Physiological Significance of the Rhythmic Secretion of Hypothalamic and Pituitary Hormones

Diagnostic algorithm in men suspected with nonobstructive azoospermia

ABSTRACT

This review focuses on the diagnostic algorithm for nonobstructive azoospermia (NOA), a significant male factor contributing to infertility. NOA, characterized by the absence of sperm in the ejaculate, requires a systematic diagnostic approach to identify reversible conditions, genetic factors, and prognosis for achieving pregnancy. The diagnostic pathway involves semen analysis and a comprehensive evaluation for hormonal deficiencies, anatomical abnormalities, and genetic factors. The importance of medical history, physical examination, endocrine evaluation, imaging, and genetic testing is emphasized. This review highlights the significance of differentiating NOA from obstructive azoospermia (OA) and outlines key considerations for effective management, including surgical sperm retrieval and assisted reproductive techniques. Testicular biopsy is discussed as a definitive method to distinguish obstructive cases from nonobstructive cases, providing valuable prognostic information. Overall, a thorough and systematic diagnostic approach is essential for the effective management of men suspected with NOA, offering insights into potential treatment options and reproductive outcomes.

Periodic injections of Relaxin 2, its pharmacokinetics and remodeling of rat hearts

Relaxin-2 (RLX), a critical hormone in pregnancy, has been investigated as a therapy for heart failure. In most studies, the peptide was delivered continuously, subcutaneously for 2 weeks in animals or intravenously for 2-days in human subjects, for stable circulating [RLX]. However, pulsatile hormone levels may better uncover the normal physiology. This premise was tested by subcutaneously injecting Sprague Dawley rats (250 g, N = 2 males, 2 females/group) with human RLX (0, 30, 100, or 500 µg/kg), every 12 h for 1 day, then measuring changes in Nav1.5, connexin43, and β-catenin, 24 h later. Pulsatile RLX was measured by taking serial blood draws, post-injection. After an injection, RLX reached a peak in ∼ 60 min, fell to 50 % in 5-6 h; injections of 0, 30, 100 or 500 µg/kg yielded peak levels of 0, 11.26 ± 3.52, 58.33 ± 16.10, and 209.42 ± 29.04 ng/ml and residual levels after 24-hrs of 0, 4.9, 45.1 and 156 pg/ml, respectively. The 30 µg/kg injections had no effect and 100 µg/kg injections increased Nav1.5 (25 %), Cx43 (30 %) and β-catenin (90 %). The 500 µg/kg injections also increased Nav1.5 and Cx43 but were less effective at upregulating β-catenin (up by 25 % vs. 90 %). Periodic injections of 100 µg/kg were highly effective at increasing the expression of Nav1.5 and Cx43 which are key determinants of conduction velocity in the heart and the suppression of arrhythmias. Periodic RLX is effective at eliciting changes in cardiac protein expression and may be a better strategy for its longer-term delivery in the clinical setting.

Long-Term Effects of Child Early Surgical Ventricular Septal Defect Repair on Maternal Stress

The ventricular septal defect (VSD) represents the most common congenital heart defect (CHD). The diagnosis of and cardiac surgery for their child's VSD are highly stressful experiences for parents; especially mothers, who are at risk of developing long-lasting stress-related symptoms. This study examined long-term alterations in maternal stress including self-reported psychological and biophysiological stress levels in a case-control design. We investigated 24 mothers of children with an isolated, surgically corrected VSD compared to non-affected controls. Maternal self-reports on psychopathology, everyday stress, parenting stress and hair cortisol concentrations (HCC) were measured during children's primary school age (6-9 years, t1) and early adolescence (10-14 years, t2). In maternal self-reports, psychopathology and stress symptoms in the VSD-group and controls were comparable at t1, whereas at t2, mothers in the VSD-group even showed a decrease in psychopathology. Maternal HCC levels in the VSD-group were significantly lower (hypocortisolism) than HCC levels of controls at t1. This effect was no longer observed at t2 reflecting an approximation of HCC levels in the VSD-group to controls' levels. This study highlights the potential for improved stress hormone balance and psychological well-being in mothers following their child's surgical VSD repair. However, the need for parent-centered interventions is discussed, particularly during peri-operative phases and in early child developmental stages.

The Impact of Chronic Stress on Behavior and Body Mass in New Animal Models

(1) Background: Exposure to different sources of stress can have a significant effect on both psychological and physical processes. (2) Methods: The study took place over a period of 34 days and included a total of 40 animals. Regarding the exposure to chronic stressors, we opted for physiological, non-invasive stressors, e.g., running, swimming, and changes in the intensity of light. An unforeseen stress batch was also created that alternated all these stress factors. The animals were divided into five experimental groups, each consisting of eight individuals. In the context of conducting the open field test for behavioral assessment before and after stress exposure, we aimed to investigate the impact of stress exposure on the affective traits of the animals. We also monitored body mass every two days. (3) Results: The control group exhibited an average increase in weight of approximately 30%. The groups exposed to stress factors showed slower growth rates, the lowest being the running group, recording a rate of 20.55%, and the unpredictable stress group at 24.02%. The anxious behavior intensified in the group with unforeseen stress, in the one with light variations, and in the running group. (4) Conclusions: Our research validates the animal model of intermittent light exposure during the dark phase as a novel method of inducing stress. The modification of some anxiety parameters was observed; they vary according to the type of stress. Body mass was found to increase in all groups, especially in the sedentary groups, likely due to the absence of cognitive, spatial, and social stimuli except for cohabitation.

Heart Rate Variability as a Translational Dynamic Biomarker of Altered Autonomic Function in Health and Psychiatric Disease

