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PubMed1979

[Circadian rhythms of the parameters of the mouse esophagus epithelial cell kinetics].

Circadian rhythms of the mitotic activity, DNA synthesis and the parameters of the mitotic cells of the mouse esophagus epithelium were studied during the periods of maximum and minimum proliferation. The number of mitoses and DNA-synthetizing cells increases rhythmically at 1--7 a. m. from 22 p. m. to 4 a. m., respectively. When 3H-thymidine was injected to the mice at 2 a. m., tG2min was 1h; tG2+1/2 M was 2h; tS was 7.1; tG1+1/2 M was 2h; tS was 7.1; tG1+1/2 M was 15.9h. When 3H-thymidine was injected at 2 p. m., tS rose up to 8.2 and tG1+1/2 M up to 14.8h. The mitotic cycle in both series of experiments totalled 25 h. Thus, the duration of various phases of the mitotic cycle depends on the time of the day and correlates with circadian rhythms of the mitotic activity and the number of DNA-synthetizing cells. Duration of the mitotic cycle of the cells passing through it at varying time of the day is the same and approximates the period of the circadian rhythm of mitoses and DNA synthesis in esophagus epithelium.

Animals↗
PubMed1975

[Circadian rhythms op ventilatory mechanical factors in healthy children].

Circadian rhythms in lung resistance (R1) and dynamic compliance (C1dyn) of 7 healthy children (6 to 10 years) were validated (p less than .05) and then quantified (cosinor method); subjects' synchronization: light on at 0700; light off at 2100. Measurements were performed at fixed per hours (0730, 1130, 1630 and 2230) before and after the inhalation of a beta sympathomimetic bronchodilatator: minus 2mg orciprenaline. The measurements carried out after orciprenaline inhalation show a flattening of the curves, both circadian rhythms in R1 and C1 dyn are not detected (p greater than .05).

Airway Resistance↗
PubMed1977

Renal electrolyte circadian rhythms: independence from feeding and activity patterns.

The interrelationships between urinary electrolyte circadian rhythms and rhythms of feeding, drinking and activity were studied in six conscious chair-acclimatized squirrel monkeys (Saimiri sciureus) kept in temperature-controlled isolation chambers on a light-dark (LD) 12:12 h cycle. With lights on (600 lx) from 0800 to 2000 h and off (less than 1 lx) from 2000 to 0800 h, renal potassium excretion in monkeys fed ad libitum fell to a daily minimum of 64 +/- 6 mueq/h at 0500 h and rose to a maximum of 274 +/- 13 mueq/h at 1700 h. Sodium excretion fell to a minimum of 13 +/- 2 mueq/h at 1000 h and rose to a maximum of 43 +/- 6 mueq/h at 2100 h, while water excretion fell to a minimum of 869 +/- 63 mul/h at 0500 h and rose to a maximum of 2,307 +/- 222 mul/h at 1700 h. Feeding, drinking, and activity occurred only during the lights-on period. Independence of the urinary rhythms from diurnal variations in feeding, drinking, and activity was established a) by depriving monkeys of food, b) by depriving monkeys of water, and c) by training monkeys to perform a 2-hourly schedule of feeding, drinking, and activity throughout day and night. None of these three regimens resulted in major reductions of the amplitude, or changes in the phase of the circadian rhythms of urinary electrolyte or water excretion. These findings indicate that the circadian rhythms of urinary potassium, sodium, and water excretion are controlled by mechanisms that are not passively dependent on the behavioral patterns of feeding, drinking, and activity.

Animals↗
PubMed1975

Absence of a circadian rhythm in crypt cell mitotic rate following chemical sympathectomy in rats.

The circadian rhythms in both consumption of food by rats and in the mitotic rate in epithelial cells lining the bases of the crypts of Lieberkühn of the proximal jejunum were studied in normal and in chemically sympathectomised rats. In normal rats both food consumption and crypt cell mitotic rat showed a distinct circadian rhythm, both parameters having a peak around 00.00 to 04.00 hours. Following chemical sympathectomy the circadian rhythm in food consumption was essentially unchanged whereas that in the crypt cell mitotic rate was abolished.

Animals↗
PubMed1976

Circadian rhythm of colonic motility in the cat.

Since circadian patterns of colonic motility are largely unknown the electrical activity of the colon musculature was recorded in 6 unanesthetized cats during day and night. All parts of the colon exhibited 6 patterns of electrical activity: spikes, oscillations, omnipresent regular slow waves, and three composite patterns, i.e. a minute-rhythmic activity, activity complexes of 1 to 18 minute duration and a nyctohemeral pattern. The circadian rhythm was different between the proximal and distal colon resulting in activity gradients. These were directed in an aborad direction from 7 to 9 a.m. and from 9 p.m. to midnight. Most of the defecations of the 6 cats occured in the late evening until 1 a.m. Spike activity of the distal colon predominated from 3 to 4 a.m. and from 11 a.m. to 5 p.m. It is concluded that a circadian rhythm exists in the motility of the cat colon. Differences in the activity between the proximal and the distal colon and resulting activity gradients may offer an explanation for the influences of the time of day on the timing of defecations.

