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Increased Luteinizing Hormone Secretion in Women with Polycystic Ovary Syndrome Is Unaltered by Prolonged Insulin Infusion

Department of Reproductive Medicine, University of California, San Diego, La Jolla, California 92093

Address all correspondence and requests for reprints to: R. Jeffrey Chang, M.D., Department of Reproductive Medicine, University of California, San Diego, School of Medicine, 9500 Gilman Drive, La Jolla, California 92093-0633. E-mail: rjchang{at}ucsd.edu.

	Abstract

Top Abstract Introduction Subjects and Methods Results Discussion References

 
In PCOS women with insulin resistance, hyperinsulinemia may contribute to inappropriate gonadotropin secretion. To determine whether insulin influences gonadotropin release in PCOS, pulsatile LH secretion and gonadotropin responses to GnRH were evaluated before (phase 1) and during (phase 2) insulin infusion. In phase 1, 11 PCOS and 9 normal women on separate days underwent 1) frequent blood sampling (q 10 min) for 12 h and 2) gonadotropin stimulation by successive doses of GnRH, 2 µg, 10 µg, and 20 µg, administered iv at 4 h intervals over a continuous 12 h. In phase 2, studies were repeated 2 h after initiation of a 12-h hyperinsulinemic-euglycemic clamp (80 mU/m²·min). Administration of insulin to both groups failed to alter mean serum gonadotropin concentrations, LH pulse frequency, or LH pulse amplitude. Moreover, gonadotropin responses to GnRH were unchanged by insulin infusion. In PCOS and normal women, a significant reduction of serum androstenedione was associated with insulin administration, whereas no differences were noted for the remaining androgens and estrogens measured.

These findings demonstrated that in PCOS women, LH secretion and gonadotropin responses to GnRH were not influenced by insulin administration. Insulin infusion had little effect on steroid hormone production with the possible exception of androstenedione. These results suggest that inappropriate LH secretion in PCOS is not a direct consequence of insulin resistance and compensatory hyperinsulinemia.

	Introduction

Top Abstract Introduction Subjects and Methods Results Discussion References

 
IT HAS BEEN well recognized that women with polycystic ovary syndrome (PCOS) exhibit inappropriate LH secretion characterized by elevated serum concentrations and increases in pulse frequency and amplitude (1, 2). This abnormal pattern of gonadotropin release has been attributed largely to increased activity of the hypothalamic GnRH pulse generator as well as to the feedback effects of ovarian steroid hormones. Insulin has also been implicated in the regulation of LH secretion as evidenced by both in vitro and in vivo studies (3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18). It has been previously demonstrated in vitro that rat pituitary cells preincubated with insulin exhibit increased LH responsiveness after administration of GnRH in a dose-dependent manner compared with those of untreated cells, which suggests a facilitative role for insulin on GnRH stimulated LH release (3, 4, 5). However, efforts to determine an effect of insulin infusion in PCOS women have not documented consistent alterations in LH secretion or LH release after GnRH stimulation (6, 7). Reduction of serum LH levels in PCOS has been associated with lowered circulating insulin concentrations induced either pharmacologically or by dietary restriction (8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18). In these studies, because the rate of ovulation improved during treatment, it was unclear whether decreased serum LH was a direct result of lowered circulating insulin levels or secondary to the feedback effect of increased ovarian estrogen production. In contrast to the above findings, several reports have been unable to show an effect of decreased serum insulin levels on serum LH or LH responses to GnRH after drug treatment or significant loss of body weight in women with PCOS (18, 19, 20, 21, 22, 23, 24, 25, 26). Interestingly, the failure to document a decline in LH levels despite improved insulin sensitivity was independent of whether ovulatory activity has resumed in these studies. To address the issue of whether hyperinsulinemia influences gonadotropin secretion in PCOS, serum LH and FSH responses to GnRH and pusatile LH secretion were evaluated before and during insulin infusion using the hyperinsulinemic-euglycemic clamp technique.