The autonomic nervous system (ANS) is responsible for the precise regulation of tissue functions and organs and, thus, is crucial for optimal stress reactivity, adaptive responses and health in basic and challenged states (survival). The fine-tuning of central ANS activity relies on the internal central autonomic regulation system of the central autonomic network (CAN), while the peripheral activity relies mainly on the two main and interdependent peripheral ANS tracts, the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS). In disease, autonomic imbalance is associated with decreased dynamic adaptability and increased morbidity and mortality. Acute or prolonged autonomic dysregulation, as observed in stress-related disorders, affects CAN core centers, thereby altering downstream peripheral ANS function. One of the best established and most widely used non-invasive methods for the quantitative assessment of ANS activity is the computerized analysis of heart rate variability (HRV). HRV, which is determined by different methods from those used to determine the fluctuation of instantaneous heart rate (HR), has been used in many studies as a powerful index of autonomic (re)activity and an indicator of cardiac risk and ageing. Psychiatric patients regularly show altered autonomic function with increased HR, reduced HRV and blunted diurnal/circadian changes compared to the healthy state. The aim of this article is to provide basic knowledge on ANS function and (re)activity assessment and, thus, to support a much broader use of HRV as a valid, transdiagnostic and fully translational dynamic biomarker of stress system sensitivity and vulnerability to stress-related disorders in neuroscience research and clinical psychiatric practice. In particular, we review the functional levels of central and peripheral ANS control, the main neurobiophysiologic theoretical models (e.g., polyvagal theory, neurovisceral integration model), the precise autonomic influence on cardiac function and the definition and main aspects of HRV and its different measures (i.e., time, frequency and nonlinear domains). We also provide recommendations for the proper use of electrocardiogram recordings for HRV assessment in clinical and research settings and highlight pathophysiological, clinical and research implications for a better functional understanding of the neural and molecular mechanisms underlying healthy and malfunctioning brain-heart interactions in individual stress reactivity and psychiatric disorders.

The neuroendocrinology of stress: the stress-related continuum of chronic disease development

Stress is defined as a state of threatened homeodynamic balance by a wide range of intrinsic or extrinsic, real or perceived challenges or stimuli, defined as stressors. To preserve this optimal homeodynamic state within a physiologic range, organisms have developed a highly sophisticated system, the stress system, which serves self-regulation and adaptability of the organism by energy redirection according to the current needs. Repeated, ephemeral, and motivating stress states lead to adaptive responses and response habituations, being fairly beneficial; in contrast, inadequate, aversive, excessive, or prolonged stress may surpass the regulatory capacity and adjustive resources of the organism and produce maladaptive responses and a chronically altered homeodynamic state associated with compromised mental and physical health and life expectancy. Neuroendocrine responses to stress depend on developmental timing, duration, time of day and nature of stressors leading to a vulnerable phenotype with disrupted stress reactivity (i.e., hyper- or hypoactivation of the stress system), impaired glucocorticoid signaling, and accumulated cacostatic load with cumulatively elevated long-term risk of mental and physical morbidity. This article offers a brief overview on the organization and physiology of the human stress system and its (re)activity, refreshes the plethora of somatic effects of acute and chronic stress and discusses a conceptual model of acute and chronic stress pathophysiology as a continuum in chronic disease development.

Crosstalk between beta-adrenergic and insulin signaling mediates mechanistic target of rapamycin hyperactivation in liver of high-fat diet-fed male mice

Nonalcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease. While increased nutrient intake and sympathetic activity have been associated with the disease, the pathogenesis of NAFLD remains incompletely understood. We investigated the impact of the interaction of high dietary fat and sugar intake with increased beta-adrenergic receptor (β-AR) signaling on the activity of nutrient-sensing pathways and fuel storage in the liver. C57BL/6J mice were fed a standard rodent diet (STD), a high-fat diet (HFD), a high-fat/high-sugar Western diet (WD), a high-sugar diet with mixed carbohydrates (HCD), or a high-sucrose diet (HSD). After 6 week on diets, mice were treated with isoproterenol (ISO) and the activity of liver mTOR complex 1 (mTORC1)-related signaling analyzed by immunoblotting and correlated with tissue triglyceride and glycogen contents. ISO-stimulated AKT- and ERK-mediated activation of mTORC1 in STD-fed mice. Consumption of all four high-calorie diets exacerbated downstream activation of ribosomal protein S6 kinase beta-1 (S6K1) in response to ISO. S6K1 activity was greater with the fat-enriched HFD and WD and correlated with the presence of metabolic syndrome and a stronger activation of AKT and ERK1/2 pathways. Fat-enriched diets also increased triglyceride accumulation and inhibited glycogen mobilization under β-AR stimulation. In conclusion, crosstalk between β-AR and insulin signaling may contribute to HFD-induced hepatic steatosis through ERK1/2- and AKT-mediated hyperactivation of the mTORC1/S6K1 axis. The findings provide further rationale for the development of therapies aimed at targeting augmented β-AR signaling in the pathogenesis of NAFLD.

Effects of Environmental Endocrine-Disrupting Chemicals on Female Reproductive Health

Environmental endocrine-disrupting chemicals (EDCs) are xenobiotic compounds that are frequently contacted in daily life. With the species and quantity of substances created and utilized by human beings significantly surpassing the self-purification capacity of nature, a large number of hazardous substances are enriched in the human body through the respiratory tract, digestive tract, and skin. Some of these compounds cause many problems endangering female reproductive health by simulating/antagonizing endogenous hormones or affecting the synthesis, metabolism, and bioavailability of endogenous hormones, including reproductive disorders, fetal birth defects, fetal developmental abnormalities, endocrine and metabolic disorders, and even gynecological malignancies. Therefore, the study of the relationship between environmental EDCs and female reproductive diseases and related mechanisms is of considerable significance to women, children health care, and improve the quality of the population.

Traumatic stress and the circadian system: neurobiology, timing and treatment of posttraumatic chronodisruption

Background: Humans have an evolutionary need for a well-preserved internal 'clock', adjusted to the 24-hour rotation period of our planet. This intrinsic circadian timing system enables the temporal organization of numerous physiologic processes, from gene expression to behaviour. The human circadian system is tightly and bidirectionally interconnected to the human stress system, as both systems regulate each other's activity along the anticipated diurnal challenges. The understanding of the temporal relationship between stressors and stress responses is critical in the molecular pathophysiology of stress-and trauma-related diseases, such as posttraumatic stress disorder (PTSD). Objectives/Methods: In this narrative review, we present the functional components of the stress and circadian system and their multilevel interactions and discuss how traumatic stress can affect the harmonious interplay between the two systems. Results: Circadian dysregulation after trauma exposure (posttraumatic chronodisruption) may represent a core feature of trauma-related disorders mediating enduring neurobiological correlates of traumatic stress through a loss of the temporal order at different organizational levels. Posttraumatic chronodisruption may, thus, affect fundamental properties of neuroendocrine, immune and autonomic systems, leading to a breakdown of biobehavioral adaptive mechanisms with increased stress sensitivity and vulnerability. Given that many traumatic events occur in the late evening or night hours, we also describe how the time of day of trauma exposure can differentially affect the stress system and, finally, discuss potential chronotherapeutic interventions. Conclusion: Understanding the stress-related mechanisms susceptible to chronodisruption and their role in PTSD could deliver new insights into stress pathophysiology, provide better psychochronobiological treatment alternatives and enhance preventive strategies in stress-exposed populations.

