Circadian and ultradian variations of leptin in normal man under continuous enteral nutrition: relationship to sleep and body temperature

Effects of continuous positive airway pressure on energy balance regulation: a systematic review

Obesity is both a cause and a possible consequence of obstructive sleep apnoea (OSA), as OSA seems to affect parameters involved in energy balance regulation, including food intake, hormonal regulation of hunger/satiety, energy metabolism and physical activity. It is known that weight loss improves OSA, yet it remains unclear why continuous positive airway pressure (CPAP) often results in weight gain.The goal of this systematic review is to explore if and how CPAP affects the behaviour and/or metabolism involved in regulating energy balance.CPAP appears to correct for a hormonal profile characterised by abnormally high leptin and ghrelin levels in OSA, by reducing the circulating levels of each. This is expected to reduce excess food intake. However, reliable measures of food intake are lacking, and not yet sufficient to make conclusions. Although studies are limited and inconsistent, CPAP may alter energy metabolism, with reports of reductions in resting metabolic rate or sleeping metabolic rate. CPAP appears to not have an appreciable effect on altering physical activity levels. More work is needed to characterise how CPAP affects energy balance regulation.It is clear that promoting CPAP in conjunction with other weight loss approaches should be used to encourage optimal outcomes in OSA patients.

Sleep and hormonal changes in aging

Age-related sleep and endocrinometabolic alterations frequently interact with each other. For many hormones, sleep curtailment in young healthy subjects results in alterations strikingly similar to those observed in healthy old subjects not submitted to sleep restriction. Thus, recurrent sleep restriction, which is currently experienced by a substantial and rapidly growing proportion of children and young adults, might contribute to accelerate the senescence of endocrine and metabolic function. The mechanisms of sleep-hormonal interactions, and therefore the endocrinometabolic consequences of age-related sleep alterations, which markedly differ from one hormone to another, are reviewed in this article.

Daily regulation of hormone profiles

The highly coordinated output of the hypothalamic biological clock does not only govern the daily rhythm in sleep/wake (or feeding/fasting) behaviour but also has direct control over many aspects of hormone release. In fact, a significant proportion of our current understanding of the circadian clock has its roots in the study of the intimate connections between the hypothalamic clock and multiple endocrine axes. This chapter will focus on the anatomical connections used by the mammalian biological clock to enforce its endogenous rhythmicity on the rest of the body, using a number of different hormone systems as a representative example. Experimental studies have revealed a highly specialised organisation of the connections between the mammalian circadian clock neurons and neuroendocrine as well as pre-autonomic neurons in the hypothalamus. These complex connections ensure a logical coordination between behavioural, endocrine and metabolic functions that will help the organism adjust to the time of day most efficiently. For example, activation of the orexin system by the hypothalamic biological clock at the start of the active phase not only ensures that we wake up on time but also that our glucose metabolism and cardiovascular system are prepared for this increased activity. Nevertheless, it is very likely that the circadian clock present within the endocrine glands plays a significant role as well, for instance, by altering these glands' sensitivity to specific stimuli throughout the day. In this way the net result of the activity of the hypothalamic and peripheral clocks ensures an optimal endocrine adaptation of the metabolism of the organism to its time-structured environment.

Age-related changes in neuroendocrine rhythmic function in the rhesus macaque

Many environmental conditions show rhythmic changes across the 24-h day; these include changes in light intensity, ambient temperature, food availability, and presence or absence of predators. Consequently, many organisms have developed corresponding adaptations, which ensure that specific physiological and behavioral events occur at an appropriate time of the day. In mammals, the underlying mechanism responsible for synchronizing internal biochemical processes with circadian environmental cues has been well studied and is thought to comprise three major components: (1) photoreception by the retina and transmission of neural signals along the retinohypothalamic tract, (2) integration of photoperiodic information with an internal reference circadian pacemaker located in the suprachiasmatic nucleus, and (3) dissemination of circadian information to target organs, via the autonomic nervous system and through humoral pathways. Given the importance that neuroendocrine rhythms play in coordinating normal circadian physiology and behavior, it is plausible that their perturbation during aging contributes to the etiology of age-related pathologies. This mini-review highlights some of the most dramatic rhythmic neuroendocrine changes that occur in primates during aging, focusing primarily on data from the male rhesus macaques (Macaca mulatta). In addition to the age-associated attenuation of hormone levels and reduction of humoral circadian signaling, there are also significant age-related changes in intracrine processing enzymes and hormone receptors which may further affect the functional efficacy of these hormones. Rhesus macaques, like humans, are large diurnal primates and show many of the same physiological and behavioral circadian changes during aging. Consequently, they represent an ideal translational animal model in which to study the causes and consequences of age-associated internal circadian disruption and in which to evaluate novel therapies.