	Subjects and Methods

Top Abstract Introduction Subjects and Methods Results Discussion References

 
Subjects

Eleven women with PCOS and nine normal women with regular menstrual cycles were recruited for study. All PCOS subjects exhibited excessive facial hair growth and had irregular menstrual bleeding ranging from three to six bleeding episodes per year. Serum androgen levels were elevated in each PCOS subject (Table 1). In addition, all women had ultrasound evidence of bilateral polycystic ovaries (27). Late onset congenital adrenal hyperplasia was excluded by a serum 17-hydroxyprogesterone level (17-OHP₄) of less than 3 ng/ml (<9.1 nmol/liter). The normal subjects were monitored by menstrual calendar for 3 months and by urinary LH testing for 1 month before study to establish the regularity of their cycles. None of the subjects had received any hormone medication for at least 3 months before study. In PCOS women, the mean (±SE) age was 28.6 ± 0.6 yr and not significantly greater than that of the normal control group, 26.3 ± 0.8 yr. The mean body mass index (BMI) was significantly greater in PCOS subjects compared with that of normal women (35.3 ± 0.8 vs. 27.4 ± 0.7, P < 0.02), whereas the difference in mean waist-to-hip ratio (0.88 ± 0.03 vs. 0.80 ± 0.06) failed to achieve statistical significance. Circulating TSH and PRL levels were normal and not significantly different between groups. The study had been approved by the Institutional Review Board at the University of California, San Diego, and written informed consent was obtained from each participant before study.

Each subject was admitted to the General Clinical Research Center at the University of California, San Diego, for 2 d of study. The PCOS subjects were tested at random, whereas normal control subjects were studied during the mid-follicular phase defined as d 6–8. On d 1 of study an iv cannula was inserted and after 30 min baseline blood samples were drawn. At 0800, blood samples were obtained at 10-min intervals for 12 h. On d 2 of study, after an overnight rest, beginning at 0800, three successive doses of GnRH (2, 10, and 20 µg) were administered iv at 4-h intervals over a continuous 12-h period. The sequence of GnRH dosing was intentional and not randomized to minimize potential residual increases in serum LH before administration of the next dose of GnRH. The GnRH (Factrel) was kindly provided by Wyeth Pharmaceuticals. None of the PCOS subjects had experienced recent ovulation as evidenced by changes in their menstrual patterns or scant bleeding episodes unaccompanied by premenstrual molimina. In addition, at the time of study each PCOS woman had serum progesterone (P₄) levels of less than 1 ng/ml (<3.0 nmol/liter) at the baseline sample. Frequent blood samples were obtained before and for up to 120 min after each dose of GnRH. Subsequently, each subject was readmitted to the General Clinical Research Center and the 2-d study protocol was repeated during a euglycemic hyperinsulinemic clamp. In PCOS and normal subjects, the repeat protocol was administered at a minimum interval of 1 month.

Hyperinsulinemic-euglycemic clamp

Studies were performed in the morning after a 12-h overnight fast. At 2100 h, an 18-gauge iv catheter was inserted into an antecubital vein and an infusion of normal saline was started. At 0700 h, another iv catheter was inserted in a retrograde fashion in a hand vein, with the hand placed in a hand warmer for sampling of arterialized blood. An iv infusion of insulin (Humulin; Eli Lilly, Indianapolis, IN) diluted in 0.15 mol/liter saline containing 1% wt/vol human albumin was then begun at a rate of 80 mU/m²·min, which was started 2 h before the first GnRH dose and continued for 12 h. Potassium and phosphate were given iv to compensate for the intracellular movement of these ions and to maintain normal blood levels. A variable infusion of 20% glucose was delivered to maintain a plasma glucose concentration of 4.72 mol/liter (85 ng/dl). Blood samples were obtained every 5 min for measurement of plasma glucose with a glucose analyzer (YSI 2700 analyzer; Yellow Springs Instrument Co., Yellow Springs, OH). During the last 30 min of insulin infusion, blood samples were obtained at 10-min intervals for determination of plasma glucose concentrations.

The glucose infusion rate in each patient was calculated as the amount of glucose (milligram) infused per kilogram body weight during the last 30 min of the clamp study. The mean steady-state insulin level achieved at the end of the clamp is known to suppress hepatic glucose output and, therefore, the glucose infusion rate was equivalent to the glucose disposal rate.

