An arousing, musically enhanced bird song stimulus mediates circadian rhythm phase advances in dim light

A musically enhanced bird song stimulus presented in the early subjective night phase delays human circadian rhythms. This study determined the phase-shifting effects of the same stimulus in the early subjective day. Eleven subjects (ages 18-63 yr; mean +/- SD: 28.0 +/- 16.6 yr) completed two 4-day laboratory sessions in constant dim light (<20 lux). They received two consecutive presentations of either a 2-h musically enhanced bird song or control stimulus from 0600 to 0800 on the second and third mornings while awake. The 4-day sessions employing either the stimulus or control were counterbalanced. Core body temperature (CBT) was collected throughout the study, and salivary melatonin was obtained every 30 min from 1900 to 2330 on the baseline and poststimulus/postcontrol nights. Dim light melatonin onset and CBT minimum circadian phase before and after stimulus or control presentation was assessed. The musically enhanced bird song stimulus produced significantly larger phase advances of the circadian melatonin (mean +/- SD: 0.87 +/- 0.36 vs. 0.24 +/- 0.22 h) and CBT (1.08 +/- 0.50 vs. 0.43 +/- 0.37 h) rhythms than the control. The stimulus also decreased fatigue and total mood disturbance, suggesting arousing effects. This study shows that a musically enhanced bird song stimulus presented during the early subjective day phase advances circadian rhythms. However, it remains unclear whether the phase shifts are due directly to effects of the stimulus on the clock or are arousal- or dim light-mediated effects. This nonphotic stimulus mediates circadian resynchronization in either the phase advance or delay direction.     

A half-yearly aspect of circulating melatonin in pregnancies complicated by intrauterine growth retardation

In investigating mechanisms underlying intrauterine growth retardation (IUGR), circulating melatonin and cortisol were radioimmunoassayed. Blood samples were collected every 4 hours during 24 hours on a strict 24-hour standardized routine in hospital from two groups of women in their third trimester of pregnancy. One group consisted of 14 healthy, uncomplicated pregnancies (HAGA); the other group consisted of 11 pregnancies complicated by intrauterine growth retardation (IUGR) confirmed at birth. The circadian characteristics of melatonin and cortisol were assessed for each woman and compared between the two groups by analyses of variance for repeated measures and by parameter tests based on the cosinor. Since a circasemiannual (about half-yearly) component prominently characterizes body weight and length at birth of children with birth characteristics below usual norms, the circadian characteristics of melatonin and cortisol were also analyzed transversely (across women within each group). The 24-hour average and the 24-hour and 12-hour amplitudes of melatonin of women in the IUGR, but not in the HAGA group, were indeed found to be modulated by an about half-yearly component. This study confirms the circadian rhythmicity of melatonin in healthy pregnant women and extends the finding to pregnancies complicated by IUGR, uncovering about half-yearly changes in melatonin in women with IUGR, thereby extending results obtained in healthy non-pregnant women and men. These variations may reflect influences from geomagnetic disturbances also characterized by a prominent half-yearly pattern, to which the pineal has been shown to be sensitive.     

Effect of shift work on the night-time secretory patterns of melatonin, prolactin, cortisol and testosterone

In a study of the internal desynchronization of circadian rhythms in 12 shift workers, 4 of them, aged 25-34 years, agreed to be sampled every 2 h during their night shift (0000 hours to 0800 hours). They were oil refinery operators with a fast rotating shift system (every 3-4 days). We found marked changes in the secretory profiles of melatonin, prolactin and testosterone. Melatonin had higher peak-values resulting in a four-times higher amplitude than in controls. With respect to prolactin and testosterone, peak and trough times were erratic and the serum concentrations were significantly decreased in shift workers. Serum cortisol presented a decreased rhythm amplitude together with higher concentrations at 0000 hours in shift workers. This study clearly shows that fast rotating shift-work modifies peak or trough values and rhythm amplitudes of melatonin, prolactin, testosterone and cortisol without any apparent phase shift of these hormones. Whether the large rhythm amplitude of melatonin may be considered as a marker of tolerance to shift work, as reported for body temperature and hand grip strength, since it would help the subjects to maintain their internal synchronization, needs further investigation.     

