Circadian Rhythms of Enzymes' Activity in Mice Tissues During Exposure to Continuous Illumination

Activity rhythms of enzymes were determined in various tissues of C57BL/6J male mice. The determinations were carried out on mice which were kept in 14 hr light: 10 hr dark regimen, and on day 2, day 5 and day 21 during exposure to continuous illumination. Locomotor activity rhythms were followed in light: dark and up to the seventh day in constant light. All the activities exhibited a significant circadian rhythm in the light: dark regimen. During the exposure to continuous illumination, the locomotor activity exhibit a free running circadian rhythm with a consistent 24 hr and 40 min, major period component. At the same time recording the rhythms of enzyme activity; enzymes exhibited various formats of response which differed from those of the locomotor activity. The results suggest that rhythms of enzyme activity, as well as the desynchronization of the rhythms, are not enzyme specific.     

Circadian and ultradian activity rhythms in male long‐evans rats: Relationship to feeding

Abstract

Rats exhibit ultradian as well as circadian rhythms in activity. Short‐term activity rhythms appear to result from bouts of feeding‐related behavior interspersed with periods of quiescence. We examined the relationship of activity to feeding in 12 male Long‐Evans derived rats during ad lib and restricted feeding (RF) conditions to determine the effect of RF on both circadian and ultradian activity rhythms. By the end of 20 days of RF all animals exhibited an ultradian periodicity of approximately 12 hours. A twenty‐four hour rhythm in feeding persisted, apparently due to the rats adapting to the diurnal feeding period. General findings were that RF resulted in anticipatory activity prior to feeding and that short‐term activity fluctuations and investigations of the food bin continued during RF even though overall nocturnal activity decreased. The results suggest that male rats of this strain exhibit ultradian activity rhythms that appear to be strongly related to feeding.     

Small bowel and plasma gastrin rhythms in cats

The purpose of this experiment was to study the possible role of the gastric antrum and small bowel in the rhythm(s) of plasma gastrin. The cat was used as the laboratory animal. Three groups of cats were provided with a gastric fistula for the study of gastric acid and plasma gastrin rhythms. The first group (N = 7) served as controls. A second group (N = 3) was antrectomized and later subjected to a 80% small bowel resection. Gastric acid secretions were collected every 30 min from 0800 to 2400. Blood samples for determination of gastrin were drawn every 2 hr from 0800 to 2400. In control animals a circadian (i.e. approximately 24 hr) and 3 ultradian (i.e. less than 24 hr) rhythms were detected for acid output. In the antrectomized cats, circadian and ultradian rhythms were documented. After small bowel resection circadian and ultradian rhythms in gastric acid secretion were observed. For plasma gastrin, circadian and ultradian rhythms were found in the control cats. In the antrectomized cats no rhythms were observed. After small bowel resection an ultradian rhythm reappeared in these antrectomized cats. Removal of the antrum in the cat induces disappearance of circadian and ultradian rhythms of plasma gastrin but fails to modify the acid rhythms. Small bowel resection results in the reappearance of an ultradian rhythm for plasma gastrin and a shift in acrophase for the circadian rhythm in acid secretion.     

Small Bowel and Plasma Gastrin Rhythms in Cats

The purpose of this experiment was to study the possible role of the gastric antrum and small bowel in the rhythm(s) of plasma gastrin. The cat was used as the laboratory animal. Three groups of cats were provided with a gastric fistula for the study of gastric acid and plasma gastrin rhythms. The first group (N = 7) served as controls. A second group (N = 3) was antrectomized and later subjected to a 80% small bowel resection. Gastric acid secretions were collected every 30 min from 0800 to 2400. Blood samples for determination of gastrin were drawn every 2hr from 0800 to 2400. In control animals a circadian (i.e.<24hr) and 3 ultradian (i.e.<24 hr) rhythms were detected for acid output. In the antrectomized cats, circadian and ultradian rhythms were documented. After small bowel resection circadian and ultradian rhythms in gastric acid secretion were observed. For plasma gastrin, circadian and ultradian rhythms were found in the control cats. In the antrectomized cats no rhythms were observed. After small bowel resection an ultradian rhythm reappeared in these antrectomized cats. Removal of the antrum in the cat induces disappearance of circadian and ultradian rhythms of plasma gastrin but fails to modify the acid rhythms. Small bowel resection results in the reappearance of an ultradian rhythm for plasma gastrin and a shift in acrophase for the circadian rhythm in acid secretion.     