Assays

Serum LH and FSH concentrations were measured by RIA with intra- and interassay coefficients of variation (CVs), respectively, of 5.4% and 8.0% for LH and 3.0% and 4.6% for FSH (Diagnostic Products Corp., Los Angeles, CA). Serum concentrations of estrone (E₁), estradiol (E₂), androstenedione (A₄), and testosterone (T) were measured by well-established RIA with intraassay CVs less than 7%. Serum P₄, 17-OHP₄, and dehydroepiandrosterone sulfate (DHEA-S) were measured by RIA with intraassay CVs less than 7% (Diagnostic Systems Laboratories, Webster, TX). Serum insulin levels were measured by a double antibody RIA with an assay sensitivity of 2 µU/ml and intra- and interassay CVs of 7% and 9%, respectively. Plasma glucose levels were determined by the glucose oxidase method (Yellow Springs Instrument Co.) with an intraassay CV less than 2% and an intraassay CV of 3%.

Pulse analysis

LH pulse activity was analyzed using the Cluster pulse detection algorithm (Veldhuis ‘86). A cluster configuration of 2 x 2 and t statistics of 2.45 x 2.45 were chosen to minimize false positive and false negative errors. Dose-dependent intrasample variance was assessed by employing a second-degree polynomial regression of SD as function of hormone concentration. Pulse number per 12 h and mean pulse amplitude (difference in serum concentration between the preceding nadir and the pulse peak) were determined for each subject.

Statistics

Depending on the analysis, LH responses were measured as the difference between the maximal and baseline levels (maximal increment), and the maximal percent change from baseline. A log-transformation was applied when appropriate, and square root transformation was used for percent change in LH response. To determine interaction between group and dose as well as main effects, two-group repeated measures ANOVA and analysis of covariance were used. Post hoc testing was done with a Bonferroni correction. Comparisons of mean baseline values between PCOS and normal women were performed using independent Student’s t tests (SPSS 11.0 software, SPSS Inc., Chicago, IL). Correlations among variables were analyzed using the Pearson correlation coefficient method.

	Results

Top Abstract Introduction Subjects and Methods Results Discussion References

 
Baseline studies

Baseline hormone values are shown in Table 1. In PCOS, mean (±SE) circulating levels of LH, T, A, E₁, E₂, 17-OHP₄, and fasting insulin were significantly greater than those of normal controls. Serum FSH, DHEA-S, P₄, and glucose levels were similar in both groups.

Hyperinsulinemic-euglycemic clamp

In the PCOS group, mean steady-state plasma insulin levels, 235 ± 25.5 µU/ml, resulting from the hyperinsulinemic clamp were significantly (P = 0.02) higher than those achieved in normal women, 173 ± 19.3 µU/ml, despite equivalent infusion rates and similar serum glucose concentrations (Fig. 1). Steady-state serum glucose levels were maintained between 85 and 90 mg/dl in both groups. The mean glucose disposal rate in PCOS subjects was significantly less (P < 0.02) than that found in normal women and indicative of insulin resistance.

View larger version (28K): [in this window] [in a new window]   FIG. 1. Mean (±SE) serum insulin levels during the hyperinsulinemic-euglycemic clamp (80 mU/m2·min) in normal and PCOS women. The mean (±SE) glucose disposal rate (GDR) for each group is also shown. In PCOS women, the mean composite serum insulin level and GDR were significantly (P < 0.05) higher and lower, respectively, than those found for normal women.

The composite mean 12-h serum LH concentration in PCOS was significantly higher than that of normal women as expected (Table 2). Assessment of pulsatile LH secretion in PCOS women revealed that the mean pulse frequency value, pulses/12 h, was significantly greater than that found in the normal women. The corresponding mean pulse amplitude in PCOS women was higher, but not statistically different from that of the normal group.

Effect of insulin infusion on gonadotropin responses to GnRH

In the absence of insulin administration, PCOS subjects exhibited significantly higher (P < 0.02) mean maximal serum LH responses to multidose GnRH compared with those of normal women (Fig. 2), which is consistent with previous results from our group (1). In PCOS women, there were subtle increases in mean baseline LH levels before each successive dose of GnRH, which likely represented carryover effect as a result of prior GnRH stimulation. These increases were accompanied by corresponding increments of LH after GnRH, in a dose-dependent manner. In normal women a similar pattern of GnRH-stimulated LH release was found. Notably, in PCOS and normal women, the mean maximal rise of LH was related to the respective baseline LH concentration as the percent incremental change with each dose of GnRH was equivalent within and between groups.

