[The circadian system in man: From the internal clock to melatonin secretion]. / À propos du système circadien chez l'homme : de l'horloge interne à la sécrétion de mélatonine.

The internal or biological clock which is located in the suprachiasmatic nuclei of the anterior hypothalamus is controlled by clock genes and environmental factors which are able to synchronize the clock to 24h. Rhythm desynchronization (shiftwork and nightwork, transmeridian flights, aging, some psychiatric diseases, blindness, intake of some drugs…) occurs when the internal clock does no longer work in harmony with the astronomical time i.e. our watch. The circadian system consists of three major elements, which are the clock, the retinohypothalamic tract and melatonin which is secreted by the pineal gland and considered as the arrow of the clock. Both light and melatonin present a phase response curve useful for the treatment of sleep circadian disorders.

[Dysfunctions of biological clocks and their treatments]. / Dysfonctionnements de l'horloge biologique et leurs traitements.

Biological rhythms are periodic phenomena entrained to environmental changes by exogenous factors called synchronizers or entraining agents namely the light-dark cycle, the rest-activity cycle and the seasons, among others. In humans the major synchronizers are the light-dark and rest activity cycles. The endogenous component of a biological rhythm is dependent upon a number of clock genes. The main biological clock (oscillator or pacemaker) is the suprachiasmatic nucleus (SCN) of the anterior hypothalamus. The photoperiod (light-dark cycle) perceived by the retina acts on the SCN genes. Peripheral clocks have also been described in a number of tissues e.g. retina, adrenals. In a number of occurrences the synchronizers are badly perceived (transmeridian flights, shiftwork, nightwork...) or are not at all perceived (blindness). This situation is named rhythm desynchronization, it is external when the desynchronization is strictly related to the environment or internal when it is related to a dysfunction of the clock like in e.g. aging, Alzheimer disease, seasonal affective disorders (SAD) or hormone-dependent cancers which results in fatigue, sleep and mood disorders... A number of drugs called resynchronizing agents or chronobiotics which act on the biological clock are able to resynchronize the clock and to improve the patients' condition. Bright light is used in the treatment of SAD, melatonin, the pineal hormone, is also of interest when administered at precise timings in the 24hours scale. Other drugs like B12 vitamin or psychotropic drugs have also been proposed as chronobiotics.

Seasonal modulation of the circadian time structure of circulating T and natural killer lymphocyte subsets from healthy subjects.

A seasonal modulation of the circadian time structure of circulating T and natural killer (NK) lymphocyte subtypes was documented in five healthy men aged 24-36 yr. Venous blood was obtained every 4 h for 24 h from each subject in January, March, June, August, and November 1984. Three subjects were also studied in April and/or August and/or November 1983 for the T subsets only. Mononuclear cells were isolated on Ficoll-Paque gradient and aliquots were incubated with OKT3, OKT4, OKT8, or HNK-1 monoclonal antibodies for characterizing all, T, T helper, T suppressor-cytotoxic, and NK lymphocytes, respectively, under an epifluorescence microscope. An effect of both sampling time and study month was statistically validated (P less than 0.01) with both two-way analysis of variance and cosinor for the peripheral counts in total, pan-T, T helper, and NK lymphocytes (cells per cubic millimeter). Seasonal changes affected both the circadian patterns and the 24-h mean values. Thus the double amplitude (total extent of variation) of the circadian rhythm in circulating total, T and T helper lymphocytes varied between 0 in March (P greater than 0.30; no rhythm) and up to 46-68% of the 24-h-mean (M) in November, with acrophases (times of maximum, 0) localized in the first half of the night (P less than 0.001). Maximal values were found at 8:30 h for both T suppressor-cytotoxic and NK lymphocytes; a smaller second peak was also found at 20:30 h, and a 12-h rhythm was validated by cosinor (P less than 0.0001), with no patient change in waveform along the year scale. A circannual rhythm was statistically validated by cosinor for total (0 in November), pan-T (0 in March), T suppressor-cytotoxic (0 in December), and NK lymphocytes (0 in October). A rhythm with a period equal to 6 mo was found for circulating T helper cells with 0 occurring both in April and October. Seasonal variations in the incidence of several immunologically related diseases may correspond to an endogenous circannual time structure.