Animals↗
PubMed2024

Circadian rhythms of macrophages are altered by the acidic tumor microenvironment.

Tumor-associated macrophages (TAMs) are prime therapeutic targets due to their pro-tumorigenic functions, but varying efficacy of macrophage-targeting therapies highlights our incomplete understanding of how macrophages are regulated within the tumor microenvironment (TME). The circadian clock is a key regulator of macrophage function, but how circadian rhythms of macrophages are influenced by the TME remains unknown. Here, we show that conditions associated with the TME such as polarizing stimuli, acidic pH, and lactate can alter circadian rhythms in macrophages. While cyclic AMP (cAMP) has been reported to play a role in macrophage response to acidic pH, our results indicate pH-driven changes in circadian rhythms are not mediated solely by cAMP signaling. Remarkably, circadian disorder of TAMs was revealed by clock correlation distance analysis. Our data suggest that heterogeneity in circadian rhythms within the TAM population level may underlie this circadian disorder. Finally, we report that circadian regulation of macrophages suppresses tumor growth in a murine model of pancreatic cancer. Our work demonstrates a novel mechanism by which the TME influences macrophage biology through modulation of circadian rhythms.

Tumor Microenvironment↗
PubMed1978

Circadian rhythm of body temperature during prolonged undersea voyages.

Circadian rhythms of oral temperature were assessed in 12 watchkeepers during a prolonged submarine voyage and compared with a "standard" rhythm obtained from nonwatchkeepers ashore. Initially, the parameters of the rhythms were similar to those of the standard; however, among eight ratings working 4-h watches in a rapidly rotating cycle, considerable changes in the rhythms occurred as the voyage progressed, and concurrent alterations in sleep patterning were observed. The most characteristic change in the rhythm was a marked decline in its amplitude. In most subjects, the rhythm also tended to depart from its original circadian pattern; in at least one case, it effectively disintegrated. One subject's rhythm appeared to "free-run" with a period greater than 24 h. A strong circadian rhythm was maintained in only one of these eight subjects. In four officers whose watch times were at fixed hours, adaptation of the rhythm to unusual times of sleep occurred in 2 of 3 cases where the schedule demanded it. The results are discussed in relation to the design of optimal watchkeeping systems for submariners.

Adaptation, Physiological↗
PubMed1978

Participation of limbic-hypothalamic structures in circadian rhythm of slow wave sleep and paradoxical sleep in the rat.

The effect of brain lesion or surgical isolation of the neural circuit on SWS and PS circadian rhythm have been studied in female rats under a 14/10 light-dark schedule. Cortical EEG'S AND DORSAL NECK EMG were used to monitor SWS, PS and alertness in female rats. Intact and operated controls showed regular 4-5-day vaginal cycles and nocturnal sleep rhythm, but the night PS value on proestrus was lower than in other cycles. Following septal lesion, MPO roof cut, vaginal cycles and SWS rhythm were regularly maintained; however, the PS appearance at night, except during proestrus, increased (night PS peak). These results were similar to those for pinealectomized or ovariectomized female rats. A frontal cut of the MBH produced persistent estrus and disturbed both SWS and PS circadian rhythm. The suprachiasmatic-lesioned rats showed persistent estrus and disrupted SWS rhythm, but regularly maintained the circadian PS rhythm. The vaginal cycles and SWS rhythm in the fornical-transected rats were regularly maintained, but the PS rhythm was disturbed during diestrus and showed ultradian rhythm. From these results, it is suggested that the pineal hormone and the gonadal feedback mechanisms may be involved in the night PS peak and this mechanism may involve the septal- and amygdaloid-hypothalamic systems. A different neural mechanism exist for SWS and PS circadian rhythm; SWS rhythm involves the suprachiasmatic-basal hypothalamic system and PS circadian rhythm is related, in part, to the hippocampal-hypothalamic system.

Animals↗
PubMed1978

Comparison of synchronization of primate circadian rhythms by light and food.