View larger version (21K): [in this window] [in a new window]   FIG. 2. Time-course of mean (±SE) serum LH concentrations after iv administration of three successive doses of GnRH given at 4-h intervals over 12 h to normal and PCOS women. In PCOS, significant increases in LH increment (P < 0.02) at each dose as well as the integrated (area under the curve) LH response (P < 0.01) over the entire course of study were detected compared with those of normal women.

At the time of insulin administration in PCOS women, the mean preinfusion concentration of serum LH was 4.0 ± 1.2 mIU/ml. An effect of insulin was not apparent 2 h after initiation of the clamp, as the mean level of circulating LH was 4.7 ± 0.9 mIU/ml (Fig. 3). In response to multidose GnRH, significant increases in serum LH responses in PCOS women were noted, the pattern of which was essentially the same as that demonstrated without insulin infusion. The progressive mean maximal rise of LH in response to 2-µg and 10-µg doses of GnRH corresponded to their respective baseline levels, in contrast to the response to 20 µg, which was of lesser absolute magnitude and, therefore, lower relative to baseline. In PCOS women, insulin infusion was not associated with differences in relative LH responsiveness to GnRH as the percent incremental change at each dose was equivalent to that found without insulin administration (Fig. 4). The similarity of responsiveness in PCOS women before and during insulin infusion was reflective of the significant positive correlation between maximal GnRH-stimulated LH levels and preinjection baseline serum LH as depicted in Fig. 5. A lack of insulin effect on LH responsiveness to GnRH was also evident in normal women. Serum LH levels before, and 2 h after beginning the infusion of insulin, did not vary and baseline preinjection LH levels and mean maximal LH responses to multidose GnRH were comparable in the presence and absence of insulin infusion (Fig. 3). In PCOS and normal women, baseline serum FSH and GnRH-stimulated FSH release were not altered by insulin administration, as responses before and during the hyperinsulinemic clamp were similar.

View larger version (22K): [in this window] [in a new window]   FIG. 3. Time-course of mean (±SE) serum LH concentrations after iv administration of three successive doses of GnRH given at 4-h intervals during the hyperinsulinemic-euglycemic clamp (80 mU/m2·min) in PCOS and normal women. In PCOS, significant increases in LH increment (P < 0.02) were detected compared with those of normal women. Note that the preinfusion mean concentration of serum LH was similar to the initial preinjection mean baseline level of LH in both PCOS and normal women.

View larger version (23K): [in this window] [in a new window]   FIG. 4. Mean (±SE) maximal percent LH change after administration of GnRH, at the indicated doses, in the absence and presence of insulin infusion in PCOS and normal women.

View larger version (26K): [in this window] [in a new window]   FIG. 5. Relationship of maximal serum LH levels after each dose of GnRH to respective preinjection baseline LH levels in PCOS women before (r = 0.84, P < 0.01) and during (r = 0.70, P < 0.01) insulin administration. The correlation between maximal response and baseline values were not altered by insulin infusion.

Effect of insulin infusion on steroid hormone levels

Determination of mean circulating levels of serum androgens before and at the end (pooled samples during the last hour) of the hyperinsulinemic clamp, conducted during frequent sampling (without GnRH stimulation), showed that in PCOS, the mean baseline serum androstenedione level, was decreased significantly (Fig. 6). The time-course response during insulin infusion revealed that serum A₄ declined significantly within 2 h of commencing insulin infusion and remained suppressed throughout the interval of insulin administration (Fig. 6). Normal women also sustained a significant reduction of mean serum A₄ after insulin infusion. By comparison, in both PCOS and normal women, serum testosterone levels before and at the end of the insulin clamp were unaltered (Table 3). In addition, circulating levels of E₁, E₂, 17-OHP₄, and DHEA-S in both groups before and at the end of insulin infusion failed to demonstrate any significant differences.

