The Relation of Shift Work Tolerance to the Circadian Adjustment

The amplitude and phasing of circadian rhythms are under discussion as possible predictors of tolerance to night work. In a field study, subjective sleepiness and oral temperature of 147 female nurses were measured at 2-hour intervals during a period with one morning shift and two consecutive night shifts. The nurses also filled out a questionnaire. Two types of tolerance indices were constructed: The “health index” was based on questions referring to general fatigue, gastrointestinal symptoms, and sleep disturbances, and the “sleepiness index” on the actual subjective ratings of sleepiness. According to the health index, the group with good tolerance had a larger circadian amplitude of the oral temperature rhythm on the day of the morning shift than the group with poor tolerance. However, with regard to the sleepiness index, the corresponding difference between the groups with good or poor tolerance was not significant. The data did not confirm the hypothesis that predicts a quick adjustment of the circadian rhythm when the circadian amplitude is small before the change to night work. The contradictory results found in this and in other studies do not yet permit prediction of tolerance to night work.     

Adaptation to night shifts and synchronisation processes of night workers

Human beings are accustomed to being active and awake during the day, and asleep and rest at night. Since we live in a society which is organised predominantly along daytime activity, therefore working in the night shift may deeply disrupt our social and family life. It is also a well-known fact that night shift causes fatigue and circadian disruption. The basic manifestation of fatigue and circadian rhythm has been linked to health and safety problems, involving decrements in psychophysical and physiological functions, plus subjective complaints. In this context quantitative relationships between shift work and circadian rhythm need to be assessed to explore suitable time schedule, and to minimise sleep depth and fatigue. There is also a great need to discuss circadian disruption, sleepiness and the increasing cost of work related illness among night workers. In this regard, some aspects of fatigue and circadian disruption caused from night shift work are revealed in this paper aiming to increase workers' health, safety and well being as well as productivity. Light/dark cycle and social stimuli issues acting on the circadian timing systems are also explored to solicit opinions and discussion on the controversy of night work. Suggestions are therefore likewise given to enhance workers' adaptation to night shift and synchronization process.     

Effect of alternate nostril breathing on cardio respiratory parameters and muscle strength among rotating shift workers

Night shifts at work is the most frequent reasons for circadian rhythm disruption and subsequent psychological and physiological disturbances, especially increased risk of cardiovascular and respiratory ailments compared to daytime workers. Alternate nostril breathing for about 15 minutes was known to have effect over cardiac, respiratory parameters and muscle strength. Hence aim is of interest to assess the effects of alternate nostril breathing (ANB) on cardio-respiratory parameters and muscle strength among the rotating shift workers in the tertiary care hospital. This observational study was carried out in the department of Physiology after getting institutional ethical committee clearance. Around 140 rotating night shift workers of both sex of age 25-40 years with normal BMI and 140 non-shift workers age, sex and BMI matched were selected as study and control group respectively. Heart rate, blood Pressure, respiratory rate, peak expiratory flow rate, respiratory endurance, respiratory burst test, muscle strength and fatigue were recorded before and after 15 minutes of ANB. Shift workers were found to have significantly altered systolic (P=0.000) and diastolic (P=0.002) blood pressure and heart rate (P=0.010) compared to non-shift workers. Fatigue is altered significantly (P< 0.05) after ANB between both shift and non- shift workers. ANB can be used as a therapeutic module among the shift workers, to maintain their sound health and to improve their performance in the night duty.     

The Relation of Shift Work Tolerance to the Circadian Adjustment

The amplitude and phasing of circadian rhythms are under discussion as possible predictors of tolerance to night work. In a field study, subjective sleepiness and oral temperature of 147 female nurses were measured at 2-hour intervals during a period with one morning shift and two consecutive night shifts. The nurses also filled out a questionnaire. Two types of tolerance indices were constructed: The “health index” was based on questions referring to general fatigue, gastrointestinal symptoms, and sleep disturbances, and the “sleepiness index” on the actual subjective ratings of sleepiness. According to the health index, the group with good tolerance had a larger circadian amplitude of the oral temperature rhythm on the day of the morning shift than the group with poor tolerance. However, with regard to the sleepiness index, the corresponding difference between the groups with good or poor tolerance was not significant. The data did not confirm the hypothesis that predicts a quick adjustment of the circadian rhythm when the circadian amplitude is small before the change to night work. The contradictory results found in this and in other studies do not yet permit prediction of tolerance to night work.     