Melatonin in circadian sleep disorders in the blind

Assessment of sleep patterns in blind people demonstrates a high prevalence of sleep disorders. Our studies have shown that subjects with no conscious light perception (NPL) have a higher occurrence and more severe sleep disorders than those with some degree of light perception (LP). A detailed study of 49 blind individuals showed that those with NPL are likely to have free-running (FR) circadian rhythms (aMT6s, cortisol) including sleep. Non-24-hour (or FR) sleep-wake disorder, characterised by periods of good and bad sleep is a condition that may benefit from melatonin treatment. Melatonin has been administered to NPL subjects with FR circadian rhythms and compared with placebo (or the no-treatment baseline) sleep parameters improved. The results suggest that prior knowledge of the subject's type of circadian rhythm, and timing of treatment in relation to the individual's circadian phase, may improve the efficacy of melatonin.     

The effects of low-dose 0.5-mg melatonin on the free-running circadian rhythms of blind subjects

Exogenous melatonin (0.5-10 mg) has been shown to entrain the free-running circadian rhythms of some blind subjects. The aim of this study was to assess further the entraining effects of a daily dose of 0.5 mg melatonin on the cortisol rhythm and its acute effects on subjective sleep in blind subjects with free-running 6-sulphatoxymelatonin (aMT6s) rhythms (circadian period [tau] 24.23-24.95 h). Ten subjects (9 males) were studied, aged 32 to 65 years, with no conscious light perception (NPL). In a placebo-controlled, single-blind design, subjects received 0.5 mg melatonin or placebo p.o. daily at 2100 h (treatment duration 26-81 days depending on individuals' circadian period). Subjective sleep was assessed from daily sleep and nap diaries. Urinary cortisol and aMT6s were assessed for 24 to 48 h weekly and measured by radioimmunoassay. Seven subjects exhibited an entrained or shortened cortisol period during melatonin treatment. Of these, 4 subjects entrained with a period indistinguishable from 24 h, 2 subjects continued to free run for up to 25 days during melatonin treatment before their cortisol rhythm became entrained, and 1 subject appeared to exhibit a shortened cortisol period throughout melatonin treatment. The subjects who entrained within 7 days did so when melatonin treatment commenced in the phase advance portion of the melatonin PRC (CT6-18). When melatonin treatment ceased, cortisol and aMT6s rhythms free ran at a similar period to before treatment. Three subjects failed to entrain with initial melatonin treatment commencing in the phase delay portion of the PRC. During melatonin treatment, there was a significant increase in nighttime sleep duration and a reduction in the number and duration of daytime naps. The positive effect of melatonin on sleep may be partly due to its acute soporific properties. The findings demonstrate that a daily dose of 0.5 mg melatonin is effective at entraining the free-running circadian systems in most of the blind subjects studied, and that circadian time (CT) of administration of melatonin may be important in determining whether a subject entrains to melatonin treatment. Optimal treatment with melatonin for this non-24-h sleep disorder should correct the underlying circadian disorder (to entrain the sleep-wake cycle) in addition to improving sleep acutely.     

Effects of light on human circadian rhythms.

Blind subjects with defective retinal processing provide a good model to study the effects of light (or absence of light) on the human circadian system. The circadian rhythms (melatonin, cortisol, timing of sleep/wake) of individuals with different degrees of light perception (n = 67) have been studied. Blind subjects with some degree of light perception (LP) mainly have normally entrained circadian rhythms, whereas subjects with no conscious light perception (NPL) are more likely to exhibit disturbed circadian rhythms. All subjects who were bilaterally enucleated showed free running melatonin and cortisol rhythms. Studies assessing the light-induced suppression of melatonin show the response to be intensity and wavelength dependent. In contrast to ocular light exposure, extraocular light failed to suppress night-time melatonin. Thus, ocular light appears to be the predominant time cue and major determinant of circadian rhythm type. Optimisation of the light for entrainment (intensity, duration, wavelength, time of administration) requires further study.     

Daily rhythms of plasma melatonin, but not plasma leptin or leptin mRNA, vary between lean, obese and type 2 diabetic men

