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At least 19 recordsLinked to original sources
PubMed1991

[Effect of shift interval for the clinical nurse with respect to circadian rhythm].

Circadian rhythm is entrained in the 24-hour time interval by periodic factors in the environment, known as zeitgeber. But most rotating work schedules are outside the range of the entrainment of the pacemaker timing the human circadian sleep-wake cycle. It has been postulated that physiological and emotional disturbances occur in most human functions when the circadian rhythm is disturbed. So application of circadian principles to the design of shift schedules can aid in maintaining the temporal integrity of the circadian system and thereby minimize for the shift worker any detrimental consequences of circadian disruption. This study was a quasi-experimental study to test the effect of shift intervals for the clinical nurse on the circadian rhythm. Twenty nurses newly employed in general units of two hospitals were selected as an experimental group and twelve college nursing students as a control group. Both groups were selected according to an established criteria using a purposive sampling technique. Ten subjects were assigned to a weekly shift group and another ten to a biweekly shift group engaged in a semi-continuous shift schedule (sunday off) with a backward direction; that is, morning-evening-night shift. The control group worked a morning shift for 42 days. Oral temperature rhythm, waking time, sleep-wake cycle, fatigue, and mental performance were measured during the experimental period. The data collection period was from April 30, 1990 to June 10, 1990. MANOVA, paired t-test, ANOVA, and Student Newman Keuls method were used for statistical analysis. The results are summarized as follows. 1. Phase delay in the acrophase of temperature rhythm was shown according to the backward rotating shift. A complete adaptation to work on the night shift was achieved between the sixth and ninth day of the night shift. 2. There was no difference in either waking time or sleep-wake cycle according to the duration of the working day for every shift group. Significant difference was found in the waking time and the sleep-wake cycle for subjects on the morning, evening, and night shift in both of the shift groups (weekly shift group: lambda = 0.121, p less than 0.01, lambda = 0.112, p less than 0.01, biweekly shift group: lambda = 0.116, p less than 0.01, lambda = 0.084, p less than 0.01). 3. There was no difference in fatigue between the first working day and the last working day for the control group and for the biweekly shift group.(ABSTRACT TRUNCATED AT 400 WORDS)

Analysis of Variance↗
PubMed1989

Sleep disorders in the elderly. Circadian rhythm.

Circadian rhythms are observable in almost every neuroendocrine, behavioral, and psychophysiologic function, in addition to the classic vital signs. This article discusses how the circadian system might change with advanced age, how these changes interact with behavior changes, and how the resultant effects might influence sleep and daytime functioning.

Aged↗
PubMed1990

Circadian rhythms in depression. Part II: Circadian rhythms in inpatients with various mental disorders.

We investigated longitudinally the circadian body temperature rhythms in 65 inpatients with various mental disorders, 38 of whom had major depressive episodes, by estimating the deep body temperature from the skin surface every 2 h for a consecutive 48-h period. To estimate the circadian rhythm, the data obtained were analyzed by the least-squares method and maximum entropy spectral analysis (MEM). Circadian rhythm disturbances in patients with depression were likely to be manifested in phase variability rather than in phase advance. The amplitude of body temperature of the depressed group was significantly less than that of the control group. A positive correlation between the mesor and the severity of the depressive symptoms was found. Moreover, the body temperature of the patients with affective disorders, both in the depressive and in the manic state, tended to fluctuate so much as not only to fit poorly to sinusoid curves, but also to reduce the periodicity of the circadian rhythm. On the basis of these findings, we conclude that the essential feature of the rhythm disturbances in affective disorders is not the phase shift but the instability of the circadian temperature rhythm.

Adult↗
PubMed1975

Studies on the circadian rhythm of phosphoenolpyruvate carboxykinase. III. Circadian rhythm in the kidney.

