Biomedical subjects

J Ehrhart

Publications and source records attributed to J Ehrhart.

At least 19 recordsLinked to original sources

PubMed2004

Galantamine and nicotine have a synergistic effect on inhibition of microglial activation induced by HIV-1 gp120.

Chronic brain inflammation is the common final pathway in the majority of neurodegenerative diseases and central to this phenomenon is the immunological activation of brain mononuclear phagocyte cells, called microglia. This inflammatory mechanism is a central component of HIV-associated dementia (HAD). In the healthy state, there are endogenous signals from neurons and astrocytes, which limit excessive central nervous system (CNS) inflammation. However, the signals controlling this process have not been fully elucidated. Studies on the peripheral nervous system suggest that a cholinergic anti-inflammatory pathway regulates systemic inflammatory response by way of acetylcholine acting at the alpha7 nicotinic acetylcholine receptor (alpha7nAChR) found on blood-borne macrophages. Recent data from our laboratory indicates that cultured microglial cells also express this same receptor and that microglial anti-inflammatory properties are mediated through it and the p44/42 mitogen-activated protein kinase (MAPK) system. Here we report for the first time the creation of an in vitro model of HAD composed of cultured microglial cells synergistically activated by the addition of IFN-gamma and the HIV-1 coat glycoprotein, gp120. Furthermore, this activation, as measured by TNF-alpha and nitric oxide (NO) release, is synergistically attenuated through the alpha7 nAChR and p44/42 MAPK system by pretreatment with nicotine, and the cholinesterase inhibitor, galantamine. Our findings suggest a novel therapeutic combination to treat or prevent the onset of HAD through this modulation of the microglia inflammatory mechanism.

Analysis of Variance↗

PubMed2004

Effects of increased training load on vagal-related indexes of heart rate variability: a novel sleep approach.

There is little doubt that moderate training improves cardiac vagal activity and thus has a cardioprotective effect against lethal arrhythmias. Our purpose was to learn whether a higher training load would further increase this beneficial effect. Cardiac autonomic control was inferred from heart rate variability (HRV) and analyzed in three groups of young subjects (24.5 +/- 3.0 yr) with different training states in a period free of stressful stimuli or overload. HRV was analyzed in 5-min segments during slow-wave sleep (SWS, a parasympathetic state that offers high electrocardiographic stationarity) and compared with data collected during quiet waking periods in the morning. Sleep parameters, fatigue, and stress levels checked by questionnaire were identical for all three groups with no signs of overtraining in the highly trained (HT) participants. During SWS, a significant (P <0.05) increase in absolute and normalized vagal-related HRV indexes was observed in moderately trained (MT) individuals compared with sedentary (Sed) subjects; this increase did not persist in HT athletes. During waking periods, most of the absolute HRV indexes indistinctly increased in MT individuals compared with controls (P < 0.05) but did not increase in HT athletes. Normalized spectral HRV indexes did not change significantly among the three groups. Heart rate was similar for MT and Sed subjects but was significantly (P <0.05) lower in HT athletes under both recording conditions. These results indicate that SWS discriminates the state of sympathovagal balance better than waking periods. A moderate training load is sufficient to increase vagal-related HRV indexes. However, in HT individuals, despite lower heart rate, vagal-related HRV indexes return to Sed values even in the absence of competition, fatigue, or overload.

Adult↗

PubMed2004

Abnormal heart rate variability in a subject with second degree atrioventricular blocks during sleep.