Circadian system, sleep and endocrinology

Levels of numerous hormones vary across the day and night. Such fluctuations are not only attributable to changes in sleep/wakefulness and other behaviors but also to a circadian timing system governed by the suprachiasmatic nucleus of the hypothalamus. Sleep has a strong effect on levels of some hormones such as growth hormone but little effect on others which are more strongly regulated by the circadian timing system (e.g., melatonin). Whereas the exact mechanisms through which sleep affects circulating hormonal levels are poorly understood, more is known about how the circadian timing system influences the secretion of hormones. The suprachiasmatic nucleus exerts its influence on hormones via neuronal and humoral signals but it is now also apparent that peripheral tissues contain circadian clock proteins, similar to those in the suprachiasmatic nucleus, that are also involved in hormone regulation. Under normal circumstances, behaviors and the circadian timing system are synchronized with an optimal phase relationship and consequently hormonal systems are exquisitely regulated. However, many individuals (e.g., shift-workers) frequently and/or chronically undergo circadian misalignment by desynchronizing their sleep/wake and fasting/feeding cycle from the circadian timing system. Recent experiments indicate that circadian misalignment has an adverse effect on metabolic and hormonal factors such as circulating glucose and insulin. Further research is needed to determine the underlying mechanisms that cause the negative effects induced by circadian misalignment. Such research could aid the development of novel countermeasures for circadian misalignment.

Sleep and metabolic function

Evidence for the role of sleep on metabolic and endocrine function has been reported more than four decades ago. In the past 30 years, the prevalence of obesity and diabetes has greatly increased in industrialized countries, and self-imposed sleep curtailment, now very common, is starting to be recognized as a contributing factor, alongside with increased caloric intake and decreased physical activity. Furthermore, obstructive sleep apnea, a chronic condition characterized by recurrent upper airway obstruction leading to intermittent hypoxemia and sleep fragmentation, has also become highly prevalent as a consequence of the epidemic of obesity and has been shown to contribute, in a vicious circle, to the metabolic disturbances observed in obese patients. In this article, we summarize the current data supporting the role of sleep in the regulation of glucose homeostasis and the hormones involved in the regulation of appetite. We also review the results of the epidemiologic and laboratory studies that investigated the impact of sleep duration and quality on the risk of developing diabetes and obesity, as well as the mechanisms underlying this increased risk. Finally, we discuss how obstructive sleep apnea affects glucose metabolism and the beneficial impact of its treatment, the continuous positive airway pressure. In conclusion, the data available in the literature highlight the importance of getting enough good sleep for metabolic health.

Sleep and immune function

Sleep and the circadian system exert a strong regulatory influence on immune functions. Investigations of the normal sleep–wake cycle showed that immune parameters like numbers of undifferentiated naïve T cells and the production of pro-inflammatory cytokines exhibit peaks during early nocturnal sleep whereas circulating numbers of immune cells with immediate effector functions, like cytotoxic natural killer cells, as well as anti-inflammatory cytokine activity peak during daytime wakefulness. Although it is difficult to entirely dissect the influence of sleep from that of the circadian rhythm, comparisons of the effects of nocturnal sleep with those of 24-h periods of wakefulness suggest that sleep facilitates the extravasation of T cells and their possible redistribution to lymph nodes. Moreover, such studies revealed a selectively enhancing influence of sleep on cytokines promoting the interaction between antigen presenting cells and T helper cells, like interleukin-12. Sleep on the night after experimental vaccinations against hepatitis A produced a strong and persistent increase in the number of antigen-specific Th cells and antibody titres. Together these findings indicate a specific role of sleep in the formation of immunological memory. This role appears to be associated in particular with the stage of slow wave sleep and the accompanying pro-inflammatory endocrine milieu that is hallmarked by high growth hormone and prolactin levels and low cortisol and catecholamine concentrations.

