Episodic leptin release is independent of luteinizing hormone secretion

Preconception Leptin and Fecundability, Pregnancy, and Live Birth Among Women With a History of Pregnancy Loss

Context

With the increase of obesity, it is imperative to understand the neuroendocrine mechanisms, including the neuroendocrine hormone leptin, by which obese or overweight women are at increased risk for subfertility and infertility.

Objective

The objective was to examine associations between preconception serum leptin concentrations, fecundability, pregnancy, and live birth.

Design

Secondary analysis of a prospective cohort among women with prior pregnancy losses.

Setting

The study was conducted at four US medical centers (2006 to 2012).

Intervention

Not available.

Materials and Methods

Preconception serum leptin concentrations were measured at baseline, and women were followed for up to six menstrual cycles, and throughout pregnancy if they conceived. Discrete Cox proportional hazard regression models were used to assess fecundability odds ratios (FORs) and log-binomial regression to estimate risk ratios (RRs) for pregnancy and live birth. Models were adjusted for age, physical activity, treatment arm, and adiposity, either by measured waist-to-hip ratio or body mass index (BMI).

Results

High leptin concentrations were associated with decreased fecundability (FOR 0.72, 95% CI 0.58, 0.90), reduced risk of pregnancy (RR 0.87, 95% CI 0.78, 0.96) and live birth (RR 0.76, 95% CI 0.65, 0.89) comparing the upper to the lower tertile. However, adjustment for BMI in lieu of waist-to-hip ratio nullified observed associations.

Conclusions

In women with a history of pregnancy loss, relations between higher preconception leptin and fecundability were attenuated after adjustment for BMI, although not after adjustment for other markers of adiposity. Leptin may serve as a complementary marker of adiposity for assessment of obesity and reproductive outcomes.

Leptin and body mass index in polycystic ovary syndrome

OBJECTIVE

Polycystic ovary syndrome (PCOS) is a common endocrine disorder associated with obesity. Human and animal studies showed a direct relationship between leptin level and obesity, however, results from different studies were mixed. This study investigated the status of leptin level in PCOS and its relationship with body mass index (BMI) in a group of Iranian women with PCOS.

METHODS

In this cross-sectional study, 40 women with PCOS and 36 healthy women were assigned to experimental and control groups, respectively. Those in the PCOS group were not prescribed any medications for 3 months prior to the study. Fasting blood samples were then collected during the 2(nd) or 3(rd) day of menstruation for laboratory measurement of serum total leptin, blood glucose (fasting blood sugar), serum insulin, follicle-stimulating hormone, and luteinizing hormone (LH).

RESULTS

Mean BMI of the PCOS and control groups were 26.62 ± 4.03 kg/m(2) and 23.52 ± 2.52 kg/m(2), respectively (P = 0.006). The mean total leptin in the PCO group was also 10.69 ± 5.37 ng/mL and 5.73 ± 2.36 ng/mL in the control group (P = 0.0001). A significant relationship was found between leptin level and BMI as well as LH level among women with PCOS (P < 0.05). However, there was no significant correlation between leptin and insulin (P > 0.05).

CONCLUSION

The results of this study indicated an increased leptin level among women with PCOS that positively associated with BMI and LH.

Role of leptin in female reproduction

Reproductive function is dependent on energy resources. The role of weight, body composition, fat distribution and the effect of diet have been largely investigated in experimental female animals as well as in women. Any alteration in diet and/or weight may induce abnormalities in timing of sexual maturation and fertility. However, the cellular mechanisms involved in the fine coordination of energy balance and reproduction are largely unknown. The brain and hypothalamic structures receive endocrine and/or metabolic signals providing information on the nutritional status and the degree of fat stores. Adipose tissue acts both as a store of energy and as an active endocrine organ, secreting a large number of biologically important molecules termed adipokines. Adipokines have been shown to be involved in regulation of the reproductive functions. The first adipokine described was leptin. Extensive research over the last 10 years has shown that leptin is not only an adipose tissue-derived messenger of the amount of energy stores to the brain, but also a crucial hormone/cytokine for a number of diverse physiological processes, such as inflammation, angiogenesis, hematopoiesis, immune function, and most importantly, reproduction. Leptin plays an integral role in the normal physiology of the reproductive system with complex interactions at all levels of the hypothalamic-pituitary gonadal (HPG) axis. In addition, leptin is also produced by placenta, where it plays an important autocrine function. Observational studies have demonstrated that states of leptin excess, deficiency, or resistance can be associated with abnormal reproductive function. This review focuses on the leptin action in female reproduction.