Effects of obstructive sleep apnea on endogenous circadian rhythms assessed during relaxed wakefulness; an exploratory analysis

ABSTRACT

Obstructive sleep apnea (OSA) is associated with hypertension, cardiovascular disease, and a change in the 24 h pattern of adverse cardiovascular events and mortality. Adverse cardiovascular events occur more frequently in the middle of the night in people with OSA, earlier than the morning prevalence of these events in the general population. It is unknown if these changes are associated with a change in the underlying circadian rhythms, independent of behaviors such as sleep, physical activity, and meal intake. In this exploratory analysis, we studied the endogenous circadian rhythms of blood pressure, heart rate, melatonin and cortisol in 11 participants (48 ± 4 years; seven with OSA) throughout a 5 day study that was originally designed to examine circadian characteristics of obstructive apnea events. After a baseline night, participants completed 10 recurring 5 h 20 min behavioral cycles divided evenly into standardized sleep and wake periods. Blood pressure and heart rate were recorded in a relaxed semirecumbent posture 15 minutes after each scheduled wake time. Salivary melatonin and cortisol concentrations were measured at 1–1.5 h intervals during wakefulness. Mixed-model cosinor analyses were performed to determine the rhythmicity of all variables with respect to external time and separately to circadian phases (aligned to the dim light melatonin onset, DLMO). The circadian rhythm of blood pressure peaked much later in OSA compared to control participants (group × circadian phase, p < .05); there was also a trend toward a slightly delayed cortisol rhythm in the OSA group. Rhythms of heart rate and melatonin did not differ between the groups. In this exploratory analysis, OSA appears to be associated with a phase change (relative to DLMO) in the endogenous circadian rhythm of blood pressure during relaxed wakefulness, independent of common daily behaviors.     

Development of Adrenocortical Cyclic Nucleotide (Cyclic AMP and Cyclic GMP) and Corticosterone Orcadian Rhythms in Male and Female Rats

The daily rhythm of the adrenocortical cyclic nucleotides (cyclic AMP and cyclic GIMP) was studied in infant male and female Wistar rats before and after the establishment of an adult-like daily rhythm of plasma corticosterone. As in this strain the rhythm of corticosterone is known to be present on postnatal day 18, pups of 2 and 3 weeks of age were studied. The dams and the pups as well as the young adult animals were kept on a controlled 12L-12D photoperiod. Groups of 8-10 pups were killed at 4-hr intervals throughout the day. Plasma corticosterone levels and adrenal cyclic AMP and cyclic GMP concentrations were simultaneously measured and the daily patterns established. Pups of 2 weeks of age showed neither plasma corticosterone nor adrenal cyclic AMP rhythms whereas pups of 3 weeks of age exhibited a typical adult-like circadian rhythm for both variables. The patterns for adrenal cyclic GMP differed according to sex: In female pups no cyclic GMP circadian rhythm could be detected at either 2 or 3 wk. In male pups of 3 wk a typical mature rhythm for adrenal cyclic GMP was evident whereas in younger male pups (2 wk) a circadian rhythm was detected. This circadian rhythm, however, differed from mature circadian rhythm in that its peak was located at 1300 hr instead of 0700 hr. These results demonstrate that, unlike that of cyclic AMP the adrenal cyclic GMP circadian rhythm does not appear at the same time as the plasma corticosterone circadian rhythm. Moreover, a circadian rhythmicity for adrenal cyclic GMP can be found in the absence of any corticosterone circadian rhythm. These facts argue against the view of cyclic GMP being a mediator of ACTH-stimulated steroidogenesis.     

