Effects of Two Types of Clothing on the Day-Night Variation of Core Temperature and Salivary Immunoglobulin a

Circadian variations in core temperature, skin temperatures, heart rate, and salivary immunoglobulin A (IgA) were compared in subjects wearing two different types of clothing that covered, or left uncovered, their extremities. The experiments were carried out on six female subjects at an ambient temperature of 24 ± 0.5°C and relative humidity of 50 ± 5%. One type of clotiiing consisted of long-sleeved shirts, full-length trousers, and socks (Type L: 1042 g, 1.048 clo); the other was half-sleeved shirts and knee-length trousers (Type H: 747 g, 0.744 clo). The main results were as follows: (i) The level of rectal temperature during night sleep was significantly lower with Type H than Type L clothing, and cosinor analysis indicated a significantly higher circadian amplitude with Type H clothing, (ii) Skin temperatures in the lower extremities increased significantly more on retiring to sleep with Type H than Type L clothing, (iii) Heart rate was significantly lower with Type H than Type L clothing during the sleep period, (iv) The day-night variation of salivary IgA showed a pattern that was the inverse of that of rectal temperature (i.e., low in the daytime and high in the nighttime), and the concentration of salivary IgA was significantly higher with Type H than Type L clothing at 02:30. (v) Subjectively, the self-assessed sleep quality was better with Type H clothing. These results suggest that clothing that leaves the extremities uncovered might be regarded as favorable at the moderate temperature since it induces good sleep and activates the immune response. (Chronobiology International, 14(6), 607–617, 1997)     

Effect of Ramadan on the diurnal variation in short-term high power output

This study examined the effects of Ramadan fasting on anaerobic performances and their diurnal fluctuations. In a balanced and randomized study design, 12 subjects were measured for maximal power (P_max; force-velocity test), peak power (P_peak), and mean power (P_mean) with the Wingate test at 07:00, 17:00, and 21:00 h on four different occasions: one week before Ramadan (BR), the second week of Ramadan (SWR), the fourth week of Ramadan (ER), and two weeks after Ramadan (AR). There was an interval of 28 h between any two successive tests. Oral temperature was measured before each test. Under each condition, the results showed a time-of-day effect on oral temperature. Analysis of variance revealed a significant (Ramadan×time-of-day of test) interaction effect on P_max. This variable improved significantly from morning to evening before Ramadan (1.1±0.2 W · kg^-1), during the second week of Ramadan (0.6±0.2 W · kg^-1), and two weeks after the end of Ramadan (0.9±0.2 W · kg^-1). However, daily fluctuations disappeared during the fourth week of Ramadan. For P_peak and P_mean, there was no significant Ramadan×test-time interaction. These variables improved significantly from morning to evening before Ramadan ([1±0.3 W · kg^-1] for P_peak and [1.7±1.6 W · kg^-1] for P_mean) and in the second week of Ramadan ([0.9±0.6 W · kg^-1] for P_peak and [1.7±1.5 W · kg^-1] for P_mean). However, they were not affected by time-of-day in the fourth week of Ramadan. Considering the effect of Ramadan on anaerobic performances, in comparison with before Ramadan, no significant difference was observed during Ramadan at 07:00 h. The variables were significantly lower in the second week of Ramadan and in the fourth week of Ramadan at 17:00 h and 21:00 h. P_mean was not affected during the second week of Ramadan. In conclusion, the time-of-day effect on anaerobic power variables tends to disappear during Ramadan. In comparison with the period before Ramadan, anaerobic performances were unaffected in the morning but impaired in the evening during Ramadan.     