Serum leptin levels and reproductive function during the menstrual cycle

OBJECTIVE

The purpose of this study was to investigate the role of leptin on reproductive hormones and ovulation.

STUDY DESIGN

The BioCycle Study (2005-2007) followed 259 healthy premenopausal women not using hormonal contraceptives for ≤2 menstrual cycles (n = 509 cycles). Serum leptin, estradiol, progesterone, luteinizing hormone (LH), follicle-stimulating hormone, and testosterone were measured ≤8 times per cycle. The association of time-varying leptin and reproductive hormones over the cycle was estimated with the use of linear mixed models that were adjusted for percent body fat and age with inverse probability weighting for time-varying physical activity, caloric intake, and other reproductive hormones. The odds ratio for sporadic anovulation (n = 42 cycles) was estimated with the use of generalized linear models that were adjusted for percent body fat and age.

RESULTS

Geometric mean serum leptin levels increased from menses to the late luteal phase (16.7-20.4 ng/mL; P < .01), with a mid-cycle peak (21.7 ng/mL) at the time of the LH surge (P < .01). A 10% higher leptin level across the menstrual cycle was associated with higher estradiol levels (2.2%; 95% CI, 1.5-3.0), luteal progesterone levels (2.1%; 95% CI, 0.5-3.7), ovulatory LH levels (1.2%; 95% CI, 0-2.3), testosterone levels (0.6%; 95% CI, 0.3-0.9), and lower follicle-stimulating hormone levels (-0.7%; 95% CI, -1.1 to -0.4). Leptin at the time of the expected LH surge was moderately inversely associated with sporadic anovulation (per log increase in leptin; adjusted odds ratio, 0.58; 95% CI, 0.28-1.22).

CONCLUSION

The association that was observed between leptin level and reproductive function points to a possible relationship between serum leptin level and enhanced fertility.

Serum leptin level in women with polycystic ovary syndrome: correlation with adiposity, insulin, and circulating testosterone

BACKGROUND

Leptin, an adipocyte-derived hormone encoded by 'ob' gene, serves as a link relaying metabolic signals to the neuronal networks in the brain to modulate hypothalamo-pituitary-ovarian axis. Circulating leptin correlates strongly with obesity, which is frequently associated with polycystic ovarian syndrome (PCOS), a major form of dysovulatory infertility in women, characterized by endocrine abnormalities such as hyperandrogenism and inappropriate LH secretion. PCOS is also often associated with insulin resistance and hyperinsulinemia, features that are linked to leptin and its receptors. However, the relationship between leptin and gonadotropins, androgens, and insulin in PCOS is still controversial.

AIM

Present investigation attempts to evaluate the interrelationship between serum leptin level with body mass index, insulin and with circulating testosterone in PCOS women.

SUBJECTS AND METHODS

Women diagnosed with either tubal block/male factor infertility (Control; n = 18) and with PCOS (n = 16), enrolled for in vitro fertilization and embryo transfer (IVF-ET), were recruited for this study. All were reviewed for body mass index (BMI), endocrine milieu (including pituitary gonadotropins, TSH, prolactin, gonadal steroids, and insulin) and for circulating serum leptin. Interpretation of data was done using PRISM Statistical Software Package (PRISM Version 4.03@1992-2005; GraphPad Software Inc).

RESULTS

Positive correlation was observed between serum leptin, BMI, and insulin in both the groups. Mean BMI, LH, and LH: FSH ratios were found elevated in the PCOS population. PCOS women also had significantly elevated androgens and fasting levels of insulin.

CONCLUSION

Hyperleptinemia in PCOS women appears to be due to the positive correlation between serum leptin, BMI, and insulin.