Development of Adrenocortical Cyclic Nucleotide (Cyclic AMP and Cyclic GMP) and Corticosterone Orcadian Rhythms in Male and Female Rats

The daily rhythm of the adrenocortical cyclic nucleotides (cyclic AMP and cyclic GIMP) was studied in infant male and female Wistar rats before and after the establishment of an adult-like daily rhythm of plasma corticosterone. As in this strain the rhythm of corticosterone is known to be present on postnatal day 18, pups of 2 and 3 weeks of age were studied. The dams and the pups as well as the young adult animals were kept on a controlled 12L-12D photoperiod. Groups of 8–10 pups were killed at 4-hr intervals throughout the day. Plasma corticosterone levels and adrenal cyclic AMP and cyclic GMP concentrations were simultaneously measured and the daily patterns established. Pups of 2 weeks of age showed neither plasma corticosterone nor adrenal cyclic AMP rhythms whereas pups of 3 weeks of age exhibited a typical adult-like circadian rhythm for both variables. The patterns for adrenal cyclic GMP differed according to sex: In female pups no cyclic GMP circadian rhythm could be detected at either 2 or 3 wk. In male pups of 3 wk a typical mature rhythm for adrenal cyclic GMP was evident whereas in younger male pups (2 wk) a circadian rhythm was detected. This circadian rhythm, however, differed from mature circadian rhythm in that its peak was located at 1300 hr instead of 0700 hr. These results demonstrate that, unlike that of cyclic AMP the adrenal cyclic GMP circadian rhythm does not appear at the same time as the plasma corticosterone circadian rhythm. Moreover, a circadian rhythmicity for adrenal cyclic GMP can be found in the absence of any corticosterone circadian rhythm. These facts argue against the view of cyclic GMP being a mediator of ACTH-stimulated steroidogenesis.     

Circadian rhythms of melatonin in European starlings exposed to different lighting conditions: relationship with locomotor and feeding rhythms

In passerine birds, the periodic secretion of melatonin by the pineal organ represents an important component of the pacemaker that controls overt circadian functions. The daily phase of low melatonin secretion generally coincides with the phase of intense activity, but the precise relationship between the melatonin and the behavioral rhythms has not been studied. Therefore, we investigated in European starlings (Sturnus vulgaris) (1) the temporal relationship between the circadian plasma melatonin rhythm and the rhythms in locomotor activity and feeding; (2) the persistence of the melatonin rhythm in constant conditions; and (3) the effects of light intensity on synchronized and free-running melatonin and behavioral rhythms. There was a marked rhythm in plasma melatonin with high levels at night and/or the inactive phase of the behavioral cycles in almost all birds. Like the behavioral rhythms, the melatonin rhythm persisted for at least 50 days in constant dim light. In the synchronized state, higher daytime light intensity resulted in more tightly synchronized rhythms and a delayed melatonin peak. While all three rhythms usually assumed a rather constant phase relationship to each other, in one bird the two behavioral rhythms dissociated from each other. In this case, the melatonin rhythm retained the appropriate phase relationship with the feeding rhythm. Accepted: 10 December 1999     

Circadian rhythms of salivary cortisol content during long-term space flight

Adaptation mechanisms of adrenal function related to secretion of cortisol were studied under conditions of microgravity. Parameters of diurnal rhythms of salivary cortisol were studied by Russian cosmonauts on board orbital station Mir during long-term space flights (SF). The preflight circadian rhythms of salivary cortisol in cosmonauts were characterized by the morning maximum occurring at 9∶43 a.m., the fluctuation amplitude 6.05 nmol/1, and the daily average concentration 8.79 nmol/l. The characteristics of cortisol diurnal rhythm changed under conditions of long-term space flight. On average, the rhythm measure and amplitude decreased after two months of flight. The postflight maximum concentration of free cortisol tended to occur later in the day. Evidently, the motor activity during SF, i.e., prophylactic exercises along with other factors, significantly influenced the parameters of cortisol circadian rhythm that was revealed by the individual variability of findings during the flight. After the long-term SF, individual ratios of salivary and plasma cortisol levels increased against the background of increased plasma content of the hormone, i.e., the fraction of free, physiologically active hormone in the total pool of circulating molecules decreased.     