View larger version (19K): [in this window] [in a new window]   FIG. 6. A, Mean (±SE) serum A levels measured before and at the end (pooled samples during the last hour) of the hyperinsulinemic-euglycemic clamp during frequent sampling in normal and PCOS women. Serum A levels were significantly (P < 0.05) lower at the end of insulin infusion in both groups. B, Mean (±SE) serum A levels measured before insulin infusion and at baseline before each injection of GnRH during insulin administration, represented by the solid bar, in normal and PCOS women. *, P < 0.03 for PCOS and P < 0.05 for normal.

	Discussion

Top Abstract Introduction Subjects and Methods Results Discussion References

These findings clarify the results of previous preliminary studies, which showed that GnRH-stimulated LH responses in both normal and PCOS women were significantly decreased during a 4-h hyperinsulinemic-euglycemic clamp compared with those found with saline infusion (28). In that study, lowered LH responsiveness during insulin infusion was associated with reduced preinfusion basal levels of circulating LH, which likely accounted for the apparent insulin-related LH suppression. Our results are consistent with previous studies, which have not been able to establish an effect of insulin on LH or FSH release. In normal women undergoing long-term insulin administration by a 16-h hyperinsulinemic-euglycemic clamp, mean serum LH levels, measured every hour, remained unchanged during the entire course of infusion (6). In women with PCOS, an attempt to identify whether insulin infusion influenced gonadotropin secretion failed to demonstrate conclusive results (7). During 6-h insulin infusions randomized to either one of a consecutive 2 d in PCOS and normal women, consistent alterations in mean serum LH, LH pulse frequency or pulse amplitude, and LH release after GnRH could not be documented. Sequence effects of study d 1 vs. study d 2 were readily apparent, which may have obscured any influence of insulin on gonadotropin release. These sequence effects were attributed to spontaneous changes in basal gonadotropin secretion.

The inability of insulin to induce alterations in LH secretion in PCOS women is relevant to studies that have shown an inverse correlation between 24-h insulin levels and both serum LH and LH pulse amplitude (29). In that study, it was also demonstrated that hyperinsulinemia was positively correlated to BMI, whereas insulin sensitivity had an inverse linear relationship to BMI. The parallel relationship between hyperinsulinemia and BMI precluded determination of a possible independent inhibitory effect of insulin on LH secretion. Considering the data of the current study, it seems as if obesity would be more likely to exert a restrictive influence on the level of circulating LH compared with an effect related to hyperinsulinemia.

Our in vivo findings are in contrast to previous results obtained from in vitro animal studies, which demonstrated that insulin enhanced GnRH-mediated LH release from rat pituitary cells by increasing gonadotrope sensitivity to GnRH in a dose-dependent manner (3, 4, 5). The concentration of insulin used to pretreat cells was physiologically relevant compared with that achieved during the hyperinsulinemic-euglycemic clamp employed in the current in vivo study. Similar studies conducted in the same rodent model have shown that high physiological doses of insulin enhanced LH responses to GnRH, whereas progressive increases in concentration inhibited LH release in a bimodal manner (30). In our study, the mean steady-state level of insulin achieved during infusion was about 275 µU/ml, which is greater than levels generally encountered in PCOS. Whether lower levels of hyperinsulinemia may have altered gonadotropin secretion or responsiveness to GnRH is unknown. Alternatively, the in vivo environment of our study may have precluded expression of an insulin effect, as insulin-mediated increases in LH responsiveness, in vitro, have not been observed using serum supplemented media (3).

We observed a significant difference in steady-state insulin levels between PCOS and normal women despite similar rates of insulin infusion and equivalent glucose concentrations. The cause for this discrepancy may have been due to decreased clearance of insulin in the PCOS group in whom the mean BMI was significantly higher. A similar disparity of circulating insulin levels during insulin infusion has been observed previously in obese, weight-matched PCOS and normal women undergoing hyperinsulinemic-euglycemic clamp studies (7). In both studies, assessment of insulin metabolic clearance was not performed.