Regulation and adaptation of endocrine axes at high altitude

As a model of extreme conditions, eight healthy women, part of a 40-member Nepal mountain-climbing expedition, were monitored for dynamic endocrine adaptations. Endocrine measurements were made at frequent intervals over a 6-10-h period at four altitudes: 450 m, 4,800 m (base camp), 6,050 m, and again at 4,800 m (on descent) after an acclimatization (A) period (4,800 mA). Quantified hormones were growth hormone (GH), prolactin (PROL), cortisol (Cort), thyroid-stimulating hormone (TSH), and free thyroxine. These hormones are important to the anabolic/catabolic balance of the body, and are vital to growth, homeostasis, hypothalamic inhibition, regulation of stress, and metabolism. A key secondary question was the degree to which acclimatization can stabilize hormonal disruption. On the basis of statistical false discovery rates, the present analyses unveil marked adaptive changes in the thyroid axis at the level of pulsatile secretion of the pituitary hormone TSH and its downstream product, free thyroxine; strong effects on the mass of GH, TSH, Cort, and PROL secretion per burst; and prominent pulsatile frequency disruption and recovery for PROL and Cort. Because pulsatility changes reflect de facto perturbations in hypothalamo-pituitary control mechanisms, the present data introduce the concept of both frequency- and amplitude-dependent adaptive control of brain-pituitary neuroendocrine signals under conditions of extreme altitude exertion and exposure.

Unextracted plasma oxytocin levels decrease following in-laboratory social exclusion in young adults with a suicide attempt history

Social exclusion is associated with greater suicide risk and more needs to be known about the biological processes contributing to this association. Oxytocin, a neuropeptide that regulates social interactions, may protect against the negative effects of exclusion by motivating social engagement. Oxytocin levels and desire for social engagement increase when non-psychiatric controls experience acute social exclusion. However, among individuals with borderline personality disorder and chronic depression, oxytocin levels decrease following exclusion. Both of these psychiatric illnesses are associated with high rates of suicidal behavior. No research has examined changes in oxytocin following social exclusion among individuals at risk for suicide. This quasi-experimental study examined differences in oxytocin levels and perceptions of social connectedness following an in-laboratory, acute social exclusion task among (a) individuals with no depression or suicide attempt histories, (b) individuals with current depression symptoms, and (c) individuals with current depression symptoms and suicide attempt histories. Young adults (N = 100) completed self-report measures and provided blood samples before and after an acute social exclusion task (Cyberball). Oxytocin was quantified via enzyme-linked immunosorbent assay. Mixed-design ANCOVAs were used to evaluate changes in unextracted and extracted oxytocin levels, desire for emotional support, thwarted belongingness, and perceived burdensomeness. Among suicide attempters, unextracted oxytocin levels decreased and desire for emotional support did not significantly change following exclusion. Among depressed and healthy controls, desire for emotional support increased and unextracted oxytocin levels did not significantly change. No significant changes in extracted oxytocin levels, thwarted belongingness and perceived burdensomeness emerged. Further research is needed to determine if dysregulated oxytocin-related processes biologically predispose individuals with suicide attempt histories to greater social disconnection and suicide risk.

Multiplex Analysis of Circulating Hormone Levels in Rat Models of Age-Related Diseases

This chapter describes the application of multiplex immunoassay of hormones which are known to be present at different levels during aging and may therefore be precipitous in age-related diseases. As an example, we have analyzed serum from 12-week-old rats using multiplexes for the hormones insulin, leptin, growth hormone, corticosterone, and testosterone, which have been implicated in sarcopenia. The same technique can be used in the investigation of other sarcopenia biomarkers as well as in other disease cases involving both clinical and preclinical biomarker studies.

The circadian expression of osteogenic factors in periodontal tissue loading mechanical force: new concepts of the personalized orthodontic care

Objective

The need for orthodontic treatment continues to increase. Strategies that shorten the treatment course and reduce discomfort are most welcome in clinic. Circadian rhythm plays important role in various physiological processes, including bone formation. This study intended to depict a possible circadian releasing property of the osteogenic factors within the periodontal tissue during orthodontic treatment, which may direct a more efficient and satisfactory orthodontic treatment to the patient.

Methods

Primary periodontal ligament cells (PDLCs) were obtained from the Sprague-Dawley (SD) rats. An equibiaxial strain value of 12% was applied on rat PDLCs (rPDLCs). After 2 h stimuli of 10^-7 M dexamethasone (DX), the osteogenic genes' expressions were detected by real-time polymerase chain reaction (RT-PCR) at Zeitgeber times 0, 4, 8, 12, 16, 20, and 24. An orthodontic appliance was placed on 45 SD rats. Animals were maintained under 12-h light/dark periods and euthanized at 9 time points over the diurnal cycle. The orthodontic sensitive tissues of the mesial root of the maxillary first molar were collected for RT-PCR and immunohistological assay.

Results

The rPDLCs displayed typical fibroblastic spindle shape, and subcultured steadily in vitro. Induced by DX, the mRNA expression of Col-1, OPN, and IBSP within the loaded/unloaded rPDLCs oscillated as that of the main clock gene Per-1. The osteogenic genes' expressions as well as the protein releases sustained a circadian oscillation trend in vivo.

Conclusions

This study indicates the existence of a circadian rhythm of the osteogenic factors within the orthodontic sensitive tissues, which highlights the importance of precise timing of force loading in further orthodontic treatment. Thus, a periodicity pattern of orthodontic traction at night may prove a more efficient tooth movement while minimizing the treatment window and discomfort complains.

Developmental Trajectories of Early Life Stress and Trauma: A Narrative Review on Neurobiological Aspects Beyond Stress System Dysregulation

Early life stressors display a high universal prevalence and constitute a major public health problem. Prolonged psychoneurobiological alterations as sequelae of early life stress (ELS) could represent a developmental risk factor and mediate risk for disease, leading to higher physical and mental morbidity rates in later life. ELS could exert a programming effect on sensitive neuronal brain networks related to the stress response during critical periods of development and thus lead to enduring hyper- or hypo-activation of the stress system and altered glucocorticoid signaling. In addition, alterations in emotional and autonomic reactivity, circadian rhythm disruption, functional and structural changes in the brain, as well as immune and metabolic dysregulation have been lately identified as important risk factors for a chronically impaired homeostatic balance after ELS. Furthermore, human genetic background and epigenetic modifications through stress-related gene expression could interact with these alterations and explain inter-individual variation in vulnerability or resilience to stress. This narrative review presents relevant evidence from mainly human research on the ten most acknowledged neurobiological allostatic pathways exerting enduring adverse effects of ELS even decades later (hypothalamic-pituitary-adrenal axis, autonomic nervous system, immune system and inflammation, oxidative stress, cardiovascular system, gut microbiome, sleep and circadian system, genetics, epigenetics, structural, and functional brain correlates). Although most findings back a causal relation between ELS and psychobiological maladjustment in later life, the precise developmental trajectories and their temporal coincidence has not been elucidated as yet. Future studies should prospectively investigate putative mediators and their temporal sequence, while considering the potentially delayed time-frame for their phenotypical expression. Better screening strategies for ELS are needed for a better individual prevention and treatment.

