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Journal of Clinical Endocrinology & Metabolism , doi:10.1210/jc.2007-0978
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The Journal of Clinical Endocrinology & Metabolism Vol. 92, No. 12 4771-4776
Copyright © 2007 by The Endocrine Society

Association of Serum and Follicular Fluid Leptin Concentrations with Granulosa Cell Phosphorylated Signal Transducer and Activator of Transcription 3 Expression in Fertile Patients with Polycystic Ovarian Syndrome

Mei-Gen Li1, Guo-Lian Ding1, Xi-Jing Chen, Xi-Ping Lu, Li-Jun Dong, Min-Yue Dong, Xiao-Fu Yang, Xiu-E Lu and He-Feng Huang

Department of Reproductive Endocrinology, Women’s Hospital, School of Medicine, Zhejiang University, Hangzhou, Zhejiang, 31006, China

Address all correspondence and requests for reprints to: He-Feng Huang, M.D., Department of Reproductive Endocrinology, Women’s Hospital, School of Medicine, Zhejiang University, 2 Xue Shi Road, Hangzhou, Zhejiang, 31006, China. E-mail: huanghefg{at}hotmail.com.


   Abstract
Top
 Abstract
Introduction
 Subjects and Methods
 Results
 Discussion
 References
 
Objective: Our objective was to evaluate whether polycystic ovarian syndrome (PCOS)-associated infertility is related to alterations of leptin, leptin receptor (Ob-R), and the phosphorylated signal transducer and activator of transcription 3 (p-STAT3)/suppressor of cytokine signal 3 (SOCS3) system in the ovary.

Design and Setting: A case-control study was conducted in a university hospital.

Patients: Thirty-one infertile PCOS women with oligoovulation plus polycystic ovarian morphology and 79 infertile women with tubal blockage (control) participated in the study. The subjects were stratified according to in vitro fertilization outcomes: successful and failed subgroups.

Methods: Serum and follicular fluid (FF) leptin levels were measured with ELISA. RT-PCR and Western blotting were performed to assess expression of mRNA encoding leptin and Ob-R and proteins of p-STAT3 and SOCS3 in granulosa cells (GCs).

Results: Leptin levels in serum and FF of PCOS women were significantly higher than those of control (P < 0.01). There were no significant differences in expression of leptin mRNA and short and long Ob-Rs between PCOS and control (P > 0.05). The p-STAT3 level was decreased in PCOS compared with control (P < 0.01), whereas SOCS3 remained significantly unchanged (P > 0.05). Further analysis showed that serum and FF leptin levels were significantly higher, whereas p-STAT3 in GCs was lower in the failed subgroup of PCOS than those in the successful subgroup of PCOS (P < 0.05).

Conclusion: Hyperleptinemia and high FF leptin are important pathologies of PCOS with infertility. Lower levels of p-STAT3 in GCs may be related to ovarian leptin resistance and fecundity in PCOS women. Relatively high serum and FF leptin and low p-STAT3 in GCs may account for decreased fertilization, implantation, and pregnancy rates of in vitro fertilization in PCOS women.


   Introduction
Top
 Abstract
 Introduction
Subjects and Methods
 Results
 Discussion
 References
 
POLYCYSTIC OVARIAN SYNDROME (PCOS) is one of the most common endocrine disorders and one of the most common causes of infertility due to anovulation in women of reproductive age. Besides infertility, women with PCOS manifest clinical features such as hyperandrogenism, hyperinsulinemia, insulin resistance, acne, hirsutism, obesity, chronic anovulation, and polycystic ovaries. PCOS may increase the risk of cardiovascular diseases, diabetes mellitus, endometrial carcinoma, and other diseases in life. Although the etiology and pathogenesis of PCOS remain unknown, it has been proposed that hyperleptinemia and leptin resistance may play a role in the pathogenesis of disease.

Leptin, a 167-amino-acid protein, is a product of the obesity (ob) gene (1). Accumulating evidence indicates that the leptin system plays an important role in the control of reproductive function (2, 3), and leptin system disorder is related to reproductive pathologies of PCOS (4). Physiological levels of leptin stimulate steroidogenesis and follicle maturation, whereas supraphysiological concentrations of leptin may produce the opposite effect (5). Due to the current state of contradiction on data regarding PCOS-associated alteration of leptin (6, 7), subsequent research should be conducted to determine whether high levels of leptin contribute to infertility in PCOS women.