Melatonin and leptin exhibit daily rhythms that may contribute towards changes in metabolic physiology. It remains unclear, however, whether this rhythmicity is altered in obesity or type 2 diabetes (T2DM). We tested the hypothesis that 24-hour profiles of melatonin, leptin and leptin mRNA are altered by metabolic status in laboratory conditions. Men between 45-65 years old were recruited into lean, obese-non-diabetic or obese-T2DM groups. Volunteers followed strict sleep-wake and dietary regimes for 1 week before the laboratory study. They were then maintained in controlled light-dark conditions, semi-recumbent posture and fed hourly iso-energetic drinks during wake periods. Hourly blood samples were collected for hormone analysis. Subcutaneous adipose biopsies were collected 6-hourly for gene expression analysis. Although there was no effect of subject group on the timing of dim light melatonin onset (DLMO), nocturnal plasma melatonin concentration was significantly higher in obese-non-diabetic subjects compared to weight-matched T2DM subjects (p<0.01) and lean controls (p<0.05). Two T2DM subjects failed to produce any detectable melatonin, although did exhibit plasma cortisol rhythms comparable to others in the group. Consistent with the literature, there was a significant (p<0.001) effect of subject group on absolute plasma leptin concentration and, when expressed relative to an individual's 24-hour mean, plasma leptin showed significant (p<0.001) diurnal variation. However, there was no difference in amplitude or timing of leptin rhythms between experimental groups. There was also no significant effect of time on leptin mRNA expression. Despite an overall effect (p<0.05) of experimental group, post-hoc analysis revealed no significant pair-wise effects of group on leptin mRNA expression. Altered plasma melatonin rhythms in weight-matched T2DM and non-diabetic individuals supports a possible role of melatonin in T2DM aetiology. However, neither obesity nor T2DM changed 24-hour rhythms of plasma leptin relative to cycle mean, or expression of subcutaneous adipose leptin gene expression, compared with lean subjects.     

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.     

Circadian phase in adults of contrasting ages

There is evidence that aging may impair phase-shifting responses to light synchronizers, which could lead to disturbed or malsynchronized circadian rhythms. To explore this hypothesis, 62 elder participants (age, 58 to 84 years) and 25 young adults (age, 19 to 40 years) were studied, first with baseline 1-wk wrist actigraphy at home and then by 72 h in-laboratory study using an ultra-short sleep-wake cycle. Subjects were awake for 60 minutes in 50 lux followed by 30 minutes of darkness for sleep. Saliva samples were collected for melatonin, and urine samples were collected for aMT6s (a urinary metabolite of melatonin) and free cortisol every 90 minutes. Oral temperatures were also measured every 90 minutes. The timing of the circadian rhythms was not significantly more variable among the elders. The times of lights-out and wake-up at home and urinary free cortisol occurred earlier among elders, but the acrophases (cosinor analysis-derived peak time) of the circadian rhythm of salivary melatonin, urinary aMT6s, and oral temperature were not significantly phase-advanced among elders. The estimated duration of melatonin secretion was 9.9 h among elders and 8.4 h among young adults (p < 0.025), though the estimated half-life of blood melatonin was shorter among elders (p < 0.025), and young adults had higher saliva melatonin and urinary aMT6s levels. In summary, there was no evidence for circadian desynchronization associated with aging, but there was evidence of some rearrangement of the internal phase-angles among the studied circadian rhythms.     

Individualized cosinor assessment of circadian hormonal variation in third trimester human pregnancy

Two clinically healthy pregnant women were studied in a single 24-h span during the third trimester. Blood drawn every 20 min was assayed for cortisol (F), dehydroepiandrosterone sulfate (DHEA-S), estriol (E3), and prolactin (PRL). Blood drawn hourly was assayed for progesterone (P), human placental lactogen (HPL) and 15alpha-hydroxyestriol (E4). Breast temperature (BT) was continuously monitored. Single cosinor analysis demonstrated statistically significant circadian rhythms for plasma concentrations of F, DHEA-S, and BT for both subjects, and of E3 for one subject. Statistically significant circadian rhythms in plasma concentrations of P, HPL, E4 or PRL could not be demonstrated in our third trimester subjects. However, analysis of data from subjects sampled at earlier gestational ages revealed highly significant PRL circadian rhythms. These results suggest that plasma concentrations of PRL show a progressive decrease in circadian amplitude despite a progressive increase in mesor with advancing gestational age. Frequent sampling and cosinor data analysis permit identification of circadian rhythms in BT. The use of BT as a potential marker for rhythms in plasma concentration of certain hormones awaits further scrutiny. The demonstration of several circadian endocrine rhythms in individual subjects in the third trimester of human pregnancy facilitates the usefulness of such marker rhythms.     

