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Biomedical subjects

J Arendt

Publications and source records attributed to J Arendt.

At least 19 recordsLinked to original sources
PubMed2003

Circularly polarised MF (500 micro T 50 Hz) does not acutely suppress melatonin secretion from cultured Wistar rat pineal glands.

Magnetic fields (MF, 50 Hz) have been proposed to affect melatonin production in mammals; however, there is very little data about the mechanism by which this possible interaction may occur. Here we describe results from the first study in which circularly polarised 50 Hz MF have been administered to isolated pineals in highly controlled conditions. Melatonin release from isolated Wistar rat pineal glands, dissected 2 h after light onset ZT 2, was measured in a flow through culture system, during and after exposure to a 4 h MF similar in nature and magnitude to that produced in extremely close proximity to a high voltage power line (500 micro T 50 Hz circularly polarised). Melatonin release from isolated pineals was comparable to that observed in previous studies, plateauing to approximately 100 pg/ml/30 min. No significant alterations in pineal melatonin release were caused by exposure to the MF when compared to sham exposure (< 1 micro T). These results suggest that if the circadian system is acutely responsive to MF exposure of this nature, an intact circadian axis may be necessary in order to observe an effect on the production on melatonin from the pineal gland

Animals↗
PubMed2003

Importance and relevance of melatonin to human biological rhythms.

The pineal hormone melatonin is a remarkable molecule, with a conserved time-keeping function across species. It is extensively used as a self-administered remedy for sleep disturbance in countries where it is freely available, and to some extent when it is available on prescription, as in the UK. In some circumstances, notably free-running sleep disorder of the blind, it is the treatment of choice. It is also the marker rhythm of choice for the determination of circadian phase and period. This review outlines the current state of knowledge within a physiological perspective with emphasis on human biological rhythms.

Biological Clocks↗
PubMed2003

Circadian neuroendocrine physiology and electromagnetic field studies: precautions and complexities.

The suppression of melatonin by exposure to low frequency electromagnetic fields (EMFs) 'the melatonin hypothesis'. has been invoked as a possible mechanism through which exposure to these fields may result in an increased incidence of cancer. While the effect of light on melatonin is well established, data showing a similar effect due to EMF exposure are sparse and, where present, are often poorly controlled. The current review focuses on the complexities associated with using melatonin as a marker and the dynamic nature of normal melatonin regulation by the circadian neuroendocrine axis. These are issues which the authors believe contribute significantly to the lack of consistency of results in the current literature. Recommendations on protocol design are also made which, if followed, should enable researchers to eliminate or control for many of the confounding factors associated with melatonin being an output from the circadian clock.

Animals↗
PubMed2003

Acute exposure to circularly polarized 50-Hz magnetic fields of 200-300 microT does not affect the pattern of melatonin secretion in young men.

Environmental exposure to time-varying (alternating current) magnetic fields (MFs) produced by electrical current flow is a perceived public health risk. Several epidemiological studies report correlations between MF exposure and carcinogenesis. It has been hypothesized that MF-induced suppression of melatonin could provide the mechanism by which this effect is mediated. Here, we describe results from a controlled laboratory-based study designed to detect changes in human melatonin secretion after a 2-h exposure to 200-300 microTesla, 50 Hz circularly polarized MF. Exposure was timed to occur before or during the nightly melatonin rise, and levels administered were some 4-6 times higher than the commonly encountered maximum levels. Results from 19 male subjects aged between 18 and 35 yr indicate that acute exposure to 50 Hz MFs of this nature does not result in significant suppression, alteration of peak levels, or a change in timing of the nighttime melatonin rise. We conclude that acute exposure to 50 Hz MFs does not have a significant effect on the normal nighttime production of melatonin in young men.

Adult↗
PubMed2002

Adaptation of the circadian rhythm of 6-sulphatoxymelatonin to a shift schedule of seven nights followed by seven days in offshore oil installation workers.

This study evaluated circadian adaptation in a 'swing shift' schedule (seven nights, 18:00-06:00 h; then 7 days, 06:00-18:00 h) on North Sea oil installations. Eleven healthy men provided sequential urine collections for the study period offshore. The urinary melatonin metabolite 6-sulphatoxymelatonin (aMT6s) was used as an index of circadian phase. A significant difference (P=0.0004) was found between the mean aMT6s acrophase (calculated peak time) at the start (+/-SD: 05:34+/-2.42 h) and end (+/-SD: 10.95+/-3.34 h) of the night shift week, but not between the start (+/-SD: 11:04+/-4.03 h) and end (+/-SD: 12:59+/-8.83 h) of the day shift week. As a group, the subjects adapted to the night shift but very large individual variations were seen during the day shift. These individual differences clearly require further study.

