Chronobiologic evolution of luteinizing hormone secretion in adolescence: developmental patterns and speculations on the onset of the polycystic ovary syndrome

The role of gonadotropin-releasing hormone neurons in polycystic ovary syndrome

Given the critical central role of gonadotropin-releasing hormone (GnRH) neurons in fertility, it is not surprising that the GnRH neural network is implicated in the pathology of polycystic ovary syndrome (PCOS), the most common cause of anovulatory infertility. Although many symptoms of PCOS relate most proximately to ovarian dysfunction, the central reproductive neuroendocrine system ultimately drives ovarian function through its regulation of anterior pituitary gonadotropin release. The typical cyclical changes in frequency of GnRH release are often absent in women with PCOS, resulting in a persistent high-frequency drive promoting gonadotropin changes (i.e., relatively high luteinizing hormone and relatively low follicle-stimulating hormone concentrations) that contribute to ovarian hyperandrogenemia and ovulatory dysfunction. However, the specific mechanisms underpinning GnRH neuron dysfunction in PCOS remain unclear. Here, we summarize several preclinical and clinical studies that explore the causes of aberrant GnRH secretion in PCOS and the role of disordered GnRH secretion in PCOS pathophysiology.

The neuroendocrine genesis of polycystic ovary syndrome: A role for arcuate nucleus GABA neurons

Polycystic ovary syndrome (PCOS) is a prevalent and distressing endocrine disorder lacking a clearly identified aetiology. Despite its name, PCOS may result from impaired neuronal circuits in the brain that regulate steroid hormone feedback to the hypothalamo-pituitary-gonadal axis. Ovarian function in all mammals is controlled by the gonadotropin-releasing hormone (GnRH) neurons, a small group of neurons that reside in the pre-optic area of the hypothalamus. GnRH neurons drive the secretion of the gonadotropins from the pituitary gland that subsequently control ovarian function, including the production of gonadal steroid hormones. These hormones, in turn, provide important feedback signals to GnRH neurons via a hormone sensitive neuronal network in the brain. In many women with PCOS this feedback pathway is impaired, resulting in the downstream consequences of the syndrome. This review will explore what is currently known from clinical and animal studies about the identity, relative contribution and significance of the individual neuronal components within the GnRH neuronal network that contribute to the pathophysiology of PCOS. We review evidence for the specific neuronal pathways hypothesised to mediate progesterone negative feedback to GnRH neurons, and discuss the potential mechanisms by which androgens may evoke disruptions in these circuits at different developmental time points. Finally, this review discusses data providing compelling support for disordered progesterone-sensitive GABAergic input to GnRH neurons, originating specifically within the arcuate nucleus in prenatal androgen induced forms of PCOS.

Scientific Statement on the Diagnostic Criteria, Epidemiology, Pathophysiology, and Molecular Genetics of Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is a heterogeneous and complex disorder that has both adverse reproductive and metabolic implications for affected women. However, there is generally poor understanding of its etiology. Varying expert-based diagnostic criteria utilize some combination of oligo-ovulation, hyperandrogenism, and the presence of polycystic ovaries. Criteria that require hyperandrogenism tend to identify a more severe reproductive and metabolic phenotype. The phenotype can vary by race and ethnicity, is difficult to define in the perimenarchal and perimenopausal period, and is exacerbated by obesity. The pathophysiology involves abnormal gonadotropin secretion from a reduced hypothalamic feedback response to circulating sex steroids, altered ovarian morphology and functional changes, and disordered insulin action in a variety of target tissues. PCOS clusters in families and both female and male relatives can show stigmata of the syndrome, including metabolic abnormalities. Genome-wide association studies have identified a number of candidate regions, although their role in contributing to PCOS is still largely unknown.

High-Throughput Sequencing Reveals Hypothalamic MicroRNAs as Novel Partners Involved in Timing the Rapid Development of Chicken (Gallus gallus) Gonads

Onset of the rapid gonad growth is a milestone in sexual development that comprises many genes and regulatory factors. The observations in model organisms and mammals including humans have shown a potential link between miRNAs and development timing. To determine whether miRNAs play roles in this process in the chicken (Gallus gallus), the Solexa deep sequencing was performed to analyze the profiles of miRNA expression in the hypothalamus of hens from two different pubertal stages, before onset of the rapid gonad development (BO) and after onset of the rapid gonad development (AO). 374 conserved and 46 novel miRNAs were identified as hypothalamus-expressed miRNAs in the chicken. 144 conserved miRNAs were showed to be differentially expressed (reads > 10, P < 0.05) during the transition from BO to AO. Five differentially expressed miRNAs were validated by real-time quantitative RT-PCR (qRT-PCR) method. 2013 putative genes were predicted as the targets of the 15 most differentially expressed miRNAs (fold-change > 4.0, P < 0.01). Of these genes, 7 putative circadian clock genes, Per2, Bmal1/2, Clock, Cry1/2, and Star were found to be targeted multiple times by the miRNAs. qRT-PCR revealed the basic transcription levels of these clock genes were much higher (P < 0.01) in AO than in BO. Further functional analysis suggested that these 15 miRNAs play important roles in transcriptional regulation and signal transduction pathways. The results provide new insights into miRNAs functions in timing the rapid development of chicken gonads. Considering the characteristics of miRNA functional conservation, the results will contribute to the research on puberty onset in humans.