Circadian Phase in Adults of Contrasting Ages

There is evidence that aging may impair phase‐shifting responses to light synchronizers, which could lead to disturbed or malsynchronized circadian rhythms. To explore this hypothesis, 62 elder participants (age, 58 to 84 years) and 25 young adults (age, 19 to 40 years) were studied, first with baseline 1‐wk wrist actigraphy at home and then by 72 h in‐laboratory study using an ultra‐short sleep‐wake cycle. Subjects were awake for 60 minutes in 50 lux followed by 30 minutes of darkness for sleep. Saliva samples were collected for melatonin, and urine samples were collected for aMT6s (a urinary metabolite of melatonin) and free cortisol every 90 minutes. Oral temperatures were also measured every 90 minutes. The timing of the circadian rhythms was not significantly more variable among the elders. The times of lights‐out and wake‐up at home and urinary free cortisol occurred earlier among elders, but the acrophases (cosinor analysis‐derived peak time) of the circadian rhythm of salivary melatonin, urinary aMT6s, and oral temperature were not significantly phase‐advanced among elders. The estimated duration of melatonin secretion was 9.9 h among elders and 8.4 h among young adults (p<0.025), though the estimated half‐life of blood melatonin was shorter among elders (p<0.025), and young adults had higher saliva melatonin and urinary aMT6s levels. In summary, there was no evidence for circadian desynchronization associated with aging, but there was evidence of some rearrangement of the internal phase‐angles among the studied circadian rhythms.     

Melatonin administration to blind people: phase advances and entrainment.

The purpose of this study was to test the phase-shifting and entraining effects of melatonin in human subjects. Five totally blind men were found in a previous study to have free-running endogenous melatonin rhythms. Their rhythms were remarkably stable, so that any deviation from the predicted phase was readily detectable. After determination of their free-running period and phase, they were given exogenous melatonin (5 mg) at bedtime (2200 hr) for 3 weeks, in a double-blind, placebo-controlled trial. The effects on the endogenous melatonin rhythm were assessed at intervals ranging from several days to 2 weeks. Exogenous administration of melatonin phase-advanced their endogenous melatonin rhythms. In three of the subjects, cortisol was shown to be phase-shifted in tandem with the melatonin rhythm. A sixth subject [one of the coauthors (JS)] was previously found to have free-running cortisol and temperature rhythms and was plagued by recurrent insomnia and daytime sleepiness. He had tried unsuccessfully to entrain his rhythms for over 10 years. After he took melatonin (7 mg at 2100 hr), his insomnia and sleepiness resolved. Determination of his endogenous melatonin rhythm after about a year of treatment demonstrated endogenous rhythms that appeared normally entrained. The treatment of blind people with free-running rhythms has many advantages for demonstrating chronobiological effects of hormones or drugs.     

Circadian Variations in Blood Coagulation Parameters, Alpha-Antitrypsin Antigen and Platelet Aggregation and Retention in Clinically Healthy Subjects

Ten clinically healthy subjects (5 men and 5 women), 31 11 yrs of age, were studied at six timepoints (0800, 1200, 1600, 2000, 0000, 0400) distributed over a 1-week span. Circadian rhythms in platelet aggregation in response to adenosine diphosphate (ADP) and adrenalin (A), platelet adhesiveness measured as retention in a glass bead column, prothrombin time (PT), activated partial thromboplastin time (APTT), thrombin time (TT), fibrinogen, Factor VIII activity and alpha-1-antitrypsin antigen showed circadian rhythms. The plasma concentrations of plasminogen, alpha-2-macroglobulin, and antithrombin III (AT III) antigen, Factor V and fibrinogen degradation products showed no circadian rhythm by ANOVA or cosinor analysis. The phase relations of the rhythms of different coagulation parameters are of interest in the physiology and pathobiology of the coagulation-fibrinolytic system. The extent of the circadian rhythm (range of change) described is not of a magnitude to lead to diagnostic problems in the clinical laboratory. The timing of these rhythms, however, may determine transient risk states for thromboembolic phenomena, including myocardial infarction and stroke. Several but not all coagulation parameters suggest a transient state of hypercoagulability during the morning hours. The recognition of these rhythmic, and thus in the time of the occurrence predictable temporary risk states for thromboembolic phenomena, may lead to timed treatment and/or effective prevention.     

Circadian placebo and ACTH effects on urinary cortisol in arthritics

The effect of placebo and ACTH-1-17 (Synchrodyn®, Hoechst) upon urinary free cortisol was examined at 5 different circadian stages on 10 men with Steinbrocker Stage II–III rheumatoid arthritis. A mean cosinor analysis of urinary cortisol data from the subjects prior to treatment with either ACTH or placebo revealed a statistically highly-significant rhythm. A circadian variation in a response of urinary free cortisol to a placebo was also seen. Moreover, the response of the midline-estimating statistic of rhythm (rhythm-adjusted circadian average) of urinary free cortisol to ACTH-1-17 by patients with rheumatoid arthritis is circadian rhythmic. This reactivity rhythm is out of phase with the spontaneous rhythm in urinary cortisol acrophases—in the tests limited thus far to midsummer. The further assessment of the circadian component in the context of broader interactions by rhythms with other frequencies in various conditions in health and disease is warranted by the demonstration of rhythms here presented for men with rheumatoid arthritis.     