OBJECTIVE: We compare the profiles of heart rate variability (HRV) during sleep stages in 9 healthy controls and one subject with second degree atrioventricular blocks (AVB), investigating the role of sympathovagal balance in such pathology. METHOD: Sleep and cardiac records were taken for one night in 9 male subjects from 21:00 to 07:00 h and for two nights in a male subject with AVB. Time and frequency domain indexes of HRV were calculated over 5 min-periods. RESULTS: In one subject without any daytime heart disease, 253 and 318 AVB of type 2 (Mobitz 2) were observed during the two experimental nights, predominantly during rapid eye movement (REM) sleep and the surrounding sleep stage 2 in the second half of the night. In the 9 control subjects, absolute HRV indexes and low frequency (LF)/(LF+high frequency, HF) (where LF and HF are low frequency and high frequency power) were low during slow wave sleep, and significantly increased during REM sleep and the preceding sleep stage 2. In the subject with AVB, these HRV indexes were abnormally low during all sleep stages, with a predominant increase in parasympathetic activity as inferred from low LF/(LF+HF). During wake, however, LF/(LF+HF) normally increased, and the tachycardia observed with the arousal that terminates SWS was preserved in the subject with AVB. CONCLUSION: These results suggest that in the subject with second degree atrioventricular blocks, sleep processes, particularly during REM sleep, create a specific neurological background that prevents an increase in sympathetic tone and triggers cardiac pauses.

Adult↗

PubMed2002

Time-courses in renin and blood pressure during sleep in humans.

We previously described a strong concordance between nocturnal oscillations in plasma renin activity (PRA) and the rapid eye movement (REM) and non-REM (NREM) sleep cycles, but the mechanisms inducing PRA oscillations remain to be identified. This study was designed to examine whether they are linked to sleep stage-related changes in arterial blood pressure (ABP). Analysis of sleep electroencephalographic (EEG) activity in the delta frequency band, intra-arterial pressure, and PRA measured every 10 min was performed in eight healthy subjects. Simultaneously, the ratio of low frequency power to low frequency power + high frequency power [LF/(LF + HF)] was calculated using spectral analysis of R--R intervals. The cascade of physiological events that led to increased renin release during NREM sleep could be characterized. First, the LF/(LF + HF) ratio significantly (P < 10(-4) decreased, indicating a reduction in sympathetic tone, concomitantly to a significant (P < 10(- 3) decrease in mean arterial pressure (MAP). Delta wave activity increased (P < 10(-4) 10-20 min later and was associated with a lag of 0-10 min with a significant rise in PRA (P < 10(-4) . Rapid eye movement sleep was characterized by a significant increase (P < 10(-4) in the LF/(LF + HF) ratio and a decrease (P < 10(-4) in delta wave activity and PRA, whereas MAP levels were highly variable. Overnight cross-correlation analysis revealed that MAP was inversely correlated with delta wave activity and with PRA (P < 0.01 in all subjects but one). These results suggest that pressure-dependent mechanisms elicit the nocturnal PRA oscillations rather than common central processes controlling both the generation of slow waves and the release of renin from the kidney.

Adult↗

PubMed2001

Inverse coupling between ultradian oscillations in delta wave activity and heart rate variability during sleep.

OBJECTIVE: We investigate the relationship between changes in heart rate variability and electroencephalographic (EEG) activity during sleep. METHOD: Nine male subjects with regular non-rapid-eye movement-rapid-eye movement (NREM-REM) sleep cycles were included in the study. They underwent EEG and cardiac recordings during one experimental night. Heart rate variability was determined over 5-min periods by the ratio of low frequency to low frequency plus high frequency power [LF/(LF+HF)] calculated using spectral analysis of R-R intervals. EEG spectra were analyzed using a fast Fourier transform algorithm. RESULTS: We found an ultradian 80-120 min rhythm in the LF/(LF+HF) ratio, with high levels during rapid eye movement (REM) sleep and low levels during slow wave sleep (SWS). During sleep stage 2 there was a progressive decrease in the transition from REM sleep to SWS, and an abrupt increase from SWS to REM sleep. These oscillations were significantly coupled in a 'mirror-image' to the overnight oscillations in delta wave activity, which reflect sleep deepening and lightening. Cardiac changes preceded EEG changes by about 5 min. CONCLUSIONS: These findings demonstrate the existence of an inverse coupling between oscillations in delta wave activity and heart rate variability. They indicate a non-uniformity in sleep stage 2 that underlies ultradian sleep regulation.

