Biomedical subjects

C Gronfier

Publications and source records attributed to C Gronfier.

25 records · Page 2Linked to original sources

PubMed1997

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. GH secretory rates were calculated by deconvolution of the plasma concentrations analyzed at 10-min intervals. The total amount of GH secreted during the 24 h did not differ between the three groups and the main secretory episode occurred, in most cases, during the first half of the sleep period. In night sleepers and night workers the enhanced amount of GH secreted at that time was followed by a significantly lower amount secreted during the second part of the sleep period (p < 0.001 and p < 0.05, respectively). For night sleepers, an enhanced GH pulse frequency was found at the beginning of sleep, whereas for night workers and day sleepers the pulses were distributed more randomly throughout the nychthemeron. After an abrupt sleep shift, all the subjects displayed a GH pulse at the usual time of early sleep, but such a pulse was present in only 8 of 11 night workers. Thus the amount of GH secreted between 23:00 h and 03:00 h in day sleepers did not differ significantly from that observed in night sleepers, whereas it differed for night workers. These results confirm the considerable influence of sleep in driving the GH rhythm and the existence of a circadian influence revealed by an acute shift in the sleep period. They also provide evidence of an incomplete adjustment of GH rhythms in night workers.

Adult↗

PubMed1996

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. They were subjected to 8 hour polysomnography, including spectral analysis of the electroencephalogram and to continuous blood sampling. Blood was sampled from 2300 to 700h every 10 min and plasma renin activity (PRA) was measured by radioimmunoassay of angiotensin 1. The nocturnal profiles were analysed using the pulse detection program ULTRA. Ritanserin produced the expected increase in slow wave sleep (SWS) duration (132 +/- 10 min under ritanserin vs 72 +/- 9 min under placebo; p < 0.001) and a significant increase in delta relative power (69 +/- 2% under ritanserin vs 60 +/- 2% under placebo; p < 0.01). The mean overnight PRA levels had a tendency to decrease under ritanserin (1.66 +/- 0.34 ngAngl/ml per h under ritanserin vs 1.48 +/- 0.31 ngAngl/ml per h under placebo; p = 0.08). Individual PRA oscillations were preserved and remained strongly associated with delta power oscillations. PRA peak levels were similar in both experimental conditions, but the absolute amplitude of the oscillations was decreased under ritanserin (1.50 +/- 0.36 ngAngl/ml per h vs 1.04 +/- 0.14 ngAngl/ml per h; p < 0.05). These results demonstrate that ritanserin, at a dose that augments delta power, only weakly affects renin release, which suggests that 5-HT2 receptors are only partially involved in the processes coupling renin release and SWS and that other mechanisms probably control the sleep-associated variations in PRA.

Adult↗

PubMed1996

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. They were subjected to 8 hours of polysomnography, including spectral analysis of the sleep EEG. Plasma GH levels were measured at 10-minute intervals. The mean delta absolute power and the mean GH secretory rates were significantly higher under ritanserin than under placebo for the first 3 hours after sleep onset (+24% and +29%, respectively). Their nocturnal profiles were significantly and positively correlated in all subjects (average r = 0.710 under placebo, 0.567 under ritanserin; p < 0.0001 in both cases). GH secretory pulses were found to be coincident with delta activity peaks in both directions. The amount of GH secreted during significant GH pulses was correlated with the amount of concomitant delta wave activity (r = 0.803 under placebo, r = 0.764 under ritanserin, p < 0.0001). Similarly, the amount of delta wave activity found during delta wave peaks was correlated with the amount of GH secreted concomitantly (r = 0.715 under placebo, r = 0.723 under ritanserin: p < 0.0001). These results demonstrate a close temporal and quantitative relationship between GH secretion and delta wave activity, which may be evidence of common stimulatory mechanisms.

Adult↗

PubMed1996

Relationships between intact parathyroid hormone 24-hour profiles, sleep-wake cycle, and sleep electroencephalographic activity in man.