Reproductive phase dependent circadian variations of plasma melatonin, testosterone, thyroxine and corticosterone in Indian palm squirrel, Funambulus pennanti

To explain the complex mechanism of environmental influence along with internal hormonal (factors) milieu on daily variations in the circulating levels of melatonin, testosterone, thyroxine and corticosterone were analyzed with the help of inferential statistics (Cosinor rhythmometry) in a seasonally breeding tropical rodent, F. pennanti during the reproductively active (RAP) and inactive phases (RIP). Plasma melatonin, thyroxine and corticosterone levels exhibited a significant circadian oscillation during both the active and inactive phases of the annual reproductive cycle. Melatonin showed higher amplitude during RIP in the circulating plasma. Testosterone presented a peak level during evening hours (16:00 - 18:00 h) during RAP only. The phase of thyroxine was noted ∼09:76 h and ∼10.35 h during active and inactive phases, respectively. Corticosterone showed a peak level at ∼12.00 h during both phases of the reproductive cycle. Further, in this tropical rodent, the minimum difference in photoperiod (∼3 - 4 hours) and maximum variation in temperature (max. 18°C - min. 10°C during RIP and max. 45°C - min. 32°C during RAP) and humidity (85% during RIP and 35% during RAP) regulated the diurnal rhythm of circulating melatonin circadian rhythm by ∼1 hour phase advance during RIP. In conclusion, the studied hormonal rhythms may be part of an integrative system to coordinate reproduction and physiological processes successfully with environmental factors.     

Sleepiness and sleep in a simulated "six hours on/six hours off" sea watch system

Ships are operated around the clock using rapidly rotating shift schedules called sea watch systems. Sea watch systems may cause fatigue, in the same way as other irregular working time arrangements. The present study investigated subjective sleepiness and sleep duration in connection with a 6 h on/6 h off duty system. The study was performed in a bridge simulator, very similar to those found on ships. Twelve officers divided into two groups participated in the study that lasted 66 h. Half of the subjects started with the 06:00-12:00 h watch and the other half with the 12:00-18:00 h watch. The subjects alternated between off-duty and on-duty for the remainder of the experimental period. Approximately halfway through the experiment, the 12:00-18:00 h watch was divided into two 3 h watches/off-duty periods. The effect of this was to reverse the on-duty/off-duty pattern between the two groups. This enabled all subjects to work the four possible watches (00:00-06:00 h, 06:00-12:00 h, 12:00-18:00 h, and 18:00-24:00 h) in an order that was essentially counterbalanced between groups. Ratings of sleepiness (Karolinska Sleepiness Scale; KSS) were obtained every 30 min during on-duty periods and if subjects were awake during off-duty periods. The subjectively rated duration of sleep was recorded after each off-duty period that preceded watch periods when KSS was rated. The results showed that the average level of sleepiness was significantly higher during the 00:00-06:00 h watch compared to the 12:00-18:00 h and 18:00-24:00 h watches, but not to the 06:00-12:00 h watch. Sleepiness also progressed significantly from the start toward the end of each watch, with the exception of the 06:00-12:00 h watch, when levels remained approximately stable. There were no differences between groups (i.e., the order between watches). Sleep duration during the 06:00-12:00 h off-duty period (3 h 29 min) was significantly longer than during the 12:00-18:00 h period (1 h 47 min) and the 18:00-24:00 h period (2 h 7 min). Sleep during the 00:00-06:00 h period (4 h 23 min) was longer than all sleep periods except the 06:00-12:00 h period. There were no differences between groups. In spite of sufficient opportunities for sleep, sleep was on the average around 1-1 h 30 min shorter than the 7-7 h 30 min that is considered “normal” during a 24 h period. This is probably a consequence of the difficulty to sleep during daytime due to the alerting effects of the circadian rhythm. Also, sleepiness during the night and early mornings reached high levels, which may be explained by a combination of working close to or during the circadian trough of alertness and the relatively short sleep periods obtained. An initial suppression of sleepiness was observed during all watches, except for the 06:00-12:00 h watch. This suppression may be explained by the “masking effect” exerted by the relative high levels of activity required when taking over the responsibility of the ship. Toward the end of watches, the levels of sleepiness progressively increased to relatively high levels, at least during the 00:00-06:00 h watch. Presumably, initially high levels of activity are replaced by routine and even boredom.     