Activity Cycles↗

PubMed2001

Sleep deprivation blunts the night time increase in aldosterone release in humans.

The aim of this study was to determine the effect of sleep deprivation on the 24-h profile of aldosterone and its consequences on renal function. Aldosterone and its main hormonal regulatory factors, ACTH (evaluated by cortisol measurement) and the renin-angiotensin system [RAS, evaluated by plasma renin activity (PRA) measurement] were determined every 10 min for 24 h in eight healthy subjects in the supine position, once with nocturnal sleep and once during total 24-h sleep deprivation. Plasma Na(+) and K(+) were measured every 10 min in four of these subjects. In an additional group of 13 subjects under enteral nutrition, diuresis, natriuresis and kaliuresis were measured once during the sleep period (23.00--07.00 h) and once during a 23.00--07.00 hours sleep deprivation period. During sleep deprivation, aldosterone displayed lower plasma levels and pulse amplitude in the 23.00--07.00-hour period than during sleep. Similarly, PRA showed reduced levels and lower pulse frequency and amplitude. Plasma cortisol levels were slightly enhanced during sleep deprivation. Overnight profiles of plasma K(+) and Na(+) were not affected. Diuresis and kaliuresis were not influenced by sleep deprivation. In contrast, natriuresis significantly increased during sleep deprivation. This study demonstrates that sleep deprivation modifies the 24-h aldosterone profile by preventing the nocturnal increase in aldosterone release and leads to altered overnight hydromineral balance.

Adrenocorticotropic Hormone↗

PubMed2001

Hydrogen peroxide removal and glutathione mixed disulfide formation during metabolic inhibition in mesencephalic cultures.

Compromised mitochondrial energy metabolism and oxidative stress have been associated with the pathophysiology of Parkinson's disease. Our previous experiments exemplified the importance of GSH in the protection of neurons exposed to malonate, a reversible inhibitor of mitochondrial succinate dehydrogenase/complex II. This study further defines the role of oxidative stress during energy inhibition and begins to unravel the mechanisms by which GSH and other antioxidants may contribute to cell survival. Treatment of mesencephalic cultures with 10 microM buthionine sulfoximine for 24 h depleted total GSH by 60%, whereas 3 h exposure to 5 mM 3-amino-1,2,4-triazole irreversibly inactivated catalase activity by 90%. Treatment of GSH-depleted cells with malonate (40 mM) for 6, 12 or 24 h both potentiated and accelerated the time course of malonate toxicity, however, inhibition of catalase had no effect. In contrast, concomitant treatment with buthionine sulfoximine plus 3-amino-1,2,4-triazole in the presence of malonate significantly potentiated toxicity over that observed with malonate plus either inhibitor alone. Consistent with these findings, GSH depletion enhanced malonate-induced reactive oxygen species generation prior to the onset of toxicity. These findings demonstrate that early generation of reactive oxygen species during mitochondrial inhibition contributes to cell damage and that GSH serves as a first line of defense in its removal. Pre-treatment of cultures with 400 microM ascorbate protected completely against malonate toxicity (50 mM, 12 h), whereas treatment with 1 mM Trolox provided partial protection. Protein-GSH mixed disulfide formation during oxidative stress has been suggested to either protect vulnerable protein thiols or conversely to contribute to toxicity. Malonate exposure (50 mM) for 12 h resulted in a modest increase in mixed disulfide formation. However, exposure to the protective combination of ascorbate plus malonate increased membrane bound protein-GSH mixed disulfides three-fold. Mixed disulfide levels returned to baseline by 72 h of recovery indicating the reversible nature of this formation. These results demonstrate an early role for oxidative events during mitochondrial impairment and stress the importance of the glutathione system for removal of reactive oxygen species. Catalase may serve as a secondary defense as the glutathione system becomes limiting. These findings also suggest that protein-GSH mixed disulfide formation under these circumstances may play a protective role.

Amitrole↗

PubMed2001

Safety profile of thalidomide after 53 weeks of oral administration in beagle dogs.