The Changes They are A-Timed: Metabolism, Endogenous Clocks, and the Timing of Puberty

Childhood obesity has increased dramatically over the last several decades, particularly in industrialized countries, often accompanied by acceleration of pubertal progression and associated reproductive abnormalities (Biro et al., 2006; Rosenfield et al., 2009). The timing of pubertal initiation and progression in mammals is likely influenced by nutritional and metabolic state, leading to the hypothesis that deviations from normal metabolic rate, such as those seen in obesity, may contribute to observed alterations in the rate of pubertal progression. While several recent reviews have addressed the effects of metabolic disorders on reproductive function in general, this review will explore previous and current models of pubertal timing, outlining a potential role of endogenous timing mechanisms such as cellular circadian clocks in the initiation of puberty, and how these clocks might be altered by metabolic factors. Additionally, we will examine recently elucidated neuroendocrine regulators of pubertal progression such as kisspeptin, explore models detailing how the mammalian reproductive axis is silenced during the juvenile period and reactivated at appropriate developmental times, and emphasize how metabolic dysfunction such as childhood obesity may alter timing cues that advance or delay pubertal progression, resulting in diminished reproductive capacity.

Maturation of sleep-wake gonadotrophin-releasing hormone secretion across puberty in girls: potential mechanisms and relevance to the pathogenesis of polycystic ovary syndrome

Neuroendocrine mechanisms underlying the progression of sleep-wake gonadotrophin-releasing hormone (GnRH) pulse secretion across puberty have remained enigmatic. Here, the changes of sleep-wake luteinising hormone (LH) (and, by inference, GnRH) pulse secretion across puberty in normal girls are reviewed, primarily focusing on available human data. It is suggested that the primary control of GnRH pulse frequency changes across puberty, with sex steroid feedback exerting minimal control during childhood, but primary control during adulthood. A working model is proposed regarding how such a transfer of GnRH pulse frequency control may partly account for the prominent day-night differences of GnRH pulse frequency characteristic of puberty. How this model may be relevant to the genesis of abnormal GnRH secretion in peripubertal girls with hyperandrogenaemia is then described.

Interictal and postictal circadian and ultradian luteinizing hormone secretion in men with temporal lobe epilepsy

PURPOSE

Hypothalamic regulation of the reproductive axis in temporal lobe epilepsy (TLE), represented by the ultradian pulsatile secretion of luteinizing hormone (LH), has been shown to be altered interictally and postictally. Our objective is to determine if epilepsy or seizures disrupt normal circadian fluctuations of LH as well as circadian organization of ultradian bursts of LH.

METHODS

We characterized LH secretion in 10 men with TLE during two 24-h blocks: an interictal epoch and a postictal epoch initiated by a seizure. Serum LH was measured every 10 min and characterized by circadian and ultradian patterns with cosinor and deconvolution analysis.

RESULTS

Mean peak serum concentrations of LH occurred at approximately 0400 in controls, were significantly delayed approximately 5 h interictally, and were randomly distributed postictally. Burst amplitudes differed significantly by phase among controls, with the largest amplitudes between 0101 and 0700 and the smallest between 1301 and 1900. No phase differences were present in interictal or postictal epochs. Burst frequency weakly but significantly was slowest between 0101 and 0700 in controls, but did not differ significantly by phase in either interictal or postictal epochs. Postictal LH burst frequencies, but not amplitudes, were significantly decreased immediately postictally.

CONCLUSION

The pulsatile secretion of LH in TLE is abnormal both in the circadian as well as the ultradian domain. Interictal effects consist mainly in loss of circadian fluctuations in LH burst amplitude, whereas postictal effects consist of altered burst timing. Altered daily patterns of neuroendocrine signals may underlie other disorders of homeostasis in TLE.

Ovarian imaging by magnetic resonance in obese adolescent girls with polycystic ovary syndrome: a pilot study

OBJECTIVE

To determine whether magnetic resonance (MR) imaging can serve as a useful investigational tool in the assessment of the polycystic ovary as compared with transabdominal ultrasound (US) for obese adolescents with polycystic ovary syndrome (PCOS).

DESIGN

Prospective observational study.

SETTING

Tertiary university hospital.

PATIENT(S)

Eleven obese adolescents with PCOS.

INTERVENTION(S)

Pelvic MR and US imaging and blood sampling.

MAIN OUTCOME MEASURE(S)

Total ovarian volume and follicle count; mean follicle count per longitudinal cross-section; stromal area; biochemical correlations with measured ovarian parameters.

