[Biologic rhythms: their changes in night-shift workers].

ENVIRONMENTAL STRESS: Environmental cycles, such as the light-dark cycle, provide information used by the biological clock in the hypothalamus to synchronize the biological systems and maintain the organism's internal cohesion. In persons whose work schedules include night hours (approximately 20% of the working population in France) the sleep-wake cycles are not in phase with these environmental cycles. BIOLOGICAL RHYTHMS: What effect does the conflicting information perceived by night-shift workers have on their biological rhythms? Indices of the processes going on in the cerebral clock, these biological rhythms are the only tool available in man to determine possible dysfunction of the clock.

Endothelin participates in increased circulating atrial natriuretic peptide early after human heart transplantation.

Background: Hemodynamic improvement after heart transplantation is expected to normalize the neuroendocrine balance, but circulating atrial natriuretic peptide (ANP) remains elevated. Endothelin stimulates ANP secretion and its concentration increases after heart transplantation, suggesting a role for this peptide in the cardiovascular adaptative response to heart transplantation.

Methods: To investigate whether endothelin may induce ANP increase in heart transplant recipients, we monitored daily ANP, endothelin, and related hormonal, biologic, and hemodynamic parameters before and during the first week after either heart transplantation (n = 15) or coronary artery bypass grafting (n = 10).

Temporal relationships between pulsatile cortisol secretion and electroencephalographic activity during sleep in man.

A temporal link between slow wave sleep and low or decreasing cortisol release has been previously demonstrated. This relationship was re-evaluated in 15 healthy male subjects using spectral analysis of their sleep electroencephalogram (EEG). EEG activity in the delta, theta, alpha and beta bands was cross-correlated with cortisol secretory rates at 10-min intervals.

Twenty-four-hour melatonin and core body temperature rhythms: their adaptation in night workers.

To determine whether the melatonin (MT) rhythm is adapted to a permanent nocturnal schedule, 11 night workers were studied during their usual 24-h cycle, and 8 day-active subjects during two 24-h cycles, once with night sleep and once after an acute shift of their sleep period to daytime. Rectal temperature (Tre) was continuously recorded. In day-active subjects, the MT rhythm was not affected by the acute shift in the sleep period, whereas the Tre rhythm was split in a biphasic pattern with the circadian descending phase during the night of sleep deprivation and a second descending trend during day sleep.

Growth hormone secretion in night workers.

We previously reported that, in night workers, cortisol and TSH rhythms, known to have a high endogenous component, adapted only partially to the nocturnal schedule. The aim of the present study was to investigate the degree of adaptation of the growth hormone (GH) rhythm, considered to be mainly sleep-dependent, but for which a weak circadian drive has also been suggested. Eleven night workers were studied during their usual sleep-wake cycle, and two groups of 11 normally day-active subjects, sleeping once during the night and once after an 8-h sleep delay, were used as control groups.

A quantitative evaluation of the relationships between growth hormone secretion and delta wave electroencephalographic activity during normal sleep and after enrichment in delta waves.

The existence of a relationship between growth hormone (GH) release and slow-wave sleep (SWS), often studied in the past using conventional scoring of sleep stages, remains controversial. In the present study, this relationship was reevaluated by spectral analysis of the sleep electroencephalogram (EEG) and deconvolution analysis of the plasma GH concentrations during normal nocturnal sleep and after enrichment in SWS by means of ritanserin, a selective 5-HT2 receptor antagonist. Eight healthy male subjects each participated in two randomized night studies after having received either a placebo or a 5-mg dose of ritanserin.

Twenty-four-hour prolactin profiles in night workers.

In addition to sleep processes, it has been suggested that an intrinsic circadian rhythmicity is involved in the temporal organization of prolactin (PRL) secretion. Eight night workers were studied to determine whether the PRL rhythm is adapted to their rest-activity schedule and whether this provides evidence in favor of an endogenous clock-driven component. Ten day-active subjects, sleeping once during the night and once after an 8-h delay in their sleep period, were used as a control group.

5-HT2 receptors are partially involved in the relationship between renin release and delta relative power.

