine nature, there is increasing evidence that the nervous system also influences ovarian steroidogenic output. The purpose of this work was to study whether the celiac ganglion modulates, via the superior ovarian nerve, the anti-steroidogenic effect of LH in the rat ovary. Using mid- and late-pregnant rats, we set up to study: 1) the influence of the noradrenergic stimulation of the celiac ganglion on the ovarian production of the luteotropic hormone androstenedione; 2) the modulatory effect of noradrenaline at the celiac ganglion on the anti-steroidogenic effect of LH in the ovary; and 3) the involvement of catecholaminergic neurotransmitters released in the ovary upon the combination of noradrenergic stimulation of the celiac ganglion and LH treatment of the ovary.

METHODS

The ex vivo celiac ganglion-superior ovarian nerve-ovary integrated system was used. This model allows studying in vitro how direct neural connections from the celiac ganglion regulate ovarian steroidogenic output. The system was incubated in buffer solution with the ganglion and the ovary located in different compartments and linked by the superior ovarian nerve. Three experiments were designed with the addition of: 1) noradrenaline in the ganglion compartment; 2) LH in the ovarian compartment; and 3) noradrenaline and LH in the ganglion and ovarian compartments, respectively. Rats of 15, 19, 20 and 21 days of pregnancy were used, and, as an end point, the concentration of the luteotropic hormone androstenedione was measured in the ovarian compartment by RIA at various times of incubation. For some of the experimental paradigms the concentration of various catecholamines (dihydroxyphenylalanine, dopamine, noradrenaline and adrenaline) was also measured in the ovarian compartment by HPLC.

RESULTS

The most relevant result concerning the action of noradrenaline in the celiac ganglion was found on day 21 of pregnancy resulting in the inhibition of androstenedione release from the ovarian compartment. In addition on day 15 of pregnancy, LH placed in the ovarian compartment led to an inhibition of the release of androstenedione, and this inhibitory effect was further reinforced by the joint action of noradrenaline in the celiac ganglion and LH in the ovary. The levels of catecholamines in the ovarian compartment showed differences among the experiments; of significance, the joint treatment of noradrenaline in the celiac ganglion and LH in the ovary resulted in a remarkable increase in the ovarian levels of noradrenaline and adrenaline when compared to the effect achieved by either one of the compounds added alone.

CONCLUSION

Our results demonstrate that the noradrenergic stimulation of the celiac ganglion reinforces the LH-induced inhibition of androstenedione production by the ovary of late pregnant rats, and that this effect is associated with marked changes in the release of catecholamines in the ovary.

GnRH in non-hypothalamic reproductive tissues

Gonadotropin releasing hormone (GnRH) is a hypothalamic neuronal secretory decapeptide that plays a pivotal role in mammalian reproduction. GnRH and its analogues are used extensively in the treatment of hormone dependent diseases and assisted reproductive technology. Fourteen structural variants and three different forms of GnRH, named as hypothalamic GnRH or GnRH-I, mid brain GnRH or GnRH-II and GnRH-III across various species of protochordates and vertebrates have been recognised. The hormone acts by binding to cell surface transmembrane G protein coupled receptors (GPCRs) and activates Gq/11 subfamily of G proteins. Although hypothalamus and pituitary are the principal source and target sites for GnRH, several reports have recently suggested extra-hypothalamic GnRH and GnRH receptors in various reproductive tissues such as ovaries, placenta, endometrium, oviducts, testes, prostrate, and mammary glands. GnRH-II appears to be predominantly expressed in extra pituitary reproductive tissues where it produces its effect by PLC, PKA2, PLD, and AC cell signalling pathways. In these tissues, GnRH is considered to act by autocrine or paracrine manner and regulate ovarian steroidogenesis by having stimulatory as well as inhibitory effect on the production of steroid hormones and apoptosis in ovarian follicle and corpus luteum. In male gonads, GnRH has been shown to cause a direct stimulatory effect on basal steroidogenesis and an inhibitory effect on gonadotropin-stimulated androgen biosynthesis. Recent studies have shown that GnRH is more abundantly present in ovarian, endometrial and prostrate carcinomas. The presence of type-II GnRH receptors in reproductive tissues (e.g. gonads, prostrate, endometrium, oviduct, placenta, and mammary glands) suggests existence of distinct role(s) for type-II GnRH molecule in these tissues. The existence of different GnRH forms indicates the presence of distinctive cognate receptors types in vertebrates and is a productive area of research and may contribute to the development of new generation of GnRH analogues with highly selective and controlled action on different reproductive tissues and the target-specific GnRH analogues could be developed.