Influence of two different light intensities from 16:00 to 20:30 hours on evening dressing behavior in the cold

The present experiment tested our hypothesis that the subjects will wear more clothing in the evening cold under the influence of bright light exposure in the late afternoon and evening. Nine young female adults participated in this study. Light intensity was controlled from 9:00 h to 16:00 h at 100 lx, and from 16:00 h to 20:30 h either at 3000 lx in the bright light (Brighte) or at 10 lx in the dim light ("Dim") conditions. Light intensity was maintained at 10 lx from 20:30 h to 23:00 h. They were instructed to wear garments to maintain themselves to feel comfortable during the fall of ambient temperature from 30 degrees C to 15 degrees C (21:00 h - 22:00 h) and its constant temperature at 15 degrees C (22:00 h - 23:00 h). Most subjects dressed in heavier clothing in the "Bright" than in the "Dim" conditions. The evening fall of core temperature was significantly smaller and the urinary melatonin secretion was significantly lower in the "Bright" condition, suggesting that the set-point of core temperature has been set at a higher level during the evening and at night, being influenced by the less amount of melatonin secretion. Thus, it is concluded that the late afternoon and evening bright light exposure could accelerate the dressing behavior in the evening cold.     

Controlled exposure to light and darkness realigns the salivary cortisol rhythm in night shift workers

The efficacy of a light/darkness intervention designed to promote circadian adaptation to night shift work was tested in this combined field and laboratory study. Six full-time night shift workers (mean age ± SD:37.1 ± 8.1 yrs) were provided an intervention consisting of an intermittent exposure to full-spectrum bright white light (∼2000 lux) in the first 6 h of their 8 h shift, shielding from morning light by tinted lenses (neutral gray density, 15% visual light transmission), and regular sleep/darkness episodes in darkened quarters beginning 2 h after the end of each shift. Five control group workers (41.1 ± 9.9 yrs) were observed in the presence of a regular sleep/darkness schedule only. Constant routines (CR) performed before and after a sequence of ∼12 night shifts over 3 weeks revealed that treatment group workers displayed significant shifts in the time of peak cortisol expression and realignment of the rhythm with the night-oriented schedule. Smaller phase shifts, suggesting an incomplete adaptation to the shift work schedule, were observed in the control group. Our observations support the careful control of the pattern of light and darkness exposure for the adaptation of physiological rhythms to night shift work.     

Morning melatonin has limited benefit as a soporific for daytime sleep after night work

Exogenous melatonin administration in humans is known to exert both chronobiotic (phase shifting) and soporific effects. In a previous study in our lab, young, healthy, subjects worked five consecutive simulated night shifts (23:00 to 07:00 h) and slept during the day (08:30 to 15:30 h). Large phase delays of various magnitudes were produced by the study interventions, which included bright light exposure during the night shifts, as assessed by the dim light melatonin onset (DLMO) before (baseline) and after (final) the five night shifts. Subjects also ingested either 1.8 mg sustained-release melatonin or placebo before daytime sleep. Although melatonin at this time should delay the circadian clock, this previous study found that it did not increase the magnitude of phase delays. To determine whether melatonin had a soporific effect, we controlled the various magnitudes of phase delay produced by the other study interventions. Melatonin (n=18) and placebo (n=18) groups were formed by matching a melatonin participant with a placebo participant that had a similar baseline and final DLMO (±1 h). Sleep log measurements of total sleep time (TST) and actigraphic measurements of sleep latency, TST, and three movement indices for the two groups were examined. Although melatonin was associated with small improvements in sleep quality and quantity, the differences were not statistically significant by analysis of variance. However, binomial analysis indicated that melatonin participants were more likely to sleep better than their placebo counterparts on some days with some measures. It was concluded that, the soporific effect of melatonin is small when administered prior to 7 h daytime sleep periods following night shift work.     