Multilevel Interactions of Stress and Circadian System: Implications for Traumatic Stress

The dramatic fluctuations in energy demands by the rhythmic succession of night and day on our planet has prompted a geophysical evolutionary need for biological temporal organization across phylogeny. The intrinsic circadian timing system (CS) represents a highly conserved and sophisticated internal "clock," adjusted to the 24-h rotation period of the earth, enabling a nyctohemeral coordination of numerous physiologic processes, from gene expression to behavior. The human CS is tightly and bidirectionally interconnected to the stress system (SS). Both systems are fundamental for survival and regulate each other's activity in order to prepare the organism for the anticipated cyclic challenges. Thereby, the understanding of the temporal relationship between stressors and stress responses is critical for the comprehension of the molecular basis of physiology and pathogenesis of disease. A critical loss of the harmonious timed order at different organizational levels may affect the fundamental properties of neuroendocrine, immune, and autonomic systems, leading to a breakdown of biobehavioral adaptative mechanisms with increased stress sensitivity and vulnerability. In this review, following an overview of the functional components of the SS and CS, we present their multilevel interactions and discuss how traumatic stress can alter the interplay between the two systems. Circadian dysregulation after traumatic stress exposure may represent a core feature of trauma-related disorders mediating enduring neurobiological correlates of trauma through maladaptive stress regulation. Understanding the mechanisms susceptible to circadian dysregulation and their role in stress-related disorders could provide new insights into disease mechanisms, advancing psychochronobiological treatment possibilities and preventive strategies in stress-exposed populations.

Early life stress and trauma: developmental neuroendocrine aspects of prolonged stress system dysregulation

Experience of early life stress (ELS) and trauma is highly prevalent in the general population and has a high public health impact, as it can trigger a health-related risk cascade and lead to impaired homeostatic balance and elevated cacostatic load even decades later. The prolonged neuropsychobiological impact of ELS can, thus, be conceptualized as a common developmental risk factor for disease associated with increased physical and mental morbidity in later life. ELS during critical periods of brain development with elevated neuroplasticity could exert a programming effect on particular neuronal networks related to the stress response and lead to enduring neuroendocrine alterations, i.e., hyper- or hypoactivation of the stress system, associated with adult hypothalamic-pituitary-adrenal axis and glucocorticoid signaling dysregulation. This paper reviews the pathophysiology of the human stress response and provides evidence from human research on the most acknowledged stress axis-related neuroendocrine pathways exerting the enduring adverse effects of ELS and mediating the cumulative long-term risk of disease vulnerability in adulthood.

Molecular basis of growth hormone daily mRNA and protein synthesis in rats

AIMS

Daily and seasonal rhythms coordinate the endocrine and metabolic functions. The pituitary gland is the master regulator of several endocrine activities, and its function is classically regulated by endocrine signals from its target glands as well as from the hypothalamus. The growth hormone (GH) produced and secreted by the anterior pituitary presents a pulsatile secretion throughout the 24-hour cycle. However, the molecular mechanisms regulating the daily pattern of GH secretion are still unclear. Herein we investigated whether circadian GH mRNA and protein synthesis is modulated by acute adjustments in the stability and expression of GH mRNA.

MAIN METHODS

GH mRNA and protein content were evaluated by real-time PCR and Western blotting, respectively, in pituitary gland of rats euthanized every 3 h during a 24-h period at the Zeitgeber times (ZT3 to ZT24). The GH mRNA poly(A) tail length was determined by RACE-PAT assay.

KEY FINDINGS

We identified two main peaks of GH mRNA level in the pituitary gland of rats; one in the middle of the light-cycle and another in the middle of the dark-cycle. The latter was associated with an increase in pituitary GH protein content. Interestingly, an increment in the poly(A) tail length of the GH transcript was observed in association to reduced migration rate of the GH transcript and increased mRNA content in the dark-cycle period.

SIGNIFICANCE

Our findings provide evidence that changes in the GH mRNA poly(A) length may underlie the circadian pattern of GH mRNA and protein levels in the pituitary gland of rats.

β-arrestin signalling and bias in hormone-responsive GPCRs

G protein-coupled receptors (GPCRs) play crucial roles in the ability of target organs to respond to hormonal cues. GPCRs' activation mechanisms have long been considered as a two-state process connecting the agonist-bound receptor to heterotrimeric G proteins. This view is now challenged as mounting evidence point to GPCRs being connected to large arrays of transduction mechanisms involving heterotrimeric G proteins as well as other players. Amongst the G protein-independent transduction mechanisms, those elicited by β-arrestins upon their recruitment to the active receptors are by far the best characterized and apply to most GPCRs. These concepts, in conjunction with remarkable advances made in the field of GPCR structural biology and biophysics, have supported the notion of ligand-selective signalling also known as pharmacological bias. Interestingly, recent reports have opened intriguing prospects to the way β-arrestins control GPCR-mediated signalling in space and time within the cells. In the present paper, we review the existing evidence linking endocrine-related GPCRs to β-arrestin recruitement, signalling, pathophysiological implications and selective activation by biased ligands and/or receptor modifications. Emerging concepts surrounding β-arrestin-mediated transduction are discussed in the light of the peculiarities of endocrine systems.

Monitoring steroid replacement therapy in children with congenital adrenal hyperplasia

BACKGROUND

The objective of this study was to compare the analysis of 17-hydroxyprogesterone (17-OHP) by radio-immunoassay (RIA) in serum with analysis by liquid chromatography tandem mass spectrometry (LC-MS/MS) on dried blood spot samples (DBSS) for monitoring therapy in children with congenital adrenal hyperplasia (CAH), and to investigate differences in 17-OHP values during the day.

METHODS

Fourteen children (8 females), median age 4.2 (0.3-16.0) years, were studied. Serum samples and DBSS were drawn before hydrocortisone dosing.

