This Article Abstract Full Text (PDF) Submit a related Letter to the Editor Purchase Article View Shopping Cart Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Copyright Permission Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Mantzoros, C. S. Articles by Flier, J. S. Search for Related Content PubMed PubMed Citation Articles by Mantzoros, C. S. Articles by Flier, J. S.

Leptin Concentrations in the Polycystic Ovary Syndrome¹

Charles A. Dana Research Institute and the Harvard-Thorndike Laboratory of the Beth Israel Deaconess Medical Center, Department of Internal Medicine, Division of Endocrinology and Metabolism, Beth Israel Deaconess Medical Center, Harvard Medical School (C.S.M., J.S.F.), Boston, Massachusetts 02215; and the Department of Medicine, Section of Diabetes and Metabolism, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033

Address all correspondence and requests for reprints to: Jeffrey S. Flier, M.D., Division of Endocrinology, RN 325, Beth Israel Deaconess Medical Center, 99 Brookline Avenue, Boston, Massachusetts 02215. E-mail: jflier{at}bih.harvard.edu

	Abstract

Top Abstract Introduction Materials and Methods Results Discussion References

 
The polycystic ovary syndrome (PCOS) is characterized by menstrual disturbances, chronic anovulation and hyperandrogenism and is associated with insulin resistance and hyperinsulinemia. Leptin, the product of the ob gene, is an adipocyte-secreted molecule that signals the magnitude of energy stores to the brain and has been recently shown to have important effects on the reproductive axis of rodents. To assess the potential contribution of leptin to the pathogenesis of PCOS, we measured leptin levels in 24 obese women with PCOS and 12 weight- and age-matched controls and determined whether alterations in hyperinsulinemia produced by administration of the insulin-sensitizing agent troglitazone had an effect on serum leptin levels. Leptin concentrations at baseline were not different in women with PCOS (38.1 ± 2.15 ng/mL) and controls (33.12 ± 2.39 ng/mL). Moreover, leptin concentrations remained unchanged after treatment with troglitazone (38.1 ± 2.15 vs. 39.21 ± 2.65 ng/mL). Baseline leptin correlated strongly with body mass index in both controls (r = 0.59; P < 0.05) and women with PCOS (r = 0.70; P = 0.0004). Leptin levels were not associated with baseline insulin, testosterone, non-sex hormone-binding globulin (SHBG)-bound testosterone, dehydroepiandrosterone sulfate, estradiol, or SHBG. Finally, despite significantly reduced insulin, non-SHBG-bound testosterone, and estradiol levels after troglitazone treatment of women with PCOS, their leptin levels remained unchanged. We conclude that circulating leptin levels in patients with PCOS do not differ from those in age- and weight-matched controls. Furthermore, increased circulating insulin due to insulin resistance does not appear to alter circulating leptin levels in women with PCOS.

	Introduction

Top Abstract Introduction Materials and Methods Results Discussion References

 
POLYCYSTIC ovary syndrome (PCOS), one of the most common disorders of premenopausal women, involves menstrual disturbances, chronic anovulation, and hyperandrogenism (1, 2, 3). Women with PCOS are frequently insulin resistant and have hyperinsulinemia (3, 4, 5, 6). Although the etiology of PCOS has not yet been elucidated, and the direction of the cause and effect relationship between hyperandrogenemia and hyperinsulinemia remains unsettled, accumulating evidence suggests that insulin is capable of stimulating ovarian androgen synthesis.

Leptin, the product of the ob gene (7), is a protein secreted from adipose tissue that signals the amount of energy stores to the brain (8) and has been implicated in the regulation of food intake and energy balance (9, 10, 11). In the fed state, circulating leptin concentrations reflect the magnitude of fat stores (12, 13), and leptin levels are elevated in many models of animal obesity and in obese humans, correlating strongly with the degree of obesity (12, 14, 15). Although leptin was discovered through its link to obesity and has been viewed as a molecular signal for the regulation of energy balance (10, 11, 16), several recent observations suggest that leptin may play a role in regulation of the reproductive axis. First, leptin-deficient ob/ob mice have central hypogonadism, which is reversed after chronic leptin treatment (17, 18). Second, leptin reverses the hypogonadotropic hypogonadism that is induced by starvation (19). Third, leptin treatment of normal female mice accelerates puberty (20). In addition to these effects of leptin on the reproductive axis, there are several additional reasons to assess the state of leptin in PCOS. PCOS is associated with insulin resistance and hyperinsulinemia (4, 5, 6), and both in vitro data and in vivo studies demonstrate that insulin can regulate ob gene expression and circulating leptin levels in rodents (21, 22, 23, 24), pointing to the existence of a potentially important interaction between these two hormones and/or a feedback loop for their regulation. By contrast, studies of the effect of insulin on leptin concentrations in humans are inconclusive (11, 23, 24, 25, 26), and the effect of leptin on the reproductive system of normal women has not been evaluated. A potential contribution of leptin to the pathogenesis of PCOS was suggested by a recent study (27) in which a subgroup of women with PCOS was claimed to have higher leptin levels than controls. Unfortunately, the confounding effect of differences in body weight and age were not adequately controlled for in that study (27). To further assess the relationship among leptin, PCOS, and hyperinsulinemia, we performed this study to compare leptin concentrations in obese women with PCOS with those in weight- and age-matched controls and to determine whether alterations in insulin concentrations and hyperinsulinemia produced by the insulin-sensitizing agent troglitazone affected serum leptin levels in women with PCOS.