Marker rhythms of circadian system function: a study of patients with metastatic colorectal cancer and good performance status

Cancer patients may exhibit normal or altered circadian rhythms in tumor and healthy tissues. Four rhythms known to reflect circadian clock function were studied in 18 patients with metastatic colorectal cancer and good performance status. Rest-activity was monitored by wrist actigraphy for 72 h before treatment, and its circadian rhythm was estimated by an autocorrelation coefficient at 24h and a dichotomy index that compared the activity level when in and out of bed. Blood samples (9-11 time points, 3-6 h apart) were drawn on day 1 and day 4 of the first course of chronochemotherapy (5-fluorouracil: 800 mg/m2/day; folinic acid: 300 mg/m2/day; oxaliplatin: 25 mg/m2/day). Group 24h rhythms were validated statistically for plasma concentrations of melatonin, 6-alpha-sulfatoxymelatonin, and cortisol and for lymphocyte counts. Significant individual 24h rhythms were displayed in melatonin by 15 patients, cortisol by seven patients, lymphocytes by five patients, and prominent circadian rhythms in activity were displayed by 10 patients; only one patient exhibited significant rhythms in all the variables. The results suggest the rhythms of melatonin, cortisol, lymphocytes, and rest/activity reflect different components of the circadian system, which may be altered differently during cancer processes. Such 24h rhythm alterations appeared to be independent of conventional clinical factors.     

Hypoxic alterations of cortisol circadian rhythm in man after simulation of a long duration flight

Fatigue is often reported after long duration flights. Mild hypobaric hypoxia caused by pressurisation may be involved in this effect through disruption of circadian rhythms, independently of the number of time zones crossed. In this controlled crossover study, we assessed the effects of two levels of hypoxia equivalent to 8000 and 12,000 ft on the circadian rhythm of plasma cortisol, a marker of the circadian time structure. Sixteen healthy young male volunteers (23-39 years) were exposed in a hypobaric chamber for 8 h (08:00-16:00 h) to 8000 ft, followed 4 weeks later to 12,000 ft. Plasma cortisol was assayed during two 24-h cycles (control and hypoxic exposure) every 2h in all subjects. We found a significant change in the pattern of cortisol secretion during both hypoxic exposures, with an initial fall in cortisol followed by a transient rebound, whereas the phase and the 24-h mean level remained unchanged. The change in cortisol pattern followed the alterations in autonomic balance assessed by heart rate variability (HRV) spectral analysis. The normalised high frequencies and the low-to-high frequencies ratio showed a significant shift toward sympathetic dominance with some differences in time course for both altitudes studied. HRV analysis improved the interpretation of cortisol 24-h profiles. Our data, which strongly suggest that prolonged mild hypoxia alters the expression of cortisol circadian rhythm, should be taken into account to interpret secretory rhythm changes after transmeridian flights.     

Urinary excretion of immunoreactive prostaglandin E: A circadian rhythm and the effect of posture

The excretion of urinary immunoreactive prostaglandin E (iPGE), sodium, potassium, creatinine and volume was studied in 4 hr collections in normal women at normal activity. iPGE exhibited a circadian rhythm with an amplitude of 29% and peak excretion at 4:55 P.M. There were also significant circadian rhythms for sodium, potassium, creatinine, and volume, all peaking in late afternoon. There were no significant changes either in the total excretion or in the circadian rhythms of iPGE, potassium, or creatinine excretion when the subjects remained in bed for an entire day while the circadian rhythms of sodium and volume were significantly modified in amplitude and phase, respectively. Urinary aldosterone excretion decreased significantly when the subjects were at bed rest. iPGE excretion increased 33% when subjects were first recumbent and then erect for consecutive 4 hr periods on the same day (but when subjects were erect 1 day for a 4 hr period, iPGE excretion was lower by 32% than for the same 4 hr period the preceding day when they were recumbent). These data indicate that: 1) the sympathetic nervous system and renin-angiotensin-aldosterone system do not affect the circadian rhythm of urinary iPGE, and 2) short-term experiments of prostaglandin E excretion must be designed to avoid misleading results due to the circadian rhythm.     

