Chronobiology international
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This study aimed to analyze individual cortisol levels in relation to work conditions, sleep, and health parameters among truck drivers working day shifts (n = 21) compared to those working irregular shifts (n = 21). A total of 42 male truck drivers (39.8 (+/-) 6.2 yrs) completed questionnaires about sociodemographics, job content, work environment, health, and lifestyle. Rest-activity profiles were measured using actigraphy, and cardiovascular blood parameters were collected. ⋯ Although no direct comparisons could be made between groups for work days, on off days the irregular-shift workers had higher cortisol levels compared to day-shift workers, suggesting a prolonged stress response in the irregular-shift group. In addition, cortisol levels were correlated with stressors and metabolic parameters. Future studies are warranted to investigate further stress responses in the context of irregular work hours.
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The aim of the study was to evaluate the influence of chronotype (morning-type versus evening-type) living in a fixed sleep-wake schedule different from one's preferred sleep schedules on the time course of neurobehavioral performance during controlled extended wakefulness. The authors studied 9 morning-type and 9 evening-type healthy male subjects (21.4 ± 1.9 yrs). Before the experiment, all participants underwent a fixed sleep-wake schedule mimicking a regular working day (bedtime: 23:30 h; wake time: 07:30 h). ⋯ These results indicate evening types living in a fixed sleep-wake schedule mimicking a regular working day (different from their preferred sleep schedules) express higher subjective sleepiness but can maintain the same level of objective alertness during a normal waking day as morning types. Furthermore, evening types were found to maintain optimal alertness throughout their nighttime, whereas morning types could not. The authors suggest that evening-type subjects have a higher voluntary engagement of wake-maintenance mechanisms during extended wakefulness due to adaptation of their sleep-wake schedule to social constraints.
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This study evaluates the administration time-of-day effects on propofol pharmacokinetics and sedative response in rabbits. Nine rabbits were sedated with 5 mg/kg propofol at three local clock times: 10:00, 16:00, and 22:00 h. Each rabbit served as its own control by being given a single infusion at the three different times of day on three separate occasions. ⋯ The degree of anesthesia was largest at 10:00 h, lowest at 16:00 h, and intermediate at 22:00 h. In summary, both the pharmacokinetics and pharmacodynamics of propofol in rabbits depended on administration time. The developed population approach may be used to assess chronopharmacokinetics and chronopharmacodynamics of medications in animals and humans.
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As heart-rate variability (HRV) is under evaluation in clinical applications, the authors sought to better define the interdependent impact of age, maximal exercise, and diurnal variation under physiologic conditions. The authors evaluated the diurnal changes in HRV 24-h pre- and post-maximal aerobic exercise testing to exhaustion in young (19-25 yrs, n = 12) and middle-aged (40-55 yrs, n = 12) adults. Subjects wore a portable 5-lead electrocardiogram holter for 48 h (24 h prior to and following a maximal aerobic capacity test). ⋯ Sleep increases variability equally and proportionally to daytime variability. Given the higher baseline awake HRV and equal rise in HRV during sleep, the change in HRV from sleep to morning with exercise is greater in younger subjects. These physiologic results have clinical significance in understanding the pathophysiology of altered variability in ill patients.
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Physiological functions of the gastrointestinal tract (GIT) are temporally controlled such that they exhibit circadian rhythms. The circadian rhythms are synchronized with the environmental light-dark cycle via signaling from the central circadian clock located in the suprachiasmatic nucleus (SCN) of the hypothalamus, and by food intake. The aim of the study was to determine the extent to which disturbance in the SCN signaling via prolonged exposure to constant light affects circadian rhythms in the liver, duodenum, and colon, as well as to determine whether and to what extent food intake can restore rhythmicity in individual parts of the GIT. ⋯ Whereas in the liver and duodenum the profiles of all clock genes and clock-controlled genes became rhythmic, in the colon only Per1, Bmal1, and Rev-erbα-but not Per2, Wee1, and Dbp-were expressed rhythmically. The data demonstrate a greater persistence of the rhythmicity of the circadian clocks in the duodenum compared with that in the liver and colon under conditions when signaling from the SCN is disrupted. Moreover, disrupted rhythmicity may be restored more effectively by a feeding regime in the duodenum and liver compared to the colon.