	Materials and Methods

Top Abstract Introduction Materials and Methods Results Discussion References

 
Study population

We studied 24 obese [body mass index (BMI), 30 kg/m²] PCOS women who were recruited from the PCOS population followed at Pennsylvania State University College of Medicine and 12 age- and weight-matched normal women with normal menstrual cycles and no evidence of hirsutism or hyperandrogenemia who served as controls (28). Twenty-one women with PCOS completed the study. All women were healthy, between 18–40 yr old, and not taking any medications known to affect carbohydrate or sex hormone metabolism. Subjects were put on a weight-maintaining diet and were allowed ad libitum activity but no new exercise programs. All studies were approved by the institutional review board of the Pennsylvania State University College of Medicine, and written informed consent was obtained from the subjects before the study. Information on these subjects has been reported previously (28) and is, thus, only briefly reviewed here.

PCOS was diagnosed by an elevation of total or free testosterone (T) levels associated with chronic oligomenorrhea (six or fewer menses per yr) or amenorrhea (28). Nonclassical 21-hydroxylase deficiency was excluded by a 1-h ACTH stimulation test. No woman had an elevated plasma PRL level. Waist to hip ratio and BMI were determined as described previously (28), and a standard 2-h 75-g oral glucose tolerance test (OGTT) was performed (29, 30). All control women had normal glucose tolerance by WHO criteria (30), and women with PCOS who had diabetes mellitus were excluded from the study.

Protocol

After the baseline OGTT, PCOS women had a modified frequently sampled iv glucose tolerance test (FSIGT) performed as previously described (28). Therapy with troglitazone was then initiated in a randomized, double blind trial of 200 or 400 mg daily for 3 months as described previously (28). Each subject took either two 200-mg tablets or a 200-mg tablet and an identical placebo tablet orally each morning with breakfast. Both OGTT and FSIGT were repeated at the end of the study. At baseline and at the end of the study, three blood samples were obtained 10 min apart between 0800–0900 h. Blood was centrifuged immediately, and equal aliquots of serum were pooled and used for measurement of nonsex hormone-binding globulin (non-SHBG) bound and total T, estradiol (E₂), SHBG, insulin, leptin, and dehydroepiandrosterone sulfate (DHEAS).

Hormonal assays

Assays for non-SHBG bound T, T, DHEAS, insulin, SHBG, and E₂ were performed as reported previously (28) (Table 1). Insulin was measured using a commercially available RIA kit (Diagnostic Products Corp., Los Angeles, CA). Leptin was measured as described previously (31, 32).

Group values for outcome measures are reported as the mean ± SE. Variables not normally distributed were log transformed before analysis by parametric methods. Means of anthropometric data as well as hormonal concentrations were compared by Student’s t test. Relationships between serum leptin and independent variables were assessed by simple and/or multiple linear regression analysis, and Pearson (r) correlation coefficients are presented. Two-sided significance levels are reported. Differences were considered significant at the conventional P 0.05. This study had a 90% power to detect, at the conventional = 0.05 level, a difference in mean leptin levels between obese women with PCOS and controls of the same magnitude as the difference previously reported (27). Statistical analyses were performed using the StatView Statistical Package (Berkeley, CA).

	Results

Top Abstract Introduction Materials and Methods Results Discussion References

 
The BMI of control women was 40.88 ± 1.87, whereas the BMI of women with PCOS was 42.89 ± 1.23 at baseline and did not change significantly after treatment with troglitazone (43.0 ± 1.24). Baseline insulin levels were higher in women with PCO (145 ± 15 pmol/L) than in controls (92 ± 18 pmol/L). Insulin levels 120 min after the OGTT were also higher in women with PCO (1231 ± 170 vs. 679 ± 150). As previously reported (28), troglitazone treatment significantly improved insulin resistance in PCOS women, as indicated by fasting and 2-h postglucose load insulin levels (144 ± 18 vs. 102 ± 18 pmol/L; P < 0.01) as well as the integrated insulin response (2046 ± 234 vs. 1392 ± 168 pmol/L; P < 0.01). Additionally, insulin sensitivity, as indicated by FSIGT, increased significantly during troglitazone treatement (P < 0.05). Finally, serum concentrations of non-SHBG-bound T (P < 0.01), DHEAS (P < 0.001), and E₂ (P < 0.01) decreased significantly after troglitazone treatment. Although there was a significant correlation between changes in non-SHBG-bound T and the integrated insulin response (P < 0.05), changes in DHEAS and E₂ levels were not correlated with insulin levels, as previously reported (28).