Marker rhythms of circadian system function: a study of patients with metastatic colorectal cancer and good performance status

Cancer patients may exhibit normal or altered circadian rhythms in tumor and healthy tissues. Four rhythms known to reflect circadian clock function were studied in 18 patients with metastatic colorectal cancer and good performance status. Rest–activity was monitored by wrist actigraphy for 72 h before treatment, and its circadian rhythm was estimated by an autocorrelation coefficient at 24h and a dichotomy index that compared the activity level when in and out of bed. Blood samples (9–11 time points, 3–6 h apart) were drawn on day 1 and day 4 of the first course of chronochemotherapy (5-fluorouracil: 800 mg/m²/day; folinic acid: 300 mg/m²/day; oxaliplatin: 25 mg/m²/day). Group 24h rhythms were validated statistically for plasma concentrations of melatonin, 6-α-sulfatoxymelatonin, and cortisol and for lymphocyte counts. Significant individual 24h rhythms were displayed in melatonin by 15 patients, cortisol by seven patients, lymphocytes by five patients, and prominent circadian rhythms in activity were displayed by 10 patients; only one patient exhibited significant rhythms in all the variables. The results suggest the rhythms of melatonin, cortisol, lymphocytes, and rest/activity reflect different components of the circadian system, which may be altered differently during cancer processes. Such 24h rhythm alterations appeared to be independent of conventional clinical factors.     

Effects of suprachiasmatic nuclei lesions on circadian and ultradian rhythms in body temperature in ocular enucleated rats

Abstract

To test the hypothesis that an oscillator located outside the suprachiasmatic nuclei (SCN) controls the circadian rhythm of body temperature, we conducted a study with 14 blinded rats, 10 of which receiving a SCN lesion. Body temperature was automatically and continuously recorded for about one month by intraperitoneal radio transmitters. Food intake, drinking and locomotor activity were also recorded. Periodograms revealed that 3 rats with histologically verified total bilateral SCN lesions did not exhibit any circadian rhythmicity. The 7 other rats appeared to have partial lesions. They showed shortening of period and severe amplitude reduction in all functions. Thus, no support was found for the hypothesis of a separate circadian ‘temperature oscillator’ located outside the SCN. Nevertheless, after large partial lesions body temperature showed more persistency than some of the other behavioral rhythms.

Ultradian rhythms in temperature persisted after partial and total lesions. Other functions showed parallel ultradian rhythms. In intact rats the ultradian peaks were restricted predominantly to the subjective night. After total lesions these peaks became more or less homogeneously distributed in time but more heterogeneously after partial lesions. So the SCN plays a role in the temporal structure of ultradian rhythms but does not generate them. Non‐24‐hour actograms showed instabilities of period and phase of ultradian rhythms. Intact and lesioned rats were similar with respect to the mean (about 3.5 hrs) and standard deviation (about 1.5 hrs) of ultradian periods in temperature. These features indicate that a mechanism outside the SCN is underlying ultradian rhythmicity, capable of generating short‐term oscillations. Two approaches, homeostatic sleep‐wake relaxation oscillations and multiple circadian oscillators, are discussed.     

Plasticity of the intrinsic period of the human circadian timing system

Human expeditions to Mars will require adaptation to the 24.65-h Martian solar day-night cycle (sol), which is outside the range of entrainment of the human circadian pacemaker under lighting intensities to which astronauts are typically exposed. Failure to entrain the circadian time-keeping system to the desired rest-activity cycle disturbs sleep and impairs cognitive function. Furthermore, differences between the intrinsic circadian period and Earth's 24-h light-dark cycle underlie human circadian rhythm sleep disorders, such as advanced sleep phase disorder and non-24-hour sleep-wake disorders. Therefore, first, we tested whether exposure to a model-based lighting regimen would entrain the human circadian pacemaker at a normal phase angle to the 24.65-h Martian sol and to the 23.5-h day length often required of astronauts during short duration space exploration. Second, we tested here whether such prior entrainment to non-24-h light-dark cycles would lead to subsequent modification of the intrinsic period of the human circadian timing system. Here we show that exposure to moderately bright light ( approximately 450 lux; approximately 1.2 W/m(2)) for the second or first half of the scheduled wake episode is effective for entraining individuals to the 24.65-h Martian sol and a 23.5-h day length, respectively. Estimations of the circadian periods of plasma melatonin, plasma cortisol, and core body temperature rhythms collected under forced desynchrony protocols revealed that the intrinsic circadian period of the human circadian pacemaker was significantly longer following entrainment to the Martian sol as compared to following entrainment to the 23.5-h day. The latter finding of after-effects of entrainment reveals for the first time plasticity of the period of the human circadian timing system. Both findings have important implications for the treatment of circadian rhythm sleep disorders and human space exploration.     