Role of sleep duration in the regulation of glucose metabolism and appetite

Sleep curtailment has become a common behavior in modern society. This review summarizes the current laboratory evidence indicating that sleep loss may contribute to the pathophysiology of diabetes mellitus and obesity. Experimentally induced sleep loss in healthy volunteers decreases insulin sensitivity without adequate compensation in beta-cell function, resulting in impaired glucose tolerance and increased diabetes risk. Lack of sleep also down-regulates the satiety hormone leptin, up-regulates the appetite-stimulating hormone ghrelin, and increases hunger and food intake. Taken together with the epidemiologic evidence for an association between short sleep and the prevalence or incidence of diabetes mellitus and/or obesity, these results support a role for reduced sleep duration in the current epidemic of these metabolic disorders. Screening for habitual sleep patterns in patients with "diabesity" is therefore of great importance. Studies are warranted to investigate the putative therapeutic impact of extending sleep in habitual short sleepers with metabolic disorders.

Oxidative stress and metabolic changes after continuous positive airway pressure treatment according to previous metabolic disorders in sleep apnea-hypopnea syndrome patients

Sleep apnea-hypopnea syndrome (SAHS) is characterized by recurrent episodes of hypoxia/reoxygenation, which seems to promote oxidative stress. SAHS patients experience increases in hypertension, obesity, and dyslipidemia, and the oxidative state has been related to the genesis of these disorders. The purpose of this study was to examine the changes in oxidative stress markers and metabolic parameters in S AHS patients after 1 month of treatment with continuous positive airway pressure (CPAP), in relation to their previous metabolic disorders. The study included 78 SAHS patients who required CPAP. The patients were classified according to their disorders, including hypertension, obesity, and dyslipidemia. Measurements were made before and after 1 month of treatment with CPAP. The diastolic blood pressure decreased after treatment in all the patients, significantly so in those who were nondyslipidemic, obese, or hypertensive (the systolic pressure also fell in these latter patients). Plasma oxidative stress biomarkers showed a significant antioxidant capacity and increased activity (P<0.05) after treatment, more so in the nondyslipidemic and hypertensive patients. Furthermore, serum lipid peroxidation levels decreased after CPAP (P<0.01). No change was observed in insulin resistance (IR) after CPAP treatment in any of the different disorders. In conclusion, oxidative stress markers improved significantly after CPAP treatment in SAHS patients, especially in the nondyslipidemic and hypertensive patients. Moreover, the blood pressure decreased after CPAP treatment, particularly in the obese, nondyslipidemic, and hypertensive patients. No significant change in IR was found in any of the SAHS patients after CPAP treatment.

A review of nighttime eating disorders

Nighttime eating is categorized as either night eating syndrome (NES) or sleep-related eating disorder (SRED). These conditions represent an interruption in the overnight fast that characterizes human sleep. A critical review of the literature on NES and SRED will suggest that they are situated at opposite poles of a disordered eating spectrum. NES could be considered an abnormality in the circadian rhythm of meal timing with a normal circadian timing of sleep onset. Conversely, the feeding behavior in SRED is characterized by recurrent episodes of eating after an arousal from nighttime sleep with or without amnesia. Both conditions are often relentless and chronic. Multiple definitions of night eating have limited our ability to determine the exact prevalence of NES. Studies have suggested that central nervous system (CNS) serotonin modulation may lead to an effective treatment of NES. SRED is frequently associated with other sleep disorders, in particular parasomnias. Early studies have shown that the anti-seizure medication topiramate may be an effective treatment for SRED.