Increased delta aminolevulinic acid and decreased pineal melatonin production. A common event in acute porphyria studies in the rat.

Tryptophan (TRP) is the precursor of melatonin, the primary secretory product of the pineal gland. Hepatic heme deficiency decreases the activity of liver tryptophan pyrrolase, leading to increased plasma TRP and serotonin. As a paradox, patients with attacks of acute intermittent porphyria (AIP), exhibit low nocturnal plasma melatonin levels. This study using a rat experimental model was designed to produce a pattern of TRP and melatonin production similar to that in AIP patients. Pineal melatonin production was measured in response to: (a) a heme synthesis inhibitor, succinylacetone, (b) a heme precursor, delta-aminolevulinic acid (Ala), (c) a structural analogue of Ala, gamma-aminobutyric acid. Studies were performed in intact rats, perifused pineal glands, and pinealocyte cultures. Ala, succinylacetone, and gamma-aminobutyric acid significantly decreased plasma melatonin levels independently of blood TRP concentration. In the pineal gland, the key enzyme activities of melatonin synthesis were unchanged for hydroxyindole-O-methyltransferase and decreased for N-acetyltransferase. Our results strongly suggest that Ala overproduced by the liver acts by mimicking the effect of gamma-aminobutyric acid on pineal melatonin in AIP. They also support the view that Ala acts as a toxic element in the pathophysiology of AIP.

[Sleep disorders and hypnotic agents: medical, social and economical impact]. / Troubles du sommeil et hypnotiques: impacts médicaux et socio-économiques.

Insomnia is a subjective complaint relating to approximately 30% of the adult population in France, described by the patient as a difficulty of initiating and/or maintaining sleep. Its prevalence increases with age and sex: women are more affected than men (24% vs 14%). Insomnia is either occasional (20%), or chronic (10%). Chronic insomnia has an important impact on patients' everyday life e.g. fatigue, perturbed diurnal waking state, impaired quality-of-life... which results in lower work productivity and drowsiness as well as relational difficulties, absenteeism. About 80% of patients consult their general practitioner first. The aim of a hypnotic agent is to obtain sleep as physiological as possible. Benzodiazepines and benzodiazepines-like agents (zopiclone, zolpidem, zaleplon) are the most widely used hypnotics. However, their indications must be limited to occasional insomnia with a limited duration: less than four weeks. There is no advantage with using a combination of hypnotic agents, a practice which should be prohibited. Adverse effects can be serious, e.g. diurnal somnolence associated with risks of road accidents and, in the elderly, the risk of falls. After chronic use, hypnotics can be addictive, as their effects wear off in three to four weeks. After withdrawal, insomnia rebound is frequent. Use of hypnotics in association with alcohol is a well-known drug-addiction behavior. According to the French health insurance fund, 9% of the general population use hypnotics and about half of them regularly. Insurance refunds for hypnotics and sedatives reach more than 110 million euros annually. The efficiency of hypnotics wears off, quickly for benzodiazepines (three - four weeks), or less quickly for zopiclone and zolpidem (a few months). Insomnia is a major public health issue, each year 10% of the incident cases of insomnia treated by hypnotics joint the group of subjects with chronic insomnia. This failure to treat insomnia properly can be explained, at least in part, by several insufficiencies: physicians and pharmacists training, medical profession awareness, research, public information on the rules of good sleep (public health campaigns, booklets, role of physicians and the pharmacists).

Enhanced cortical extracellular levels of cholecystokinin-like material in a model of anticipation of social defeat in the rat.