Leptin concentrations at baseline, similarly to BMI, tended to be higher, but mean levels were not significantly different in women with PCOS and controls (38.1 ± 2.15 vs. 33.12 ± 2.39 ng/mL). Furthermore, despite the above endocrine changes, leptin concentrations did not change significantly after treatment of PCOS with troglitazone (38.1 ± 2.15 vs. 39.21 ± 2.65 ng/mL; Fig. 1).

View larger version (50K): [in this window] [in a new window]   Figure 1. Mean leptin concentrations in controls and women with PCOS before and after treatment with troglitazone.

View larger version (12K): [in this window] [in a new window]   Figure 2. Correlation between BMI and leptin concentrations in women with PCOS (r = 0.70; P = 0.0004) and weight- and age-matched controls (r = 0.59; P < 0.05).

	Discussion

Top Abstract Introduction Materials and Methods Results Discussion References

 
In this study, we tested the hypothesis that PCOS is associated with dysregulation of the circulating levels of the adipocyte-derived hormone, leptin. We showed that leptin levels in obese women with PCOS are not significantly different from those in age- and weight- matched controls, and that the relationship between BMI and leptin is similar in PCOS and control women. Moreover, there was no statistically significant correlation between leptin and circulating levels of gonadal steroids in either group of study subjects. There are several reasons why these negative results are noteworthy. Leptin was discovered as the product of the ob gene (7), and its total absence or failure to act due to mutations of its receptor (ob/ob and db/db mice, and fa/fa rats, respectively) produces a phenotype most noted for severe obesity (7, 33, 34, 35). Repletion of leptin-deficient ob/ob mice with recombinant leptin reverses their obesity (8, 36, 37, 38), suggesting that leptin plays a role in a physiological feedback loop for the prevention of obesity (8, 10, 11, 16, 39). However, several lines of evidence suggest that leptin has a broader physiological role, with significant effects on the reproductive system that could have important implications for the pathogenesis of PCOS.

The potential reproductive impact of leptin derives from several observations. First, chronic leptin treatment, in addition to reducing body weight and improving hyperinsulinemia and insulin resistance, corrects the hypogonadism of ob/ob mice (17, 18). Second, leptin treatment corrects the hypogonadotropic hypogonadism induced by starvation in normal mice (19). Third, leptin treatment of normal mice accelerates puberty (20), and longitudinal assessment of leptin levels during normal puberty in boys reveals that leptin concentrations increase immediately before or at the onset of puberty and may signal the onset of puberty in humans (32). Taken together, these data suggest that leptin may be a metabolic signal that plays an important role in the regulation of the hypothalamic-pituitary-gonadal axis. As PCOS is a disorder (or a group of disorders) of currently unknown pathogenesis in which dysregulation of the hypothalamic-pituitary-gonadal axis is observed (1, 2), possible alterations in leptin levels are a matter of considerable interest. For example, increased peripheral leptin concentrations could promote the pathophysiology of PCOS through actions at a number of levels, including the GnRH neuron, the pituitary gonadotrophs, or the ovary (18). The present study failed to reveal increased levels of leptin in the serum of obese women with PCOS compared to those in age- and weight-matched controls. However, it remains possible that leptin could play a role in the pathogenesis of PCOS, as small differences in leptin levels could have escaped detection in the small number of subjects studied. It is also possible that PCOS women were more susceptible than weight-matched women without PCOS to the possible reproductive action of leptin. In addition, this study did not address the status of leptin in lean women with PCOS. Another recent study reported that a subgroup of women with PCOS had higher leptin levels than controls, although the PCOS and control women were not appropriately matched for weight, and statistical adjustment for the potential confounding effect of BMI was not performed (27). In addition, the subgroup of women with high leptin levels did not have higher insulin or sex steroid levels, suggesting that increased leptin did not have a detectable impact on the reproductive or metabolic features of the syndrome. Thus, the lack of any correlation between leptin and gonadal hormones in both this and the previous study fails to support an action of leptin on gonadotropin and/or sex steroid secretion in PCOS women (27). As there may be subgroups of women with PCOS, it is possible that a subgroup of PCOS women exists that has higher leptin levels. It has been hypothesized that PCOS women with higher leptin levels may produce a less potent form of leptin or have a diminished response to leptin at the target level (27). Whether such a defect exists and whether it represents a causal or a contributing factor to the pathogenesis of PCOS (27) needs to be further elucidated. When recombinant leptin or leptin analogs become available for administration to humans, direct studies of leptin action across a wide dose range will help clarify this issue.