Do Permanent Night Workers Show Circadian Adjustment? A Review Based on the Endogenous Melatonin Rhythm

“Permanent” or “fixed” night shifts have been argued to offer a potential benefit over rotating shift systems in that they may serve to maximize circadian adjustment and hence minimize the various health and safety problems associated with night work. For this reason, some authors have argued in favor of permanent shift systems, but their arguments assume at least a substantial, if not complete, adjustment of the circadian clock. They have emphasized the finding that the day sleeps taken between successive night shifts by permanent night workers are rather longer than those of either slowly or rapidly rotating shift workers, but this could simply reflect increased pressure for sleep. The present paper reviews the literature on the adjustment to permanent night work of the circadian rhythm in the secretion of melatonin, which is generally considered to be the best known indicator of the state of the endogenous circadian body clock. Studies of workers in “abnormal” environments, such as oil rigs and remote mining operations, were excluded, as the nature of these unique settings might serve to assist adjustment. The results of the six studies included indicate that only a very small minority (<3%) of permanent night workers evidence “complete” adjustment of their endogenous melatonin rhythm to night work, less than one in four permanent night workers evidence sufficiently “substantial” adjustment to derive any benefit from it, there is no difference between studies conducted in normal or dim lighting, and there is no evidence of gender difference in the adjustment to permanent night work. It is concluded that in normal environments, permanent night‐shift systems are unlikely to result in sufficient circadian adjustment in most individuals to benefit health and safety.     

Functional diversities of two activity components of circadian rhythm in genetical splitting mice (CS strain)

CS mice, an inbred strain, showed two distinctive characteristics in the circadian rhythm of locomotor activity: (1) large variation in the freerunning period, and (2) spontaneous rhythm splitting under continuous darkness. In the splitting rhythm there was a positive correlation between the freerunning period of the evening component and the activity time of the morning component. The phase-shifting effect of a 15-min light pulse was examined on the two activity components of the splitting rhythm. There were significant differences in the amount of light-induced phase response between the two components. A light pulse during the late subjective night induced a phase advance shift only in the morning component, while a light pulse during the early subjective night induced a phase delay shift only in the evening component. These results indicate functional diversities of the two activity components in the circadian locomotor rhythm of CS mice, and suggest that the circadian system in CS mice consists of two mutually coupled oscillators which have different circadian periods and different responsiveness to light. The CS mouse is a useful model to explore a genetic background of oscillator coupling in the circadian system of nocturnal rodents. Accepted: 19 November 1998     

Angiotensin receptor blockers shift the circadian rhythm of blood pressure by suppressing tubular sodium reabsorption

Recently, we found that an angiotensin II receptor blocker (ARB) restored the circadian rhythm of the blood pressure (BP) from a nondipper to a dipper pattern, similar to that achieved with sodium intake restriction and diuretics (Fukuda M, Yamanaka T, Mizuno M, Motokawa M, Shirasawa Y, Miyagi S, Nishio T, Yoshida A, Kimura G. J Hypertens 26: 583-588, 2008). ARB enhanced natriuresis during the day, while BP was markedly lower during the night, resulting in the dipper pattern. In the present study, we examined whether the suppression of tubular sodium reabsorption, similar to the action of diuretics, was the mechanism by which ARB normalized the circadian BP rhythm. BP and glomerulotubular balance were compared in 41 patients with chronic kidney disease before and during ARB treatment with olmesartan once a day in the morning for 8 wk. ARB increased natriuresis (sodium excretion rate; U(Na)V) during the day (4.5 ± 2.2 to 5.5 ± 2.1 mmol/h, P = 0.002), while it had no effect during the night (4.3 ± 2.0 to 3.8 ± 1.6 mmol/h, P = 0.1). The night/day ratios of both BP and U(Na)V were decreased. The decrease in the night/day ratio of BP correlated with the increase in the daytime U(Na)V (r = 0.42, P = 0.006). Throughout the whole day, the glomerular filtration rate (P = 0.0006) and tubular sodium reabsorption (P = 0.0005) were both reduced significantly by ARB, although U(Na)V remained constant (107 ± 45 vs. 118 ± 36 mmol/day, P = 0.07). These findings indicate that the suppression of tubular sodium reabsorption, showing a resemblance to the action of diuretics, is the primary mechanism by which ARB can shift the circadian BP rhythm into a dipper pattern.     