Antidepressant effects of combination of sleep deprivation and early evening treatment with melatonin or placebo for winter depression

Patients with winter depression (seasonal affective disorder) respond beneficially to sleep deprivation and bright light, but the mechanisms of these responses remain unknown. The study was designed to test whether afternoon/evening melatonin can prevent further relapse after sleep deprivation (presumably due to a pharmacologically induced advance shift of circadian phase). Compared to phase advancing by alteration of sleep - wake schedule or by bright light exposure, the melatonin intake is a more tolerated treatment procedure, and it provides a possibility of blind comparison between chronotherapeutic and placebo treatments. The depression was scored in 16 female patients with winter depression and 17 age-matched female controls before and after total night sleep deprivation and after subsequent six-day administration of melatonin (0.5 mg) or placebo under double blind conditions. The melatonin intake was scheduled at 17:00 in order to produce a phase advance of circadian rhythms. Sleep deprivation resulted in 38% reduction of depression score in patients, but it did not reduce depression score in controls. After subsequent treatment with placebo or melatonin, slight but significant improvement of mood was found in controls. These treatments also stabilized the antidepressant response to sleep deprivation in patients. However, neither differential effect of melatonin and placebo on depression score nor alteration of habitual sleep timing was found in patients and controls. Thus, the study results do not provide evidence for the antidepressant potential of melatonin in patients with winter depression under realistic clinical conditions. The finding of stabilization of mood in patients with placebo points to the contribution of psychological factors to the therapeutic action of this and other types of innovative treatments for winter depression. To include psychosocial aspects in the theoretical framework of seasonal depression, we conceptualized depression as an evolved feature of emotional response to psychosocial rather than physical environment. The seasonality of depression might be explained by cumulative effects of aperiodical psychosocial factors and periodical physical factors on one of the mechanisms of brain neurotransmission.     

Prolonged mild hypoxia modifies human circadian core body temperature and may be associated with sleep disturbances

Fatigue is often reported after long-haul airplane flights. Hypobaric hypoxia, observed in pressurized cabins, may play a role in this phenomenon by altering circadian rhythms. In a controlled cross-over study, we assessed the effects of two levels of hypoxia, corresponding to cabin altitudes of 8000 and 12,000 ft, on the rhythm of core body temperature (CBT), a marker of circadian rhythmicity, and on subjective sleep. Twenty healthy young male volunteers were exposed for 8 h (08:00-16:00 h) in a hypobaric chamber to a cabin altitude of 8000 ft and, 4 weeks later, 12,000 ft. Each subject served as his own control. For each exposure, CBT was recorded by telemetry for two 24 h cycles (control and hypoxic exposure). After filtering out nonphysiological values, the individual CBT data were fitted with a five-order moving average before statistical group analysis. Sleep latency, sleep time, and sleep efficiency were studied by sleep logs completed every day in the morning. Our results show that the CBT rhythm expression was altered, mainly at 12,000 ft, with a significant increase of amplitude and a delay in the evening decline in CBT, associated with alterations of sleep latency. Mild hypoxia may therefore alter circadian structure and result in sleep disturbances. These results may explain in part the frequent complaints of prolonged post-flight fatigue after long flights, even when no time zones are crossed.     

Accidents in children do not happen at random: predictable time-of-day incidence of childhood trauma