This study also provides some new information on the relationship between insulin and leptin. First, severe deficiency of leptin (as in ob/ob mice) is associated with severe insulin resistance that is corrected by leptin treatment (8, 36, 37, 38). On the other hand, insulin appears to be capable of regulating leptin expression in a number of models in rodents and after prolonged infusion in man (21, 22, 23, 24). Insulin directly stimulates leptin messenger ribonucleic acid expression and secretion in human and primary rat adipocytes in vitro (21, 23, 40). Additionally, in vivo data suggest that leptin messenger ribonucleic acid expression in rat adipose tissue is stimulated by short term insulin infusion (41), postprandial hyperinsulinemia (22), and a single insulin injection (22). By contrast, postprandial hyperinsulinemia and short term hyperinsulinemia do not increase leptin secretion in humans (24, 25, 42, 43). However, long term hyperinsulinemia accompanying prolonged hyperglycemic clamp results in increased leptin secretion from isolated human abdominal adipocytes (24) and increased circulating leptin concentrations in lean humans (24). Thus, it has been proposed that only long term, not short term, hyperinsulinemia affects leptin levels in humans (11).

As PCOS is a well characterized state of insulin resistance with compensatory hyperinsulinemia (4, 5), it is interesting that combined hyperinsulinemia and insulin resistance in obese women with PCOS do not result in any detectable difference in leptin levels compared to those in insulin-resistant/hyperinsulinemic age- and weight-matched controls. In addition, treatment with troglitazone, which improved insulin resistance and hyperinsulinemia without changing BMI, did not alter leptin levels, a fact also reported recently in a noninsulin-dependent diabetes mellitus population without PCOS (40). This lack of effect of troglitazone could have several explanations. First, the improvement of insulin resistance and the resultant decreased circulating insulin levels could have a counterbalancing effect(s) that effectively canceled out any changes in leptin expression exerted by insulin. Second, an effect of increased insulin action to increase circulating leptin might have been counterbalanced by a direct action of troglitazone, via PPARg, the receptor for this class of drugs (10, 44), to decrease leptin expression, as seen in vitro and in rodents (45, 46, 47). Finally, the actions of both insulin and troglitazone to regulate leptin expression in human white adipose tissue may be less than that observed in the rodent (11). This may be of particular importance in patients with syndromes of insulin resistance. It has been previously shown that hyperinsulinemia accompanying noninsulin-dependent diabetes mellitus does not increase leptin levels in diabetics (26). This study demonstrates a similar phenomenon in PCOS, another syndrome associated with insulin resistance (4, 5).

In summary, circulating leptin levels in patients with PCOS, although increased compared to those in lean individuals, do not differ from those in age- and weight-matched controls. Furthermore, improvement of insulin resistance and hyperinsulinemia produced by the insulin-sensitizing agent troglitazone does not alter circulating leptin levels in women with PCOS. A more complete understanding of the potential significance of leptin for the pathophysiology of PCOS will await direct studies of the effects of exogenous leptin on the reproductive axis of women, including those with PCOS.

	Footnotes

 
¹ This work was supported by NIH Grant DK-28082 (to J.S.F.), Beth Israel Hospital General Clinical Research Center Grant M01-RR-01032, a grant from Parke-Davis Pharmaceutical Research (to A.D.), and USPHS Grant M01-RR-10732 (to the Pennsylvania State University College of Medicine).

² Supported by the Division of Endocrinology, Beth Israel Deaconess Medical Center, and the Clinical Investigator Training Program, Beth Israel Deaconess Medical Center, Harvard-Massachusetts Institute of Technology, Health Sciences and Technology, in collaboration with Pfizer.

Received January 15, 1997.

Revised March 4, 1997.

Accepted March 6, 1997.

	References

Top Abstract Introduction Materials and Methods Results Discussion References

 