The role of leptin in female adolescence

Leptin, the ob gene product, is related to the onset of puberty in animal models, but its role in human puberty is still rather undefined. In prepubertal girls and boys, leptin concentrations increase slowly with age and body-fat mass. In boys, this increase is interrupted in early puberty, when testosterone and lean body mass increase. In girls, leptin, along with the body-fat mass, continue to increase during puberty. Plasma leptin concentrations are significantly correlated with fat mass at all Tanner stages in males and females. The diurnal variation of leptin concentrations seen in adults is apparent for all age groups with no significant changes in the pattern across puberty. Leptin is bound in blood by a high-affinity binding protein identical with the soluble leptin receptor (sOB-R). In the first year of life, the concentration of sOB-R is high, and then a continuous decline of sOB-R follows until midpuberty. The therapeutic response to leptin treatment in a child with leptin deficiency confirms the importance of leptin in the regulation of body weight in humans, and establishes an important role for this hormone in the regulation of appetite. Still no evidence is available that would indicate leptin is a primary signal that initiates the onset of human puberty. Instead, it may act in a permissive way as one of several metabolic factors to allow pubertal maturation to proceed and later reproduction to occur.

Possible interactions between leptin, gonadotrophin-releasing hormone (GnRH-I and II) and human chorionic gonadotrophin (hCG)

Leptin is a metabolic signal to the reproductive axis, where it increases the plasma levels of luteinising hormone (LH) and follicle stimulating hormone (FSH). Since the placental regulation of human chorionic gonadotrophin (hCG) mimics that of the pituitary LH, we undertook this study to see if leptin could be involved in the secretion and synthesis of hCG in first-trimester trophoblast. We incubated cytotrophoblastic cells (CTB) with GnRH-I or GnRH-II, for 4 or 48 h and collected the media at different times thereafter. GnRH-II was more potent than GnRH-I when incubated for 4 h with CTB. Leptin secretion, as measured at 4 h, was significantly stimulated by GnRH-II. When measured at 24 h leptin values were also increased as compared to controls. Neither GnRH-I, nor GnRH-II had any effect on leptin secretion when incubated for 48 h with CTB. Leptin was also added to perifused placental explants, and samples (in which hCG was measured) were collected every 3 min. Leptin significantly stimulated hCG secretion by explants and induced a pulse of hCG immediately (within 6 min) after its injection, increasing significantly the area under the curve (P=0.04) and the amplitude (P=0.02) of hCG pulses. We conclude that GnRH-II is more effective than GnRH-I in stimulating leptin secretion. This difference could be explained by the existence of two different types of placental GnRH receptors or two different pathways of GnRH degradation. Furthermore, we observe that leptin has a significant stimulatory effect on hCG pulsatility.

High versus low body condition in mares: interactions with responses to somatotropin, GnRH analog, and dexamethasone

Mares that had previously been fed to attain body condition scores (BCS) of 7.5 to 8.5 (high) or 3.0 to 3.5 (low) were used to determine the interaction of BCS with the responses to 1) administration of equine somatotropin (eST) daily for 14 d beginning January 20 followed by administration of GnRH analog (GnRHa) daily for 21 d and 2) 4-d treatment with dexamethasone later in the spring when mares in low BCS had begun to ovulate. The majority of mares with high BCS continued to cycle throughout the winter, as evidenced by larger ovaries (P < 0.002), more corpora lutea (P < 0.05), greater progesterone concentrations during eST treatment (P < 0.04), and more (P < 0.05) large- and medium-sized follicles. Treatment with eST alone or in combination with GnRHa had no effect (P > 0.05) on ovarian activity or ovulation. Plasma leptin concentrations were greater (P < 0.002) in mares with high BCS; however, there was no effect (P > 0.10) of eST treatment. Plasma IGF-I concentrations were greater (P < 0.0001) in mares treated with eST compared with mares given vehicle, and mares with high BCS had greater IGF-I (P < 0.02) and LH concentrations (P < 0.02) than mares with low BCS. Plasma leptin concentrations in mares with high BCS were increased (P < 0.001) within 12 h of dexamethasone treatment; the leptin response (P < 0.001) in mares with low BCS was greatly reduced (P < 0.001) and transient. Glucose and insulin concentrations also increased (P < 0.0001) after dexamethasone treatment in both groups, and the magnitude of the response was greater (P < 0.0001) in mares with high BCS than in mares with low BCS. In summary,low BCS in mares was associated with a consistent seasonal anovulatory state that was affected little by eST and GnRHa administration. In contrast, all but one mare with high BCS continued to experience estrous cycles and(or) have abundant follicular activity on their ovaries. The IGF-I response to eST treatment was also reduced in mares with low BCS, as was the basal leptin concentration and leptin response to dexamethasone. Although low BCS and leptin concentrations were associated with inactive ovaries during winter and early spring, mares with low BCS eventually ovulated in April and May while leptin concentrations remained low.