A strong relationship was previously described between the nocturnal oscillations of plasma renin activity (PRA) and the sleep cycles, with levels of PRA that increase during non rapid eye movement sleep and decrease during rapid eye movement sleep. This study was designed to determine whether ritanserin, a 5-hydroxytryptamine-2 (5-HT2) receptor antagonist known to increase slow wave sleep both in human and in animals and to decrease plasma renin activity response to serotonergic stimulation in the rat, would uncouple this relationship. Eight subjects underwent two randomized night studies after having received either placebo or 5 mg ritanserin administered in the morning.

Internal dissociation of the circadian markers of the cortisol rhythm in night workers.

To determine whether the circadian system of night workers is adapted to a night-active schedule, we submitted 11 night workers and 11 day-active subjects to a 10-min blood sampling procedure during their usual sleep-wake cycle, permitting a precise determination of circadian and ultradian cortisol variations. In night works, the usual shift of 8 h in the sleep period was associated with a distortion of the normal 24-h cortisol rhythm. The acrophase exhibited a shift of approximately 6.

Atrial natriuretic factor secretion: a role for atrial systolic ejection force?

The increase in plasma concentration of atrial natriuretic factor in heart transplant patients has not been fully elucidated. Besides an eventual pressure or volume overload leading to passive atrial distension, the atrial tension developed during atrial systole, or atrial ejection force, which may be increased by the transplantation procedure, is an important determinant of atrial natriuretic factor release. We therefore determined the plasma concentration of atrial natriuretic factor and the maximal atrial ejection force in 15 heart transplant patients and 8 controls, matched for age and body mass.

Effect of short-term endurance training on exercise capacity, haemodynamics and atrial natriuretic peptide secretion in heart transplant recipients.

Exercise tolerance of heart transplant patients is often limited. Central and peripheral factors have been proposed to explain such exercise limitation but, to date, the leading factors remain to be determined. We examined how a short-term endurance exercise training programme may improve exercise capacity after heart transplantation, and whether atrial natriuretic peptide (ANP) release may contribute to the beneficial effects of exercise training by minimizing ischaemia and/or cardiac and circulatory congestion through its vasodilatation and haemoconcentration properties.

Temporal link between plasma thyrotropin levels and electroencephalographic activity in man.

Plasma thyrotropin (TSH) levels have been previously shown to be associated with the internal sleep structure determined by conventional scoring of sleep stages. This temporal relationship was re-evaluated using spectral analysis of the sleep electroencephalogram (EEG). Eight healthy male subjects underwent two randomized night studies after having received either placebo or 5 mg ritanserin, a selective 5-HT2 receptor antagonist known to increase slow-wave sleep.

Slow wave electroencephalic activity parallels renin oscillations during sleep in humans.

Previous studies have demonstrated that the nocturnal oscillations of plasma renin activity (PRA) exactly reflect rapid eye movement (REM) non-REM (NREM) sleep alternation with levels of PRA that increase during NREM sleep and decrease during REM sleep. These studies were based exclusively on conventional scoring of sleep stages. In the present study, we used spectral analysis of the sleep EEG to determine the variations in the different EEG frequency bands, together with PRA profiles.

Comparative effect of night and daytime sleep on the 24-hour cortisol secretory profile.

To determine whether cortisol secretion interacts with daytime sleep in a similar manner to that reported for night sleep, 14 healthy young men were studied during two 24-hour cycles. During one cycle they slept during the night, during the other the sleep period was delayed by 8 hours. Secretory rates were calculated by a deconvolution procedure from plasma cortisol, measured at 10-minute intervals.

Temporal relationship between prolactin secretion and slow-wave electroencephalic activity during sleep.

It is well established that plasma prolactin (PRL) concentrations exhibit a sleep-dependent pattern, with the highest levels occurring during sleep and the lowest during waking. Still, controversy exists concerning an association between rapid eye movement (REM) and non-REM sleep cycles and plasma PRL pulses. These studies were all based on conventional scoring of sleep stages.

Distinct modes of melatonin secretion in normal men.

As for many hormones, melatonin levels in the blood suggest that it is discharged from the pineal gland in a pulsatile manner. Recently, the existence of short-term episodes, superimposed on the circadian pattern of circulating melatonin, has been questioned. Because plasma melatonin levels reflect not only the secretory process, but also the effects of distribution and degradation, secretory rates were estimated from peripheral levels, using a deconvolution procedure.

The circadian thyrotropin rhythm is delayed in regular night workers.