Impact of sleep and sleep loss on glucose homeostasis and appetite regulation

Over the past 30 years there has been an increase in the prevalence of obesity and diabetes, both of which can have serious consequences for longevity and quality of life. Sleep durations may have also decreased over this time period. This chapter reviews laboratory and epidemiologic evidence for an association between sleep loss and impairments in glucose metabolism and appetite regulation, which could increase the risk of diabetes or weight gain.

The metabolic consequences of sleep deprivation

The prevalence of diabetes and obesity is increasing at an alarming rate worldwide, and the causes of this pandemic are not fully understood. Chronic sleep curtailment is a behavior that has developed over the past 2-3 decades. Laboratory and epidemiological studies suggest that sleep loss may play a role in the increased prevalence of diabetes and/or obesity. Current data suggest the relationship between sleep restriction, weight gain and diabetes risk may involve at least three pathways: (1) alterations in glucose metabolism; (2) upregulation of appetite; and (3) decreased energy expenditure. The present article reviews the current evidence in support of these three mechanisms that might link short sleep and increased obesity and diabetes risk.

Sleep and metabolic control: waking to a problem?

1. The aim of the present review is to outline: (i) the association between sleep and metabolism; (ii) how sleep duration influences the development of disease; and (iii) how sex differences, ageing and obesity may potentially influence the relationship between sleep, metabolic control and subsequent disease. 2. Sleep is associated with a number of endocrine changes, including a change in insulin action in healthy young individuals. Sleep duration shows a prospective U-shaped relationship with all-cause mortality, cardiovascular disease and Type 2 diabetes. 3. Chronic sleep restriction is becoming more common. Experimental sleep restriction impedes daytime glucose control and increases appetite. 4. The sex hormones oestrogen and testosterone influence sleep duration and quality and may account for sex differences in the prevalence of sleep-related disorders. 5. Ageing is associated with a decreased sleep duration, decreased muscle mass and impaired insulin action. 6. Obesity impairs insulin action and is associated with the incidence and severity of obstructive sleep apnoea. 7. Sleep plays an integral role in metabolic control. Consequently, insufficient sleep may represent a modifiable risk factor for the development of Type 2 diabetes. The challenge ahead is to identify how sex differences, ageing and obesity could potentially influence the relationship between sleep and metabolism.

Intermittent and rhythmic exposure to melatonin in primary cultured adipocytes enhances the insulin and dexamethasone effects on leptin expression

Considering the cyclic characteristic of production and secretion of pineal melatonin, it is reasonable to assume that this oscillation might be important in determining the variety of its circadian and seasonal effects. To simulate this physiological condition in vitro, isolated adipocytes were exposed to melatonin in a circadian-like pattern by adding the hormone to the incubating medium during 12 hr (mimicking the night), followed by an equal period without melatonin (mimicking the day). This intermittent procedure was interrupted when three cycles with melatonin were fulfilled (60-hr incubation). Here, we report the effects of melatonin (1 nM) added intermittently or continuously to the incubating medium alone or in combination with insulin (5 nM) and/or dexamethasone (7 nM) on leptin release and expression by rat adipocytes. After acute 12-hr incubation neither melatonin nor insulin alone affected leptin expression, but together they increased it by 105%. Dexamethasone increased leptin mRNA content and release (70%) but this effect was not enhanced by melatonin. Nevertheless, after 60 hr under intermittent melatonin, we observed a synergism between melatonin and dexamethasone. This interaction promoted an increment (75% compared with dexamethasone alone) in leptin release and expression. Our results suggest that circadian-like exposure to melatonin potentiates the dexamethasone action and is important to the effects promoted by insulin on leptin expression. Based on an in vitro approach, this work helps to clarify the physiological relevance and the repercussions of the in vivo circadian pattern of melatonin secretion.

Tetraplegic subjects have hyperleptinaemia with marked circadian variation

OBJECTIVE

The disruption between the brain and the spinal cord leads to a decentralized sympathetic nervous system in people with chronic, cervical spinal cord lesions. These tetraplegic subjects are prone to disorders of energy metabolism and osteoporosis, and they experience alterations in their body composition with a relative accumulation of fat. The adipocyte-derived cytokine leptin is a key signal in caloric intake and energy expenditure, and it might modify bone remodelling, possibly regulated by sympathetic neuronal signalling. In able-bodied subjects leptin exhibits circadian variations, possibly mediated via sympathetic neurones. We have examined the plasma concentration of leptin among tetraplegics, to determine whether plasma leptin in these subjects exhibits circadian variations.