Phosphoenolypyruvate carboxykinase [EC 4.1.1.21] activity in rat kidney shows a circadian rhythm with the highest activity between 0200 h and 0800 h and the lowest activity between 1400 h and 2000 h. The rhythm was observed in both sexes and throughout the year. Actinomycin D and cycloheximide effectively blocked the circadian increase in enzyme activity. These findings suggest that the circadian increase in phosphoenolypyruvate carboxykinase activity is due to net synthesis of enzyme protein through newly synthesized mRNA. In experiments with kidney cortex slices, gluconeogenesis from the radioactive precursor, [14C]malic acid, was considerably higher at 0200 h than at 1400 h, varying in parallel with the change in the enzyme activity.

Acclimatization↗
PubMed1989

A circadian rhythm of aqueous flow underlies the circadian rhythm of IOP in NZW rabbits.

There is a daily rhythm of aqueous flow in New Zealand White rabbits entrained to 12 hr light:12 hr dark. The phase of the rhythm of flow is determined by the phase of the light:dark cycle, and the rhythm persists in constant dark. Therefore, in New Zealand White rabbits the rhythm of aqueous flow, like the rhythm of intraocular pressure, is circadian. The range of the circadian rhythm of flow suggests it plays a major role in producing the circadian rhythm of intraocular pressure. This animal model provides a powerful tool for studying endogenous mechanisms which regulate aqueous humor formation and intraocular pressure.

Animals↗
PubMed1986

Relationships between behavioral rhythms, plasma corticosterone and hypothalamic circadian rhythms.

Circadian rhythms in physiological processes and behaviors were compared with hypothalamic circadian rhythms in norepinephrine (NE) metabolites, adrenergic transmitter receptors, cAMP, cGMP and suprachiasmatic nucleus (SCN) arginine vasopressin (AVP) in a single population of rats under D:D conditions. Eating, drinking and locomotor activity were high during the subjective night (the time when lights were out in L:D) and low during the subjective day (the time when lights were on in L:D). Plasma corticosterone concentration rose at subjective dusk and remained high until subjective dawn. Binding to hypothalamic alpha 1- and beta-adrenergic receptors also peaked during the subjective night. Cyclic cGMP concentration was elevated throughout the 24-hr period except for a trough at dusk, whereas DHPG concentration peaked at dawn. Arginine vasopressin levels in the suprachiasmatic nucleus peaked in the middle of the day. No rhythm was found either in binding to the alpha 2-adrenergic receptor, or in MHPG or cAMP concentration. Behavioral and corticosterone rhythms, therefore, are parallel to rhythms in hypothalamic alpha 1- and beta-receptor binding and NE-release. Cyclic GMP falls only at dusk, suggesting the possibility that cGMP inhibits activity much of the day and that at dusk the inhibition of nocturnal activity is removed. SCN AVP, on the other hand, peaking at 1400 hr, may play a role in the pacemaking function of the SCN that drives these other rhythms.

Animals↗
PubMed1992

Seasonal variation in the human circadian rhythm: dissociation between sleep and temperature rhythm.

The circadian rhythms of sleep-wakefulness, rectal temperature, and plasma melatonin were measured in 10 healthy male subjects for five consecutive seasons. To minimize direct effects of seasonally changing environmental factors, the subjects stayed in a living facility for 4 days in each season, where ambient temperature, humidity, and social contacts were controlled, while the light intensity of the living room was substantially influenced by natural daylight. Seasonal variations were found in the timing of sleep, the mean body temperature, the phases of circadian temperature and melatonin rhythms, and the phase relation between sleep and the rectal temperature rhythm. The subjects went to bed earliest in summer, intermediate in spring and autumn, and latest in winter. A similar but more pronounced seasonality was observed in the wake-up time, which was earlier in summer than in winter. The acrophases of the rectal temperature and plasma melatonin rhythms, which were calculated by fitting a cosine curve, were located in an earlier time of day in summer than in winter. The phase-angle difference of the rectal temperature rhythm to sleep varied seasonally and was more positive in summer than in winter. These findings indicate that not only the external (to the local time) but also the internal (between circadian rhythms) phase relations of the human circadian rhythms depend on season.