Circadian synchronization of hepatocyte proliferation in young rats: the role played by adrenal hormones

The circadian rhythm of hepatic cell proliferation in rats appears on the 20th day of life, when the hypothalamo-adrenal axis is mature enough for circadian activity to occur. From the 20th day to the 30th day of life, the mitotic rhythm is progressively induced by a reduction in nocturnal values, while diurnal rhythms remain unchanged. Mitotic peaks emerge at 10.00 hours. A labelling index wave occurs 8 hr before the corresponding mitotic wave, with a peak at 02.00 hours and a minimum in the evening, coincidental with the acrophase of plasma corticosterone level (activity phase). Labelled mitoses curves and metaphase accumulation after colchicine injection show that the duration of the S, G2 and M phases remain approximately constant and that the circadian variation is due to a variation in the rate of cells that enter these successive phases. During the synchronization period (from day 20 to 30), the growth fraction decreases progressively. Adrenalectomy at this time is followed by a higher cell proliferation and all rhythms disappear after 2 days. Corticosterone injected before the triggering of the rhythmic activity in 17-day-old rats immediately reduces the labelling index, while the mitotic index is decreased 10 hr later; this delay is equal to the S + G2 duration. The results are discussed. They favour the hypothesis that the circadian variation of corticosterone is responsible for the induction of a circadian variation in developmental cell proliferation by inhibition of the G1-S transition when it is higher in the evening.     

Effects of constant darkness and constant light on circadian organization and reproductive responses in the ram

The relationship between circadian rhythms in the blood plasma concentrations of melatonin and rhythms in locomotor activity was studied in adult male sheep (Soay rams) exposed to 16-week periods of short days (8 hr of light and 16 hr of darkness; LD 8:16) or long days (LD 16:8) followed by 16-week periods of constant darkness (dim red light; DD) or constant light (LL). Under both LD 8:16 and LD 16:8, there was a clearly defined 24-hr rhythm in plasma concentrations of melatonin, with high levels throughout the dark phase. Periodogram analysis revealed a 24-hr rhythm in locomotor activity under LD 8:16 and LD 16:8. The main bouts of activity occurred during the light phase. A change from LD 8:16 to LD 16:8 resulted in a decrease in the duration of elevated melatonin secretion (melatonin peak) and an increase in the duration of activity corresponding to the changes in the ratio of light to darkness. In all rams, a significant circadian rhythm of activity persisted over the first 2 weeks following transfer from an entraining photoperiod to DD, with a mean period of 23.77 hr. However, the activity rhythms subsequently became disorganized, as did the 24-hr melatonin rhythms. The introduction of a 1-hr light pulse every 24 hr (LD 1:23) for 2 weeks after 8 weeks under DD reinduced a rhythm in both melatonin secretion and activity: the end of the 1-hr light period acted as the dusk signal, producing a normal temporal association of the two rhythms. Under LL, the 24-hr melatonin rhythms were disrupted, though several rams still showed periods of elevated melatonin secretion. Significant activity rhythms were either absent or a weak component occurred with a period of 24 hr. The introduction of a 1-hr dark period every 24 hr for 2 weeks after 8 weeks under LL (LD 23:1) failed to induce or entrain rhythms in either of the parameters. The occurrence of 24-hr activity rhythm in some rams under LL may indicate nonphotoperiodic entrainment signals in our experimental facility. Reproductive responses to the changes in photoperiod were also monitored. After pretreatment with LD 8:16, the rams were sexually active; exposure to LD 16:8, DD, or LL resulted in a decline in all measures of reproductive function. The decline was slower under DD than LD 16:8 or LL.(ABSTRACT TRUNCATED AT 400 WORDS)     

Plasma Corticosterone, Motor Activity and Metabolic Circadian Patterns in Streptozotocin-Induced Diabetic Rats

Experiments were conducted in male rats to study the effects of streptozotocin-induced diabetes on circadian rhythms of (a) plasma corticosterone concentrations; (b) motor activity; and (c) metabolic patterns. Animals were entrained to LD cycles of 12: 12 hr and fed ad libitum.