Leptin receptors (Ob-R) belong to the cytokine I receptor family. It can be further classified into the long and short isoforms. Upon binding to its receptor, leptin activates a cytokine-like signal transduction pathway, which involves the stimulation of the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway. Interaction of leptin with Ob-R results in phosphorylation and activation of STAT3. Suppressor of cytokine signal 3 (SOCS3), a postreceptor inhibitor of the signal transduction, modulates leptin signaling (8, 9). Impairment of any of the above-mentioned molecular events may result in deficient leptin signaling and hyperleptinemia, leading to a state of leptin resistance. Impaired phosphorylation of STAT3 was found in obese women (10), but the alteration in expression of Ob-Rs and postreceptor signaling in granulosa cells (GCs) has never been investigated in humans.

The present study aimed to investigate whether the levels of leptin in serum and follicular fluid (FF), the expression of Ob-Rs, and/or Ob-R signaling in GCs were altered in women with PCOS. We examined the concentrations of serum and FF leptin, the expression of mRNA for Ob-Rs, phosphorylated STAT3 (p-STAT3), and SOCS3 in GCs of infertile women with or without PCOS undergoing in vitro fertilization (IVF). The fertilization rate (FR), implantation rate (IR), and pregnancy rate (PR) per IVF cycle were also calculated. To further explore whether an alteration of leptin level and p-STAT3 is related to infertility in PCOS women, we compared leptin concentrations in serum and FF and the level of p-STAT3 in GCs between women who became pregnant after IVF (successful subgroup) and those who did not (failed subgroup).


   Subjects and Methods
Top
 Abstract
 Introduction
 Subjects and Methods
Results
 Discussion
 References
 
Subjects

This study was approved by the Institutional Review Board of Zhejiang University School of Medicine. All participants provided their informed consent before their inclusion in this study. Subjects included 31 women with PCOS who were referred to our department for IVF because of anovulation and 79 infertile women with tubal blockage who served as controls in this study.

PCOS was diagnosed according to Rotterdam Consensus (ESHRE/ASRM criteria), i.e. the presence of two of the three criteria: oligo- or anovulation, signs of clinical hyperandrogenism, and/or biochemical signs of hyperandrogenism and polycystic ovaries on ultrasonography after exclusion of specific identifiable disorders (congenital adrenal hyperplasia, androgen-secreting tumors, and Cushing’s syndrome) (11, 12). All PCOS patients in the present study had the oligoovulation plus polycystic ovarian morphology phenotype of the Rotterdam definition, and those with possible ovarian tumors and congenital adrenal hyperplasia were excluded. In addition, the control women had regular menstrual cycles and normal sex hormone levels. No structural abnormalities of uterus and ovaries were found by vaginal ultrasound or laparoscope. All partners had normal spermiograms and morphology.

Collection of serum, FF, and GCs

The long agonist protocol for controlled ovarian hyperstimulation (COH) was used as previously described (13). Briefly, COH was performed by administration of recombinant FSH (Gonal-F; Serono International S.A., Geneva, Switzerland) after pituitary suppression with triptorelin (Serono) started in the midluteal phase of the preceding cycle. The dosages of gonadotropins were individualized according to serum estradiol (E2) levels and transvaginally ultrasonic measurements of the follicles. When at least three follicles had reached diameters of 16–18 mm, ovulation was induced by the administration of 10,000 IU human chorionic gonadotropin (Libao Biochemistry Co., Zhuhai, China). Transvaginal oocyte aspiration was performed with ultrasound guidance under general anesthesia 36 h after injection of human chorionic gonadotropin.

Before oocyte aspiration, a peripheral blood sample was taken from each patient and serum was collected and stored at –80 C. FF was sampled by transvaginal ultrasound-guided puncture. The FF samples were carefully collected from the first aspiration follicle of each ovary as previously described (14), and those FF samples that did not contain any visible blood contamination were used in this study. The FF samples were immediately centrifuged for 10 min at 3000 rpm, and the supernatants were stored at –80 C for further analysis.

The GCs were obtained by follicular aspiration from FSH-treated women undergoing oocyte retrieval for IVF as described above. Follicular aspirates were transported on ice to the laboratory and centrifuged at 3000 rpm for 5 min. The pellet was resuspended in DMEM (Sigma Chemical Co., St. Louis, MO). The GCs were isolated from the blood cells and cellular debris using Percoll gradient centrifugation. The GCs were frozen and stored at –80 C until the time of the assay (15, 16).