To determine whether the 24-h intact PTH (iPTH) profile is influenced by the sleep-wake cycle, and whether iPTH pulses show a temporal relationship with internal sleep structure, eight normal young men were studied during 24 h under basal conditions, once with normal nighttime sleep from 2300-0700 h and once after a night of sleep deprivation followed by an 8-h period of daytime sleep from 0700-1500 h. During the 8-h nighttime sleep period, mean iPTH levels were significantly increased by +13% and mean iPTH pulse amplitudes by +31% as compared with the 8-h subsequent waking periods. During the 8 h of total sleep deprivation, mean iPTH levels were not significantly different from the corresponding period in nighttime sleep condition, but mean iPTH pulse amplitudes were significantly lower (P < 0.01). The 8-h daytime sleep period was associated with increased mean iPTH levels and mean iPTH pulse amplitudes (+15% and +57%, respectively, as compared with the corresponding period in nighttime sleep condition). The number of pulses was similar in both experimental series and was not influenced by sleep or by time of day. Analysis of coincidence between iPTH pulses, plasma ionized calcium and plasma phosphate pulses, and slow wave sleep, as well as with rapid eye movement sleep episodes, did not reveal any significant association. Cross-correlation analysis between iPTH, plasma ionized calcium, and plasma phosphate fluctuations during sleep also showed no systematic association. Seven other subjects were studied during a nighttime sleep period in which temporal relationships between iPTH and internal sleep structure were reevaluated using spectral analysis of the sleep electroencephalogram. Cross-correlation analysis between iPTH levels and delta-relative power fluctuations showed nonsignificant results, which confirms the lack of relationship with slow wave sleep. This study demonstrates that the iPTH 24-h profile is influenced by sleep processes with a weak circadian component. However, iPTH pulses are not temporally linked with sleep electroencephalographic activity nor with calcemia and phosphatemia fluctuations. This evidence raises questions about the origin of iPTH pulses.

Adult↗

PubMed1996

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. Plasma PRL, body temperature, and plasma melatonin were measured at 10-min intervals. Twenty-four-hour PRL profiles did not differ between night workers sleeping as usual during the daytime and day-active subjects submitted to an abrupt sleep shift to daytime. For the two groups of subjects a transient PRL peak, similar in size and time of occurrence, was observed during the night. Melatonin, a strong marker of the primary circadian oscillator, displayed a phase shift that differed widely among night workers. Body temperature, on the other hand, was found to be more regularly adapted despite the persistence of a small decrease or leveling off during the night. Although no relationship was found between the melatonin increase and the nocturnal PRL peak, a concomitance with this transient temperature decrease could be demonstrated. The persistence of this PRL peak in night workers raises the question of its significance.

Acclimatization↗

PubMed1995

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. Delta relative power and TSH levels, determined at 10 min intervals, were found to be inversely related with an average cross-correlation coefficient highly significant (P < 0.0001) in both experimental conditions. Alpha slow-wave index, an estimator of awakenings, and TSH pulses exhibited a significant temporal association in both conditions. These results demonstrate that TSH fluctuations are linked to the sleep EEG activity in man.

Adult↗

PubMed1994

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. Plasma PRL concentrations were analysed at 10 min intervals and underlying secretory rates calculated by a deconvolution procedure. For both experiments the drug intake led to significant increases in PRL secretion, acting preferentially on tonic secretion as pulse amplitude and frequency did not differ significantly from corresponding control values. During the night clomipramine ingestion altered the complete sleep architecture in that it suppressed REM sleep and the sleep cycles and induced increased wakefulness. As the relative increase in PRL secretion expressed as a percentage of the mean did not significantly differ between the night and day time studies (46 +/- 19% vs 34 +/- 10%), it can be concluded that the observed sleep disturbance did not interfere with the drug action per se. The presence of REM sleep was shown not to be a determining factor either for secretory pulse amplitude and frequency, as, for both, mean nocturnal values were similar with and without prior clomipramine ingestion.

Administration, Oral↗