In a prospective study, 15,110 childhood traumas were recorded by the Pediatric Surgery Service (CHUV, Lausanne) between January 1, 1990 and December 31, 1997. The exact clock hour when the injury occurred and other germane data were obtained. Time series thus obtained were analyzed by several statistical (ANOVA, cosinor, χ², Table Curve, etc.) methods. High statistically significant circadian patterns were detected with a trough at night—almost no traumas/hour (t/h), and a peak in the afternoon (∼16:00h)—9.3±0.4 (SD) t/h. Such 24h variation was validated for the whole sample for the entire 8yr study span as well as the data of each year. Neither gender- nor age-related differences in the 24h pattern were detected between children under 5 yr of age, who have not yet attended school and children from 5 to 16 yr of age, who attend school. Small but statistically significant differences in the 24h patterns were observed when categorized by the type of activity associated with the trauma and the place of trauma occurrence. The great stability of the 24h pattern in childhood trauma over the 8yr study span suggests an endogenous origin in addition to the role presumably played by environmental factors. Periods of 12 and 8 h were also detected in the time series. The afternoon peak time of childhood traumas differs from that of adults, which is located ∼04:00h in rotating shift workers and automobile drivers and 06:00-08:00h in adult day-workers. The validation of a circadian pattern in childhood traumas with an afternoon peak should be taken into account in the design of children's preventative injury programs.     

Circadian variation in oxidative stress markers in healthy and type II diabetic men

Seven clinically healthy, nondiabetic (ND) and four Type II diabetic (D) men were assessed for circadian rhythms in oxidative “stress markers.” Blood samples were collected at 3h intervals for ∼27 h beginning at 19:00h. Urine samples were collected every 3 h beginning with the 16:00h-19:00h sample. The dark (sleep) phase of the light-dark cycle extended from 22:30h to 06:30h, with brief awakening for sampling at 01:00h and 04:00h. Subjects were offered general hospital meals at 16:30h, 07:30h, and 13:30h (2400 cal in total/24 h). Serum samples were analyzed for uric acid (UA) and nitrite (NO) concentrations, and urine samples were assayed for 8-hydroxydeoxyguanosine (8-OHdG), malondialdehyde (MDA), and 8-isoprostane (ISP). Data were analyzed statistically both by the population multiple-components method and by the analysis of variance (ANOVA). The 24h mean level of UA and NO was greater in D than in ND subjects (424 vs. 338 μmol/L and 39.2 vs. 12.7 μM, respectively). A significant circadian rhythm in UA (p=0.001) and NO (p=0.048) was evident in ND but not in D (p=0.214 and 0.065). A circadian rhythm (p=0.004, amplitude=8.6 pmol/kgbw/3h urine vol.) was also evident in urine 8-OHdG of ND but not of D. The 24h mean levels of ND and D were comparable (76.8 vs. 65.7 pmol/kgbw/3h urine vol.). No circadian rhythm by population multiple-components was evident in MDA and ISP levels of ND subjects, or in 8-OHdG, MDA, and ISP in D. However, a significant time-effect was demonstrated by ANOVA in all variables and groups. The 24h mean of MDA and ISP in D was significantly greater than in ND (214 vs. 119 nmol/3h urine vol. and 622 vs. 465 ng/3h urine vol.). The peak concentrations of the three oxidative “stress markers” in urine, like those of serum NO, occurred early in the evening in both groups of men. This observation suggests a correlation between increased oxidative damage and increased rate of anabolic-catabolic events as evidenced by similarities in the timing of peak NO production and in parameters relevant to metabolic functions.     