LONG-TERM ALTERATION OF DAILY MELATONIN, 6-SULFATOXYMELATONIN,CORTISOL, AND TEMPERATURE PROFILES IN BURN PATIENTS: A PRELIMINARY REPORT

Melatonin, which shows a robust nycthemeral rhythm, plays the role of an endogenous synchronizer, able to stabilize and reinforce circadian rhythms and maintain their mutual phase relationships. Additionally, melatonin is a potent antioxidant and displays immunological properties. Because free radical generation, immune dysfunction, and sleep and metabolic disorders are involved in the short- and long-term pathophysiology of the burn syndrome, we undertook the study of daily urine melatonin, 6-sulfatoxymelatonin (aMT6s, the main hepatic melatonin metabolite), and cortisol variations plus temperature profiles in burn patients using a non-invasive protocol. Eight patients (6 males, 2 females) were studied on three occasions after admission to the intensive care unit (early session: days 1 to 3; intermediate session: day 10; late session: days 20 to 30). Melatonin, aMT6s, and free cortisol levels were determined in urine samples collected at 4 h intervals over a continuous 24 h span. Core temperature was recorded daily. Controls consisted of healthy subjects in the same age range. Cosinor analysis of the data provided an evaluation of mesor, amplitude, and acrophase of circadian rhythms. Also, we calculated day (D), night (N), and 24 h hormone excretions, N/D ratio for melatonin and aMT6s, and D/N ratio for cortisol. These data were analyzed using Kruskal-Wallis test followed by multiple comparisons. Cosinor analysis did not detect a circadian rhythm in melatonin, aMT6s, or cortisol in any of the three sessions. D melatonin excretion displayed a major increase, resulting in a decreased N/D melatonin ratio, and the melatonin mesor (24 h mean) was increased in the early session, compared with controls. For aMT6s, only the early N/D ratio was decreased, and the mesor of the intermediate session increased. These results were not the consequence of hepatic and/or kidney alteration, as the patients' hepatic and renal parameters were in the normal range. The D and N melatonin/aMT6s ratios of controls and patients were similar, and the aMT6s profiles were superimposed on the melatonin ones, mainly during the day. The D, N, and 24 h cortisol values were increased in all sessions, except for the D level of the early session. The consistently increased mesors in the three sessions provided confirmation. The core temperature profiles were abnormal in all three sessions, mainly during the night, although there was a tendency toward normalization with time. The individual mesors were consistently increased compared with controls. Globally, the abnormalities we report could participate in the pathophysiology of short- and long-term alterations observed in burn syndrome, especially disturbances of sleep, metabolism, and immune function. (Author correspondence: bruno.claustrat@chu-lyon.fr).     

General and unspecific damping by malignancy of the circadian amplitude of circulating human melatonin?

The circadian rhythm of serum melatonin of 39 cancer patients is compared with that of 28 healthy subjects matched by gender and age. Each subject provided 6 blood samples at 4-hour intervals for determination of melatonin by RIA. After log10-transformation, data series were analyzed by single and population-mean cosinor and compared between the two groups and among patients subgrouped by cancer site, stage and treatment. A circadian rhythm (P<0.001) is demonstrated for both groups, with a contributing 12-hour harmonic (P<0.001). In the absence of a difference in MESOR, the circadian amplitude of the cancer patients is smaller than that of the healthy subjects (P=0.003). Numerically, nocturnal (00:00 and 04:00) melatonin concentrations are lower and daytime (08:00-20:00) melatonin concentrations are higher in the cancer patients than in the healthy subjects (P=0.032 at 12:00 and P=0.058 at 16:00). In the age ranges examined, no differences are found with age in either group or by gender in health. No differences are found among cancer patients subgrouped either by site, stage (localized vs. metastasized) or treatment. If these results are validated, other Janus-like (two-faced: stimulation or inhibition, depending on chronome stage) effects of malignancy should be taken into consideration for screening and for timing treatment.     