MEASUREMENTS AND RESULTS

Blood samples were collected during a 24-h study period from tetraplegic subjects (n = 6) and from able-bodied controls (n = 8). Fasting, tetraplegic subjects had mean plasma concentrations of leptin about four times those of able-bodied controls (P < 0.05). In tetraplegia, plasma leptin was negatively correlated with total lean mass (r =-0.88, P < 0.05) but correlated positively with total fat mass (r = 0.89, P < 0.05). A marked circadian variation in plasma leptin concentrations was more evident in tetraplegia than in able-bodied controls.

CONCLUSION

Plasma leptin is markedly elevated and it shows more prominent circadian variations in tetraplegia compared with able-bodied subjects. Possibly the regulation of leptin metabolism is impaired among these patients. This might distort thermogenesis and energy expenditure, thus explaining the enhanced risk of the metabolic syndrome and of osteoporosis among tetraplegic subjects.

Circadian phase difference of leptin in android versus gynoid obesity

A circadian rhythm in serum leptin, measured every 4 h for 24 h, characterizes normal-weight women (N = 14), and women with gynoid (N = 17) or android (N = 26) obesity, peaking around midnight (P < 0.05), but differing by about 3 h between android and gynoid women (P < 0.01). Obesity is associated with a higher MESOR (rhythm-adjusted mean; P < 0.001) and a smaller relative circadian amplitude (P < 0.05). Gynoid obesity is associated with a larger circadian amplitude of cortisol (P < 0.05), whereas android obesity is associated with a larger circadian amplitude and a higher MESOR of insulin (P < 0.05). Understanding putative mechanisms underlying different body fat distribution may lead to improved chronotherapeutic measures.

The evaluation of serum leptin level and other hormonal parameters in children with severe malnutrition

OBJECTIVES

Protein-energy malnutrition (PEM) is a clinical problem caused by inadequate intake of one or more nutritional elements, and remains as one of the most important health problems in developing countries. The aim of this study is to determine the relationship among leptin concentrations, body weight and concentrations of some serum hormones, e.g., basal GH, IGF-1, basal cortisol and IGF-BP3, in severe malnourished children, and to determine the effects of leptin in malnourished children.

DESIGN AND METHODS

The study group consisted of 36 children diagnosed with PEM. Thirty healthy children were enrolled as the control group. After an overnight fast and before initiation of feedings, fasting venous blood samples were obtained from a forearm vein with needle technique for routine tests, and leptin, IGF-1, IGF-BP3, basal GH and cortisol levels were measured. Tests were carried out in the laboratories of the Department of Biochemistry by commercial kits.

RESULTS

Serum leptin levels of infants with marasmus and kwashiorkor were significantly lower than that of the controls (2.09 +/- 0.93 and 2.27 +/- 1.01, 6.82 +/- 2.28 ng/ml, respectively, P < 0.001). However, there was no significant difference between serum leptin levels in children with marasmus and those with kwashiorkor (P > 0.05). Serum IGF-1 and IGF-BP3 levels were significantly lower in malnourished children (P < 0.001, both). Also, basal GH and cortisol levels were significantly higher in malnourished children (P < 0.001, both). There was a positive correlation among serum leptin levels and IGF-1 and IGF-BP3 levels and also a negative correlation among serum leptin levels and basal GH and cortisol levels in children diagnosed with marasmus or kwashiorkor and the control group.

CONCLUSIONS

The decrease of energy intake and adipose tissue and serum IGF-1 levels in children with PEM may result in decrease of leptin secretion. Decrease in serum leptin levels may initiate food intake by increasing appetite and stimulating the secretion of cortisol and GH that might increase energy expenditure through an autocrine mechanism. Moreover, serum leptin level may be an important signal to reflect the metabolism of children with PEM.