RESULT(S)

With MR, the mean (+/-SE) total follicle count (21.9 +/- 1.3) was significantly greater than that observed with US (5.5 +/- 1.7) and significantly correlated with total ovarian volume. Two-dimensional cross-sectional analysis of the ovary by MR revealed a significantly greater mean follicle count (12.1 +/- 0.8) compared with the results obtained by US (3.0 +/- 0.5). The stromal area (173.3 +/- 25.1 mm2) was approximately 35% of the total ovarian surface area. No correlations were observed between biochemical indices and measured ovarian parameters.

CONCLUSION(S)

In contrast to US, MR provides vastly greater delineation of the structural components of the ovary in obese girls with PCOS and thus can serve as an excellent investigational technique to assess the morphological transformation of the adolescent ovary.

Direct visual and circadian pathways target neuroendocrine cells in primates

The effect of light on neuroendocrine functions is thought to be mediated through retinal inputs to the circadian pacemaker, the hypothalamic suprachiasmatic nucleus (SCN). The present studies were conducted to provide experimental evidence for this signaling modality in non-human primates. In the St. Kitts vervet monkey, anterograde tracing of SCN efferents revealed a monosynaptic pathway between the circadian clock and hypothalamic neurons producing luteinizing hormone-releasing hormone (LHRH). Using a variety of tracing techniques, direct retinal input was found to be abundant in the SCN and in other hypothalamic sites. Strikingly, in hypothalamic areas other than the SCN, primary visual afferents established direct contacts with neuroendocrine cells including those producing LHRH and dopamine, neurons that are the hypothalamic regulators of pituitary gonadotrops and prolactin. Thus, our data reveal for the first time in primates that light stimuli can reach the hypothalamo-pituitary-gonadal axis, directly providing a pathway independent of but parallel to that of the circadian clock for the photic modulation of hormone release.

Interictal and postictal alterations of pulsatile secretions of luteinizing hormone in temporal lobe epilepsy in men

Mesial temporal lobe epilepsy has been associated with abnormalities of reproductive physiology, but the mechanisms of hormonal dysregulation are not clear. Chronic effects of the epileptic state and the acute impact of seizures could alter hypothalamic function, which is represented by the downstream pulsatile secretion of luteinizing hormone. This study evaluates the interictal and postictal secretion of luteinizing hormone in mesial temporal lobe epilepsy. We characterized luteinizing hormone secretion in patients with mesial temporal lobe epilepsy during two 24-hour epochs: an interictal baseline and a postictal interval initiated by an electrographically confirmed spontaneous seizure. Males, rather than females, were studied so that menstrual cycles could not account for differences between epochs. Blood luteinizing hormone and prolactin (as a positive control) were measured every 10 minutes. Deconvolution analysis defined luteinizing hormone secretion in terms of interpulse interval, amplitude, and mass. Approximate entropy quantitated relative degradation in the orderliness of serial luteinizing hormone release. Interictal baseline epochs were compared to those of healthy controls with unpaired Student's t tests and between interictal and postictal epochs within epileptic patients with paired t tests. Ten epileptic men completed both interictal and postictal epochs. Interictally, seizure patients had lower mean concentrations, slower pulse rates, and higher peak amplitudes than healthy male controls. Within epileptic patients, mean interpulse interval, pulse amplitude, and pulse mass were not affected by the occurrence of seizures, whereas the orderliness of pulse mass decreased postictally. Acute seizures induced timing irregularity in luteinizing hormone secretion, whereas chronic epilepsy was associated with changes in luteinizing hormone pulse frequency, amplitude, and mass. Altered timing and regularity of neuroendocrine pulse patterns may underlie other disorders of homeostasis in mesial temporal lobe epilepsy.

Temporal coupling of luteinizing hormone and follicle stimulating hormone secretion in polycystic ovary syndrome

The aim of this study was to assess the luteinizing hormone (LH) and follicle stimulating hormone (FSH) pulsatile secretion and their temporal relation (concordance) in subjects with polycystic ovary syndrome (PCOS). Fifteen subjects were included in the study (age 17-30 years, body mass index (BMI) 19.38-33.46 kg/m2). For the LH and FSH determinations, blood sampling started at 23.00 and lasted for 6 h with an intersample interval of 10 min. Pulse analysis was carried out using the PulsDetekt program. LH/FSH pulse concordance was calculated using the specific concordance index. Gonadotropin co-pulsatility was found in six subjects who were significantly younger than the others (median 18.5 vs. 22.5 years, p = 0.036). BMI, hirsutism grade, insulin sensitivity, estradiol, progesterone, testosterone, prolactin, cortisol and results obtained from the pulsatility analysis did not significantly differ between the groups. A serum cortisol concentration was correlated with the increased LH/FSH lag time (p = 0.851, p = 0.036) all subjects were included. In conclusion, two distinct LH/FSH secretory patterns were found in PCOS patients, manifested by the presence or absence of the concordance of gonadotropin secretion. In the group where LH/FSH co-pulsatility was present, correlation was found between the serum cortisol and the LH/FSH lag. We also confirmed the finding of previous studies that LH and FSH secretion are regulated by two different mechanisms.