Measurement of hormone and leptin concentrations in serum and FF

The levels of LH, FSH, E2, and testosterone (T) were measured with immunochemiluminescent assays (Roche, Basel, Switzerland). Commercial ELISA kits (Diagnostic Systems Laboratories, Los Angeles, CA) were used to measure the concentrations of leptin in serum and FF (17). All measurements were carried out in duplicate. The intra- and interassay coefficients of variation were less than 9 and 12%, respectively.

RT-PCR

The expression of leptin and two isoforms of Ob-R in GCs were assayed by the RT-PCR protocol as previously described (18). Total RNA was extracted from GCs using TRIzol (Invitrogen, Karlsruhe, Germany). Five micrograms of total RNA were reverse transcribed into cDNA. Four microliters of RT reaction mixture were used for PCR amplification using specific primer pairs as follows: forward 5'-CCT CAC TGA ATG CCT CAA TG-3' and reverse 5'-CCA GCT CTT GCT CAG ATG AA-3' for leptin, forward 5'-TCA GAA GGA TTG GAT GAA CT-3' and reverse 5'-GGA ATT GAG GCA TGT AAG AT-3' for long Ob-R, forward 5'-ATC CCC ATT GAG AAG TAC CAG-3' and reverse 5'-GAA GTT GGC ACA TTG GGT TC-3' for short Ob-R, and forward 5'-TTC CAG CCT TCC TTC CTG G-3' and reverse 5'-TTG CGC TAC AGG AGG AGC AAT-3' for β-actin as internal control.

The reaction conditions were as follows: RT for 90 min at 37 C, pre-denaturation for 5 min at 94 C, denaturation for 60 sec at 94 C, annealing for 60 sec at 55 C, and extension for 60 sec at 72 C followed by a 10-min final extension at 72 C. After 35 cycles, the PCR products (352 bp for leptin, 277 bp for long Ob-R, 332 bp for short Ob-R, and 224 bp for β-actin) were visualized on agarose gel with ethidium bromide staining and normalized against β-actin by densitometric analysis using a Gel Doc 1000 imager, (Bio-Rad, Hercules, CA).

Western blotting

The GCs were lysed in lysis buffer (1x PBS, 1% Nonidet P-40, 0.5% sodium deoxycholate, 0.1% SDS, 100 µg/ml phenylmethylsulfonyl fluoride, 100 µg/ml leupeptin), and cell lysates were centrifuged at 12,000 rpm for 15 min at 4 C. Bicinchoninic acid protein assay (Santa Cruz Biotechnology, Santa Cruz, CA) was used to determine the protein concentration. Twenty micrograms of protein in loading buffer [final buffer composition: 50 mM Tris-HCl, 100 mM dithiothreitol, 2% SDS (wt/vol), 10% glycerol (vol/vol), and a trace amount of bromophenol blue] were incubated at 95 C for 10 min, cooled, and then loaded per lane. Gel electrophoresis was performed on a Protean III mini-gel apparatus (Bio-Rad) using 8% gel with 0.1% (wt/vol) SDS under a constant current of 30 mA and then transferred to nitrocellulose membranes (Dingguo Biotechnology Co., Beijing, China) for 1.5 h. The membranes were blocked for 1 h at room temperature with 5% milk in Tris-buffered saline with Tween 20 [10 mM Tris (pH 7.6), 150 mM NaCl, and 0.05% Tween 20]. Membranes were incubated with primary antibody dilution (p-STAT3 antibody from Santa Cruz at 1:2000, SOCS3 antibody from Santa Cruz at 1:500, or β-actin antibody from Sigma at 1:500) overnight at 4 C. After being washed, the membranes were incubated with their corresponding secondary antibody at room temperature for 1 h. The proteins were detected with the enhanced chemiluminescence reagent (Amersham Biosciences, Piscataway, NJ). Densitometric intensity was measured with a GS-800 densitometer (Bio-Rad) and normalized against internal control β-actin, as previously described (18).