Adaptation, Physiological↗
PubMed2002

[The treatment of assisted reproduction--clinical and preclinical aspects, functioning of the Unit of Human Reproduction at the Central Hospital of Luxembourg].

Since a few years the OBGYN department at the Centre Hospitalier in Luxembourg has intensified its practice of ART with the introduction of a multidisciplinary team and a decentralized IVF program. While clinical investigations, cycle-monitoring and surgery, oocyte pick-up are commonly performed at the CHL, the biological supplement is transferred to next situated Belgian laboratories. As Luxembourg has no national bio-ethical law, we apply partly the French law of 1994.

Female↗
PubMed2001

Health in a 24-h society.

With increasing economic and social demands, we are rapidly evolving into a 24-h society. In any urban economy, about 20% of the population are required to work outside the regular 0800-1700 h working day and this figure is likely to increase. Although the increase in shiftwork has led to greater flexibility in work schedules, the ability to provide goods and services throughout the day and night, and possibly greater employment opportunities, the negative effects of shiftwork and chronic sleep loss on health and productivity are now being appreciated. For example, sleepiness surpasses alcohol and drugs as the greatest identifiable and preventable cause of accidents in all modes of transport. Industrial accidents associated with night work are common, perhaps the most famous being Chernobyl, Three Mile Island, and Bhopal.

Accidents, Occupational↗
PubMed2001

An action spectrum for melatonin suppression: evidence for a novel non-rod, non-cone photoreceptor system in humans.

1. Non-image forming, irradiance-dependent responses mediated by the human eye include synchronisation of the circadian axis and suppression of pineal melatonin production. The retinal photopigment(s) transducing these light responses in humans have not been characterised. 2. Using the ability of light to suppress nocturnal melatonin production, we aimed to investigate its spectral sensitivity and produce an action spectrum. Melatonin suppression was quantified in 22 volunteers in 215 light exposure trials using monochromatic light (30 min pulse administered at circadian time (CT) 16-18) of different wavelengths (lambda(max) 424, 456, 472, 496, 520 and 548 nm) and irradiances (0.7-65.0 microW cm(-2)). 3. At each wavelength, suppression of plasma melatonin increased with increasing irradiance. Irradiance-response curves (IRCs) were fitted and the generated half-maximal responses (IR(50)) were corrected for lens filtering and used to construct an action spectrum. 4. The resulting action spectrum showed unique short-wavelength sensitivity very different from the classical scotopic and photopic visual systems. The lack of fit (r(2) < 0.1) of our action spectrum with the published rod and cone absorption spectra precluded these photoreceptors from having a major role. Cryptochromes 1 and 2 also had a poor fit to the data. Fitting a series of Dartnall nomograms generated for rhodopsin-based photopigments over the lambda(max) range 420-480 nm showed that rhodopsin templates between lambda(max) 457 and 462 nm fitted the data well (r(2) > or =0.73). Of these, the best fit was to the rhodopsin template with lambda(max) 459 nm (r(2) = 0.74). 5. Our data strongly support a primary role for a novel short-wavelength photopigment in light-induced melatonin suppression and provide the first direct evidence of a non-rod, non-cone photoreceptive system in humans.

Adult↗
PubMed2001

Melatonin in older people with age-related sleep maintenance problems: a comparison with age matched normal sleepers.

STUDY OBJECTIVES: To determine whether older people with age-related sleep maintenance problems have significantly lower melatonin levels than comparable normal sleepers. DESIGN: Case-control study. SETTING: A largely urban population, Auckland, New Zealand. PARTICIPANTS: People over the age of 65 years, who either slept normally, or had age-related sleep maintenance problems. Participants were recruited through media advertising, and local interest groups. Initial screening was by mail (Pittsburgh Sleep Quality Index), followed by interviews at a hospital day clinic. Exclusions included those with depression, cognitive impairment, medical and/or environmental problems which might impair sleep. INTERVENTIONS: N/A. MEASUREMENTS AND RESULTS: A metabolite of plasma melatonin, 6-sulphatoxymelatonin (aMT6s) was measured in the urine of 57 normal sleepers, and 53 people with age-related problems over 24 hours in three aliquots: 12:00-19:00h, 19:00-07:00h, 07:00-12:00h. There were clear differences in self reported quality of sleep but no difference in mean aMT6s 24 hour or total night excretory levels, or night/day ratios. CONCLUSIONS: Older people with age-related sleep maintenance problems do not have lower melatonin levels than older people reporting normal sleep.

Aged↗
PubMed2001

Postprandial triacylglycerol responses in simulated night and day shift: gender differences.