RESULTS

17-OHP by LC-MS/MS in DBSS were highly correlated to 17-OHP by RIA in serum, r=0.956, p<0.01. A total of 26 three-time-point series were investigated. Using only the afternoon 17-OHP values to determine the hydrocortisone doses would have led to overdosing seven times and underdosing six times.

CONCLUSIONS

Good agreement was demonstrated between 17-OHP determination by RIA in serum and LC-MS/MS on DBSS. Multiple 17-OHP measurements per day are required to ensure sufficient hydrocortisone dose adjustment.

Potential pleiotropic beneficial effects of adjuvant melatonergic treatment in posttraumatic stress disorder

Loss of circadian rhythmicity fundamentally affects the neuroendocrine, immune, and autonomic system, similar to chronic stress and may play a central role in the development of stress-related disorders. Recent articles have focused on the role of sleep and circadian disruption in the pathophysiology of posttraumatic stress disorder (PTSD), suggesting that chronodisruption plays a causal role in PTSD development. Direct and indirect human and animal PTSD research suggests circadian system-linked neuroendocrine, immune, metabolic and autonomic dysregulation, linking circadian misalignment to PTSD pathophysiology. Recent experimental findings also support a specific role of the fundamental synchronizing pineal hormone melatonin in mechanisms of sleep, cognition and memory, metabolism, pain, neuroimmunomodulation, stress endocrinology and physiology, circadian gene expression, oxidative stress and epigenetics, all processes affected in PTSD. In the current paper, we review available literature underpinning a potentially beneficiary role of an add-on melatonergic treatment in PTSD pathophysiology and PTSD-related symptoms. The literature is presented as a narrative review, providing an overview on the most important and clinically relevant publications. We conclude that adjuvant melatonergic treatment could provide a potentially promising treatment strategy in the management of PTSD and especially PTSD-related syndromes and comorbidities. Rigorous preclinical and clinical studies are needed to validate this hypothesis.

The Blood-Brain Barrier: Regulatory Roles in Wakefulness and Sleep

Sleep and its disorders are known to affect the functions of essential organs and systems in the body. However, very little is known about how the blood-brain barrier (BBB) is regulated. A few years ago, we launched a project to determine the impact of sleep fragmentation and chronic sleep restriction on BBB functions, including permeability to fluorescent tracers, tight junction protein expression and distribution, glucose and other solute transporter activities, and mediation of cellular mechanisms. Recent publications and relevant literature allow us to summarize here the sleep-BBB interactions in five sections: (1) the structural basis enabling the BBB to serve as a huge regulatory interface; (2) BBB transport and permeation of substances participating in sleep-wake regulation; (3) the circadian rhythm of BBB function; (4) the effect of experimental sleep disruption maneuvers on BBB activities, including regional heterogeneity, possible threshold effect, and reversibility; and (5) implications of sleep disruption-induced BBB dysfunction in neurodegeneration and CNS autoimmune diseases. After reading the review, the general audience should be convinced that the BBB is an important mediating interface for sleep-wake regulation and a crucial relay station of mind-body crosstalk. The pharmaceutical industry should take into consideration that sleep disruption alters the pharmacokinetics of BBB permeation and CNS drug delivery, being attentive to the chrono timing and activation of co-transporters in subjects with sleep disorders.

Intranasal Human Growth Hormone (hGH) Induces IGF-1 Levels Comparable With Subcutaneous Injection With Lower Systemic Exposure to hGH in Healthy Volunteers

CONTEXT

The development of an improved, efficacious human GH (hGH) product administered by a noninjectable route of delivery such as the nasal route is highly desirable. We have developed a novel nasal hGH product (CP024) that showed excellent nasal absorption in animal models; however, the translation of these results into the clinical setting is essential because past attempts to develop such formulations by other groups have been unable to induce IGF-1 in man.

OBJECTIVE

The objective of the study was to assess the pharmacokinetics, pharmacodynamics, and tolerability of CP024 compared with a sc hGH injection.

DESIGN

This was a single-center, nonrandomized placebo-controlled, open-label, five-way crossover study in eight healthy volunteers.

SETTING

The study was carried out at a contract research organization, Quotient Bioresearch.

VOLUNTEERS

Eight healthy male volunteers, given an iv infusion of octreotide to suppress the endogenous GH secretion during the study period, participated in the study. No volunteers were withdrawn due to side effects.

MAIN OUTCOME MEASURES

Measurement of hGH and IGF-1 levels and tolerability of the drug product was performed.

RESULTS

No serious adverse events were reported and no subjects withdrawn from study due to the treatment. After the nasal administration of CP024, 3-fold higher hGH blood levels were obtained as compared with hGH nasal control. The relative bioavailability was about 3%. CP024 (given twice daily) induced a significant increase in IGF-1 levels up to 19 hours after administration, with no significant difference to those obtained after the sc injection of hGH.

CONCLUSIONS

The study indicates that CP024 is a promising candidate for an efficacious nasal product for the treatment of GH deficiency due to induction of IGF-1 similar to that after a sc injection, despite the lower plasma hGH concentration obtained. A dose-response study is needed to evaluate the optimal nasal dose.

Neuropeptidergic control of sleep and wakefulness

Sleep and wake are fundamental behavioral states whose molecular regulation remains mysterious. Brain states and body functions change dramatically between sleep and wake, are regulated by circadian and homeostatic processes, and depend on the nutritional and emotional condition of the animal. Sleep-wake transitions require the coordination of several brain regions and engage multiple neurochemical systems, including neuropeptides. Neuropeptides serve two main functions in sleep-wake regulation. First, they represent physiological states such as energy level or stress in response to environmental and internal stimuli. Second, neuropeptides excite or inhibit their target neurons to induce, stabilize, or switch between sleep-wake states. Thus, neuropeptides integrate physiological subsystems such as circadian time, previous neuron usage, energy homeostasis, and stress and growth status to generate appropriate sleep-wake behaviors. We review the roles of more than 20 neuropeptides in sleep and wake to lay the foundation for future studies uncovering the mechanisms that underlie the initiation, maintenance, and exit of sleep and wake states.