Adult↗
PubMed2026

GIRK Channels Regulate Circadian Rhythms of Excitability in Prokineticin 2 Neurons of the Suprachiasmatic Nucleus and Modulate Behavioral Circadian Rhythms.

The suprachiasmatic nucleus (SCN), the central circadian clock in mammals, generates robust yet adaptable circadian rhythms through electrically mediated coordination among heterogeneous peptidergic neuronal populations with presumed cell type-specific roles. Previous studies have proposed that circadian changes in membrane excitability of individual SCN neurons arise from time-of-day-dependent shifts in the relative balance of subthreshold Na+ and K+ conductances. Although multiple channels have been implicated in these processes, how nocturnally dominant K+ conductances are implemented in a cell type-specific manner remains poorly understood. Prokineticin 2 (Prok2) has been identified as a SCN signaling peptide essential for behavioral circadian regulation; however, the electrophysiological properties of Prok2-expressing neurons and the mechanisms underlying their diurnal rhythmicity remain largely unexplored. Here, using electrophysiological approaches in mice of either sex, we show that Prok2 neurons exhibit diurnal variations in electrical properties, with higher excitability during the day and reduced excitability at night, and that G-protein-coupled inwardly rectifying potassium (GIRK) channel-mediated basal current contributes to nighttime hyperpolarization. Immunofluorescence and single-cell RT-PCR analyses revealed that GIRK1 and GIRK3 are the predominant GIRK subunits expressed in Prok2 neurons. Moreover, Prok2 neuron-specific deletion of GIRK3 using in vivo genome editing resulted in significant nocturnal depolarization and induced abnormalities in behavioral rhythms, including delayed activity onset and circadian period lengthening, with altered SCN network activity. Together, these findings suggest that tonic, G-protein-dependent regulation of GIRK channels provides a night-specific inhibitory mechanism that contributes to intrinsic diurnal neuronal excitability in Prok2 neurons and supports the regulation of behavioral circadian rhythms.

Animals↗
PubMed1986

Affective disorders and circadian rhythms.

Abnormal circadian rhythms have been associated with affective disorders. A review of this rapidly expanding area of investigation shows that while a clear causal relationship has not yet been proven, a knowledge of the circadian system and its dysfunction can help in understanding unipolar and bipolar depression. Evidence suggests that existing therapies such as lithium and antidepressants act upon the circadian system. Better identification of individuals at risk for affective disorders and the development of new preventive and therapeutic interventions may result from further study of circadian dysfunction.

Affect↗
PubMed1991

Immunoreactive inhibin concentrations in adult men: presence of a circadian rhythm.

The circadian and chronological changes in inhibin secretion were studied in normal adult men. To determine the diurnal release of inhibin, blood samples were collected every hour for 24 h from five healthy young adult men, and serum inhibin was measured by RIA. During the evening and the night, serum inhibin concentrations were relatively low; the lowest value was observed at 2200 h. At 0700 h, inhibin started to increase, reached a peak at 0900 h, and then gradually decreased. These results suggest that inhibin secretion is circadian. Testosterone and cortisol also showed circadian rhythms. In some of the five volunteers, the serum concentrations of inhibin, testosterone, and cortisol were superimposable, but no significant relationship was observed between the serum inhibin and FSH concentrations. With regard to the age-related changes in basal inhibin levels, the highest values were observed in the twenties, and lower values were found with aging. This relationship suggests that increased FSH in elderly men might be due to the reduced amount of peripheral inhibin.

Adult↗
PubMed1987

Corticotropin-releasing factor: a marked circadian rhythm in primate cerebrospinal fluid peaks in the evening and is inversely related to the cortisol circadian rhythm.