The involvement of cholecystokinin (CCK) in the mechanisms of stress and/or anxiety was assessed by in vivo microdialysis in rats subjected to a social stress paradigm. During the initial 30 min period of each conditioning session, a male Sprague Dawley rat (intruder) was placed in a protective cage inside the cage of a male Tryon Maze Dull rat (resident), allowing unrestricted visual, olfactory, and auditory contacts but precluding close physical contact between them. During the following 15 min period, both the protective cage and the resident were removed (nondefeated intruders) or only the protective cage was removed allowing the resident to attack the intruder (defeated rats). This procedure was repeated once daily for 4 d. On the fifth day, a guide cannula was implanted into the prefrontal cortex of intruders. During a single 30 min test session, performed 4 d later, intruders were subjected to only the 30 min protected confrontation to the resident. Anxiety-like behavior (immobility, ultrasonic vocalizations, and defensive postures), associated with an increase (approximately +100% above baseline) in cortical outflow of CCK-like material (CCKLM), were observed in defeated intruders. Pretreatment with diazepam (5 mg/kg, i.p.), but not buspirone (0.5-2 mg/kg, i.p.), prevented both the anxiety-related behavior and CCKLM overflow. The selective CCK-B receptor antagonist CI-988 (2 mg/kg, i.p.) reduced the anxiety-like behavior without affecting the increase in CCKLM outflow. These data indicate that anticipation of social defeat induces a marked activation of cortical CCKergic neurons associated with anxiety-related behaviors in rats.

Prolactin rhythms-oscillators' response to photoperiodic cues is age and circadian time dependent.

In vivo prolactin release patterns exhibit a compound rhythm with circadian (24 h), semicircadian (12 h) and ultradian (6-8 h) periods. Changes in these rhythmic patterns were observed at different photoperiodic conditions, and in elderly. Since in vitro prolactin release was related to the photoperiodic history of the animal, we studied the effect of varying photoperioda upon the in vitro rhythmic output of prolactin release from young and old male rat pituitaries, isolated at different circadian times from animals housed at LD 12:12, 18:6 for 10 days or 6 weeks. The results indicate that, both, mean levels and rhythmic prolactin release in vitro are determined by the age of the animal, the circadian time of pituitary isolation, the photoperiodic conditions in which the animal was housed, and the duration of housing in the long day conditions. The change of the rhythmic output pattern is gradual, reflecting a process by which the oscillators respond to the external cues to fit prolactin release pattern to the environmental conditions. Each of the oscillators (e.g. circadian, semicircadian, ultradian) shows different sensitivity to the changing photoperiodic signal and is regulated at the level of phase and amplitude but not the period. In old rats the response of the oscillators to the change in photoperioda is attenuated and not sufficient to induce a change in the output of prolactin release suggesting a loss in adaptation ability.

Impairment in clock-time estimation following right hemisphere ischemic damage.

In order to assess clock-time estimation (CTE), we asked "what time is it in your opinion?" to 48 recent stroke in-patients, 21 with right (RH), 27 with left hemispheric (LH) lesions, and to 20 control in-patients without brain lesions (C). Errors were measured in terms of the number of minutes by which the estimated clock-time was later (advance errors) or earlier (delay errors) than the real clock-time. CTE was considered pathological when exceeding the mean advance or delay errors observed in control patients plus 2.5 standard deviations. The estimation of the duration of a short psychological interview was also assessed. CTE, and not duration estimation, was disturbed in patients. RH patients made significantly more pathological advance errors than LH patients (43% vs. 12%). This study points out the RH dominance for CTE in stroke patients.

Marked 24-h rest/activity rhythms are associated with better quality of life, better response, and longer survival in patients with metastatic colorectal cancer and good performance status.

The rest/activity circadian cycle has been used as a reference for chemotherapy administration at specific times to improve tolerability and efficacy. Because cancer processes may be associated with alterations of circadian rhythms, the rest/activity cycle was monitored noninvasively to assess its relationship with tumor response, survival, and quality of life in 200 patients with metastatic colorectal cancer. Patients wore an actigraph, a wristwatch that records the number of accelerations per minute, for 3 days before receiving chronomodulated chemotherapy. The circadian rhythms in activity were estimated by two robust parameters: the autocorrelation coefficient at 24 h (r24), and the dichotomy index (I

An alternate pathway to androstenedione synthesis by human adrenals: evidence of a balance in 11 beta-hydroxylase and 17,20-lyase activities leading to androstenedione.