Several circadian rhythms in squirrel monkeys (Saimiri sciureus) entrained by two different agents were studied to compare their mode of coupling with the environmental zeitgebers. Synchronization was accomplished either by light-dark cycles consisting of 12 h of 600 lx followed by 12 h of less than 1 lx (LD 12:12), or by eat-fast cycles in which the animals could eat for 3 h and then had to fast for the remaining 21 h each day (EF 3:21). The rhythms of drinking, colonic temperature, and urinary potassium and water excretion were measured in chair-acclimatized monkeys. The drinking and urinary rhythms were more reproducible (smaller mean variance) and more stable (smaller standard deviation of the timing of a phase reference point) in EF than in LD cycles, whereas the temperature rhythm was more tightly controlled by LD cycles than by EF cycles. In constant light an 8-h phase delay in the EF cycle caused the drinking and urinary rhythms to resynchronize to the EF cycle within one day, while the temperature rhythm required about 6 days to resynchronize. In contrast, previously published data for a similar phase delay in the LD cycle with food available ad libitum show that the drinking and temperature rhythms resynchronized more rapidly than the urinary rhythms. These results indicate that separate mechanisms are involved in transducing temporal cues from LD and EF cycles in the circadian timekeeping system of these nonhuman primates.

Animals↗
PubMedDate not supplied

Circadian rhythms of corticosterone and nucleic acids in the rat adrenal in relation to age.

For 3 successive days, at 0600, 1200, 1800 and 0000, the circadian variations of corticosterone, RNA and DNA were followed up in the adrenals of 3 lots of prebuertal (30 days old), adult (120 days old) and old (28 months old) white Wistar male rats. There is a correlation between the circadian rhythm of corticosterone secretion and the circadian rhythms of RNA and DNA synthesis all along ontogenesis. These rhythms appear to be formed at 30 days of life, but they still differ from the ones in the adult rats by the levels recorded in the second half of the nocturnal period. In old rats the adrenal circadian variations have a considerably smaller amplitude, their curve taking a plateau form. The results support the hypothesis of the circadian rhythm ontogenesis in the rat adrenal.

Adrenal Glands↗
PubMed1977

Individual differences in human circadian rhythms.

Research into individual differences in circadian rhythms is reviewed, particularly morningness-eveningness. It was hypothesised that extraverts would be inclined towards eveningness and introverts towards morningness. Forty-eight subjects took regularly their oral temperature. Peak times were identified from smoothed temperature curves. Results showed that extraverts had a peak time insignificantly later than introverts. Re-grouping of the data into the morningness-eveningness dimension, based upon the results of a self assessment questionnaire, showed that evening types had significantly later peak times than morning types. Morningness-eveningness was not significantly ocrrelated with extraversion-introversion, although there was a trend. No significant differences were found for sleep lengths with either groupings, or for sleep-wake habits within extraversion-introversion. Morning types retired and arose significantly earlier than evening types. Although sleep-wake habits and extraversion-introversion help to determine peak times there are other contributory factors to peak time which appear to be partly covered by the questionnaire.

Adolescent↗
PubMed1978

Phase relations between a circadian rhythm and its zeitgeber within the range of entrainment.

The regular day-night changes in tissues, physiologic functions, and behavior of organisms are based on endogenous rhythmic processes which under constant conditions continue with periods slightly deviating from 24 h. These 'circadian' rhythms have properties of self-sustained oscillators. Under natural conditions, circadian rhythms are synchronized (entrained) to 24 h by periodic factors in the environment, the so-called 'zeitgebers'. In the laboratory, circadian rhythms can also be entrained to periods other than 24 h within certain limits. Data on the phase relationship between the circadian rhythm and an entraining light-dark cycle for vertebrates, insects, plants, and unicellular organisms are reviewed.

Activity Cycles↗
PubMed1978

The effect of beta-adrenergic and cholinergic blockade on the circadian rhythm of gastrins in serum.

The importance of beta-adrenergic and cholinergic mechanisms to the circadian rhythm of gastrins in serum was studied in 15 healthy volunteers. The subjects were investigated during peroral treatment with 1) a beta-adrenergic blocking drug (propranolol), 2) an anticholinergic drug (glycopyrron), 3) both drugs, and 4) without treatment. Gastrin concentrations were measured with an antiserum that measures all four main components of gastrin in serum, and with a gastrin-17 specific antiserum. A circadian rhythm was observed with both antisera. The total immunoreactivity in serum increased from 39 pg per ml +/- 3 (mean and S.E.M.) in the morning to a peak at 2300 (77 +/- 7), followed by a nadir at 0400 (38 +/- 2). The circadian rhythm was maintained during administration of the drugs, but the concentrations of component III (gastrin-17) were reduced by beta-adrenergic blockade, while the anticholinergic treatment increased the concentrations of the other gastrin components. The inhibition of gastric secretion of acid by anticholinergics is presumably due to an action on the parietal cells; according to this study, the inhibition is connected by an increased gastrin stimulus. Beta-adrenergic blockade, on the other hand, seems to reduce the gastrin stimulus and might be of therapeutical interest in duodenal ulcer disease.