Fifty-six adult beagle dogs (28 male, 28 female) were orally administered thalidomide at 43, 200, or 1000 mg/kg/day for 53 weeks. Sixteen (2/sex/dose group) and 32 (4/sex/dose group) dogs were euthanized and necropsied after 26 and 53 weeks of dosing, respectively. The remaining 8 animals (2/sex/group; high-dose and control groups) were dosed for 53 weeks, euthanized, and necropsied at 58 weeks after a 5-week recovery period. There were no deaths during the study. The only observed clinical signs attributable to thalidomide administration were green-colored urine, white-colored fecal residue presumed to be unchanged thalidomide, enlarged and/or blue coloration of female mammary tissue, and prolonged estrus. There were no thalidomide-related changes in body weights, food consumption, electrocardiography, ophthalmoscopy, neurological function, and endocrine function. The mostly slight and/or transient variations observed in some hematology and blood chemistry values of dosed dogs were considered to be toxicologically insignificant and were supported by the lack of histopathologic correlates. The only gross finding attributable to thalidomide was a yellow-green discoloration of the femur, rib, and/or calvarium that was observed at each euthanization interval including recovery. There was no microscopic correlate for this finding. No thalidomide-related microscopic changes were seen in any of the organs and tissues at 26 weeks. Mammary duct dilatation and/or glandular hyperplasia observed in females at 53 and 58 weeks and hepatic bile pigment exhibited by high-dose males at 53 weeks were microscopic changes considered to be thalidomide-related. There was no gross and histopathologic evidence of any tumors. In summary, thalidomide at up to 1000 mg/kg/day for 53 weeks did not induce any major systemic toxicity or tumors in dogs. The NOAEL was 200 mg/kg/day.

Animals↗

PubMed2001

[Altered heart rate variability but preserved temporal relationship with sleep stages in a patient with primary aldosteronism].

OBJECTIVE: In a previous study, we found oscillations in the autonomic nervous system activity--as estimated by spectral analysis of R-R intervals--strongly linked to the non-rapid-eye movement (NREM)--REM sleep cycles, with low sympathetic activity during NREM sleep and predominant sympathetic activity during REM sleep. In the present study we established the 5-min nighttime profiles in various measures of heart rate variability (HRV) in one patient with primary aldosteronism before and after successful surgery of Conn adenoma. METHODS: One patient (female, 36 years old) with primary aldosteronism underwent two experimental nights a few weeks before and after surgery by coeliscopy in which sleep and cardiac recordings were made. Power spectral analysis was performed on ectopic-free R-R intervals with a fast Fourier transform. We calculated also the standard deviation of normal R-R intervals (SDNN) and the root mean square difference among successive R-R intervals (RMSSD). RESULTS: While removal of adenoma resulted in a rapid complete normalization of blood pressure and classical signs and biological symptoms of aldosterone hypersecretion, HRV profile did not changed a few weeks after surgery. The overnight SDNN was low although not abnormal at 38 and 33 ms before and after surgery respectively vs 58 +/- 15 ms (33 to 83) in normal female controls. RMSSD was low although not abnormal at 33 and 31 ms before and after surgery respectively vs 60 +/- 20 ms (20 to 105). The total spectrum power was low although not abnormal at 2.3 and 1.8 ms2 before and after surgery, respectively vs 3.2 +/- 1.1 ms2 (1.4 to 4.9). One out of the 8 controls had comparable or lower SDNN (33 ms), RMSSD (20 ms) and total power (1.4 ms2) values. While LF/HF ratio was comparable, the VLF (0.003-0.04 Hz) and LF (0.04-0.15 Hz) relative power were decreased and increased respectively in the patient compared in controls. Despite this reduced HRV, the normal temporal relationship of spectral parameters with specific sleep stages was preserved. CONCLUSION: Altered HRV with normal temporal relationships with specific sleep stages was observed in a patient with primary hyperaldosteronism. This HRV profile did not changed 20 weeks after successful surgery i.e. complete remission of classical signs and symptoms of aldosterone hypersecretion.