Until now, dehydroepiandrosterone and 17-hydroxyprogesterone were thought to be the main precursors for the synthesis of androstenedione by the human adrenal cortex. However, secretion of androstenedione and 11-deoxycortisol are increased when 11 beta-hydroxylase activity is impaired, e.g. by metyrapone test or by congenital adrenal hyperplasia resulting from 11 beta-hydroxylase deficiency. The present study with human adrenals shows that 11-deoxycortisol, the precursor of cortisol synthesis, is also a precursor of androstenedione in humans. Our data show that androstenedione synthesis is inversely related to the synthesis of cortisol and cortisone. This new pathway is thus triggered by a lower activity of 11 beta-hydroxylase that is responsible for the last step of cortisol. Indeed, when the activity of this enzyme is impaired, 11-deoxycortisol follows the pathway that leads to androstenedione synthesis in the adrenals. These data, together with the increase in ACTH secretion, may explain the increased androstenedione plasma levels observed in patients with congenital adrenal hyperplasia caused by 11 beta-hydroxylase deficiency and in patients given inhibitors of 11 beta-hydroxylase for therapeutic purposes.

Ramadan diet restrictions modify the circadian time structure in humans. A study on plasma gastrin, insulin, glucose, and calcium and on gastric pH.

The rule of Ramadan (1 month of food and water intakes restricted to night hours) is followed by the majority of the Moslem fraction of the human population, but the possible consequences of this long-lasting modification of food intake schedule on public health have not yet been extensively documented. Therefore, a group of healthy control subjects and a group of healed duodenal ulcer patients were studied before (controls), during (both groups), and after (both groups) the month of Ramadan. The time-restricted food and water intakes were associated with variations of gastric pH, plasma gastrin, insulin, glucose, and calcium documented on a circadian basis. All of the studied biological variables, except insulin, underwent changes in their 24-h mean concentration (e.g. decrease in gastric pH, increase in plasma gastrin), some of which were still present 1 month after the end of Ramadan. The circadian patterns of all the studied variables were altered during the month of Ramadan. Some differences between the group of healthy control subjects and the group of healed duodenal ulcer patients may suggest a greater susceptibility of the latter to the modifications of feeding and sleeping schedule, which could possibly be a risk factor for the disease.

Plasma melatonin and cortisol in patients with obsessive-compulsive disorder: relationship with axillary temperature, physical activity, and clinical symptoms.

BACKGROUND: Many studies have found biological abnormalities in obsessive-compulsive disorder (OCD), although most of them have not been replicated. The investigation of melatonin rhythm may thus provide an indirect clue to neurotransmitter alterations, and allow a biological comparison with depression. METHODS: The circadian variations of plasma melatonin, plasma cortisol, axillary temperature, motor activity, and obsessive-compulsive symptoms have been documented on a circadian basis in 8 patients with OCD compared to 8 paired healthy volunteers. RESULTS: The circadian pattern of axillary temperature was slightly different in OCD patients when compared to control subjects. No significant difference between the two groups could be observed for any other variable studied. CONCLUSIONS: The discrepancies with previous studies are discussed on the basis of the methods used (patients and control subjects samples, biological measurement procedures). An alteration of temperature circadian rhythm hypothesis is suggested.

Spontaneous or imposed circadian changes in plasma concentrations of 5-fluorouracil coadministered with folinic acid and oxaliplatin: relationship with mucosal toxicity in patients with cancer.

Pharmacokinetics of total platinum, 5-fluorouracil, l-folinic and d-folinic acid, and 5-methyltetrahydrofolate were studied in plasma from nine patients with advanced colorectal cancer treated with oxaliplatin (20 mg/m2/day), 5-fluorouracil (600 mg/m2/day), and folinic acid (300 mg/m2/day). Drugs were administered with a programmable-in-time pump by continuous infusion for 5 days. We compared two drug delivery schedules: constant rate versus chronomodulated rate with peak of oxaliplatin at 4 pm and peak of 5-fluorouracil and folinic acid at 4 am. In the chronomodulated schedule, plasma concentrations of the drugs paralleled the pump functioning: maximum platinum concentration near 4 pm, and maximum 5-fluorouracil and folate concentrations near 4 am. When drugs were administered at a constant rate, mean plasma concentration of 5-fluorouracil varied in a circadian manner each treatment day, that is, a peak at 4 am (approximately 800 ng/ml) and a trough at 1 pm (approximately 100 ng/ml). Mean plasma levels of total platinum and folate compounds increased over the first 24 hours. Total platinum mean level and that of the inactive d-folinic acid isomer reached a constant plasma concentration, whereas biologically active folates exhibited circadian variation in their plasma concentrations (peak around 7 am, trough near 6 pm, and amplitude approximately 10%). Severe mucositis was exhibited by all four patients on the flat schedule, but only by one on the chronomodulated schedule (p < 0.008). Individual pharmacokinetic and toxicity data showed that patients with circadian rhythms in 5-fluorouracil concentrations were least sensitive to 5-fluorouracil-related toxicity. Thus amplification or induction of such rhythm in 5-fluorouracil exposure may permit dose escalation.