1. Franks S. 1995 Polycystic ovary syndrome. N Engl J Med. 333:853–861.[Free Full Text]
2. Dunaif A. 1993Insulin resistance and ovarian dysfunction. In: Moller DE, ed. Insulin resistance, 1st ed. Chichester: Wiley and Sons; 301–325.
3. Mantzoros CS, Flier JS. 1995 Insulin resistance: the clinical spectrum. Adv Endcorinol Metab. 6:193–232.
4. Book CB, Dunaif A. 1996 Insulin resistance in the polycystic ovary syndrome. In: Chang RJ, ed. Polycystic ovary syndrome. Serono Symp USA. New York: Springer-Verlag; 117–125.
5. Dunaif A. 1995 Hyperandrogenic anovulation (PCOS): a unique disorder of insulin action associated with an increased risk of non-insulin-dependent diabetes mellitus. Am J Med. 98:33S–39S.[CrossRef]
6. Dunaif A, Xia J, Book CB, Schenker E, Tang Z. 1995 Excessive insulin receptor serine phosphorylation in cultured fibroblasts and in skeletal muscle. A potential mechanism for insulin resistance in the polycystic ovary syndrome. J Clin Invest. 96:801–810.
7. Zhang Y, Proenca R, Maffei M, Barone M, Leopold L, Friedman JM. 1994 Positional cloning of the mouse ob gene and its human homologue. Nature. 372:425–432.[CrossRef][Medline]
8. Campfield LA, Smith FJ, Guisez Y, Devos R, Burn P.1995 Recombinant mouse ob protein: evidence for a peripheral signal linking adiposity and central neural networks. Science. 269:546–548.
9. Rink TJ. 1995 In search of a satiety factor. Nature. 372:406–407.
10. Spiegelman BM, Flier JS. 1996 Adipogenesis and obesity: rounding out the big picture. Cell. 87:377–389.[CrossRef][Medline]
11. Caro JF, Sinha MK, Kolaczynski JW, Zhary PL, Considine RV. 1996 Leptin: the tale of an obesity gene. Diabetes. 45:1455–1462.[Medline]
12. Maffei M, Halaas J, Ravussin E, et al. 1995 Leptin levels in human and rodent: measurement of plasma leptin and ob RNA in obese and weight-reduced subjects. Nat Med. 1:1155–1161.[CrossRef][Medline]
13. Frederich RC, Hamann A, Anderson S, Lollman B, Lowell BB, Flier JS. 1995 Leptin reflects body lipid content in mice: evidence for diet-induced leptin resistance. Nat Med. 1:1311–1314.[CrossRef][Medline]
14. Considine R, Sinha M, Heiman M, et al. 1996 Serum immunoreactive leptin concentrations in normal weight and obese humans. N Engl J Med. 334:292–295.[Abstract/Free Full Text]
15. Frederich RC, Lollmann B, Hamann A, et al. 1995 Expression of ob mRNA and its encoded protein in rodents. Impact of nutrition and obesity. J Clin Invest. 96:1658–1663.
16. Rohner-Jeanrenaud F, Jeanrenaud B. 1996 Obesity, leptin, and the brain. N Engl J Med. 334:324–325.[Free Full Text]
17. Chehab F, Lim M, Lu R. 1996 Correction of the sterility defect in homozygous obese female mice by treatment with the human recombinant leptin. Nat Genet. 12:318.[CrossRef][Medline]
18. Barash IA, Cheung CC, Weigle DS, et al. 1996 Leptin is a metabolic signal to the reproductive system. Endocrinology. 137:3144–3147.[Abstract]
19. Ahima R, Prabakaran D, Mantzoros C, et al. 1996 Role of leptin in the neuroendocrine responce to fasting. Nature. 382:250–252.[CrossRef][Medline]
20. Ahima RS, Dushay J, Flier SN, Prabakaran D, Flier JS. Leptin accelerates the timing of puberty in normal female mice. J Clin Invest. In press.
21. Saladin R, De Vos P, Guerre-Millo M, et al. 1995 Transient increase in obese gene expression after food intake or insulin administration. Nature. 377:527–529.[CrossRef][Medline]
22. Cusin I, Sainsbury A, Doyle P, Rohner-Jeanrenaud F, Jeanrenaud B. 1995 The ob gene and insulin. A relationship leading to clues to the understanding of obesity. Diabetes. 44:1467–1470.[Abstract]
23. Vidal H, Auboeuf D, De Vos P, et al. 1996 The expression of ob gene is not acutely regulated by insulin and fasting in human abdominal subcutaneous adipose tissue. J Clin Invest. 98:251–255.[Medline]
24. Kolaczynski JW, Nyce MR, Considine RV, et al. 1996 Acute and chronic effect of insulin on leptin production in humans. Diabetes. 45:699–701.[Abstract]
25. Dagogo-Jack S, Fanelli C, Paramore D, Brothers J, Landt M. 1996 Plasma leptin and insulin relationships in obese and nonobese humans. Diabetes. 45:695–698.[Abstract]