Statistical analysis

SPSS 12.0 was used for the data analysis. The Kolmogorov-Smirnov test was used to test whether data were normally distributed. Unpaired Student’s t test was used for variables with normal distribution and the Mann-Whitney U test was used for variables with skewed distribution. The {chi}2 test was used to compare IVF outcome (FR, IR, and PR). A two-way ANOVA was used to estimate the statistical difference between control and PCOS subjects for the level of leptin (serum and FF) and expression of p-STAT3 (successful and failed subgroups). P < 0.05 was considered statistically significant.


   Results
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
Discussion
 References
 
Comparison of demographic and clinical data

Demographic and clinical data regarding subsequent IVF of these infertile women with or without PCOS are shown in Table 1Go. The age and body mass index (BMI) displayed no significant difference between groups (P > 0.05 for both). The number of small follicles on the d 5 of the cycle in each ovary was much higher in PCOS patients than that in control women (P < 0.01). Serum LH level and LH/FSH ratio on d 3 of the natural cycle were significantly higher in the PCOS group than those in the control group (P < 0.01 for both). Serum T level was higher in PCOS patients than in control, but there was no statistical significance. E2 and FSH levels were not significantly different (P > 0.05 for all). Serum progesterone level was significantly much lower in PCOS patients than in control women (P < 0.01). Although the recombinant FSH dosage, induction length, and the number and quality of transplanted embryos demonstrated no significant difference (P > 0.05 for all), significantly decreased FR (P < 0.01), IR (P < 0.05), and PR (P < 0.05) were noted in the PCOS group compared with the control group. Statistical significance was also observed in the percentage of good quality embryos between the two groups (75.60% in control vs. 50.87% in PCOS, P < 0.01).


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  		TABLE 1. Demographic data and clinic characteristics

 
Leptin concentrations in serum and FF of infertile women with or without PCOS

The mean level of leptin in either serum or FF of PCOS patients was significantly higher than that of control (P < 0.01 for both, Fig. 1Go). However, the serum leptin level was not different from that of FF in either PCOS patients or control (P > 0.05 for all).


Figure 1
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  		FIG. 1. Comparison of serum and FF levels of leptin. The leptin level of either serum or FF was significantly higher in PCOS patients than that in control (**, P < 0.01). Data are shown as mean ± SEM; n = 79 and 31 for controls and PCOS, respectively.

 
mRNA expression of leptin and Ob-R isoforms in GCs

mRNA encoding leptin (Fig. 2Go, lanes 1 and 4), short Ob-R (Fig. 2Go, lanes 2 and 5), and long Ob-R (Fig. 2Go, lanes 3 and 6) were detected in GCs of control (lanes 1–3) and PCOS patients (lanes 4–6). There was no significant difference in the expression of mRNA for leptin or short and long Ob-Rs between PCOS women and control (P > 0.05 for all).


Figure 2
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  		FIG. 2. The expression of mRNA encoding leptin and Ob-R isoforms in human GCs. A, mRNAs encoding leptin (352 bp, lanes 1 and 4), short Ob-R (332 bp, lanes 2 and 5), and long Ob-R (277 bp, lanes 3 and 6) were expressed in human GCs of controls (lanes 1–3) and PCOS patients (lanes 4–6). M, DNA marker.

 
p-STAT3 and SOCS3 protein expression in GCs

Western blot analysis confirmed the presence of p-STAT3 and SOCS3 proteins in all samples of the GCs from PCOS patients and control women (Fig. 3AGo, lanes 1 and 2 for PCOS, lanes 3 and 4 for control). The relative expression of p-STAT3 was significantly lower in PCOS patients compared with control (P < 0.01), whereas that of SOCS3 was not significantly different between PCOS patients and control women (P > 0.05, Fig. 3BGo).


Figure 3
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  		FIG. 3. The determination of p-STAT3 and SOCS3 protein in GCs by Western blotting. A, p-STAT3 and SOCS were detected in human GCs of PCOS patients (lanes 1 and 2) and controls (lanes 3 and 4); B, relative level of p-STAT3 as normalized against β-actin was significantly lower in PCOS patients than in controls (**, P < 0.01), whereas the levels of SOCS were not significantly different (P > 0.05). Data are shown as mean ± SEM; n = 79 and 31 for controls and PCOS, respectively.