Developmental perspectives on oxytocin and vasopressin

The related neuropeptides oxytocin and vasopressin are involved in species-typical behavior, including social recognition behavior, maternal behavior, social bonding, communication, and aggression. A wealth of evidence from animal models demonstrates significant modulation of adult social behavior by both of these neuropeptides and their receptors. Over the last decade, there has been a flood of studies in humans also implicating a role for these neuropeptides in human social behavior. Despite popular assumptions that oxytocin is a molecule of social bonding in the infant brain, less mechanistic research emphasis has been placed on the potential role of these neuropeptides in the developmental emergence of the neural substrates of behavior. This review summarizes what is known and assumed about the developmental influence of these neuropeptides and outlines the important unanswered questions and testable hypotheses. There is tremendous translational need to understand the functions of these neuropeptides in mammalian experience-dependent development of the social brain. The activity of oxytocin and vasopressin during development should inform our understanding of individual, sex, and species differences in social behavior later in life.

Episodic hormone secretion: a comparison of the basis of pulsatile secretion of insulin and GnRH

Rhythms govern many endocrine functions. Examples of such rhythmic systems include the insulin-secreting pancreatic beta-cell, which regulates blood glucose, and the gonadotropin-releasing hormone (GnRH) neuron, which governs reproductive function. Although serving very different functions within the body, these cell types share many important features. Both GnRH neurons and beta-cells, for instance, are hypothesized to generate at least two rhythms endogenously: (1) a burst firing electrical rhythm and (2) a slower rhythm involving metabolic or other intracellular processes. This review discusses the importance of hormone rhythms to both physiology and disease and compares and contrasts the rhythms generated by each system.

Impact of light/dark cycle patterns on oxidative stress in an adriamycin-induced nephropathy model in rats

The principal goal of this study was to determine the effect of the photoperiod on oxidative damage biomarkers in rats submitted to different light/darkness patterns, in a hyperlipidemic nephropathy model (induced by adriamycin), as well as its possible relationship with melatonin and leptin secretion rhythms. To test this hypothesis, six different groups were used (N = 6 rats per group): control (12 h/12h light:dark); exposure to permanent illumination (24 h light); exposure to darkness (22 h dark); injected with adriamycin, 12h/12h light:dark; injected with adriamycin + exposure to permanent illumination and injected with adriamycin + exposure to darkness (22 h dark). The different photoperiods were begun two weeks prior to medication and were maintained up to the day of the animal's sacrifice, ten days after medication. The following parameters were analysed: i) weight evolution; ii) in plasma: urea, creatinine, uric acid, total proteins, albumen, lactate dehydrogenase, creatinine-quinase, aspartate aminotransferase, alanine aminotransferase and total cholesterol; iii) in urine: urea, creatinine, total proteins and microalbumen; iv) biomarkers of oxidative damage in kidneys, heart, liver and brain: lipoperoxides, total glutathione, reduced glutathione, catalase, glutathione peroxidase, glutathione reductase and glutathione transferase; v) melatonin (pineal gland tissue and plasma) and leptin (plasma). From the results obtained it was concluded that the administration of adriamycin generated oxidative stress in renal, cerebral, hepatic and cardiac tissue. Additionally, in the healthy animal, but of a lesser relevance in the adriamycin animal, permanent light worsened the oxidative stress, whereas darkness improved it. This could be related to the circadian rhythm of the inverse release shown by melatonin and leptin, accentuating the release of melatonin in the darkness phase and that of leptin in the light phase. The correlation between melatonin and leptin in the healthy animal seemed to confirm the relationship between both variables and their influence on oxidative damage biomarkers.

The trouble with circadian clock dysfunction: multiple deleterious effects on the brain and body

This review consolidates research employing human correlational and experimental work across brain and body with experimental animal models to provide a more complete representation of how circadian rhythms influence almost all aspects of life. In doing so, we will cover the morphological and biochemical pathways responsible for rhythm generation as well as interactions between these systems and others (e.g., stress, feeding, reproduction). The effects of circadian disruption on the health of humans, including time of day effects, cognitive sequelae, dementia, Alzheimer's disease, diet, obesity, food preferences, mood disorders, and cancer will also be discussed. Subsequently, experimental support for these largely correlational human studies conducted in non-human animal models will be described.

Low-dose effects of hormones and endocrine disruptors

Endogenous hormones have effects on tissue morphology, cell physiology, and behaviors at low doses. In fact, hormones are known to circulate in the part-per-trillion and part-per-billion concentrations, making them highly effective and potent signaling molecules. Many endocrine-disrupting chemicals (EDCs) mimic hormones, yet there is strong debate over whether these chemicals can also have effects at low doses. In the 1990s, scientists proposed the "low-dose hypothesis," which postulated that EDCs affect humans and animals at environmentally relevant doses. This chapter focuses on data that support and refute the low-dose hypothesis. A case study examining the highly controversial example of bisphenol A and its low-dose effects on the prostate is examined through the lens of endocrinology. Finally, the chapter concludes with a discussion of factors that can influence the ability of a study to detect and interpret low-dose effects appropriately.

Principles of endocrinology

The endocrine system plays a major role in human survival. Endocrine glands secrete chemical messengers or hormones that affect every tissue of the body, including the periodontium, during the life of the individual. As the endocrine system influences a broad assortment of biological activities necessary for life, a general understanding of the principal components and functions of this system is essential. A fundamental assessment of hormone structure, mechanism of action and hormone transport, as well as influence on homeostasis is reviewed. A concise evaluation of the functions of the central endocrine glands, the functions of the major peripheral endocrine glands (other than gonadal tissues) and the known relationships of these hormones to the periodontium is examined.

Testosterone Restoration by Enclomiphene Citrate in Men with Secondary Hypogonadism: Pharmacodynamics and Pharmacokinetics

OBJECTIVES

To determine the pharmacodynamic (PD) profile of serum total testosterone levels (TT) and luteinizing hormone (LH) in men with secondary hypogonadism following initial and chronic daily oral doses of enclomiphene citrate in comparison to transdermal testosterone. To determine the effects of daily oral doses of enclomiphene citrate (Androxal®) in comparison to transdermal testosterone on other hormones and markers in men with secondary hypogonadism.

PATIENTS AND METHODS

This was a randomized, single blind, two-center phase II study to evaluate three different doses of enclomiphene citrate (6.25mg, 12.5mg and 25 mg Androxal®), versus AndroGel®, a transdermal testosterone, on 24-hour LH and TT in otherwise normal healthy men with secondary hypogonadism. Forty-eight men were enrolled in the trial (ITT Population), but 4 men had T levels >350 ng/dL at baseline. Forty-four men completed the study per protocol (PP population). All subjects enrolled in this trial had serum TT in the low range (<350 ng/dL) and had low to normal LH (<12 IU/L) on at least two occasions. TT and LH levels were assessed each hour for 24 hours to examine the effects at each of three treatment doses of enclomiphene versus a standard dose (5 grams) of transdermal testosterone (AndroGel). In the initial profile TT and LH were determined in a naïve population following a single initial oral or transdermal treatment (Day 1). This was contrasted to that seen after six weeks of continuous daily oral or transdermal treatment (Day 42). The pharmacokinetics of enclomiphene was performed in a select subpopulation. Serum samples were obtained over the course of the study to determine levels of various hormones and lipids.