Circadian placebo and ACTH effects on urinary cortisol in arthritics

The effect of placebo and ACTH-1-17 (Synchrodyn®, Hoechst) upon urinary free cortisol was examined at 5 different circadian stages on 10 men with Steinbrocker Stage II–III rheumatoid arthritis. A mean cosinor analysis of urinary cortisol data from the subjects prior to treatment with either ACTH or placebo revealed a statistically highly-significant rhythm. A circadian variation in a response of urinary free cortisol to a placebo was also seen. Moreover, the response of the midline-estimating statistic of rhythm (rhythm-adjusted circadian average) of urinary free cortisol to ACTH-1-17 by patients with rheumatoid arthritis is circadian rhythmic. This reactivity rhythm is out of phase with the spontaneous rhythm in urinary cortisol acrophases—in the tests limited thus far to midsummer. The further assessment of the circadian component in the context of broader interactions by rhythms with other frequencies in various conditions in health and disease is warranted by the demonstration of rhythms here presented for men with rheumatoid arthritis.     

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.     

Late-night presentation of an auditory stimulus phase delays human circadian rhythms

Although light is considered the primary entrainer of circadian rhythms in humans, nonphotic stimuli, including exercise and melatonin also phase shift the biological clock. Furthermore, in birds and nonhuman mammals, auditory stimuli are effective zeitgebers. This study investigated whether a nonphotic auditory stimulus phase shifts human circadian rhythms. Ten subjects (5 men and 5 women, ages 18-72, mean age +/- SD, 44.7 +/- 21.4 yr) completed two 4-day laboratory sessions in constant dim light (<20 lux). They received two consecutive presentations of either a 2-h auditory or control stimulus from 0100 to 0300 on the second and third nights (presentation order of the stimulus and control was counterbalanced). Core body temperature (CBT) was collected and stored in 2-min bins throughout the study and salivary melatonin was obtained every 30 min from 1900 to 2330 on the baseline and poststimulus/postcontrol nights. Circadian phase of dim light melatonin onset (DLMO) and of CBT minimum, before and after auditory or control presentation was assessed. The auditory stimulus produced significantly larger phase delays of the circadian melatonin (mean +/- SD, -0.89 +/- 0.40 h vs. -0.27 +/- 0.16 h) and CBT (-1.16 +/- 0.69 h vs. -0.44 +/- 0.27 h) rhythms than the control. Phase changes for the two circadian rhythms also positively correlated, indicating direct effects on the biological clock. In addition, the auditory stimulus significantly decreased fatigue compared with the control. This study is the first demonstration of an auditory stimulus phase-shifting circadian rhythms in humans, with shifts similar in size and direction to those of other nonphotic stimuli presented during the early subjective night. This novel stimulus may be a useful countermeasure to facilitate circadian adaptation after transmeridian travel or shift work.     

Sleep and Circadian Rhythms of Temperature and Urinary Excretion on a 22.8 hr “Day”

Two groups of subjects (total N = 6) were studied in an isolation chamber for a period of 3 weeks whilst living on a 22.8 hr “day”. Regular samples of urine were taken when the subjects were awake, deep body temperature was recorded continuously and polygraphic EEG recordings were made of alternate sleeps. The excretion in the urine of potassium, sodium, phosphate, calcium and a metabolite of melatonin were estimated.

Measurements of the quantity and quality of sleep were made together with assessments of the temperature profiles associated with sleep. In addition, cosinor analysis of circadian rhythmicity in urinary variables and temperature was performed.

The 22.8 hr “days” affected variables and subjects differently. These differences were interpreted as indicating that the endogenous component of half the subjects adjusted to the 22.8 hr “days” but that, for the other three, adjustment did not occur. When the behaviour of different variables was considered then some (including urinary potassium and melatonin, sleep length and REM sleep) appeared to possess a larger endogenous component than others (for example, urinary sodium, phosphate and calcium), with rectal temperature behaving in an intermediate manner. In addition, a comparison between different rhythms in any subject enabled inferences to be drawn regarding any links (or lack of them) that might exist between the rhythms. In this respect also, there was a considerable range in the results and no links between any of the rhythms appeared to exist in the group of subjects as a whole.

Two further groups (total N=8) were treated similarly except that the chamber clock ran at the correct rate. In these subjects, circadian rhythms of urinary excretion and deep body temperature (sleep stages and urinary melatonin were not measured) gave no evidence for deterioration. We conclude, therefore, that the results on the 22.8 hr “day” were directly due to the abnormal “day” length rather than to a prolonged stay in the isolation chamber.