Adenoma↗

PubMed2000

Alpha activity and cardiac correlates: three types of relationships during nocturnal sleep.

OBJECTIVE: We examined simultaneously alpha activity and cardiac changes during nocturnal sleep, in order to differentiate non-rapid eye movement (NREM) sleep, REM sleep, and intra-sleep awakening. METHODS: Ten male subjects displaying occasionally spontaneous intra-sleep awakenings underwent EEG and cardiac recordings during one experimental night. The heart rate and heart rate variability were calculated over 5 min periods. Heart rate variability was estimated: (1) by the ratio of low frequency (LF) to high frequency (HF) power calculated from spectral analysis of R-R intervals; and (2) by the interbeat autocorrelation coefficient of R-R intervals (rRR). EEG spectral analysis was performed using a fast Fourier transform algorithm. RESULTS: Three types of relationships between alpha waves (8-13 Hz) and cardiac correlates could be distinguished. During NREM sleep, alpha activity and cardiac correlates showed opposite variations, with high levels of alpha power associated with decreased heart rate, rRR and LF/HF ratio, indicating low sympathetic activity. Conversely, during REM sleep, alpha activity was low whereas heart rate, rRR, and the LF/HF ratio peaked, indicating high sympathetic activity. During intra-sleep awakenings, alpha activity and cardiac correlates both increased. No difference in time-course between alpha 1 (8-10 Hz) and alpha 2 (10-13 Hz) activity could be shown. Alpha waves occurred in fronto-central areas during slow wave sleep (SWS), migrated to posterior areas during REM sleep, and were localized in occipital areas during intra-sleep awakenings. CONCLUSIONS: These results suggest that alpha waves are not simply a sign of arousal, as is commonly thought. Fronto-central alpha waves, associated with decreased heart rate, possibly reflect sleep-maintaining processes.

Adult↗

PubMed2000

Lack of peripheral neuropathy in Beagle dogs after 53 weeks oral administration of thalidomide capsules.

Thalidomide (Thalomid) is approved for use in the US to treat complications from leprosy. Peripheral neuropathy is a dose-limiting adverse event in humans. As part of a nonrodent regulatory toxicology study, Beagle dogs were fed orally via encapsulation for 53 weeks. A component of this study was to determine if the dogs developed peripheral neuropathy. Twenty-eight male and 28 female Beagle dogs approximately 8-10 months of age were used. They were dosed at 43, 200 or 1000 mg/kg for 53 weeks followed by a 4-week treatment-free recovery period. Nerve function was assessed by electrophysiological measurements of the tibial nerve prior to dosing and at weeks 13, 27, 38 and 51. Representative dogs from each group were sacrificed at 26, 53 and 58 weeks and histologic and ultrastructural evaluations were performed on the sural nerve. Thalidomide had no effect on sensory nerve conduction velocity, duration or amplitude of the action potential. At 27 weeks, mean sensory nerve action potential amplitude for females at 43 mg/kg was significantly greater than control but was not evident at 39 weeks. Mean duration of sensory nerve action potential seemed to increase with similar magnitude over time in all dose groups including controls. Histological and ultrastructural evaluation of sections of sural nerve did not identify treatment-induced differences between control and thalidomide-dosed animals after 26 and 53 weeks of treatment. Additionally, no differences were observed following a 5-week treatment-free period at week 58. In contrast to humans, Beagle dogs did not develop thalidomide-induced peripheral neuropathy under conditions of the study.

Action Potentials↗

PubMed1999

Neuroendocrine processes underlying ultradian sleep regulation in man.