Effect of pedal rate on diurnal variations in cardiorespiratory variables

Recently, it was observed that the freely chosen pedal rate of elite cyclists was significantly lower at 06:00 than at 18:00 h, and that ankle kinematics during cycling exhibits diurnal variation. The modification of the pedaling technique and pedal rate observed throughout the day could be brought about to limit the effect of diurnal variation on physiological variables. Imposing a pedal rate should limit the subject's possibility of adaptation and clarify the influence of time of day on physiological variables. The purpose of this study was to determine whether diurnal variation in cardiorespiratory variables depends on pedal rate. Ten male cyclists performed a submaximal 15 min exercise on a cycle ergometer (50% W_max). Five test sessions were performed at 06:00, 10:00, 14:00, 18:00, and 22:00 h. The exercise bout was divided into three equivalent 5 min periods during which different pedal rates were imposed (70 rev · min^-1, 90 rev · min^-1 and 120 rev · min^-1). No significant diurnal variation was observed in heart rate and oxygen consumption, whatever the pedal rate. A significant diurnal variation was observed in minute ventilation (p=0.01). In addition, the amplitude of the diurnal variation in minute ventilation depended on pedal rate: the higher the pedal rate, the greater the amplitude of its diurnal variation (p=0.03). The increase of minute ventilation throughout the day is mainly due to variation in breath frequency (p=0.01)—the diurnal variation of tidal volume (all pedal rate conditions taken together) being non-significant—but the effect of pedal rate×time of day interaction on minute ventilation specific to the higher pedal rate conditions (p=0.03) can only be explained by the increase of tidal volume throughout the day. Even though an influence of pedal rate on diurnal rhythms in overall physiological variables was not also evidenced, high pedal rate should have been imposed when diurnal variations of physiological variables in cycling were studied.     

SLEEP LOGS OF YOUNG ADULTS WITH SELF-SELECTED SLEEP TIMES PREDICT THE DIM LIGHT MELATONIN ONSET

The purpose of this study was to determine whether a sleep log parameter could be used to estimate the circadian phase of normal, healthy, young adults who sleep at their normal times, and thus naturally have day-to-day variability in their times of sleep. Thus, we did not impose any restrictions on the sleep schedules of our subjects (n=26). For 14 d, they completed daily sleep logs that were verified with wrist activity monitors. On day 14, salivary melatonin was sampled every 30 min in dim light from 19:00 to 07:30h to determine the dim light melatonin onset (DLMO). Daily sleep parameters (onset, midpoint, and wake) were taken from sleep logs and averaged over the last 5, 7, and 14 d before determination of the DLMO. The mean DLMO was 22:48±01:30 h. Sleep onset and wake time averaged over the last 5 d were 01:44±01:41 and 08:44±01:26 h, respectively. The DLMO was significantly correlated with sleep onset, midpoint, and wake time, but was most strongly correlated with the mean midpoint of sleep from the last 5 d (r=0.89). The DLMO predicted using the mean midpoint of sleep from the last 5 d was within 1 h of the DLMO determined from salivary melatonin for 92% of the subjects; in no case did the difference exceed 1.5 h. The correlation between the DLMO and the score on the morningness-eveningness questionnaire was significant but comparatively weak (r=-0.48). We conclude that the circadian phase of normal, healthy day-active young adults can be accurately predicted using sleep times recorded on sleep logs (and verified by actigraphy), even when the sleep schedules are irregular.     

Thermal biology of the fossorial rodent Ctenomys fulvus from the Atacama desert, northern Chile

The Andean tuco-tuco, Ctenomys fulvus (Rodentia: Ctenomyidae) inhabits one of the most arid regions of the world, the Salar de Atacama, Northeast of Antofagasta, Chile (23°17′06″S, 68°05′43″W; 2.240 m.a.s.l). We found that a stable microclimate in burrows, a low evaporative water loss (EWL), and a diet of roots (59% water content) are the main factors that permit the survival of this fossorial species in harsh desert conditions. Large circadian variation in T_a was observed above ground. Daily ΔT_a (T_a max − T_a min) = 37.9±0.2°C in summer and in winter. In contrast, circadian variation of T_a inside the burrows was only 5.8±0.5°C in the same seasons. Relative humidity (RH) was 1.9–3.1% during the day, increasing to maximum values of 27% at night and early morning. Inside the burrows RH was higher and quite stable, ranging between 53.1 and 65%, independent of the time of day and season. EWL, measured between 10 and 25°C, was low (1.26 mg/g h), and a moderate increase of 13–20% was observed at higher temperatures. The low EWL may prevent dehydration. However, because of the low heat loss capability, animals became hyperthermic (0.8–1.6°C) in dry air at T_a=30–35°C. As T_a during afternoon normally exceeded 35°C, the microclimate of burrows provided the only way to avoid the lethal effects of hyperthermia.     