 
Association of serum and FF leptin levels and expression of p-STAT3 in GCs with IVF prognosis

Successful and failed subgroups of either the control or PCOS group were stratified according to their IVF results. Women who developed pregnancy after an IVF cycle were designated the successful subgroup, whereas women who remained infertile were designated the failed subgroup. There was no significant difference in serum and FF levels of leptin or the expression of p-STAT3 in GCs between successful and failed subgroups of controls (Fig. 4Go). The levels of serum and FF leptin in PCOS patients in the failed subgroup were significantly higher than those in PCOS patients in the successful subgroup as well as in the successful or failed subgroup of control (Fig. 4Go, A and B). However, the PCOS patients in the failed subgroup showed a significantly lower level of p-STAT3 expression than that in PCOS patients in the successful subgroup and the control in the successful or failed subgroup (Fig. 4CGo).


Figure 4
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  		FIG. 4. The association of levels of leptin in serum and FF and p-STAT3 in GCs with IVF outcomes. Women who developed pregnancy after IVF cycle were designated the successful subgroup and those not pregnant were designated the failed subgroup. Levels of leptin in serum (A), FF (B), and p-STAT3 (C) were significantly different among the subgroups. Serum and FF leptin levels were significantly increased, whereas the expression of p-STAT3 was significantly lower in the failed subgroup of PCOS patients compared with other subgroups. Data are shown as mean ± SEM. *, P < 0.05 compared with PCOS successful subgroup; # and ##, P < 0.05 and P < 0.01, compared with controls, respectively. n = 37 and 42 for successful and failed subgroups in controls, respectively; n = 8 and 23 for successful and failed subgroups in PCOS, respectively.

 

   Discussion
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
References
 
In the current investigation, it was revealed that serum and FF leptin levels were increased, the mRNA of leptin and its receptors in GCs were unchanged, and p-STAT3 in GCs was down-regulated in PCOS women when compared with controls. Furthermore, we noticed an association of serum and FF leptin levels and p-STAT3 expression in GCs with IVF outcome. Our findings suggest an involvement of the leptin system in PCOS and PCOS-associated infertility.

Leptin is the product of the Ob gene (1). It is involved in body weight control via inhibition of food intake and enhancement of energy expenditure. It is also recognized as an important hormone regulating ovarian function and is closely related to infertility and PCOS (19). Malfunction of the leptin system may impair human reproduction through altering hypothalamic and/or pituitary function, affecting ovarian function through direct actions on the ovarian follicle and other mechanisms including induction of insulin resistance, hyperandrogenism, and elevated leptin levels (20, 21).

Some investigators found increased leptin levels in women with PCOS and proposed that leptin played a role in the pathogenesis of PCOS (4, 5, 8, 9, 10), but others reported no change of leptin in PCOS women (6, 7). Pasquali et al. (4) suggested that the higher levels of leptin in PCOS were BMI dependent, whereas other investigators showed that the leptin level was elevated in a substantial proportion of women with PCOS, regardless of obesity (22). In the present study, we found that serum and FF levels of leptin were increased in infertile PCOS women compared with infertile women without PCOS. On the contrary, the BMI was comparable in all groups, indicating that hyperleptinemia and enhancement of FF leptin may be BMI independent and an intrinsic pathology of PCOS.

Enhanced leptin level may inhibit aromatase activities and prevent the transformation of androgen to estrogen, leading to the elevation of serum androgen and interfering with ovarian follicle growth and ovulation by suppressing estrogen production (23). Hyperleptinemia and/or high FF leptin in PCOS women may result in impaired reproductive function and infertility. Recent studies suggested that leptin level was negatively associated with FR, embryo quality, and PR of IVF (24, 25, 26), and lower leptin concentration in FF was proposed to be a marker of successful assisted reproduction outcome (27). In the present study, decreased FR, IR, and PR were observed in PCOS patients compared with the controls. An association of elevated serum and FF leptin with poor IVF outcome was noted and evident in proposing that enhancement of leptin might impair reproduction. It has been reported that leptin at a physiological level promoted oocyte maturation by activating the STAT signal transduction pathway (28). The present study demonstrates a high leptin level in FF and impaired STAT signal pathway in GCs. These results suggest that leptin may have a potential role in modulating preovulatory follicular development, oocyte fertilization ability, and subsequent embryo implantation potential.