RESULTS

After six weeks of continuous use, the mean ± SD concentration of TT at Day 42 C0hrTT, was 604 ± 160 ng/dL for men taking the highest of dose of enclomiphene citrate (enclomiphene, 25 mg daily) and 500 ± 278 ng in those men treated with transdermal testosterone. These values were higher than Day 1 values but not different from each other (p = 0.23, T-test). All three doses of enclomiphene increased C0hrTT, CavgTT, CmaxTT, CminTT and CrangeTT. Transdermal testosterone also raised TT, albeit with more variability, and with suppressed LH levels. The patterns of TT over 24 hour period following six weeks of dosing could be fit to a non-linear function with morning elevations, mid-day troughs, and rising night-time levels. Enclomiphene and transdermal testosterone increased levels of TT within two weeks, but they had opposite effects on FSH and LH Treatment with enclomiphene did not significantly affect levels of TSH, ACTH, cortisol, lipids, or bone markers. Both transdermal testosterone and enclomiphene citrate decreased IGF-1 levels (p<0.05) but suppression was greater in the enclomiphene citrate groups.

CONCLUSIONS

Enclomiphene citrate increased serum LH and TT; however, there was not a temporal association between the peak drug levels and the Cmax levels LH or TT. Enclomiphene citrate consistently increased serum TT into the normal range and increased LH and FSH above the normal range. The effects on LH and TT persisted for at least one week after stopping treatment.

Analysis of the impact of intravenous LH pulses versus continuous LH infusion on testosterone secretion during GnRH-receptor blockade

Gonadotrophin-releasing hormone (GnRH) pulsatility is required for optimal luteinizing hormone (LH) secretion, but whether LH pulsatility is required for physiological testosterone (T) secretion is not known. To test the postulate that pulses of recombinant human (rh) LH stimulate greater T secretion than continuous infusion of the same dose, a potent selective GnRH antagonist was administered overnight to 19 healthy men ages 18-49 yr. Subjects then received saline or rhLH intravenously continuously or as 6-min pulses intravenously every 1 or 2 h at the same total dose. Blood was sampled every 10 min for 10 h to quantify T responses. For the four interventions, the descending rank order of mean LH and mean T concentrations was 1-h = 2-h rhLH pulses > continuous rhLH > saline (P < 10(-3)). Plateau LH and T concentrations correlated positively (R(2) = 0.943, P = 0.029) as did LH concentrations and LH half-lives (R(2) = 0.962, P = 0.019). Percentage pulsatile T secretion assessed by deconvolution analysis (Keenan DM, Takahashi PY, Liu PY, Roebuck PD, Nehra AX, Iranmanesh A, Veldhuis JD. Endocrinology 147: 2817-2828, 2006) was the highest (P = 0.019), and half-time to attain peak T concentrations was the shortest (P < 10(-6)), for 1-h rhLH pulses. Approximate entropy (a pattern-regularity measure) revealed more orderly T secretion for 1- than 2-h rhLH pulses (P = 0.0076). Accordingly, a pulsatile LH signal, while not obligatory to maintain mean T concentrations, controls the mean plasma LH concentration and determines quantifiable patterns of T secretion. These data introduce the question whether blood T patterns in turn supervise distinctive target-tissue responses.

Hormones and endocrine-disrupting chemicals: low-dose effects and nonmonotonic dose responses

For decades, studies of endocrine-disrupting chemicals (EDCs) have challenged traditional concepts in toxicology, in particular the dogma of "the dose makes the poison," because EDCs can have effects at low doses that are not predicted by effects at higher doses. Here, we review two major concepts in EDC studies: low dose and nonmonotonicity. Low-dose effects were defined by the National Toxicology Program as those that occur in the range of human exposures or effects observed at doses below those used for traditional toxicological studies. We review the mechanistic data for low-dose effects and use a weight-of-evidence approach to analyze five examples from the EDC literature. Additionally, we explore nonmonotonic dose-response curves, defined as a nonlinear relationship between dose and effect where the slope of the curve changes sign somewhere within the range of doses examined. We provide a detailed discussion of the mechanisms responsible for generating these phenomena, plus hundreds of examples from the cell culture, animal, and epidemiology literature. We illustrate that nonmonotonic responses and low-dose effects are remarkably common in studies of natural hormones and EDCs. Whether low doses of EDCs influence certain human disorders is no longer conjecture, because epidemiological studies show that environmental exposures to EDCs are associated with human diseases and disabilities. We conclude that when nonmonotonic dose-response curves occur, the effects of low doses cannot be predicted by the effects observed at high doses. Thus, fundamental changes in chemical testing and safety determination are needed to protect human health.

Deficiency in androgens and upregulation of insulin-like growth factor-1 are involved in high bone turnover in men receiving androgen deprivation therapy for prostate cancer

OBJECTIVE

This study was performed to elucidate the mechanism of high bone turnover during androgen deprivation therapy (ADT) in terms of osteogenic endocrine activity by testosterone, adrenal androgens, and insulin-like growth factor-1 (IGF-I), and to identify markers reflecting the bone mineral density (BMD) during ADT.

DESIGN

BMD and samples of blood and urine were studied before and after 6months of ADT in 70 patients with localized prostate cancer.

RESULTS

Before ADT, serum free-testosterone, dehydroepiandrosterone sulfate (DHEA-S), androstenedione, and IGF-I levels were correlated with BMD (rs=0.344, p=0.004; rs=0.264, p=0.027; rs=0.329, p=0.005; rs=0.300, p=0.012, respectively). The serum IGF-I level was independently correlated with the pretreatment BMD (Multivariate p=0.001). These relationships disappeared after ADT (p=0.519, 0.316, 0.116, and 0.597, respectively). After ADT, serum levels of free-testosterone decreased (7.9 to 0.2pg/mL), and DHEA-S and androstenedione were also reduced (3.6 to 2.3μmol/L and 5.6 to 2.9nmol/L, respectively) (p<0.001 in all). In contrast, IGF-I levels were elevated after ADT by 11.6% (19.9 to 22.3nmol/L, p<0.001). Delta-values of IGF-I (post- minus pretreatment levels, mean: +2.2, ranged between -7.1 and +15.3) were inversely correlated with the pretreatment (rs=-0.333 p=0.005) and post-treatment (rs=-0.408, p=0.001) BMD. After ADT, the serum IGF-I level was closely correlated with the serum level of the bone formation marker bone-specific alkaline phosphatase (BAP) (rs=0.328, p=0.006), and delta-IGF-I and delta-BAP showed a close positive correlation (rs=0.388, p=0.001). The post-treatment BMD was correlated only with the urine deoxypyridinoline (DPD) concentration (rs=-0.302, p=0.024) among the bone formation/resorption markers including serum/urine N-telopeptide.