Sleep is not a uniform state but is characterized by the cyclic alternation between rapid eye movement (REM) and non-REM sleep with a periodicity of 90-110 min. This cycle length corresponds to one of the oscillations in electroencephalographic (EEG) activity in the delta frequency band (0.5-3.5 Hz), which reflect the depth of sleep. To demonstrate the intimate link between EEG and neuroendocrine rhythmic activities in man, we adopted a procedure permitting simultaneous analysis of sleep EEG activity in the delta band and of two activating systems: the adrenocorticotropic system and the autonomic nervous system. Adrenocorticotropic activity was evaluated by calculating the cortisol secretory rate in blood samples taken at 10-min intervals. Autonomic activity was estimated by two measures of heart rate variability: 1) by the ratio of low-frequency (LF) to high-frequency (HF) power from spectral analysis of R-R intervals; and 2) by the interbeat autocorrelation coefficient of R-R intervals (rRR intervals between two successive cardiac beats). The results revealed that oscillations in delta wave activity, adrenocorticotropic activity, and autonomic activity are linked in a well-defined manner. Delta wave activity developed when cortisol secretory rates had returned to low levels and sympathetic tone was low or decreasing, as reflected by a low LF/HF ratio and by low levels in rRR. Conversely, the decrease in delta wave activity occurred together with an increase in the LF/HF ratio and in rRR. REM sleep was associated with a decrease in cortisol secretory rates preceding REM sleep onset, whereas the LF/HF ratio and rRR remained high. These results demonstrate a close coupling of adrenocorticotropic, autonomic, and EEG ultradian rhythms during sleep in man. They suggest that low neuroendocrine activity is a prerequisite for the increase in slow wave activity.

Adult↗

PubMed1998

Dynamic heart rate variability: a tool for exploring sympathovagal balance continuously during sleep in men.

We have recently demonstrated that the overnight profiles of cardiac interbeat autocorrelation coefficient of R-R intervals (rRR) calculated at 1-min intervals are related to the changes in sleep electroencephalographic (EEG) mean frequency, which reflect depth of sleep. Other quantitative measures of the Poincaré plots, i.e., the standard deviation of normal R-R intervals (SDNN) and the root mean square difference among successive R-R normal intervals (RMSSD), are commonly used to evaluate heart rate variability. The present study was designed to compare the nocturnal profiles of rRR, SDNN, and RMSSD with the R-R spectral power components: high-frequency (HF) power, reflecting parasympathetic activity; low-frequency (LF) power, reflecting a predominance of sympathetic activity with a parasympathetic component; and the LF-to-HF ratio (LF/HF), regarded as an index of sympathovagal balance. rRR, SDNN, RMSSD, and the spectral power components were calculated every 5 min during sleep in 15 healthy subjects. The overnight profiles of rRR and LF/HF showed coordinate variations with highly significant correlation coefficients (P < 0.001 in all subjects). SDNN correlated with LF power (P < 0.001), and RMSSD correlated with HF power (P < 0.001). The overnight profiles of rRR and EEG mean frequency were found to be closely related with highly cross-correlated coefficients (P < 0. 001). SDNN and EEG mean frequency were also highly cross correlated (P < 0.001 in all subjects but 1). No systematic relationship was found between RMSSD and EEG mean frequency. In conclusion, rRR appears to be a new tool for evaluating the dynamic beat-to-beat interval behavior and the sympathovagal balance continuously during sleep. This nonlinear method may provide new insight into autonomic disorders.

Adult↗

PubMed1998

Excitotoxicity and oxidative stress during inhibition of energy metabolism.