Estradiol and testosterone concentrations in follicular fluid as criteria to discriminate between mature and immature oocytes

The objective of the present study was to examine the association between follicular fluid (FF) steroid concentration and oocyte maturity and fertilization rates. Seventeen infertile patients were submitted to ovulation induction with urinary human follicle-stimulating hormone, human menopausal gonadotropin and human chorionic gonadotropin (hCG). A total of 107 follicles were aspirated after hCG administration, the oocytes were analyzed for maturity and 81 of them were incubated and inseminated in vitro. Progesterone, estradiol (E2), estrone, androstenedione, and testosterone were measured in the FF. E2 and testosterone levels were significantly higher in FF containing immature oocytes (median = 618.2 and 16 ng/ml, respectively) than in FF containing mature oocytes (median = 368 and 5.7 ng/ml, respectively; P < 0.05). Progesterone, androstenedione and estrone levels were not significantly different between mature and immature oocytes. The application of the receiver-operating characteristic curve statistical approach to determine the best cut-off point for the discrimination between mature and immature oocytes indicated levels of 505.8 ng/ml for E2 (81.0% sensitivity and 81.8% specificity) and of 10.4 ng/ml for testosterone (90.9% sensitivity and 82.4% specificity). Follicular diameter was associated negatively with E2 and testosterone levels in FF. There was a significant increase in progesterone/testosterone, progesterone/E2 and E2/testosterone ratios in FF containing mature oocytes, suggesting a reduction in conversion of C21 to C19, but not in aromatase activity. The overall fertility rate was 61% but there was no correlation between the steroid levels or their ratios and the fertilization rates. E2 and testosterone levels in FF may be used as a predictive parameter of oocyte maturity, but not for the in vitro fertilization rate.

Gonadotropin-releasing hormone-agonist inhibits synthesis of nitric oxide and steroidogenesis by luteal cells in the pregnant rat

We have demonstrated that continuous administration of a gonadotropin-releasing hormone agonist (GnRH-Ag) in vivo suppressed progesterone production and induced apoptosis in the corpus luteum (CL) of the pregnant rat. To investigate the mechanism(s) by which progesterone secretion is suppressed and apoptosis is induced in the luteal cells, we studied nitric oxide (NO) as a messenger molecule for GnRH action. Rats were treated individually on Day 8 of pregnancy with 5 microg/day of GnRH-Ag for 4, 8, and 24 h. GnRH-Ag decreased the production of progesterone and pregnenolone 8 and 24 h after the administration. Corresponding with the reduction in these steroid hormones, luteal NO concentrations decreased at 8 and 24 h. Western blotting and immunohistochemical studies of endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS), and neuronal nitric oxide synthase (nNOS) in the CL demonstrated that administration of GnRH-Ag was associated with a marked decrease in eNOS and iNOS compared with sham controls at 4 and 8 h, but nNOS did not change throughout the experimental period. We demonstrated, for the first time, the presence of nNOS protein in the CL of the pregnant rat. To determine if this suppressive action of GnRH-Ag is directly on the CL, luteal cells were treated with GnRH-Ag for 4, 8, 12, and 24 h in vitro. Progesterone and NO concentrations in the media decreased at 8 and 12 h after the treatment and recovered at 24 h. Western blots revealed that eNOS and iNOS decreased in luteal cells treated with GnRH-Ag compared with controls at 4 and 8 h. These results demonstrate that suppression of luteal NO synthesis by GnRH-Ag is direct and leads to a decrease in the luteal production and release of progesterone and pregnenolone and thus suggest that GnRH could induce luteolysis in pregnant rats via NO.