CONCLUSIONS

Serum IGF-I levels increased during ADT in men with a low BMD. Coupled with reduced androgen levels, elevated IGF-I levels, which were positively correlated with BAP during ADT, possibly explain the mechanism of ADT-related high bone turnover. The increase of IGF-I is more prominent in men whose BMD is already low at the baseline, and urine DPD might be a marker that reflects BMD during ADT.

Regulated recovery of pulsatile growth hormone secretion from negative feedback: a preclinical investigation

Although stimulatory (feedforward) and inhibitory (feedback) dynamics jointly control neurohormone secretion, the factors that supervise feedback restraint are poorly understood. To parse the regulation of growth hormone (GH) escape from negative feedback, 25 healthy men and women were studied eight times each during an experimental GH feedback clamp. The clamp comprised combined bolus infusion of GH or saline and continuous stimulation by saline GH-releasing hormone (GHRH), GHRP-2, or both peptides after randomly ordered supplementation with placebo (both sexes) vs. E(2) (estrogen; women) and T (testosterone; men). Endpoints were GH pulsatility and entropy (a model-free measure of feedback quenching). Gender determined recovery of pulsatile GH secretion from negative feedback in all four secretagog regimens (0.003 ≤ P ≤ 0.017 for women>men). Peptidyl secretagog controlled the mass, number, and duration of feedback-inhibited GH secretory bursts (each, P < 0.001). E(2)/T administration potentiated both pulsatile (P = 0.006) and entropic (P < 0.001) modes of GH recovery. IGF-I positively predicted the escape of GH secretory burst number and mode (P = 0.022), whereas body mass index negatively forecast GH secretory burst number and mass (P = 0.005). The composite of gender, body mass index, E(2), IGF-I, and peptidyl secretagog strongly regulates the escape of pulsatile and entropic GH secretion from autonegative feedback. The ensemble factors identified in this preclinical investigation enlarge the dynamic model of GH control in humans.

Insulin-like growth factor-1 is associated with regulation of the luteinizing hormone production in men receiving androgen deprivation therapy with gonadotropin-releasing hormone analogues for localized prostate cancer

BACKGROUND

Luteinizing hormone (LH) during androgen-deprivation therapy (ADT) with gonadotropin-releasing hormone analogues (GnRHa) has been thought to be biologically inactive, and the regulation of LH during ADT with GnRHa is thus unknown. Insulin-like growth factor-1 (IGF-1) is involved in the regulation of cell proliferation and differentiation, and IGF-1 production in the liver is dependent on growth hormone (GH) secretion from the anterior pituitary. Despite the presence of IGF-1 receptors in the gonadotroph, associations between the GH/IGF-1 and pituitary-gonadal axes, e.g., whether IGF-1 elicits the LH secretion, remain unclear.

METHODS

Seventy-one patients with localized prostate cancer, who received ADT with GnRHa, were prospectively studied based on their blood samples before treatment and after ADT for 6 months. We employed highly sensitive assays for measurement of serum testosterone (electrochemiluminescence immunoassay), GH/IGF-1 (radioimmunoassay), adrenocorticotropic hormone (ACTH: immunoradiometric assay), LH (chemiluminescent immunoassay), and dehydroepiandrosterone sulfate (DHEA-S: chemiluminescent enzyme immunoassay).

RESULTS

No correlation was noted between the pretreatment LH and IGF-1 levels; after ADT, the serum LH level was closely correlated with the IGF-1 concentration [Spearman's correlation coefficient (rs) = 0.370, P = 0.001]. The serum levels of androgens and gonadotropins reduced following ADT (P < 0.001 in all). The serum IGF-1 level increased (22 ± 6 nmol/L) compared with that at the baseline (19 ± 5 nmol/L) (P < 0.001), but no change was observed in the serum GH concentration between before and after ADT (1.4 ± 2.3 vs. 0.9 ± 0.9 μg/L, respectively, P = 0.691). The serum testosterone level was not correlated with the LH level either before or after ADT. The testosterone and DHEA-S levels after ADT were correlated with ACTH concentration (rs = 0.367, P = 0.002 and rs = 0.354, P = 0.002, respectively). We did not identify any correlations between the serum IGF-1 concentration and Gleason score, PSA value, or androgen levels.

CONCLUSIONS

During ADT with GnRHa, IGF-1 possibly promotes LH production, although its role is unclear. Associations among pituitary-gonadal, pituitary-adrenal, and GH/IGF-1 axes represented by IGF-1-mediated LH secretion and ACTH-mediated androgen synthesis are of interest, since both prostate epithelium proliferation and male anabolic activity are involved in these 3 axes. Assessment of oncologic outcomes is warranted for their significance in patients with prostate cancer.

Role of circadian neuroendocrine rhythms in the control of behavior and physiology

Hormones play a major role in regulating behavior and physiology, and their efficacy is often dependent on the temporal pattern in which they are secreted. Significant insights into the mechanisms underlying rhythmic hormone secretion have been gained from transgenic rodent models, suggesting that many of the body's rhythmic functions are regulated by a coordinated network of central and peripheral circadian pacemakers. Some neuroendocrine rhythms are driven by transcriptional-posttranslational feedback circuits comprising 'core clock genes', while others represent a cyclic cascade of neuroendocrine events. This review focuses on recent data from the rhesus macaque, a non-human primate model with high clinical translation potential. With primary emphasis on adrenal and gonadal steroids, it illustrates the rhythmic nature of hormone secretion, and discusses the impact that fluctuating hormone levels have on the accuracy of clinical diagnoses and on the design of effective hormone replacement therapies in the elderly. In addition, this minireview raises awareness of the rhythmic expression patterns shown by many genes, and discusses how this could impact interpretation of data obtained from gene profiling studies, especially from nocturnal rodents.