Working under daylight intensity lamp: an occupational risk for developing circadian rhythm sleep disorder?

A 47-yr-old male was admitted to the Institute for Fatigue and Sleep Medicine complaining of severe fatigue and daytime sleepiness. His medical history included diagnosis of depression and chronic fatigue syndrome. Antidepressant drugs failed to improve his condition. He described a gradual evolvement of an irregular sleep-wake pattern within the past 20 yrs, causing marked distress and severe impairment of daily functioning. He had to change to a part-time position 7 yrs ago, because he was unable to maintain a regular full-time job schedule. A 10-day actigraphic record revealed an irregular sleep-wake pattern with extensive day-to-day variability in sleep onset time and sleep duration, and a 36 h sampling of both melatonin level and oral temperature (12 samples, once every 3 h) showed abnormal patterns, with the melatonin peak around noon and oral temperature peak around dawn. Thus, the patient was diagnosed as suffering from irregular sleep-wake pattern. Treatment with melatonin (5 mg, 2 h before bedtime) did not improve his condition. A further investigation of the patient's daily habits and environmental conditions revealed two important facts. First, his occupation required work under a daylight intensity lamp (professional diamond-grading equipment of more than 8000 lux), and second, since the patient tended to work late, the exposure to bright light occurred mostly at night. To recover his circadian rhythmicity and stabilize his sleep-wake pattern, we recommended combined treatment consisting of evening melatonin ingestion combined with morning (09:00 h) bright light therapy (0800 lux for 1 h) plus the avoidance of bright light in the evening. Another 10-day actigraphic study done only 1 wk after initiating the combined treatment protocol revealed stabilization of the sleep-wake pattern with advancement of sleep phase. In addition, the patient reported profound improvement in maintaining wakefulness during the day. This case study shows that chronic exposure to bright light at the wrong biological time, during the nighttime, may have serious effects on the circadian sleep-wake patterns and circadian time structure. Therefore, night bright light exposure must be considered to be a risk factor of previously unrecognized occupational diseases of altered circadian time structure manifested as irregularity of the 24 h sleep-wake cycle and melancholy.     

Shifts of the hormonal rhythms of melatonin and cortisol after a 4 h bright-light pulse in different diurnal types

If applied during corresponding times of the individual melatonin profiles, bright light shifts the circadian phase equally, irrespective of diurnal type. We examined 32 young men: 10 morning types, 11 evening types, and 11 with no predisposition; 16 with high and 16 with low melatonin production. Each completed a 40 h session that included two consecutive nights during which the participants remained, apart from two short breaks during the second day, in bed under an illumination level of 30 lux. A 4 h bright light pulse was applied just after the expected individual melatonin onset the first night to cause a delay of the hormonal profile the second night. Salivary levels of melatonin and cortisol were determined hourly. Melatonin was delayed by 108 min, and cortisol offset and onset by 47 and 110 min, respectively. The cortisol quiescent period (start and end of the quiescent period being defined by the decrease below and the increase above 60% of the average cortisol production between 18:00 and 09:00 h) was prolonged. In contrast to the other subgroups, the delay of melatonin synthesis was about 0.5 h shorter in morning types, and their cortisol quiescent period was shortened. The present study leads to the hypothesis that, despite individually scheduled light exposure, morning types are potentially disadvantaged due to elevated cortisol levels, if persisting, in career night workers.     