The mean serum A₄ level was significantly decreased during insulin infusion in both PCOS and normal women whereas serum 17-OH P₄, DHEA-S, and T levels were unchanged. Previously, it has been demonstrated in normal men and women that short-term insulin infusions at physiological doses of less than 100 µU/ml were associated with an acute rise of circulating A₄ levels (31). At insulin levels beyond 100 µU/ml, the serum A₄ increment was not significant from baseline values. Similar results were found in women with PCOS who were randomly studied on the first of two consecutive study days (7). In those PCOS subjects studied on the second day of study, insulin administration failed to induce a significant rise in circulating A₄ levels. The lack of serum A₄ response on d 2 may have represented a carry over effect of the first day of study or, possibly, attributed to the relatively short length of infusion of 6 h. The latter consideration was not corroborated by our findings, as the length of insulin administration was 10 h. In addition, an acute effect of insulin was indicated by the significant decline of serum A₄ within 2 h of infusion, as indicated by the time-course pattern of response. That the serum A₄ response may have reflected alteration in clearance is unlikely because corresponding changes in serum E₁ were not observed during insulin infusion. Serum T levels did not vary throughout 10 h of insulin administration, which is consistent with some, but not all studies (6, 7, 31). Dunaif (7) found significant reductions in serum T during insulin infusion, which was unlikely due to increased 17-oxido-reductase, as suggested by concomitant increases in serum estradiol. Studies to determine differences in the metabolic clearance of testosterone were not performed. We were also unable to detect alterations in 17-OHP₄ and DHEA-S. However, Nestler et al. (6) demonstrated a significant decline in serum DHEA-S levels in normal women and a woman with hyperandrogenism at the end of a 16-h hyperinsulinemic clamp. The length of insulin administration or resultant steady-state concentration during the present experiments may have been insufficient to expose an effect of insulin on DHEA-S. Summarily, our findings strongly suggest that insulin administration by the hyperinsulinemic-euglycemic clamp method exerts little effect on basal steroid hormone levels in women with PCOS with the possible exception of serum A₄. The significant decrease of circulating A₄ must be considered in light of inconsistent findings from other studies, which have demonstrated either an increase or no change as a result of insulin infusion. Further investigation of insulin action on ovarian steroidogenesis is necessary to fully elucidate the role of insulin.

In summary, our findings have clearly shown that in PCOS women, LH secretion and gonadotropin responses to GnRH were not influenced by insulin administration. Moreover, insulin infusion appeared to have little effect on ovarian steroid or adrenal androgen production with the possible exception of androstenedione. These results suggest that inappropriate LH secretion in PCOS is not a consequence of insulin resistance and compensatory hyperinsulinemia. Alternatively, additional studies are necessary in PCOS to determine whether gonadotropin secretion is susceptible to hyperinsulinemia after reversal of insulin resistance.

	Acknowledgments

 
We express our most sincere gratitude to Muttukrishna Sathanandan, Sam Yen, and the late Joe Mortola, whose preliminary data formed the basis for this study. We are also grateful to Mr. Jeff Wong for his technical expertise, Geri Schmotzer, R.N., for her research assistance, and the nurses and staff of the General Clinical Research Center for their dedicated care. We also thank Sandra Stanton for assistance in the preparation of the manuscript.

	Footnotes

 
This research was supported by National Institute of Child Health and Human Development/NIH through cooperative agreement (U54 HD 12303-20) as part of the Specialized Cooperative Centers Program in Reproduction Research and in part by NIH Grant MO1 RR00827.

Abbreviations: A₄, Androstenedione; BMI, body mass index; CV, coefficient of variation; DHEA-S, dehydroepiandrosterone sulfate; E₁, estrone; E₂, estradiol; 17-OHP₄, 17-hydroxyprogesterone; P4, progesterone; PCOS, polycystic ovary syndrome; T, testosterone.

Received May 12, 2003.

Accepted August 11, 2003.

	References

Top Abstract Introduction Subjects and Methods Results Discussion References

 