Steroidogenic acute regulatory protein in ovarian follicles of gonadotropin-stimulated rats is regulated by a gonadotropin-releasing hormone agonist

The aim of the present study was to examine the acute and chronic effects of the gonadotropin-releasing hormone agonist (GnRH-a) leuprolide acetate (LA) on the expression of the steroidogenic acute regulatory protein (StAR), the cytochrome P450 side-chain cleavage enzyme (P450scc), and steroid production in antral ovarian follicles obtained from prepubertal equine choriogonadotropin (eCG)-treated rats. Follicular contents of StAR and P450scc proteins were measured by Western blotting following in vivo injection of eCG (control) and eCG+LA (LA) to prepubertal rats. Treatment with eCG for 2 h resulted in no change in StAR protein content, but it was markedly increased at 4 and 8 h after hormone treatment. However, coadministration of eCG+LA produced a significant increase (P < 0.05) in StAR protein levels at 2, 4, and 8 h when compared with eCG treatment. Acute and chronic treatment with either eCG or eCG+LA did not alter the P450scc protein levels in freshly isolated follicles. The increase in StAR protein expression following LA treatment was qualitatively similar to StAR mRNA expression, as determined by quantitative reverse transcription-polymerase chain reaction (RT-PCR) analysis. Furthermore, administration of eCG demonstrated a time-dependent increase (2-8 h) in the levels of StAR mRNA, and these levels were markedly increased by eCG+LA. However, the temporal response pattern of StAR mRNA was much greater at 2 h following LA administration when compared with controls. In addition, 48 h of LA treatment in eCG-treated rats resulted in a significant increase (P < 0.05) in follicular progesterone levels, whereas significant decreases in androgen (testosterone and androsterone) and estradiol levels were observed. Similar results were obtained when serum androgens and estradiol were measured, but serum progesterone levels were unchanged. Collectively, these findings demonstrate that the inhibitory effect of LA on ovarian androgen and estradiol levels is related to changes in the follicular levels of StAR protein and steroid production.

Multi-factorial role of GnRH-I and GnRH-II in the human ovary

Normal ovarian functions are regulated by a wide variety of endocrine hormones, local paracrine and autocrine factors, which functionally interact with each other in a highly coordinated fashion. Recent findings have demonstrated that both forms of gonadotropin-releasing hormone (GnRH-I and GnRH-II) are expressed in various compartments of the human ovary including the granulosa-luteal cells, ovarian surface epithelial cells and ovarian tumors, and their expressions have been shown to be tightly regulated by gonadal steroids and gonadotropins. Functionally, these neuropeptides exert diverse biological effects in the ovary via binding to their cognate receptors, supporting the notion that these peptides act as paracrine and autocrine factors in modulating local ovarian functions. In this review, we will summarize recent literatures regarding the regulation of GnRH-I and GnRH-II gene expressions in the human ovary, and discuss the possible signal transduction mechanisms by which these hormones exert their actions in the gonad. Recent cloning of the second form of the GnRH receptor (GnRH-II receptor) in primates and other vertebrates demonstrated that it was structurally, and thus, functionally distinct from the GnRH-I receptor. Cell proliferation studies showed that GnRH-II inhibited the growth of human ovarian cancer cells that express GnRH-II but not GnRH-I receptor, indicating that the GnRH-II binding sites are functional in these cells. However, it remains unknown if GnRH-II receptor is expressed as a full-length, properly processed and functional gene transcript in humans, and its potential physiological roles such as differential regulation of gonadotropin secretion, neuroendocrine modulation and female sexual behavior await further investigation.