Comparison of the feedback effect of magnesium and calcium on parathyroid hormone secretion in man.

Administration of high doses of magnesium is known to produce a decrease in parathyroid hormone (PTH) secretion in human patients but the effect of magnesium on the secretion of PTH in healthy man is not known. We have looked at the effect of a relatively moderate i.v. dose of magnesium (7.08 mmol) in seven healthy men. In addition and for comparison the effect of calcium (4.25 mmol) was studied. Two magnesium salts were considered, magnesium sulphate (MgSO4) and magnesium pyrrolidone carboxylate (MgPC). Four i.v. injections were given at 08.00 h (MgPC, NaCl (control), MgSO4 and Ca gluconate), with an interval of 1 week between each injection. Whatever the magnesium salt the variations in plasma concentrations of magnesium were the same whereas no change in erythrocyte magnesium was observed. Plasma concentration of C-terminal PTH did not show significant variations after MgPC or saline injection. Both MgSO4 and Ca gluconate produced a statistically significant 30% decrease in plasma PTH levels 45 min after the injection. The effect was more sustained with calcium (2 h) than with magnesium (45 min). The urinary excretion of magnesium was significantly higher after injection of MgSO4 than after MgPC. These results suggest that magnesium was, on a molar basis, less potent than calcium in regulating PTH secretion in vivo, that the nature of the magnesium salt used must be kept in mind for the interpretation of the effect of magnesium on PTH secretion in vivo and that the decrease in plasma PTH can partly explain the larger urinary excretion of magnesium after MgSO4 than after MgPC.

Seasonal rhythms of plasma gonadotrophins: their persistence in elderly men and women.

Circannual changes of immunoreactive LH and FSH were documented on a circadian basis in January, March, June and October in four groups of subjects: seven young men, six elderly men, six elderly women and six men and women suffering from senile dementia. The sampling was serially dependent only for the young men and the core subgroups of elderly men and elderly women. A circadian rhythm for FSH was not detected in any group of subjects during any of the sampling sessions, whereas a circadian rhythm for LH was detected twice (June and October) in young men, once (October) in elderly demented patients, and not at all in the groups of elderly men and women. Both 24-h and yearly mean levels of gonadotrophins were higher in elderly subjects (two-to 25-fold according to the hormone, sex and season) than in young men. Circannual rhythms of plasma LH with large amplitudes were validated by the cosinor method, with an acrophase located in April or May. A circannual rhythm of plasma FSH was validated only in young men, with an acrophase in October. The persistence of a circannual rhythm of plasma LH with large amplitude in elderly subjects, associated with high mean levels of the hormone, especially in elderly women, suggests that this bioperiodicity of the pituitary gland is independent of gonadal function.

Differences in the seasonal rhythmicity of plasma prolactin in elderly human subjects: detection in women but not in men.

Effects of age, sex and mental condition on the circadian and circannual rhythmicity of plasma prolactin in human subjects were investigated. Circannual changes were recorded on a circadian basis in January, March, June and October in four groups of subjects: seven young men, six elderly men, six elderly women and six senile demented patients (two men and four women). Blood samples were drawn every 4 h over a 24-h period at the four sampling sessions. Circadian rhythms of the hormone were validated in all groups and at all sampling sessions except twice in elderly demented subjects. The 24-h mean levels of prolactin in plasma were approximately the same in young and elderly subjects. The circadian acrophases were most often located in the vicinity of 02.00-04.00 h. The circannual rhythmicity of the hormone showed a sex difference; the rhythm was not validated in either young or elderly men but was detected in the groups of elderly women and elderly demented patients (mainly women). The acrophases were located in May. This paper strongly suggests a sex difference in the circannual rhythmicity of plasma prolactin levels in elderly subjects.