1. Rebar R, Judd HL, Yen SSC, Rakoff J, Vandenberg G, Naftolin F 1976 Characterization of the inappropriate gonadotropin secretion in polycystic ovary syndrome. J Clin Invest 57:1320–1329
2. Yen SSC 1980 The polycystic ovary syndrome. Clin Endocrinol 12:177–207[Medline]
3. Adashi EY, Hsueh AJW, Yen SSC 1981 Insulin enhancement of luteinizing hormone and follicle-stimulating hormone release by cultured pituitary cells. Endocrinology 108:1441–1449[Abstract/Free Full Text]
4. Soldani R, Cagnacci A, Yen SSC 1994 Insulin, insulin-like growth factor I (IGF-I) and IGF-II enhance basal and gonadotrophin-releasing hormone-stimulated luteinizing hormone release from rat anterior pituitary cells in vitro. Eur J Endocrinol 131:641–645[Abstract/Free Full Text]
5. Soldani R, Cagnacci A, Paoletti AM, Yen SS, Melis GB 1995 Modulation of anterior pituitary luteinizing hormone response to gonadotropin-releasing hormone by insulin-like growth factor I in vitro. Fertil Steril 64:634–637[Medline]
6. Nestler JE, Clore JN, Strauss 3rd JF, Blackard WG 1987 The effects of hyperinsulinemia on serum testosterone, progesterone, dehydroepiandrosterone sulfate, and cortisol levels in normal women and in a woman with hyperandrogenism, insulin resistance, and acanthosis nigricans. J Clin Endocrinol Metab 64:180–184[Abstract/Free Full Text]
7. Dunaif A, Graf M 1989 Insulin administration alters gonadal steroid metabolism independent of changes in gonadotropin secretion in insulin-resistant women with the polycystic ovary syndrome. J Clin Invest 83:23–29
8. Velazquez EM, Mendoza S, Hamer T, Sosa F, Glueck CJ 1994 Metformin therapy in polycystic ovary syndrome reduces hyperinsulinemia, insulin resistance, hyperandrogenemia, and systolic blood pressure, while facilitating normal menses and pregnancy. Metabolism 43:647–654[CrossRef][Medline]
9. Nestler JE, Jakubowicz D 1996 Decreases in ovarian cytochrome P450c17 activity and serum free testosterone after reduction of insulin secretion in polycystic ovary syndrome. N Engl J Med 335:617–622[Abstract/Free Full Text]
10. Pirwany IR, Yates RW, Cameron IT, Fleming R 1999 Effects of the insulin sensitizing drug metformin on ovarian function, follicular growth and ovulation rate in obese women with oligomenorrhoea. Hum Reprod 14:2963–298[Abstract/Free Full Text]
11. Hasegawa I, Murakawa H, Suzuki M, Yamamoto Y, Kurabayashi T, Tanaka K 1999 Effect of troglitazone on endocrine and ovulatory performance in women with insulin resistance-related polycystic ovary syndrome. Fertil Steril 71:323–327[CrossRef][Medline]
12. Velazquez E, Acosta A, Mendoza SG 1997 Menstrual cyclicity after metformin therapy in polycystic ovary syndrome. Obstet Gynecol 90:392–395[CrossRef][Medline]
13. Nestler JE, Jakubowicz DJ 1997 Lean women with polycystic ovary syndrome respond to insulin reduction with decreases in ovarian P450c17 activity and serum androgens. J Clin Endocrinol Metab 82:4075–4079[Abstract/Free Full Text]
14. Dunaif A, Scott D, Finegood D, Quintana B, Whitcomb R 1996 The insulin-sensitizing agent troglitazone improves metabolic and reproductive abnormalities in the polycystic ovary syndrome. J Clin Endocrinol Metab 81:3299–3306[Abstract]
15. Pasquali R, Antenucci D, Casimirri F, Venturoli S, Paradisi R, Fabbri R, Balestra V, Melchionda N, Barbara L 1989 Clinical and hormonal characteristics of obese amenorrheic hyperandrogenic women before and after weight loss. J Clin Endocrinol Metab 68:173–179[Abstract/Free Full Text]
16. Huber-Buchholz MM, Carey DGP, Norman RJ 1999 Restoration of reproductive potential by lifestyle modification in obese polycystic ovary syndrome: role of insulin sensitivity and luteinizing hormone. J Clin Endocrinol Metab 84:1470–1474[Abstract/Free Full Text]
17. Butzow TL, Lehtovirta M, Siegberg R, Hovatta O, Koistinen R, Seppala M, Apter D 2000 The decrease in luteinizing hormone secretion in response to weight reduction is inversely related to the severity of insulin resistance in overweight women. J Clin Endocrinol Metab 85:3271–3275[Abstract/Free Full Text]