Protein synthesis is a required process for the optic lobe circadian clock in the cricket Gryllus bimaculatus

The effects of a translation inhibitor, cycloheximide (CHX), on the circadian neuronal activity rhythm of the optic lamina-medulla compound eye complex cultured in vitro were investigated in the cricket Gryllus bimaculatus. When the complex was treated with 10(-5) M CHX for 6 h, the rhythm exhibited a marked phase shift. The magnitude and direction of the phase shift were dependent on the phase at which the complex was treated with CHX; phase delays occurred during the late subjective day to early subjective night, whereas phase advances occurred around the late subjective night. Continuous application of CHX abolished circadian rhythms of both the spontaneous neuronal activity and the visually evoked response. However, it abolished neither the spontaneous activity nor the visually evoked response. As washed with fresh medium after CHX treatment, the rhythm soon reappeared and the subsequent phase was clearly correlated to the termination time of the treatment. These results suggest that protein synthesis is also involved in the cricket optic lobe circadian clock, and that the clock-related protein synthesis may be active during the late subjective day to subjective night.     

Do permanent night workers show circadian adjustment? A review based on the endogenous melatonin rhythm

"Permanent" or "fixed" night shifts have been argued to offer a potential benefit over rotating shift systems in that they may serve to maximize circadian adjustment and hence minimize the various health and safety problems associated with night work. For this reason, some authors have argued in favor of permanent shift systems, but their arguments assume at least a substantial, if not complete, adjustment of the circadian clock. They have emphasized the finding that the day sleeps taken between successive night shifts by permanent night workers are rather longer than those of either slowly or rapidly rotating shift workers, but this could simply reflect increased pressure for sleep. The present paper reviews the literature on the adjustment to permanent night work of the circadian rhythm in the secretion of melatonin, which is generally considered to be the best known indicator of the state of the endogenous circadian body clock. Studies of workers in "abnormal" environments, such as oil rigs and remote mining operations, were excluded, as the nature of these unique settings might serve to assist adjustment. The results of the six studies included indicate that only a very small minority (<3%) of permanent night workers evidence "complete"adjustment of their endogenous melatonin rhythm to night work, less than one in four permanent night workers evidence sufficiently "substantial" adjustment to derive any benefit from it, there is no difference between studies conducted in normal or dim lighting, and there is no evidence of gender difference in the adjustment to permanent night work. It is concluded that in normal environments, permanent night-shift systems are unlikely to result in sufficient circadian adjustment in most individuals to benefit health and safety.     

Association between misalignment of circadian rhythm and obesity in Korean men: Sixth Korea National Health and Nutrition Examination Survey

ABSTRACT

Background: The disruption of circadian rhythm has been found to associate with obesity in vivo and in vitro. Sleep duration, eating habits, total feeding time, and nightshift work can also affect circadian rhythms. This study investigated the association between misalignment of circadian rhythm and obesity in Korean men, using a cross-sectional database.

Methods: This study used data from the Korean National Health and Nutrition Examination Survey (KNHANES), whose study population was 3,658 men aged 18 to 60 years. General and abdominal obesity was defined as a body mass index (BMI) ≥ 25 kg/m² and waist circumference ≥ 90 cm, respectively. Circadian rhythm factors were determined with a self-report questionnaire and included breakfast frequency, sleep duration, and work time. Frequency of breakfast was divided into regular breakfast (five to seven times a week) and irregular breakfast (less than five times a week). Sleep duration was divided into less than 7 hours, 7–9 hours, and over 9 hours. Working time was defined as day/evening, night shift, and other type. The adjusted odds ratios (aORs) and 95% confidence intervals (CIs) for general and abdominal obesity were calculated using multivariable logistic regression according to the number of factors that disturb the circadian rhythm.

Results: Participants with 1 (aOR 1.34, 95% Cl 1.10–1.61) and ≥2 (aOR 1.62, 95% Cl 1.29–2.05) factors disturbing circadian rhythms were associated with elevated risk for general obesity. Similarly, those with 1 (aOR 1.33, 95% Cl 1.09–1.63) and ≥2 (aOR 1.70, 95% Cl 1.32–2.20) factors had elevated risk for abdominal obesity.

Conclusions: Factors disturbing the circadian rhythm were associated with general and abdominal obesity. Additional studies are needed, and associations with metabolic diseases should be investigated.     

Circadian rhythm of blood glucose and tissue glycogen in fed and fasted rats

Blood glucose and tissue glucogen circadian rhythms were determined in male Wistar rats adapted 3 weeks to an artificial lighting regimen of 12 hours' light and 12 hours' darkness. Over a period of 24 hours we examined at 3-hour intervals the blood glucose concentration and the glycogen content of the liver, heart, skeletal muscle (quadriceps femoris) and white (epididymal) and brown (interscapular) adipose tissue of fed rats and rats fasted for 24 hours. The experiments were carried out in the autumn and the results were evaluated statistically by an analysis of variance and the cosinor test. The blood glucose level and the glycogen concentration in all the given tissues, in both fed and starved rats, displayed rhythmic oscillations with a 24- or 12-hour period in the course of the day, with the exception of glycogen in the white adipose tissue of fed rats, in which cosinor analysis failed to demonstrate any rhythm. One day's fasting did not affect the character of circadian rhythm.     