Adrenergic beta-Antagonists↗
PubMed1976

[Sex difference in the circadian rhythm of corticotropin-releasing activity in the rat hypothalamus (author's transl)].

Sex difference in the circadian rhythm of the hypothalamic content of Corticotropin-Releasing Factor (CRF) and plasma corticosterone levels was examined in the rat. In the male rat the CRF content was higher in the afternoon than in the morning. In contrast, the hypothalamic CRF content in the female rat was higher in the morning. The peak value was found at 8 a.m. and it fell rapidly around noon with a concomitant sharp rise in the plasma corticosterone. Thus, the whole pattern of CRF content during a 24-hour period makes a mirror image of that of plasma corticosterone. The influence of gonadal hormones on the sex difference was then examined by following variations in the CRF content after ovariectomy. Even after chronic ovariectomy, essential features of the female pattern of CRF rhythm persisted: rapid fall of the CRF content was accompanied by a sharp rise in the plasma corticosterone level. It is noteworthy however that ovariectomy reduced the morning level of CRF activity without elevating the afternoon level, resulting in a peak shift toward noon. The female pattern of CRF rhythmpersisted similarly after bilateral ganglionectomy which is known to affect the biogenic amine rhythm in the pineal gland. The persistence of the female pattern may suggest some endogenous nature of the rhythm. It was then possibly that sex differentiation in the central nervous system (CNS) might be related with manifestation of the female pattern. In order to elucidate this point, postnatal development of circadian rhythm of CRF activity was examined in male and female rats separately. It was found that the CRF rhythm became manifest both in male and female rats around the third week of postnatal life and there was no essential difference in their rhythm pattern. In other words, both male and female rats begin their CRF rhythm with so-called male pattern, with higher values in the afternoon than in the end of the third week of life. In contrast, the CRF rhythm in females rats showed a marked change at ages of five to six weeks during which the onset of puberty intervened in our series of experiment;during this period, the CRF rhythm in female rats turned into the so-called female pattern, with higher values of CRF activity in the morning than in the afternoon. It was of interest that a marked rise in the plasma corticosterone, characteristic of mature female rats, concomitantly appeared. Further attempt were made to examine the effect of gonadal hormones in the periratal period. The hypothalamic CRF content in androgen sterilized female rats as well as in neonatally castrated male rats showed no circadian rhythm. The results implicate subtleness of hormonal effect in simulating physiological processes. In fact, CRF rhythms are variable depending on stages of the estrous cycle: during proestrus and estrus, the CRF content was markedly higher in the morning (9 a.m.) than in the afternoon (4 p.m.). But no significant difference was observed between them during diestrus I and II...

Age Factors↗
PubMed1977

[The effect of eating behavior on the circadian rhythm of plasma corticosterone in growing rats].

The circadian rhythm of plasma corticosterone was studied in growing Rats fed on an ad libitum or controlled feeding schedule (six meals per day). Circadian plasma corticosterone rhythm was conventional in ad libitum Rats. Increases of circulating hormone occurred during the last light hours and the first dark hours. Plasma corticosterone rhythm was modified by controlled feeding. Meal feeders exhibited a high value during the last light hours and a secondary hump at midnight. Feeding schedule was not the main synchronizing factor in rat circadian corticosterone rhythm.

Animals↗
PubMed1978

Ontogenesis of circadian rhythm of melatonin synthesis in pineal gland of rat.

Serotonin N-acetyltransferase (NAT) activity regulates the circadian rhythm of melatonin synthesis in pineal gland. NAT rhythm persisted in continuous darkness or in blinded rats. Development of the circadian rhythm of NAT activity was followed in the infant rats raised under various lighting schedules. The pups born and raised in continuous darkness or under constant illumination showed a rhythmic change indicating that the biological clock for NAT is generated inborn independent of environmental light-dark schedules. In the absence of light, the rhythms of pups synchronized with mother's rhythm. When rats were maintained under a ultradian light-dark schedule (LD 6:6), NAT activity showed a circadian change increasing once a day. When pups were born and raised under the ultradian lighting condition, NAT activity rhythm coincided with mother's rhythm. When pups were raised by a foster mother who had an inverted rhythm from that of an original mother, the rhythm of the pups synchronized with that of the foster mother. Whe pups were separated from their mother daily for 12 hours, their NAT rhythms reappeared when they were separated from their mother. These observations indicated a novel mechanism that in the absence of light-dark schedule, mothers taught the circadian rhythm to the pups as they raised them.

Acetyltransferases↗