A number of reports suggest that shift workers have an increased risk of coronary heart disease (CHD). One contributing factor may be the consumption of meals at night with consequent altered postprandial responses. This study investigated circulating triacylglycerol (TAG), a possible risk factor for CHD, after meals during a simulated day and night shift. Twenty-five healthy participants (10 women and 15 men) were studied. They were given a pre-meal at 0800 h and a test meal at 1330 h on a simulated day shift and then an identical pre-meal at 2000 h and test meal at 0130 h, respectively, on a simulated night shift with maintained wakefulness. Blood was sampled for 9 h after the test meal for analysis of basal and postprandial plasma TAG levels. ANOVA for repeated measures indicated higher TAG in men compared with women (p < 0.0001) and higher responses at night in both genders (p = 0.027). Incremental area under the curve (IAUC) analysis indicated that men had significantly increased postprandial TAG levels at night compared with the day: (IAUC 0-540 min, mean +/- SEM) 253.29 +/- 28.73 versus 148.33 +/- 17.28 mmol/L x min, respectively, p = 0.025. In women, night and day responses (61.16 +/- 8.93 versus 34.09 +/- 7.87 mmol/L x min, respectively, p = 0.457) were not significantly different. Circulating TAG remained elevated for longer at night in the men compared with the women (p = 0.009). This study demonstrates the existence of gender and time-of-day differences in TAG responses to a meal. These raised TAG levels at night, for a prolonged time in men, may be relevant to the increased risk of CHD in shift workers.

Adult↗
PubMed2001

Postprandial hormone and metabolic responses amongst shift workers in Antarctica.

The circadian rhythms of many night-shift workers are maladapted to their imposed behavioural schedule, and this factor may be implicated in the increased occurrence of cardiovascular disease (CVD) reported in shift workers. One way in which CVD risk could be mediated is through inappropriate hormonal and metabolic responses to meals. This study investigated the responses to standard meals at different circadian times in a group of night-shift workers on a British Antarctic Survey station at Halley Bay (75 degrees S) in Antarctica. Twelve healthy subjects (ten men and two women) were recruited. Their postprandial hormone and metabolic responses to an identical mixed test meal of 3330 kJ were measured on three occasions: (i) during daytime on a normal working day, (ii) during night-time at the beginning of a period of night-shift work, and (iii) during the daytime on return from night working to daytime working. Venous blood was taken for 9 h after the meal for the measurement of glucose, insulin, triacylglycerol (TAG) and non-esterified fatty acids. Urine was collected 4-hourly (longer during sleep) on each test day for assessment of the circadian phase via 6-sulphatoxymelatonin (aMT6s) assay. During normal daytime working, aMT6s acrophase was delayed (7.7+/-1.0 h (s.e.m.)) compared with that previously found in temperate zones in a comparable age-group. During the night shift a further delay was evident (11.8+/-1.9 h) and subjects' acrophases remained delayed 2 days after return to daytime working (12.4+/-1.8 h). Integrated postprandial glucose, insulin and TAG responses were significantly elevated during the night shift compared with normal daytime working. Two days after their return to daytime working, subjects' postprandial glucose and insulin responses had returned to pre-shift levels; however, integrated TAG levels remained significantly elevated. These results are very similar to those previously found in simulated night-shift conditions; it is the first time such changes have been reported in real shift workers in field conditions. They provide evidence that the abnormal metabolic responses to meals taken at night during unadapted night shifts are due, at least in part, to a relative insulin resistance, which could contribute to the documented cardiovascular morbidity associated with shift work. When applied to the 20% of the UK workforce currently employed on shift work, these findings have major significance from an occupational health perspective.

Adult↗
PubMed2001

[The long-term evaluation of artificial myoplastic anus and artificial classical anus based on manometric and radiological examinations].

The aim of this study was comparative evaluation of the pressure profile in the artificial myoplastic anus and the one created by the use of classical method. Radiological examinations of the colon by the use of the contrasting agent were performed in all patients in each group. In the group of patients with artificial myoplastic anus radiological examinations showed the narrowing of the lumen 4-7 cm in length in all patients. Above the narrowing the widening of the lumen was present. Reflexive flow of the contrasting agent from the colon was not present. In the group of patients with the artificial classical anus the narrowing of the terminal part of the colon was not noticed in the radiological examination. In all patients the reverse flow of the contrasting agent through the artificial anus was observed. Patients with the artificial myoplastic anus created by the use of pedunculated fold of the muscular coat of the colon have much higher average pressures around the myoplastic sphincter than in the presphincteric area, while the patients with the artificial classical anus did not present the area with the increased pressure in the terminal part of the colon. The possibility of preventing uncontrolled defecation and flatulence by the patients with the artificial myoplastic anus is related to the repeatedly higher pressures around the sphincter than in the presphincteric area, which do not decrease as the time passes by after the surgery.