Circadian rhythm in Schistosoma haematobium egg excretion

The usual peak daily egg excretion period in persons harbouring Schistosoma haematobium is the late morning and early afternoon. No evidence was found to support a hypothesis that the rhythm is mechanical in origin being due to rapid increase of bladder activity in the early morning.A partial reversion of the rhythm occurred when day shift workers changed to night shift.The possible role in the circadian rhythm of host factors—temperature and metabolism and of proteolytic enzyme secretion by miracidia are discussed.     

High‐fat Diet Followed by Fasting Disrupts Circadian Expression of Adiponectin Signaling Pathway in Muscle and Adipose Tissue

The circadian clock controls energy homeostasis by regulating circadian expression of proteins involved in metabolism. Disruption of circadian rhythms leads to obesity and metabolic disorders. Little is known regarding the control of the biological clock over adiponectin signaling pathway in adipose tissue, the adiponectin producer, and muscle, an adiponectin target tissue under fasting, low‐fat (LF), or high‐fat (HF) diet. Mice were fed LF or HF diet for 7 weeks and fasted on the last day. The circadian mRNA expression of clock genes and components of adiponectin metabolic pathway (mAdipoR1, mAdipoR2, mPparα, mPparγ, mAmpk, and mAcc) in the muscle and adipose tissue were tested. Using average daily levels of multiple time points around the circadian cycle, we assessed mRNA levels of the different adiponectin signaling components. In addition, serum glucose, adiponectin, and insulin were measured. Under LF diet, adiponectin signaling pathway components exhibited circadian rhythmicity at the mRNA levels. Fasting and HF diet followed by fasting disrupted this circadian expression causing a phase advance or delay, respectively. Changes were also found in the expression levels of adiponectin receptor, mAmpk, mAcc, mPparα, and mPparγ reflecting a defect in adiponectin signaling. As both peroxisome proliferator‐activated receptor α (PPARα) and mAMPK are linked to the core clock mechanism, they could mediate the disruptions seen in clock gene expression under HF diet. In turn, the circadian clock affects the daily rhythm of these adiponectin signaling components.     

Characteristics of organization of the rat circadian locomotor rhythm after pinealectomy

As compared with sham operated animals, an increase in night and daytime locomotion and a shift of the acrophase of the circadian locomotor rhythm to earlier night hours were observed in pinealectomized rats. A reorganization of the rhythm spectral characteristics took place with increase in the share of ultradian waves (14-20 h) and decrease in the number of short periodic (2-5 h) fluctuations.     

Circadian expression of clock genes in the rat eye and brain

The light sensing system in the eye directly affects the circadian oscillator in the mammalian suprachiasmatic nucleus (SCN). To investigate this relationship in the rat, we examined the circadian expression of clock genes in the SCN and eye tissue during a 24 h day/night cycle. In the SCN, rPer1 and rPer2 mRNAs were expressed in a clear circadian rhythm like rCry1 and rCry2 mRNAs, whereas the level of BMAL1 and CLOCK mRNAs decreased during the day and increased during the night with a relatively low amplitude. It seems that the clock genes of the SCN may function in response to a master clock oscillation in the rat. In the eye, the rCry1 and rCry2 were expressed in a circadian rhythm with an increase during subjective day and a decrease during subjective night. However, the expression of Opn4 mRNA did not exhibit a clear circadian pattern, although its expression was higher in daytime than at night. This suggests that cryptochromes located in the eye, rather than melanopsin, are the major photoreceptive system for synchronizing the circadian rhythm of the SCN in the rat.     

The effect of striatal stimulation and damage in rats on the dynamics of circadian mobility]

Prolonged and repeated low-frequency stimulation (2 imp/s, 20-30 min, 3-4 times) of the striatum disorganized rat's circadian motility. Attenuation of amplitude rhythm and shift of its acrophase to early night hours were observed. Bilateral striatectomy increased the motor activity after light switching-off and rhythm splitting to ultradian components. It is suggested that the striatum as a secondary oscillatory messenger may participate in motor maintenance of circadian motility.     

Gender specific correlations of adrenal gland size and body fat distribution: a whole body MRI study.