Glucocorticoid and mineralocorticoid pathways in two adrenocortical carcinomas: comparison of the effects of o,p'-dichlorodiphenyldichloroethane, aminoglutethimide and 2-p-aminophenyl-2-phenylethylamine in vitro.

The synthesis of glucocorticoids and mineralocorticoids in vitro was studied in an adrenocortical carcinoma after alblation from an 11.5-year-old boy. This patient had been unsuccessfully treated with high doses of o,p'-dichlorodiphenyldichloroethane (o,p'-DDD) and aminoglutethimide. These in-vitro results were compared with those obtained with another adrenocortical carcinoma removed from a 26-year-old woman who had received no preoperative treatment. The sensitivity of these adrenocortical carcinomas to o,p'-DDD, aminoglutethimide and 2-(p-aminophenyl)-2-phenylethylamine (SKF 12185) was investigated. Synthesis of cortisol (47%) and corticosterone (45%) in control incubations showed that 11 beta-hydroxylase activity was not affected by the treatment. This explains the raised level of plasma cortisol in the treated child. All three compounds inhibited both 11 beta-hydroxylase and 18-hydroxylase activities up to 95%, depending on the inhibitor. This study shows (a) an inhibitory effect of o,p'-DDD on the steroidogenesis of an adrenocortical carcinoma in vitro, an effect not previously reported in man or laboratory animals, and (b) the in-vitro efficacy of o,p-DDD and aminoglutethimide on corticosteroidogenesis by a carcinoma unresponsive to treatment in vivo. This discrepancy between data obtained in vivo and in vitro could possibly be explained by either an insufficient ratio of ingested dose: tumour mass, or a malabsorption of the drugs in this patient.

Adrenocortical hormones, ageing and mental condition: seasonal and circadian rhythms of plasma 18-hydroxy-11-deoxycorticosterone, total and free cortisol and urinary corticosteroids.

The circannual rhythms of plasma 18-hydroxy-11-deoxycorticosterone (18-OH-DOC), total and free cortisol have been documented on a circadian basis in January, March, June and October in seven young men (24 years old), six elderly men, six elderly women and six elderly demented subjects, both men and women, in their eighties. Blood samples were drawn every 4 h over a 24-h period at each sampling session and urine samples were collected at 4-h intervals only from the young men. A circadian rhythm of 17-hydroxy-corticosteroids (17-OH-CS), 17-ketosteroids (17-KS), urinary free cortisol and 18-OH-DOC was defined for each of the four seasons with stable acrophases throughout the year and the same excretory profiles. A circannual rhythm was validated in young men for 17-OH-CS, urinary free cortisol and 18-OH-DOC but not for 17-KS. A circadian rhythm of plasma free cortisol, the active form of the hormone, plasma total cortisol and plasma 18-OH-DOC was validated in all groups and at all the seasons at which samples were taken. The secretory profiles of 18-OH-DOC, free and total cortisol were very similar, with no differences attributable to age, sex or mental condition except for the levels of plasma free cortisol and 18-OH-DOC which were higher and lower respectively in the elderly subjects. Whereas a circannual rhythm of plasma 18-OH-DOC was validated for all groups, a circannual rhythm of both free and total cortisol in the plasma was validated in young men but not in any group of elderly subjects. This loss of the circannual rhythmicity of cortisol in the elderly may reflect the decrease with age of the capacity to adapt to seasonal external factors.

The genetic background of circadian and ultradian rhythm patterns of 17-hydroxycorticosteroids: a cross-twin study.

Circadian and ultradian rhythms in urinary excretion of 17-hydroxycorticosteroids were documented individually during an 8-day span in two pairs of young male twins. Studies were performed once at the age of 6 years for dizygotic twins and twice at the ages of 4.3 and 10.3 years for monozygotic twins. Four different methods were used for time-series analyses: chronograms (raw data), best-fitting curves resulting from cosinor analyses, power spectra and correlations of time-qualified data. Estimates of rhythm parameters (prominent periods, acrophases, etc.) as well as shapes of curves were closer in mono- than in dizygotic twins. Both similarities and small differences in rhythm characteristics of monozygotic twins were detected at both ages considered.