Daily rhythms of nonshivering thermogenesis in common spiny mice Acomys cahirinus under short and long photoperiods

Daily rhythms of nonshivering thermogenesis NST were studied in common spiny mice Acomys cahirinus, acclimated to different photoperiod regimes (16L:8D and 8L:16D) at a constant ambient temperature of 26°C. Noradrenaline NA (1.5 mg/kg subcutaneous) was injected at: 06:00, 12:00, 18:00 and 24:00 h (±15 min). NST was measured as the ratio between the maximal oxygen consumption (VO₂) as response to NA — VO₂NA and VO₂ measured at 26°C — VO_{2 min}. Rectal temperatures T_bNA and T_{b min} respectively were recorded at the end of VO₂ measurements. Significant variations in T_{b min}, T_bNA, and NST were revealed, under the two different photoperiod regimes. Significant differences in VO_{2 min}, NST, T_{b min} and T_bNA were also recorded within each photoperiod acclimation group. These results suggest that daily and photoperiod depended variations in the brown adipose tissue activity, presumably emerge from amount of unoccupied receptors or changes in the receptors affinity to NA.     

Effect of fasting and repeat feeding on metabolic rate in Southern Catfish, Silurus meridionalis chen

Southern catfish juvenile (37.6-65.9 g) were fasted for two weeks and fed with cutlets of freshly killed loach species at 2% body mass per meal twice daily (06:00 and 18:00) for four days at 27.5°C. Metabolic rates were measured during the fasting and feeding periods and all metabolic rates were adjusted to a standard body mass of 1 kg using an exponent of 0.75. The aim of this study was to investigate the effect of fasting and repeat feeding on the resting metabolic rate and the feeding metabolic rate. The results demonstrated that the standardized value of the resting metabolic rate gradually decreased from 69.6 ± 2.7 (means ± S.E.) to 42.8 ± 2.3 mgO₂ h^-1 during the two weeks of fasting. The peak feeding metabolic rate and average metabolic rate of each feeding (12 h) gradually increased with repeat feeding before leveling off. The results of this study suggest that southern catfish can regulate digestive function and gradually alter the characteristics of metabolism according to the availability of a food resource.     

Thermophysiological responses under the influences of two types of clothing at an ambient temperature of 32 degrees C with sun radiation

This study aimed to examine the different thermophysiological responses between two types of clothing (HALF, shirts with half sleeves and knee-length trousers; and LONG, shirts with long sleeves and long trousers) in a warm environment with artificial sun radiation. Seven females volunteered as subjects. The subject sat on a balance for 1 h in a climatic chamber with artificial sun. The artificial sun radiation was 600 kcal.m-2.h-1 in front of the subject. The ambient temperature was increased gradually from 27 to 31 degrees C over the experimental period. The globe temperature also increased from 27 to 43 degrees C in 15 min and was kept at 44 degrees C on additional 45 min. The main results were summarized as follows: 1) Extent of rise in rectal and mean skin temperatures during 1 h exposure was significantly higher in HALF than in LONG. 2) Local sweat rate was greater in HALF. 3) The subjects felt wetter and less comfortable in LONG. These results suggest that LONG could weaken heat stress when the subjects were exposed to sun radiation even under moderate warm ambient temperature.     

Structural characteristics and rheological properties of partially hydrolyzed oat β-glucan: the effects of molecular weight and hydrolysis method

Partial hydrolysates of (1→3)(1→4)-β- -glucan from oats were produced by three hydrolysis methods: acid, cellulase or lichenase. The molecular weights ranged from 31 000 to 237 000 g/mol. Six percent solutions of small molecular weight β-glucans formed elastic gels after 4 days at 4 °C whereas larger molecular weight β-glucans remained viscous liquids after 7 days. The melting temperature of the gels increased as they aged and the peak heat flow temperature, measured by differential scanning calorimetry, was 62±2 °C. Partial hydrolysates produced with cellulase, which was shown to preferentially cleave regions of the molecule with longer contiguous β-(1→4)-linked -glucopyranosyl units, tended to produce more elastic gels with stronger junction zones than partial hydrolysates produced with lichenase which cleaves the β-(1→4) glycosidic 3-o-substituted glucose links. This suggests that β-(1→3)-linked cellotriose sections of the polymer are probably the segments which form the junction zones in the gel network rather than cellulose-like segments.