Continuous sampling of cerebrospinal fluid (CSF) over 24-h periods in 10 rhesus monkeys revealed a 2-fold, highly reproducible circadian rhythm in CRF concentrations. Peak CRF values of 77.9 +/- 6.4 pg/ml occurred in the evening at 1930 h, while the CRF nadir (38.4 +/- 4.2 pg/ml) occurred at 0745 h. Simultaneously sampled CSF cortisol peaked at 0913 h, with a nadir at 2226 h. Both CRF and cortisol rhythms closely fit sinusoidal circadian models, with r2 values of 0.94 and 0.92, respectively. While hypothalamic CRF is regarded as a major physiological regulator of pituitary ACTH secretion and, thereby, of the circadian and stress-related release of cortisol from the adrenal gland, CRF and CRF receptors are also widely distributed in other brain areas of primates and rodents. The marked difference in the circadian rhythm of CRF vs. that of cortisol suggests that CRF in CSF reflects or mediates some nonhypophysiotropic brain functions of this peptide.

Animals↗
PubMed1990

[Effects of simulated space rhythm (L:D = 0.75h:0.75h) on circadian rhythm in tree shrews (Tupaia belangeri chinensis)].

It is known that contemporary space station revolves at the altitude of 400-500 km in the outer space. The present study was undertaken to investigate the effects of simulated space rhythm (L:D = 0.75 h:0.75 h) at this altitude on circadian rhythm in tree shrews (Tupaia belangeri chinensis) and the effects of endogenous sleep inducing neuropeptide Asp5-alpha-DSIP on the space-rhythm-entrained circadian rhythm. This primitive stock serves as one species of Tupaiidae and is a unique native of South China. Our previous studies have shown that this species showed striking differences in natural circadian rhythm between day and night (e.g. 3.03 degrees C of rectal temperature). Results showed that the above mentioned space rhythm (L:D = 0.75h:0.75h) could drastically disturb the inherent circadian rhythm of Tupaia belangeri chinensis. The maximal peak of motor activity dropped significantly in the morning (0600-1200) and a new enhanced peak (more than 20 times greater than that of the control) was found between 1800-2400, whereas the maximal trough of motor activity (2400-0600) remained basically unchanged. Concurrently, the total amount of 24-h motor activity was significantly decreased and the recovery after the cessation of space rhythm was slow. Experimental results also demonstrated that consecutive administration of Asp5-alpha-DSIP (30 micrograms/kg, i.p.) for 5 days (2 days before and 3 days during space rhythm) did not prevent the basic disturbance of circadian rhythm of Tupaia belangeri chinensis caused by the space rhythm (L:D = 0.75h:0.75h). Nevertheless, no decrease or even some enhancement of the total amount of 24th motor activity was observed during space rhythm or after its cessation.

Animals↗
PubMedDate not supplied

Circadian rhythms in general.

Circadian rhythms in humans are a mixture of endogenous and exogenous components that are derived from the body clock and the interaction between our environment and lifestyle. Inherently, the body clock tends to run slow (by solar time) with a period of about 25 hours. Under normal circumstances, however, zeitgebers adjust it to run with a period of exactly 24 hours. The important zeitgebers in humans appear to be a mixture of bright light and social factors. Recent evidence favors the hypothalamic suprachiasmatic nuclei as a site of the body clock in mammals, though other sites, including the pineal gland, might also play some role. Circadian rhythms not only enable us to adjust better to our rhythmic environment but also influence our responses to disease processes and drugs. Moreover, when our lifestyles are altered abruptly, our body clock is slow to adjust. The result is the symptoms associated with "jet lag" and the general malaise suffered by many nightworkers.

Adaptation, Physiological↗
PubMed1988

Age-related changes in plasma dehydroepiandrosterone sulphate, cortisol, testosterone and free testosterone circadian rhythms in adult men.