Periodograms and pulse detection methods for pulsatile hormone data

Pulse detection algorithms and spectral analysis are the two most common methods for analysing pulsatile hormone data. We compared a popular high quality pulse detection algorithm (CLUSTER) to spectral analysis on a data set comparing luteinizing hormone data in depressed and control women. For these data, periodogram analysis methods, in particular Fisher's periodicity test, were superior in distinguishing the groups. Extending the pulse detection method to include measures of intra-individual variability improved its discriminatory performance. The two methods complement each other.

Effect of short-term feed restriction and refeeding on serum concentrations of leptin, luteinizing hormone and insulin in ovariectomized gilts

Ovariectomized gilts were either placed on full feed (FF) or restricted to one-third of the full feed amount (RST) for 7 days. Blood samples were taken through jugular catheters every 15 min for 4 h at the end of the 7-day period. Then dietary treatments were reversed and 7 days later samples were taken as before. Serum concentrations of leptin, insulin and luteinizing hormone (LH) were determined by radioimmunoassay. LH pulse frequency and mean serum leptin and insulin concentrations were lower (P < 0.01) in RST than FF gilts. Reversal of treatment reversed the patterns of hormone secretion. These results confirm previous observations that feed restriction can inhibit pulsatile LH secretion and also decrease leptin and insulin secretion.

Leptin and reproduction: a review

OBJECTIVE

To review recent advances in understanding the role of leptin in the physiology and pathophysiology of reproduction, with a focus on relevant clinical situations.

DESIGN

A MEDLINE computer search was performed to identify relevant articles.

RESULT(S)

Leptin, an adipocyte hormone important in regulating energy homeostasis, interacts with the reproductive axis at multiple sites, with stimulatory effects at the hypothalamus and pituitary and inhibitory actions at the gonads. More recently, leptin has been shown to play a role in other target reproductive organs, such as the endometrium, placenta, and mammary gland, with corresponding influences on important physiologic processes such as menstruation, pregnancy, and lactation. As a marker of whether nutritional stores are adequate, leptin may act in concert with gonadotropins and the growth hormone axis to initiate the complex process of puberty. Conditions in which nutritional status is suboptimal, such as eating disorders, exercise-induced amenorrhea, and functional hypothalamic amenorrhea, are associated with low serum leptin levels; and conditions with excess energy stores or metabolic disturbances, such as obesity and polycystic ovarian syndrome, often have elevated serum or follicular fluid leptin levels, raising the possibility that relative leptin deficiency or resistance may be at least partly responsible for the reproductive abnormalities that occur with these conditions.

CONCLUSION(S)

Leptin may act as the critical link between adipose tissue and the reproductive system, indicating whether adequate energy reserves are present for normal reproductive function. Future interventional studies involving leptin administration are expected to further clarify this role of leptin and may provide new therapeutic options for the reproductive dysfunction associated with states of relative leptin deficiency or resistance.

Baseline non-fasting serum leptin concentration to body mass index ratio is predictive of IVF outcomes

BACKGROUND

The present study was designed to determine whether circulating leptin concentrations and/or body mass index (BMI) in women undergoing IVF are predictive of outcomes.

METHODS

IVF cycle outcomes, e.g. fertilization, embryo development, implantation, pregnancy, were analysed relative to baseline (i.e. day gonadotrophin stimulation was initiated) non-fasting serum leptin concentrations and BMI.