Glutamate receptor involvement and oxidative stress have both been implicated in damage to neurons due to impairment of energy metabolism. Using two different neuronal in vitro model systems, an ex vivo chick retinal preparation and dopamine neurons in mesencephalic culture, the involvement and interaction of these events as early occurring contributors to irreversible neuronal damage have been examined. Consistent with previous reports, the early acute changes in the retinal preparation, as well as irreversible loss of dopamine neurons due to inhibition of metabolism, can be prevented by blocking NMDA receptors during the time of energy inhibition. Oxidative stress was suggested to be a downstream consequence and contributor to neuronal cell loss due to either glutamate receptor overstimulation or metabolic inhibition since trapping of free radicals with the cyclic nitrone spin-trapping agent MDL 102,832 (1 mM) attenuated acute excitotoxicity in the retinal preparation or loss of mesencephalic dopamine neurons due to either metabolic inhibition by the succinate dehydrogenase inhibitor, malonate, or exposure to excitotoxins. In mesencephalic culture, malonate caused an enhanced efflux of both oxidized and reduced glutathione into the medium, a significant reduction in total reduced glutathione and a significant increase in total oxidized glutathione at time points that preceded those necessary to cause toxicity. These findings provide direct evidence for early oxidative events occurring following malonate exposure and suggest that the glutathione system is important for protecting neurons during inhibition of energy metabolism. Consistent with this, lowering of glutathione by buthionine sulfoxamine (BSO) pretreatment greatly potentiated malonate toxicity in the mesencephalic dopamine population. In contrast, BSO pretreatment did not potentiate glutamate toxicity. This latter finding indicates dissimilarities in the type of oxidative stress that is generated by the two insults and suggests that the oxidative challenge during energy inhibition is not solely a downstream consequence of glutamate receptor overstimulation.

Animals↗

PubMed1996

Advances of human core temperature minimum and maximal paradoxical sleep propensity by ambient thermal transients.

By using slow thermal transients of reduced amplitude (+/- 3 degrees C (thermoneutrality in humans sleeping nude) during only 1 night (experimental, EX), we have advanced the minimum of rectal temperature (Tre) and the peak of their paradoxical sleep propensity (PPSP) of sleeping subjects. During this EX night Tre minimum was significantly (P = 0.0001) advanced by 143 min versus that observed during baseline night spent at thermoneutrality. The advance of PPSP was objectivated by the more rapid cumulation of paradoxical sleep (P = 0.02) during the second half of EX night, i.e. strictly after the occurrence (around 0330 h) of the new Tre minimum, and by the earlier occurrence of its barycentric point (P = 0.04) between 0330 and 0700 h. The involvement of the central thermoregulatory system on phase-shifting mechanisms is discussed.

Adult↗

PubMed1996

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 6.5 h, whereas the quiescent period, abruptly interrupted by a large peak, underwent a shift of only 3 h and lasted for approximately 5 h, as in day-active subjects. Slow-wave sleep and sleep onset occurred during periods of low or decreasing cortisol secretory rates, whereas awakenings were associated with an increase in cortisol secretory rates. These results revealed that the circadian system of night workers only partially adapts to night work and that adaptation processes rely on an internal dissociation of the markers of the cortisol pattern, without disturbing the processes that couple cortisol release and specific sleep stages.

Activity Cycles↗

PubMed1995

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. TSH and temperature rhythms had similar amplitudes in the two groups. However, mean TSH values in night workers returned more rapidly to basal values. These results demonstrate that, together with body temperature, TSH acrophase is adapted to regular night work, suggesting that TSH may be a good index for evaluating the orientation of the endogenous clock.

Adult↗

PubMed1995

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. The amount of cortisol secreted during night sleep was lower than during the corresponding period of sleep deprivation (12.7 +/- 1.1 vs. 16.3 +/- 1.6 mg; p < 0.05), but daytime sleep beginning at the habitual time of morning awakening failed to inhibit cortisol secretion significantly. There was no difference between the amount of cortisol secreted from 0700 to 1500 hours in sleeping subjects and in subjects who were awake during the same period of time (24.2 +/- 1.5 vs. 22.5 +/- 1.4 mg). Even if the comparison between sleeping and waking subjects was restricted to the period 0700-1100 hours or 0700-0900 hours, no significant difference was found. Neither secretory pulse amplitude nor frequency differed significantly in either period. However, detailed analysis of the secretory rates in day sleepers demonstrated a transient decrease in cortisol secretion at about the time of sleep onset, which began 10 minutes before and lasted 20 minutes after falling asleep. Spontaneous or provoked awakenings had a determining influence on the secretory profiles. Ten to 20 minutes after awakening from either night or day sleep cortisol secretion increased significantly.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