A daily rhythm of plasma corticosterone concentrations was found in controls animals with peak levels at 2400 hr and low values during the remaining hours. This rhythm was statistically confirmed by the cosinor method and had an amplitude of 3.37μg/100 ml and the acrophase at 100 hr. A loss of the normal circadian variation was observed in diabetic animals, with a nadir at the onset of light period and high values throughout the remaining hours; cosinor analysis of these data showed no circadian rhythm, delete and a higher mean level than controls.

As expected, normal rats presented most of their motor activity during the dark period with 80+ of total daily activity; the cosinor method demonstrated a circadian rhythm with an amplitude of 60+ of the mean level and the acrophase at 0852 hr. Both diabetic and control rats showed a similar activity during the light phase, but diabetic animals had less activity than controls during the night and their percentage of total daily activity was similar in both phases of the LD cycle (50+ for each one). With the cosinor method we were able to show the persistence of a circadian rhythm in the motor activity of diabetic rats, but with a mesor and amplitude lower than in controls (amplitude rested at 60+ of the mean level) and its acrophase advanced to 0148 hr.

The metabolic activity pattern of diabetic rats also changed: whereas controls showed a greater metabolic activity during the night (70+ food; 82+ water; 54+ urine; 67+ faeces), diabetics did not show differences between both phases of the LD cycle. Water ingested and urine excreted by the diabetic group were higher than normal during light and dark periods; food consumed and faeces excreted were higher than controls only in the light phase.

These data suggest that alterations in circadian rhythms of plasma corticosterone and motor activity are consecutive to the loss of the feeding circadian pattern, due to polyphagia and polydipsia showed by these animals, which need to extend intakes during the light and dark phases.     

Interindividual Differences in a Set of Biological Rhythms Documented During the High Arctic Summer (79°N) In Three Healthy Subjects

The High Arctic summer with its permanent sunlight provides a situation in which one of the natural synchronizers, the light-dark alternation, is minimal. During the summers of 1981 and 1982 three healthy right-handed geographers who were performing field studies in Svalbard as part of their own research volunteered to document, 4–6 times per 24 hr for respectively 63,141 and 147 days, a set of circadian rhythms: self-rated fatigue, oral temperature, grip strength of both hands, heart rate and times of awakening and retiring. Tests were performed before departure from France, in Svalbard (79°IN latitude) where their daily activities were often strenuous, and after returning to France. Time series were treated individually according to three methods: display of data as a function of time, cosinor analyses to quantify rhythm parameters, and spectral analyses to estimate component periods of rhythms. Circadian parameters such as period and acrophase of activity-rest, oral temperature and fatigue rhythms were not altered. On the other hand, the circadian rhythm in grip strength was altered: the period differed from 24 hr in one subject, while grip strength acrophase of the left, but not the right, hand of the other two subjects was phase shifted during the sojourn in Svalbard. A prominent circahemidian (about 12 hr) rhythm was observed in two subjects for their heart rate in Svalbard, while a prominent circadian rhythm (differing from exactly 24 hr) was observed in France associated with a small circahemidian component.     

Interindividual differences in a set of biological rhythms documented during the high arctic summer (79 degrees N) in three healthy subjects

The High Arctic summer with its permanent sunlight provides a situation in which one of the natural synchronizers, the light-dark alternation, is minimal. During the summers of 1981 and 1982 three healthy right-handed geographers who were performing field studies in Svalbard as part of their own research volunteered to document, 4-6 times per 24 hr for respectively 63,141 and 147 days, a set of circadian rhythms: self-rated fatigue, oral temperature, grip strength of both hands, heart rate and times of awakening and retiring. Tests were performed before departure from France, in Svalbard (79°IN latitude) where their daily activities were often strenuous, and after returning to France. Time series were treated individually according to three methods: display of data as a function of time, cosinor analyses to quantify rhythm parameters, and spectral analyses to estimate component periods of rhythms. Circadian parameters such as period and acrophase of activity-rest, oral temperature and fatigue rhythms were not altered. On the other hand, the circadian rhythm in grip strength was altered: the period differed from 24 hr in one subject, while grip strength acrophase of the left, but not the right, hand of the other two subjects was phase shifted during the sojourn in Svalbard. A prominent circahemidian (about 12 hr) rhythm was observed in two subjects for their heart rate in Svalbard, while a prominent circadian rhythm (differing from exactly 24 hr) was observed in France associated with a small circahemidian component.