26. Haffner SM, Stern MP, Miettinen H, Wei M, Gingerich RL. 1996 Leptin concentrations in diabetic and nondiabetic Mexican-Americans. Diabetes. 45:822–824.[Abstract]
27. Brzechffa PR, Jakimiuk AJ, Agarwal SK, et al. 1996 Serum immunoreactive leptin concentrations in women with polycystic ovarian disease. J Clin Endocrinol Metab. 81:4166–4169.[Abstract/Free Full Text]
28. 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]
29. Dunaif A, Segal KR, Shelley DR, Green G, Dobrjansky A, Licholai T. 1992 Evidence for distinctive and intrinsic defects in insulin action in polycystic ovary syndrome. Diabetes. 41:1257–1266.[Abstract]
30. Modan M, Harris MI, Halkin H. 1989 Evaluation of WHO, and NDDG criteria for impaired glucose tolerance. Diabetes. 38:1603–1635.
31. Houseknecht KL, Mantzoros CS, Kuliawat R, Hadro E, Flier JS, Khan BB. 1996 Evidence for leptin binding to proteins in serum of rodents and humans: modulation with obesity. Diabetes. 45:1638–1643.[Abstract]
32. Mantzoros CS, Flier JS, Rogol AD. 1997 A longitudinal assessment of hormonal and physical alterations during normal puberty in boys. V. Rising leptin levels may signal the onset of puberty. J Clin Endocrinol Metab. 82:1066–1070.[Abstract/Free Full Text]
33. Chua SC, White DW, Wu-Peng X, et al. 1996 Phenotype of fatty due to Gln²⁶⁹Pro mutation in the leptin receptor (Lepr). Diabetes 45:1141–1143.
34. Lee GH, Proenca R, Montez JM, et al. 1996 Abnormal splicing of the leptin receptor in diabetic mice. Nature. 379:632–635.[CrossRef][Medline]
35. Chen H, Charlat O, Tartaglia LA, et al. 1996 Evidence that the diabetes gene encodes the leptin receptor: identification of a mutation in the leptin receptor gene in db/db mice. Cell. 84:491–495.[CrossRef][Medline]
36. Halaas JL, Gajiwala KS, Maffei M, et al. 1995 Weight-reducing effects of the plasma protein encoded by the obese gene. Science. 269:543–546.[Abstract/Free Full Text]
37. Pelleymounter MA, Cullen MJ, Baker MB, et al. 1995 Effects of the obese gene product on body weight regulation in ob/ob mice. Science. 269:540–543.[Abstract/Free Full Text]
38. Weigle DS, Bukowski TR, Foster DC, et al. 1995 Recombinant ob protein reduces feeding and body weight in the ob/ob mouse. J Clin Invest. 96:2065–2070.
39. Collins S, Kuhn CM, Petro AE, Swick AG, Chrunyk BA, Surwit RS. 1996 Leptin and fat regulation. Nature. 360:677.
40. Nolan JJ, Olefsky JM, Nyce MR, Considine RV, Caro JF. 1996 Effect of troglitazone on leptin production. Studies in vitro and in human subjects. Diabetes. 45:1276–1278.[Abstract]
41. Hardie LJ, Rayner DV, Holmes S, Trayhurn P. 1996 Circulating leptin levels are modulated by fasting, cold exposure, and insulin administration in lean but not Zucker (fa/fa) rats as measured by ELISA. Biochem Biophys Res Commun. 223:660–665.[CrossRef][Medline]
42. Segal KR, Landt M, Klein S. 1996 Relationship between insulin sensitivity and plasma leptin concentration in lean and obese men. Diabetes. 45:988–991.[Abstract]
43. Sinha MK, Ohanessian JP, Heinman ML, et al. 1996 Nocturnal rise of leptin in lean, obese, and non-insulin dependent diabetes mellitus subjects. J Clin Invest. 97:1344–1347.[Medline]
44. Lehman JM, Moore LB, Smith-Oliver TA, Wilkinson WO, Willson TM, Kliever SA. 1995 An antidiabetic thiazolidinedione is a high affinity ligand for peroxisome proliferator activator receptor gamma. J Biol Chem. 270:12953–12956.[Abstract/Free Full Text]
45. Kallen CB, Lazar MA. 1996 Antidiabetic thiazolidinediones inhibit leptin (ob) gene expression in 3T3–L1 adipocytes. Proc Natl Acad Sci USA. 93:5793–5796.[Abstract/Free Full Text]
46. De Vos P, Lefebre AM, Miller SG, et al. 1996 Thiazolidinediones repress ob gene expression in rodents via activation of peroxisome proliferator activator receptor gamma. J Clin Invest. 98:1004–1009.[Medline]
47. Zhang B, Graziano MP, Doebber TW, et al. 1996 Down-regulation of the expression of the obese gene by an antiadiabetic thiazolidinedione in Zucker diabetic fatty rats and db/db mice. J Biol Chem. 271:9455–9459.[Abstract/Free Full Text]