18. Pasquali R, Gambineri A, Biscotti D, Vicennati V, Gagliardi L, Colitta D, Fiorini S, Cognigni GE, Filicori M, Morselli-Labate AM 2000 The effect of long-term treatment with Metformin added to hypocaloric diet on body composition, fat distribution, and androgen and insulin levels in abdominally obese women with and without the polycystic ovary syndrome. J Clin Endocrinol Metab 85:2767–2774[Abstract/Free Full Text]
19. Nestler JE, Barlascini CO, Matt DW, Steingold KA, Plymate SR, Clore JN, Blackard WG 1989 Suppression of serum insulin by diazoxide reduces serum testosterone levels in obese women with polycystic ovary syndrome. J Clin Endocrinol Metab 68:1027–1032[Abstract/Free Full Text]
20. Nestler JE, Singh R, Matt DW, Clore JN, Blackard WG 1990 Suppression of serum insulin level by diazoxide does not alter serum testosterone or sex hormone-binding globulin levels in healthy, nonobese women. Am J Obstet Gynecol 163:1243–1246[Medline]
21. Kiddy DS, Hamilton-Fairley D, Bush A, Kiddy DS, Hamilton-Fairley D, Bush A 1992 Improvement in endocrine and ovarian function during dietary treatment of obese women with polycystic ovary syndrome. Clin Endocrinol 36:105–111[Medline]
22. Holte J, Bergh T, Berne C, Wide L, Lithell H 1995 Restored insulin sensitivity but persistently increased early insulin secretion after weight loss in obese women with polycystic ovary syndrome. J Clin Endocrinol Metab 80:2586–2593[Abstract]
23. Ehrmann DA, Schneider DJ, Sobel BE, Cavaghan MK, Imperial J, Rosenfield RL, Polonsky KS 1997 Troglitazone improves defects in insulin action, insulin secretion, ovarian steroidogenesis, and fibrinolysis in women with polycystic ovary syndrome. J Clin Endocrinol Metab 82:2108–2116[Abstract/Free Full Text]
24. Moghetti P, Castello R, Negri C, Tosi F, Perrone F, Caputo M, Zanolin E, Muggeo M 2000 Metformin effects on clinical features, endocrine and metabolic profiles, and insulin sensitivity in polycystic ovary syndrome: a randomized, double-blind, placebo-controlled 6 month trial, followed by open, long-term clinical evaluation. J Clin Endocrinol Metab 85:139–146[Abstract/Free Full Text]
25. Azziz R, Ehrmann D, Legro RS, Whitcomb RW, Hanley R, Fereshetian AG, O’Keefe M, Ghazzi MN; PCOS/Troglitazone Study Group 2001 Troglitazone improves ovulation and hirsutism in the polycystic ovary syndrome: a multicenter, double blind, placebo-controlled trial. J Clin Endocrinol Metab 86:1626–1632[Abstract/Free Full Text]
26. Nestler JE, Jakubowicz DJ, Reamer P, Gunn RD, Allan G 1999 Ovulatory and metabolic effects of D-Chiro-inositol in the polycystic ovary syndrome. N Engl J Med 340:1314–1320[Abstract/Free Full Text]
27. Adams J, Polson DW, Franks S 1986 Prevalence of polycystic ovaries in women with anovulation and idiopathic hirsutism. Br Med J (Clin Res Ed) 293:355–359
28. Mortola JF, Sathanandan M, Kolterman O, Yen SCC Insulin modulates gonadotropin release and gonadotrope sensitivity to GnRH in polycystic ovary syndrome and normal women. Proc Annual Meeting of the Society for Gynecological Investigation, San Diego, CA, 1989 (Abstract 420)
29. Arroyo A, Laughlin GA, Morales AJ, Yen SS 1997 Inappropriate gonadotropin secretion in polycystic ovary syndrome: influence of adiposity. J Clin Endocrinol Metab 82:3728–3733[Abstract/Free Full Text]
30. Xia YX, Weiss JM, Polack S, Diedrich K, Ortmann O 2001 Interactions of insulin-like growth factor-I, insulin and estradiol with GnRH-stimulated luteinizing hormone release from female rat gonadotrophs. Eur J Endocrinol 144:73–79[Abstract]
31. Stuart CA, Prince MJ, Peters EJ, Meyer 3rd WJ 1987 Hyperinsulinemia and hyperandrogenemia: in vivo androgen response to insulin infusion. Obstet Gynecol 69:921–925[Medline]

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