The effects of nocturnal life on endocrine circadian patterns in healthy adults

We observed the 24-hour patterns of endocrine in medical students who lived either a diurnal life or nocturnal life. Nocturnal life was designed by skipping their breakfast but consuming much (>50% of their daily food intake) in the evening and at night with the sleep from 0130 h to 0830 h the next morning. After 3 weeks in the experimental life, the 24-hour plasma concentrations of melatonin, leptin, glucose and insulin were measured every three hours. Both plasma melatonin and leptin showed peaks at 0300 h in the diurnal lifestyle group, and the night peaks decreased in the nocturnal lifestyle group. The changes in the patterns of melatonin and leptin were highly consistent with that of night-eating syndrome (NES). Plasma glucose increased after all meals in both groups. Its concentration maintained a high level in the nocturnal lifestyle group between midnight and early morning while insulin secretion decreased markedly during this period. Furthermore, the strong association between glucose and insulin in the diurnal lifestyle group after meals was damaged in the nocturnal lifestyle group. It was suggested that nocturnal life leads to the impairment of insulin response to glucose. Taking these results together, nocturnal life is likely to be one of the risk factors to health of modern people, including NES, obesity and diabetes.

Growth hormone-insulin-like growth factor-1 axis, leptin and sleep in anorexia nervosa patients

The present study characterizes the relationships between severe malnutrition, sleep, growth hormone-insulin-like growth factor-1 (GH-IGF-1) axis, and leptin levels in anorexia nervosa (AN) patients before and after weight gain. Eleven restricting-type anorectic females (mean age = 19.7 years) with severe starvation state [mean body mass index (BMI) = 13.3] were studied using polysomnography and spectral power analysis. The hormone levels were measured in the morning after sleep recording. Eleven normal-weight, age- and gender-matched healthy volunteers without a history of any eating disorder served as controls. After nutritional treatment for about 2 months (65.7 +/- 6.4 days), sleep examinations and blood tests were repeated. At this stage, the study group consisted of 5 patients (mean BMI = 15.6). Higher IGF-1 and leptin levels were associated with longer and deeper sleep among anorectics. The sleep parameters including the percentages of stage 1 sleep and SWS as well as IGF-1 tended to normalize after only limited weight gain. Sleep disturbances in anorectics may be mediated through changes in the levels of the GH-IGF-1 axis hormones, as well as the levels of leptin.

Simultaneous measurements of serum insulin-like growth factor-I and leptin reflect the postoperative nutrition status of oral tumor patients

OBJECTIVE

Recent evidence has shown that circulating levels of insulin-like growth factor-I (IGF-I) and leptin are regulated by nutrition support. Our objective was to investigate the reliability of IGF-I and leptin in monitoring the efficacy of nutrition support and nutrition status in oral tumor patients.

METHODS

Fifty-one male patients scheduled to receive resection operation for oral tumor were recruited. Fasted blood samples were collected before surgery (d0), on the first postoperative day before feeding (d1), and on the seventh postoperative day (d7) with nasogastric tube feeding (35 kcal x kg(-1) x d(-1)). Fifty male healthy volunteers were recruited as controls.

RESULTS

After adjustment for age, patients had significantly greater serum concentrations of transferrin and significantly lower serum concentrations of prealbumin and tumor-necrosis factor-alpha than did healthy volunteers on d0. In oral tumor patients, resection with prolonged fasting significantly increased levels of growth hormone and interleukin-6 and significantly decreased levels prealbumin, retinol-binding protein, IGF-I, and leptin, and these alterations were reversed by nutrition support for 6 d in oral tumor patients. Serum IGF-I was further increased on d7 compared with d0. In addition, leptin was the only nutrition-related serum protein showing significantly positive correlation with body mass index in healthy volunteers and patients.

CONCLUSIONS

Our results suggested that simultaneous measurements of serum IGF-I and leptin may provide information with regard to the efficacy of nutrition support and nutrition status in oral tumor patients undergoing surgery.