This article has been cited by other articles:

				L. Manneras, I. H. Jonsdottir, A. Holmang, M. Lonn, and E. Stener-Victorin Low-Frequency Electro-Acupuncture and Physical Exercise Improve Metabolic Disturbances and Modulate Gene Expression in Adipose Tissue in Rats with Dihydrotestosterone-Induced Polycystic Ovary Syndrome Endocrinology, July 1, 2008; 149(7): 3559 - 3568. [Abstract] [Full Text] [PDF]

				L. Manneras, S. Cajander, A. Holmang, Z. Seleskovic, T. Lystig, M. Lonn, and E. Stener-Victorin A New Rat Model Exhibiting Both Ovarian and Metabolic Characteristics of Polycystic Ovary Syndrome Endocrinology, August 1, 2007; 148(8): 3781 - 3791. [Abstract] [Full Text] [PDF]

				A.K. Ludwig, J.M. Weiss, S. Tauchert, T. Dietze, S. Rudolf, K. Diedrich, A. Peters, and K.M. Oltmanns Influence of hypo- and hyperglycaemia on plasma leptin concentrations in healthy women and in women with polycystic ovary syndrome Hum. Reprod., June 1, 2007; 22(6): 1555 - 1561. [Abstract] [Full Text] [PDF]

				D. Glintborg, M. Andersen, C. Hagen, J. Frystyk, V. Hulstrom, A. Flyvbjerg, and A. P. Hermann Evaluation of metabolic risk markers in polycystic ovary syndrome (PCOS). Adiponectin, ghrelin, leptin and body composition in hirsute PCOS patients and controls. Eur. J. Endocrinol., August 1, 2006; 155(2): 337 - 345. [Abstract] [Full Text] [PDF]

				Y. L. Pagan, S. S. Srouji, Y. Jimenez, A. Emerson, S. Gill, and J. E. Hall Inverse Relationship between Luteinizing Hormone and Body Mass Index in Polycystic Ovarian Syndrome: Investigation of Hypothalamic and Pituitary Contributions J. Clin. Endocrinol. Metab., April 1, 2006; 91(4): 1309 - 1316. [Abstract] [Full Text] [PDF]

				S. Hahn, U. Haselhorst, B. Quadbeck, S. Tan, R. Kimmig, K. Mann, and O. E Janssen Decreased soluble leptin receptor levels in women with polycystic ovary syndrome Eur. J. Endocrinol., February 1, 2006; 154(2): 287 - 294. [Abstract] [Full Text] [PDF]

				E Carmina, F Orio, S Palomba, T Cascella, R A Longo, A M Colao, G Lombardi, and R A Lobo Evidence for altered adipocyte function in polycystic ovary syndrome Eur. J. Endocrinol., March 1, 2005; 152(3): 389 - 394. [Abstract] [Full Text] [PDF]

				J. E. Swain, R. L. Dunn, D. McConnell, J. Gonzalez-Martinez, and G. D. Smith Direct Effects of Leptin on Mouse Reproductive Function: Regulation of Follicular, Oocyte, and Embryo Development Biol Reprod, November 1, 2004; 71(5): 1446 - 1452. [Abstract] [Full Text] [PDF]

				F. Orio Jr., G. Matarese, S. Di Biase, S. Palomba, D. Labella, V. Sanna, S. Savastano, F. Zullo, A. Colao, and G. Lombardi Exon 6 and 2 Peroxisome Proliferator-Activated Receptor-{gamma} Polymorphisms in Polycystic Ovary Syndrome J. Clin. Endocrinol. Metab., December 1, 2003; 88(12): 5887 - 5892. [Abstract] [Full Text] [PDF]

				J. T. Kero, E. Savontaus, M. Mikola, U. Pesonen, M. Koulu, R. A. Keri, J. H. Nilson, M. Poutanen, and I. T. Huhtaniemi Obesity in transgenic female mice with constitutively elevated luteinizing hormone secretion Am J Physiol Endocrinol Metab, October 1, 2003; 285(4): E812 - E818. [Abstract] [Full Text] [PDF]

				P.-H. Ducluzeau, P. Cousin, E. Malvoisin, H. Bornet, H. Vidal, M. Laville, and M. Pugeat Glucose-to-Insulin Ratio Rather than Sex Hormone-Binding Globulin and Adiponectin Levels Is the Best Predictor of Insulin Resistance in Nonobese Women with Polycystic Ovary Syndrome J. Clin. Endocrinol. Metab., August 1, 2003; 88(8): 3626 - 3631. [Abstract] [Full Text] [PDF]

				F. C. W. Wu and A. von Eckardstein Androgens and Coronary Artery Disease Endocr. Rev., April 1, 2003; 24(2): 183 - 217. [Abstract] [Full Text] [PDF]

				R. S. Legro, R. Bentley-Lewis, D. Driscoll, S. C. Wang, and A. Dunaif Insulin Resistance in the Sisters of Women with Polycystic Ovary Syndrome: Association with Hyperandrogenemia Rather Than Menstrual Irregularity J. Clin. Endocrinol. Metab., May 1, 2002; 87(5): 2128 - 2133. [Abstract] [Full Text] [PDF]

				A. B. Mayerson, R. S. Hundal, S. Dufour, V. Lebon, D. Befroy, G. W. Cline, S. Enocksson, S. E. Inzucchi, G. I. Shulman, and K. F. Petersen The Effects of Rosiglitazone on Insulin Sensitivity, Lipolysis, and Hepatic and Skeletal Muscle Triglyceride Content in Patients With Type 2 Diabetes Diabetes, March 1, 2002; 51(3): 797 - 802. [Abstract] [Full Text] [PDF]

				J. D. Veldhuis, S. M. Pincus, M. C. Garcia-Rudaz, M. G. Ropelato, M. E. Escobar, and M. Barontini Disruption of the Synchronous Secretion of Leptin, LH, and Ovarian Androgens in Nonobese Adolescents with the Polycystic Ovarian Syndrome J. Clin. Endocrinol. Metab., August 1, 2001; 86(8): 3772 - 3778. [Abstract] [Full Text] [PDF]

				P.M. Spritzer, M. Poy, D. Wiltgen, L.S. Mylius, and E. Capp Leptin concentrations in hirsute women with polycystic ovary syndrome or idiopathic hirsutism: influence on LH and relationship with hormonal, metabolic, and anthropometric measurements Hum. Reprod., July 1, 2001; 16(7): 1340 - 1346. [Abstract] [Full Text] [PDF]