In order to determine whether the circadian thyrotropin (TSH) rhythm is adapted to a night-active schedule, plasma TSH and body temperature were measured for 28 h every 10-min in 8 regular night workers and in 8 day-active subjects. In night workers, the shift of 8-h in the sleep period induced a mean shift of 6 h 30 min of the TSH acrophase which remained located, as in day-active subjects, at about the time of sleep onset. The nadir of the body temperature rhythm was shifted by an equivalent amount and occurred systematically during the sleep period, so that both parameters maintained a fixed phase relationship.

Prolactin secretion during sleep in obstructive sleep apnoea patients.

Plasma prolactin (PRL) concentration exhibits a sleep-dependent pattern, with highest levels during sleep and lowest levels during the waking period. The syndrome of obstructive sleep apnoea (OSA) is associated with severe hypoxaemia and chronic sleep fragmentation, both of which could affect the sleep-entrained PRL rhythm. Treatment with nasal continuous positive airway pressure (CPAP) immediately restores a normal sleep structure by successful abolition of the apnoeas.

Slow oscillations of plasma glucose and insulin secretion rate are amplified during sleep in humans under continuous enteral nutrition.

Concomitant oscillations of plasma glucose and insulin secretion rate with a periodicity of about 80 minutes have been identified in normal humans. To determine whether these slow oscillations are influenced by sleep, peripheral levels of glucose and C-peptide were measured at 10-minute intervals over 24 hours in seven subjects, once with a normal nocturnal sleep from 2300 to 0700 hours, and once with a shifted daytime sleep from 0700 to 1500 hours. The subjects received continuous enteral nutrition and remained supine for the 8 hours preceding blood sampling and throughout the whole experiment.

Clomipramine-induced sleep disturbance does not impair its prolactin-releasing action.

The present study was undertaken to examine the role of sleep disturbance, induced by clomipramine administration, on the secretory rate of prolactin (PRL) in addition to the direct drug effect. Two groups of supine subjects were studied under placebo-controlled conditions, one during the night, when sleeping (n = 7) and the other at daytime, when awake (n = 6). Each subject received a single 50 mg dose of clomipramine given orally 2 hours before blood collection.

Renin as a biological marker of the NREM-REM sleep cycle: effect of REM sleep suppression.

We have previously described that, in normal man, the nocturnal oscillations of plasma renin activity (PRA) exactly reflect the rapid eye movement (REM)-non(N)REM sleep cycles, with increasing PRA levels during NREM sleep and decreasing levels during REM sleep. This study was carried out to determine whether REM sleep suppression affects nocturnal renin profiles and to define which sleep stage is essential for renin release. In a first experimental series, REM sleep was suppressed by using clomipramine, a tricyclic antidepressant.

Nycthemeral patterns of thyroid hormones and their relationships with thyrotropin variations and sleep structure.

In order to precise the relationships between TSH, FT3, and FT4 nycthemeral variations and the relationships between thyroid hormone variations and sleep, 8 healthy young males were studied twice, once during a 24-h experiment with normal nocturnal sleep, and once during a night of sleep deprivation. The subjects received continuous enteral nutrition and remained supine during the whole experiment. Blood was sampled every 10 min for TSH, FT3, and FT4 measurements.

Twenty-four-hour profiles of plasma renin activity in relation to the sleep-wake cycle.

Objective: To evaluate the relative contribution of sleep and the endogenous circadian rhythmicity in producing the 24-h variations in the plasma renin activity.

Methods: Ten normal young men were studied, under basal conditions with normal nocturnal sleep from 2300-0700 h and once after a night of total sleep deprivation followed by 8 h daytime sleep from 0700 to 1500 h. Plasma renin activity was measured every 10 min for 24 h and the profiles were analysed using the pulse detection program ULTRA.

Prolactin secretion and sleep.

To clarify the relationship between prolactin (PRL) secretion and sleep, three experimental procedures were employed and secretory rates were estimated from plasma levels using a deconvolution procedure. Eight healthy young men participated in two 24-hour studies, one using normal night sleep and one using delayed sleep, to determine the influence of sleep as a whole on the PRL rhythm. Another group of 24 subjects underwent a 1-night study to investigate the relationship between PRL secretion and the internal sleep structure.