A novel pathophysiologic phenomenon in cachexic patients with chronic obstructive pulmonary disease: the relationship between the circadian rhythm of circulating leptin and the very low-frequency component of heart rate variability

Cachexic patients with chronic obstructive pulmonary disease (COPD) show abnormalities of the autonomic nervous system (ANS), neuroendocrine function, and energy expenditure. Leptin has been implicated in the regulation of ANS, neuroendocine function, and thermogenesis in humans. We assessed the physiologic significance of the circadian rhythm of circulating leptin using power spectrum analysis of heart rate variability (HRV) in nine cachexic male patients with COPD, eight noncachexic patients with COPD, and seven healthy control subjects. A diurnal pattern of 24-h leptin levels was present in both the control subjects (analysis of variance [ANOVA]; F = 7.80, p < 0.0001) and noncachexic COPD patients (F = 9.29, p < 0.0001), but was strikingly absent in the cachexic COPD patients (F = 2.09, p = NS). Analysis of HRV demonstrated that the diurnal rhythm of 24-h very low frequency (VLF; 0.003 to 0.04 Hz) showed significantly identical fluctuations with those of 24-h leptin levels, in all of the three groups (r = 0.388, p < 0.0001). Because VLF has been considered to reflect neuroendocrine and thermoregulatory influences, these data may suggest that the loss of circadian rhythm of circulating leptin has clinical importance in the pathophysiologic features in cachexic patients with COPD.

Glucocorticoid effects on the diurnal rhythm of circulating leptin levels

It is known that circulating leptin shows diurnal variation with a nocturnal rise; however, the mechanisms generating this rhythm have not been fully elucidated. Glucocorticoids are a potent stimulator of leptin secretion, and there is a reciprocal relationship between circulating leptin and glucocorticoid levels. We hypothesized that glucocorticoids could modulate the diurnal rhythm of circulating leptin. We therefore explored the diurnal variation of leptin under situations in which subjects showed no or some shift of glucocorticoid diurnal rhythm, such as prednisolone-administered humans, and adrenalectomized and corticosterone-replaced (ADX+B) rats. The peak level of plasma cortisol immunoreactivity was shifted from early morning to noon by prednisolone administration. The nocturnal increment of plasma leptin in prednisolone-administered patients (71.2 +/- 14.2% from 08:00 h value) was significantly greater than that in normal volunteers (12.2 +/- 7.5% from 08:00 h value), but the timing of nadir and the peak of plasma leptin was not shifted. In normal rats, the plasma concentration of leptin showed the diurnal rhythm with the bottom at 16:00 h and the top between midnight and early morning. The amplitude of leptin diurnal rhythm was significantly reduced in ADX+B rats (08:00 h: 3.0 +/- 0.2, 16:00 h: 2.7 +/- 0.2, 00:00 h; 3.7 +/- 0.2 ng/ml) compared with sham operated rats (08:00 h: 3.0 +/- 0.2, 16:00 h 2.2 +/- 0.2, 00:00 h: 4.7 +/- 0.4 ng/ml); but ADX+B rats still retained similar timing of nadir and the peak of plasma leptin as observed in sham rats. These results indicate that glucocorticoids enhance the amplitude of leptin diurnal rhythm, and are consistent with previous findings showing that glucocorticoids increase leptin secretion. Glucocorticoids appear to play modulatory, but not essential roles in generating leptin diurnal rhythm.

Role of leptin during childhood growth and development

Leptin, the product of the ob/ob gene in rodents, regulates energy balance and fertility. Two genetic models, the ob/ob mouse (deletion of leptin protein) and the db/db mouse (deletion of leptin receptor) have markedly augmented research in obesity. Human obesity is more closely linked to leptin resistance than to the absence of leptin. Serum leptin concentrations reflect the size of the subcutaneous fat depot better than total fat mass or abdominal visceral fat. At the initiation of puberty there is a divergence in circulating leptin concentrations between boys and girls. In boys, leptin concentrations increase and then markedly decrease to prepubertal concentration levels. In girls there are only increasing concentrations. The authors believe these patterns are relevant to the markedly different alterations in the regional distribution of body fat that occurs in boys and girls at puberty.