RESULTS

Serum leptin concentrations correlated with BMI (r = 0.739, P < 0.0001) as expected. Multiple logistic regression analyses showed correlation between serum leptin and pregnancy success (likelihood ratio = 5.198, P < 0.05), but there was no association between pregnancy and BMI. However, the serum leptin to BMI ratio was more strongly correlated (likelihood ratio = 7.258, P < 0.01) with pregnancy success than was leptin alone. Moreover, women with a low leptin:BMI ratio (< or =0.3) had significantly more superior quality embryos on day 3 post-retrieval (2.5 versus 1.4, P < 0.05, Kruskal-Wallis) and a greater implantation rate (26.7 versus 13.2%, P < 0.025, chi(2)) than women with a high leptin:BMI ratio (> or =0.7).

CONCLUSIONS

The leptin:BMI ratio appears to be highly predictive of IVF success. Elevated leptin concentrations, particularly relative to BMI, may negatively impact fertility by assisted reproduction, possibly through direct ovarian actions resulting in impaired oocyte quality and/or early embryo development.

Neuromodulation in polycystic ovary syndrome

Although central and peripheral factors have been implicated in the neuromodulation of GnRH in PCOS, there are no definitive or conclusive data to establish a primary causal role for any one factor. Because increased GnRH pulse frequency is at least a contributor to the secretion of excess LH and insufficient FSH that are the proximate cause of chronic anovulation in PCOS, strategies to slow the GnRH pulse generator are likely to promote ovulation in women with PCOS. Several pharmacologic agents, such as dopamine agonists and antagonists, have been tried, but the lack of consistent effects in women with PCOS limits their clinical utility. Current treatment strategies include the use of the combined oral contraceptive pills, antiandrogens or androgen receptor blockers, and insulin sensitizers. Oral contraceptive preparations are effective in suppressing ovarian hyperandrogenemia, regulating menstrual cycles, and reducing the risk of endometrial hyperplasia. Androgen blockade and antiandrogens provide symptomatic relief from androgen-induced acne and hirsutism and have been reported to restore ovulation in women with PCOS. Whether this effect is mediated peripherally or centrally remains to be clarified. The most recent class of pharmacologic agents to gain popularity are the "insulin modifiers." With increasing evidence that insulin resistance constitutes a key metabolic element, it seems logical that improving insulin sensitivity and glucose disposal might wholly, or partially, reverse certain features of PCOS, including anovulation. To date, insulin modifiers have proved most promising in improving the clinical features and promoting fertility, but whether this effect is centrally mediated is yet to be elucidated.

Leptin and the hypothalamic-pituitary regulation of the gonadotropin-gonadal axis

Leptin is an adipocyte-derived protein hormone which not only conveys a signal of the amount of energy stores to the central nervous system but also plays an important role in regulating neuroendocrine function. The importance of leptin in the reproductive system has been suggested by the reproductive dysfunction associated with leptin deficiency and resistance in both animal models and humans as well as the ability of leptin to accelerate the onset of reproductive function in normal mice. Transgenic mice overexpressing leptin also have accelerated puberty, and leptin administration reverses the fasting-induced suppression of sexual maturation in rodents, indicating that leptin may serve as the critical link between sufficient energy stores and proper functioning of the reproductive system. Normal women have a pulsatile release pattern of leptin that is significantly associated with the variations in luteinizing hormone (LH) and estradiol levels. In various animal models, leptin administration restores the LH pulsatility pattern which is suppressed during fasting, indicating a hypothalamic site of action since LH pulsatility is under the control of gonadotropin-releasing hormone (GnRH). In humans, leptin has been administered to a 9-year-old leptin-deficient girl, resulting in a gonadotropin secretory pattern consistent with early puberty. While in vitro experiments with hypothalamic explants and a GnRH-secreting neuronal cell line have shown that leptin can directly stimulate GnRH secretion, the lack of leptin receptors on GnRH neurons suggests that leptin may act through other hypothalamic neuropeptides. Several neuropeptides which act as downstream effectors of leptin have been investigated, and recent studies indicate that cocaine and amphetamine-regulated transcript may be such a mediator of leptin's effect on GnRH. Leptin receptors have also been identified in human pituitaries, and leptin may influence LH release from the pituitary. However, the current evidence is conflicting, and further studies are needed in order to clarify leptin's role at the level of the pituitary. Thus, accumulating evidence suggests that leptin can regulate gonadotropin levels, and its secretion may, in turn, be influenced by GnRH or gonadal steroids but appears to be independent of LH control.