OBJECTIVE: The aim of this study was to investigate the gender specific correlations of stress related tissues [adrenal gland volume (AV), visceral fat] and alimentary dependent fat compartments with cortisol concentrations in healthy male and female subjects. METHODS: Fourteen men and 13 women were examined. Fat compartments [whole body fat, visceral adipose tissue (VAT) and subcutaneous adipose tissue (SCAT)] were determined using whole body MRI. Adrenal gland volume was assessed by a 3D MR data set. The salivary cortisol was determined at 9 AM and 4 PM. RESULTS: Men had significantly more visceral fat and less subcutaneous fat than women. Adrenal gland size correlated significantly with the visceral and subcutaneous fat in women (r=0.7, p=0.008), but not in men (r=0.2, p=0.4). There was a negative correlation between the decrease of cortisol between 9 AM and 4 PM with VAT (r=-0.451, p=0.027) in the whole group. DISCUSSION: The high correlation between the adrenal gland volume and VAT in women underlines the link between hypothalamic-pituitary-adrenal (HPA) axis, stress, and circadian cortisol rhythm, respectively, and an increased abdominal fat volume. The lack of correlation between visceral fat and adrenal volume in men points to an additional influence of sex hormones.     

Circadian Rhythm of Glucose Uptake in Cultures of Skeletal Muscle Cells and Adipocytes in Wistar-Kyoto,Wistar, Goto-Kakizaki,and Spontaneously Hypertensive Rats

Hypertension and noninsulin-dependent diabetes mellitus are usually associated with marked glucose intolerance. Hypertensive and even nonhypertensive diabetic individuals display disturbances of the normal circadian blood pressure rhythm. However, little is known about circadian changes of the glucose uptake in muscle and fat cells, the major glucose utilizing tissues. Therefore, we investigated circadian rhythms of glucose uptake in primary muscle and fat cell cultures of hypertensive and type II diabetic rats and their respective control strains. 2-Deoxy-d-(1-³H)glucose uptake was measured over 48 h after synchronization of cells by means of medium change with and without addition of insulin, phloretine, and/or staurosporine. The circadian changes of glucose uptake were assessed by fitting cosine curves to the uptake values. Insulin stimulation of deoxyglucose uptake was only present in control animals, not in hypertensive and diabetic rats. Deoxyglucose uptake displayed a circadian rhythm in control animals, and was markedly disturbed in hypertensive and diabetic animals. Blocking of glucose transporters by phloretine abolished the circadian pattern of deoxyglucose uptake indicating a role of glucose transporters in its generation. Inhibition of kinases by staurosporine inhibited the insulin-stimulated deoxyglucose uptake, but did not dampen the circadian rhythmicity of basal deoxyglucose uptake. The generation of the circadian rhythm of glucose uptake in muscle and fat cell cultures is therefore probably insulin independent and independent of protein kinases. In summary, our results show for the first time: (a) a circadian rhythm of deoxyglucose uptake in glucose utilizing muscle and fat cells in vitro, (b) a disruption of this rhythm in cells of hypertensive and diabetic rats.     

基于低场核磁共振T1-T2谱技术定性和定量分析罗非鱼各组织的方法探究

形体指标的检测是鱼类常规营养评定的重要组成部分。目前,分析鱼类组织体重比的方法会对鱼体造成损伤,且取样过程复杂,迫切需要无损快速检测技术分析鱼体组织占比。低场核磁共振技术具有快速无损检测的特点,已有研究利用低场核磁共振T1谱技术检测小鼠内脂肪组织体积,但尚未有研究应用低场核磁共振T1-T2谱技术对鱼类各组织器官进行定性和定量分析。基于此,利用低场核磁共振T1-T2谱技术,将分离后的罗非鱼的肌肉组织、腹腔脂肪组织、肝脏组织、肠道组织单独以及混合后进行扫描分析,结果发现利用低场核磁共振T1-T2谱技术可以分离罗非鱼肌肉组织和腹腔脂肪组织,但是无法区分肝脏组织和肠道组织。进一步对能够实现分离的肌肉组织和脂肪组织建立定量分析的模型,分析罗非鱼组织信号强度与组织重量相关性,结果显示,肌肉组织相关性R2=0.974 3,腹腔脂肪组织相关性R2=0965 0。并利用罗非鱼活体验证了肌肉组织定量分析模型的可靠性,将活体扫描肌肉信号大小转换成肌肉组织重量并分析其与全鱼体重相关性,结果显示肌肉组织重量与体重相关性R2=0.806 9。研究表明,在鱼类营养代谢研究中,可以利用低场核磁共振T1-T2谱技术快速无损地定量分析鱼体内肌肉组织含量。