The circadian rhythms of serum luteinizing hormone, follicle-stimulating hormone, testosterone (T), free testosterone (fT), sex hormone-binding globulin (SHBG), oestradiol, cortisol and dehydroepiandrosterone sulphate (DHA-s) have been investigated in 5 normal male adults and 6 elderly men. Circadian rhythms were detected statistically significant (p less than 0.05) by population mean cosinor analysis, for T, fT, cortisol and DHA-s in the young group. In the elderly population, serum cortisol showed a clear circadian rhythm, although with some phase modification, whereas DHA-s secretion lost its circadian rhythmicity. This demonstrates that ageing differently affects the two major adrenal functions, glucocorticoid and androgenic; further, the data suggest that an independent adrenal androgen-regulating system could be selectively impaired in the older subjects. In the elderly group the loss of T circadian rhythm was confirmed, but a statistically significant circadian rhythm of fT was recorded. It was characterized by a marked phase advance and not related with the SHBG modifications found in elderly men. This finding leads us to reconsider the role of fT, which appears more sensitive than total T, in studying circadian rhythm of gonadal androgen secretion.

Adult↗
PubMed1992

Circadian rhythm in patients with hydranencephaly.

Circadian rhythm and sleep were studied in three hydranencephalic infants who were diagnosed on the basis of computed tomographic and/or magnetic resonance imaging scans and electrophysiologic findings. In all three cases, although the active sleep cycle was preserved, quiet sleep decreased and indeterminate sleep increased. The sleep-circadian rhythm was disturbed in all three cases. The hormone secretion rhythm was studied in two cases (cases 1 and 3). In both cases, cortisol secretion showed two or three peaks during the day. In one case (case 3), growth hormone secretion did not show sleep enhancement. Prolactin secretion showed an increase during sleep in both cases. The circadian rhythm of body temperature appeared at 6 months of age and disappeared after 1 year of age in case 1. Case 2 did not show a circadian rhythm of body temperature, but case 3 did at 2 years 6 months of age. However, it was thought that the circadian rhythm of body temperature in case 3 was a false one due to severe opisthotonus. Thus, it is suggested that the development of the circadian rhythm may require the rostral brain structure more than the midbrain and that there may be multiple oscillators in humans.

Brain Stem↗
PubMed1986

Characteristics of circadian rhythms in human functions.

Circadian rhythms are of endogenous origin, in humans as in all organisms. Under temporal isolation, i.e., after exclusion of all environmental time cues, circadian rhythmicity persists but with a period slightly deviating from 24 hours; in human, freerunning circadian rhythms always show periods close to 25 hours. In a minority of experiments, overt rhythms of different variables do not run in mutual synchrony but internally desynchronized in the steady state. This means that, indeed, most physiological rhythms, and particularly that of body temperature, hold a period close to 25 hours; it is mainly the sleep-wake rhythm (but also the overt rhythms of several more variables) which shows freerunning periods being considerably longer or shorter than 25 hours. This state of the rhythm is not concerned by the presence or absence of naps; rather, this state is characterized by a considerable stretching or compressing of the entire sleep-wake cycle. The period and other parameters of freerunning rhythms can be modified by continuously operating stimuli. Also the tendency toward the spontaneous occurrence of internal desynchronization does not depend only on personality data (e.g., neuroticism, or age) but also on the external conditions. Whereas constant light in the normal range of artificial illumination (intensities between 0 and 1500 lux) does not affect freerunning human circadian rhythms, the period is longer and the tendency toward internal desynchronization is higher under constant bright light (intensity greater than 3000 lux) than under constant light of normal intensity (or total darkness). This result has been confirmed with various physiological functions, e.g. the rhythms of deep body temperature and melatonin excretion. Social contacts (when subjects do not live singly isolated but in groups) or behavioral stress operates in the same direction as bright light. On the other hand, physical workload does not affect freerunning rhythms. Under natural conditions, the endogenously generated rhythms are synchronized to the 24-hour day. Under laboratory conditions (i.e., under temporal isolation), also artificial zeitgebers can be effective but only within limited ranges of periods; the width of such a range of entrainment is an indicator of the strength of the zeitgeber under consideration.(ABSTRACT TRUNCATED AT 400 WORDS)

Body Temperature↗