Effects of a gonadotropin-releasing hormone agonist on rat ovarian follicle apoptosis: regulation by epidermal growth factor and the expression of Bcl-2-related genes

The purpose of the present study was to evaluate the in vivo effect of the GnRH analogue leuprolide acetate (LA) on follicular development and apoptosis-related mechanisms in preovulatory ovarian follicles (POF) obtained from prepubertal eCG-treated rats. Serum progesterone and estradiol levels were measured, and a significant decrease in circulating estradiol levels was observed in the LA group, whereas serum progesterone levels remained unchanged. Ovarian histology revealed an inhibitory effect of LA treatment on the follicular development induced by eCG. After 48 h of LA treatment, the numbers of atretic and preantral follicles were increased as compared with controls, whereas the number of antral follicles had decreased. Cells undergoing DNA fragmentation were quantified by performing in situ 3' end labeling of DNA with digoxygenin-dUTP on ovarian sections. LA treatment caused an increase in the percentage of apoptotic cells in preantral and antral follicles. DNA isolated from these POF incubated 24 h in serum-free medium exhibited the typical apoptotic DNA degradation pattern. Treatment of follicles with epidermal growth factor (EGF) suppressed the spontaneous onset of DNA fragmentation, and a similar effect was observed in LA follicles. POF obtained from LA-treated rats showed no changes in Bcl-2 or Bax protein levels. However, a reduction in the Bcl-xL:Bcl-xS ratio was observed, with a greater decrease in Bcl-xL compared with Bcl-xS during the incubation, suggesting a lower stability of the Bcl-xL isoform in the LA group. These results indicate that in vivo GnRH agonist treatment produces an increase in the apoptosis process in POF from eCG-treated rats, and this effect is reversed in vitro by EGF. This GnRH analogue also reduced the stability of the Bcl-xL protein, thus interfering with follicular development by an as yet unknown mechanism.

Differential regulation of two forms of gonadotropin-releasing hormone messenger ribonucleic acid in human granulosa-luteal cells

Until recently, the primate brain was thought to contain only one form of GnRH known as mammalian GnRH (GnRH-I). The recent cloning of a second form of GnRH (GnRH-II) with characteristics of chicken GnRH-II in the primate brain has prompted a reevaluation of the role of GnRH in reproductive functions. In the present study, we investigated the hormonal regulation of GnRH-II messenger RNA (mRNA) and its functional role in the human granulosa-luteal cells (hGLCs), and we provided novel evidence for differential hormonal regulation of GnRH-II vs. GnRH-I mRNA expression. Human GLCs were treated with various concentrations of GnRH-II, GnRH-II agonist (GnRH-II-a), or GnRH-I agonist (GnRH-I-a; leuprolide) in the absence or presence of FSH or human CG (hCG). The expression levels of GnRH-II, GnRH-I, and GnRH receptor (GnRHR) mRNA were investigated using semiquantitative or competitive RT-PCR. A significant decrease in GnRH-II and GnRHR mRNA levels was observed in cells treated with GnRH-II or GnRH-II-a. In contrast, GnRH-I-a revealed a biphasic effect (up- and down-regulation) of GnRH-I and GnRHR mRNA, suggesting that GnRH-I and GnRH-II may differentially regulate GnRHR and their ligands (GnRH-I and GnRH-II). Treatment with FSH or hCG increased GnRH-II mRNA levels but decreased GnRH-I mRNA levels, further indicating that GnRH-I and GnRH-II mRNA levels are differentially regulated. To investigate the physiological role of GnRH-II, hGLCs were treated with GnRH-II or GnRH-II-a in the presence or absence of hCG, for 24 h, and progesterone secretion was measured by RIA. Both GnRH-II and GnRH-II-a inhibited basal and hCG-stimulated progesterone secretion, effects which were similar to the effects of GnRH-I treatment on ovarian steroidogenesis. Next, hGLCs were treated with various concentrations of GnRH-II, GnRH-II-a, or GnRH-I-a; and the expression levels of FSH receptor and LH receptor were investigated using semiquantitative RT-PCR. A significant down-regulation of FSH receptor and LH receptor was observed in cells treated with GnRH-II, GnRH-II-a, and GnRH-I-a, demonstrating that GnRH-II and GnRH-I may exert their antigonadotropic effect by down-regulating gonadotropin receptors. Interestingly, GnRH-II and GnRH-II-a did not affect basal and hCG-stimulated intracellular cAMP accumulation, suggesting that the antigonadotropic effect of GnRH-II may be independent of modulation of cAMP levels. Taken together, these results suggest that GnRH-II may have biological effects similar to those of GnRH-I but is under differential hormonal regulation in the human ovary.