				R. Azziz, D. Ehrmann, R. S. Legro, R. W. Whitcomb, R. Hanley, A. G. Fereshetian, M. O’Keefe, and M. N. Ghazzi Troglitazone Improves Ovulation and Hirsutism in the Polycystic Ovary Syndrome: A Multicenter, Double Blind, Placebo-Controlled Trial J. Clin. Endocrinol. Metab., April 1, 2001; 86(4): 1626 - 1632. [Abstract] [Full Text]

				L. B. Williams, R. L. Fawcett, A. S. Waechter, P. Zhang, B. E. Kogon, R. Jones, M. Inman, J. Huse, and R. V. Considine Leptin Production in Adipocytes from Morbidly Obese Subjects: Stimulation by Dexamethasone, Inhibition with Troglitazone, and Influence of Gender J. Clin. Endocrinol. Metab., August 1, 2000; 85(8): 2678 - 2684. [Abstract] [Full Text]

				C. S.Mantzoros, D. W.Cramer, R. F.Liberman, and R. L.Barbieri Predictive value of serum and follicular fluid leptin concentrations during assisted reproductive cycles in normal women and in women with the polycystic ovarian syndrome Hum. Reprod., March 1, 2000; 15(3): 539 - 544. [Abstract] [Full Text] [PDF]

				F. Sun and J. Yu The Effect of a Special Herbal Tea on Obesity and Anovulation in Androgen-Sterilized Rats Experimental Biology and Medicine, March 1, 2000; 223(3): 295 - 301. [Abstract] [Full Text]

				L. Poretsky, N. A. Cataldo, Z. Rosenwaks, and L. C. Giudice The Insulin-Related Ovarian Regulatory System in Health and Disease Endocr. Rev., August 1, 1999; 20(4): 535 - 582. [Abstract] [Full Text] [PDF]

				M. Rosenbaum and R. L. Leibel Role of Gonadal Steroids in the Sexual Dimorphisms in Body Composition and Circulating Concentrations of Leptin J. Clin. Endocrinol. Metab., June 1, 1999; 84(6): 1784 - 1789. [Full Text]

				T. Sir-Petermann, V. Piwonka, F. Perez, M. Maliqueo, S.E. Recabarren, and L. Wildt Are circulating leptin and luteinizing hormone synchronized in patients with polycystic ovary syndrome? Hum. Reprod., June 1, 1999; 14(6): 1435 - 1439. [Abstract] [Full Text] [PDF]

				C. S. Mantzoros The Role of Leptin in Human Obesity and Disease: A Review of Current Evidence Ann Intern Med, April 20, 1999; 130(8): 671 - 680. [Abstract] [Full Text] [PDF]

				M.-M. Huber-Buchholz, D. G. P. Carey, and R. J. Norman Restoration of Reproductive Potential by Lifestyle Modification in Obese Polycystic Ovary Syndrome: Role of Insulin Sensitivity and Luteinizing Hormone J. Clin. Endocrinol. Metab., April 1, 1999; 84(4): 1470 - 1474. [Abstract] [Full Text]

				I.E. Messinis, S.D. Milingos, E. Alexandris, I. Kariotis, G. Kollios, and K. Seferiadis Leptin concentrations in normal women following bilateral ovariectomy Hum. Reprod., April 1, 1999; 14(4): 913 - 918. [Abstract] [Full Text] [PDF]

				S. K. Agarwal, K. Vogel, S. R. Weitsman, and D. A. Magoffin Leptin Antagonizes the Insulin-Like Growth Factor-I Augmentation of Steroidogenesis in Granulosa and Theca Cells of the Human Ovary J. Clin. Endocrinol. Metab., March 1, 1999; 84(3): 1072 - 1076. [Abstract] [Full Text]

				L. C. Morin-Papunen, R. M. Koivunen, C. Tomás, A. Ruokonen, and H. K. Martikainen Decreased Serum Leptin Concentrations during Metformin Therapy in Obese Women with Polycystic Ovary Syndrome J. Clin. Endocrinol. Metab., July 1, 1998; 83(7): 2566 - 2568. [Abstract] [Full Text]

				J. Licinio, A. B. Negrao, C. Mantzoros, V. Kaklamani, M.-L. Wong, P. B. Bongiorno, A. Mulla, L. Cearnal, J. D. Veldhuis, J. S. Flier, et al. Synchronicity of frequently sampled, 24-h concentrations of circulating leptin, luteinizing hormone, and estradiol in healthy women PNAS, March 3, 1998; 95(5): 2541 - 2546. [Abstract] [Full Text] [PDF]

				A. Dunaif Insulin Resistance and the Polycystic Ovary Syndrome: Mechanism and Implications for Pathogenesis Endocr. Rev., December 1, 1997; 18(6): 774 - 800. [Abstract] [Full Text]