Leptin acts through binding with its receptors, which are classified into short and long isoforms. The long isoform is functional because it has an intracellular domain containing motifs required for interaction with other proteins and subsequent signaling (29, 30). The JAK/STAT pathway is the major pathway of Ob-R signal transduction and is regulated by SOCS3, which inhibits tyrosine phosphorylation of Ob-R (31, 32). p-STAT3 is the transcriptional factor of the JAK/STAT pathway and is crucial to the effect of leptin (29, 30). Intravenous administration of leptin increased STAT3 phosphorylation in adipose tissue, liver, muscle, and hypothalamus of rodents (33, 34). In rats, the impaired STAT3 phosphorylation is related to the diminished response to leptin (10, 35).

In the current investigation, expression of mRNA for the long and short receptors of leptin in GCs was comparable in PCOS women and controls. Interestingly, we observed a decrease in phosphorylated STAT3 and no change in SOCS3 in luteinized GCs from women with PCOS as compared with those from control, indicating the existence of a deficiency of postreceptor signal transduction in GCs from PCOS women. An altered postreceptor signaling pathway is suggested to be the important pathophysiology of PCOS. To the best of our knowledge, this is the first investigation revealing the change of Ob-R signaling in PCOS.

Poor IVF prognosis as indicated by impaired embryo quality, FR, and PR per IVF cycle has been associated with an enhanced leptin level (24, 25, 26). In this study, we verified the association of increased leptin level with poor IVF prognosis in PCOS patients and, more importantly, revealed for the first time that down-regulation of p-STAT3, a transcriptional factor of leptin signal transduction, in GCs was related to failure of IVF in PCOS patients. Our results provide additional evidence to support that alterations in the level of leptin and its interaction with the Ob-R and/or subsequent signal transduction may be involved in the fecundity in PCOS. Furthermore, enhanced serum and FF levels of leptin may serve as markers of poor prognosis in PCOS women undergoing IVF.

In the present study, no alteration was detected in the expression of SOCS3 in luteinized GCs of PCOS patients compared with controls. There are eight members in the SOCS family, including SOCS1–7 and cytokine-inducible Src homology 2 protein. Lavens et al. showed that cytokine-inducible Src homology 2 protein and SOCS2 also interact with the Ob-Rs (36). The possibility that other members of SOCS rather than SOCS3 may be involved in the negative regulation of the JAK/STAT signaling pathway in GCs of PCOS women warrants more investigation.

Because literature regarding Ob-R signaling of GCs in PCOS is limited, more investigations are needed to reveal the profile of the signal pathway of GCs and other tissues in PCOS and to explore the additional mechanisms by which leptin-associated abnormalities induce fecundity in PCOS. Nonetheless, our present findings may provide a new strategy to improve reproductive ability of PCOS women by interfering with leptin signaling.

Although the PCOS patients in the present study showed a higher serum T level than that in controls, there was no statistical significance between PCOS and control groups. This condition may limit our results to be applied to the PCOS with classic hyperandrogenic phenotypes. More study is needed to clarify whether the present results also exist in the PCOS with significant hyperandrogenic phenotypes.

In conclusion, it was revealed in PCOS patients that increased leptin levels in serum and FF were associated with down-regulated phosphorylation of STAT3 but with no change of Ob-R expression in GCs. These results indicate that alterations in leptin and its intracellular signaling may be important to the pathophysiology and/or pathogenesis of PCOS. Our data further showed that increased serum and FF levels of leptin and decreased expression of p-STAT3 in GCs were associated with poor outcome of IVF, suggesting that abnormalities of leptin and its signaling pathway may be involved in the causes of PCOS-associated infertility.


   Footnotes
 
This work was supported by National Key Research Program of China (2006CB944006) and Basic Research Program of China (973: 2006CB504004) and National Key Technology R&D Program of China (2007BAI04B04).

Disclosure Statement: The authors have nothing to disclose.

First Published Online September 25, 2007

1 M.-G.L. and G.-L.D. contributed equally to the study. Back

Abbreviations: BMI, Body mass index; COH, controlled ovarian hyperstimulation; E2, estradiol; FF, follicular fluid; FR, fertility rate; GC, granulosa cell; IR, implantation rate; IVF, in vitro fertilization; JAK, Janus kinase; Ob-R, leptin receptor; PCOS, polycystic ovarian syndrome; PR, pregnancy rate; p-STAT3, phosphorylated STAT3; SOCS3, suppressor of cytokine signal 3; STAT, signal transducer and activator of transcription; T, testosterone.

Received May 1, 2007.

Accepted September 13, 2007.


   References
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
 References
 

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