Anal Canal↗
PubMed2000

Artificial selection of microbial ecosystems for 3-chloroaniline biodegradation.

We present a method for selecting entire microbial ecosystems for bioremediation and other practical purposes. A population of ecosystems is established in the laboratory, each ecosystem is measured for a desired property (in our case, degradation of the environmental pollutant 3-chloroaniline), and the best ecosystems are used as 'parents' to inoculate a new generation of 'offspring' ecosystems. Over many generations of variation and selection, the ecosystems become increasingly well adapted to produce the desired property. The procedure is similar to standard artificial selection experiments except that whole ecosystems, rather than single individuals, are the units of selection. The procedure can also be understood in terms of complex system theory as a way of searching a vast combinatorial space (many thousands of microbial species and many thousands of genes within species) for combinations that are especially good at producing the desired property. Ecosystem-level selection can be performed without any specific knowledge of the species that comprise the ecosystems and can select ensembles of species that would be difficult to discover with more reductionistic methods. Once a 'designer ecosystem' has been created by ecosystem-level selection, reductionistic methods can be used to identify the component species and to discover how they interact to produce the desired effect.

Aniline Compounds↗
PubMed2000

Melatonin administration can entrain the free-running circadian system of blind subjects.

Although melatonin treatment has been shown to phase shift human circadian rhythms, it still remains ambiguous as to whether exogenous melatonin can entrain a free-running circadian system. We have studied seven blind male subjects with no light perception who exhibited free-running urinary 6-sulphatoxymelatonin (aMT6s) and cortisol rhythms. In a single-blind design, five subjects received placebo or 5 mg melatonin p.o. daily at 2100 h for a full circadian cycle (35-71 days). The remaining two subjects also received melatonin (35-62 days) but not placebo. Urinary aMT6s and cortisol (n=7) and core body temperature (n=1) were used as phase markers to assess the effects of melatonin on the During melatonin treatment, four of the seven free-running subjects exhibited a shortening of their cortisol circadian period (tau). Three of these had taus which were statistically indistinguishable from entrainment. In contrast, the remaining three subjects continued to free-run during the melatonin treatment at a similar tau as prior to and following treatment. The efficacy of melatonin to entrain the free-running cortisol rhythms appeared to be dependent on the circadian phase at which the melatonin treatment commenced. These results show for the first time that daily melatonin administration can entrain free-running circadian rhythms in some blind subjects assessed using reliable physiological markers of the circadian system.

Adult↗
PubMed2000

[Primary gastric non-Hodgkin lymphoma].

Authors discussed etiology, diagnostic and therapeutical problems in the treatment of primary gastric non-Hodgkin lymphoma. The first one was limited to the gastric region and was cured favourably. The second one extended gastric region and affected all alimentary tract. This case was terminated by death of the patient.

Aged↗
PubMed1999

Sleep and activity rhythms are related to circadian phase in the blind.

STUDY OBJECTIVES: Sleep is controlled by both circadian and homeostatic mechanisms. As the light-dark cycle is the most important time cue in humans, blind individuals may have circadian rhythm disorders including sleep. The aim of the study was to assess sleep with simultaneous measurement of an endogenous marker of the circadian clock, namely 6-sulphatoxymelatonin (aMT6s). SETTING AND PARTICIPANTS: 59 registered blind subjects were studied in their own homes. DESIGN: Subjects completed daily sleep and nap diaries for at least four weeks, wore activity monitors continuously, and collected urine samples over 48 hours each week for 3-5 weeks for assessment of aMT6s rhythms. RESULTS: The most sensitive indicator of a circadian rhythm disorder was day-time napping. Subjects with normally entrained (NE) aMT6s rhythms had fewer naps of a shorter duration than abnormally entrained (AE) or free-running (FR) subjects. The timing of these naps was not random; significantly more naps occurred within a five-hour range before and after the aMT6s acrophase (phi (phi)) than outside this range. Disorders in the timing and duration of night sleep in AE subjects manifested as either a permanent advance (advanced sleep phase syndrome, ASPS) or delay (delayed sleep phase syndrome, DSPS). In FR subjects there were transient advances and delays in sleep timing that paralleled aMT6s timing with increased night sleep duration and reduced number and duration of day-time naps associated with a normal aMT6s phase. CONCLUSIONS: Changes in sleep and activity rhythms reflect changes in circadian phase.

Adult↗