Biomedical subjects

M Follénius

Publications and source records attributed to M Follénius.

4 recordsLinked to original sources

PubMed1999

[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. Several studies have identified these rhythms in night-shift workers but results have been contradictory. PARTIAL ADAPTATION: Recently we made repeated measurements every 10 min over a 24 hour period in night-shift workers to determine the precise melatonin, cortisol, and thyrotropin (TSH) patterns, which reflect the endogenous clock, and prolactin (PRL) and growth hormone (GH) patterns which are influenced by sleep but also have a circadian component. This study demonstrated that there is some, but partial, adaptation of the biological rhythms in these persons. The shift in the melatonin pattern is quite variable from one individual to another. Night work causes a distortion in the cortisol and TSH rhythms. This partial adaptation is also seen in the GH and PRL curves, mainly related to sleep, but whose endogenous component previously described in other experimental situations is found in night workers with a distribution incompletely adapted to the secretory episodes. RESEARCH PERSPECTIVES: Both daytime sleep and night-time work are associated with perturbed endocrine functions which could explain certain health problems and sleep disorders observed (or avowed) after several years of night-shift work. These problems require further research into factors susceptible of resynchronizing the biological clock.

Adaptation, Physiological↗

PubMed1995

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. Eight male volunteers participated in a 1 night study. They were subjected to 8 h polysomnography including spectral analysis of the EEG, and to blood sampling every 10 min. Delta relative power and Sleep Intensity Index and PRA oscillations ran parallel in all individuals. An increase in slow waves was associated with an increase in PRA, whereas a decrease was associated with a decrease in PRA. Cross-correlation coefficients were significant and ranged between 0.34 and 0.74. Conversely, theta, alpha and beta bands and the EEG mean frequency were inversely proportional to PRA, with lower cross-correlation coefficients. These results may give further support to the hypothesis of a common mechanism controlling both SWA and renin release from the kidney.

Adult↗

PubMed1984

Interactions between spontaneous and provoked cortisol secretory episodes in man.

This study describes the interactions between cortisol peaks due to spontaneous episodic release and peaks provoked by external stimuli. Successive and equidistant transitory rises of similar amplitude and duration were produced either by muscular exercise (30 min, 75% VO2max) or by injecting ACTH1-24 (Synacthen: 250 ng) before and after the midday meal-related peak. ACTH1-24 was also injected during sleep before the nocturnal sequence of the major secretory episodes. In all instances, cortisol levels had reverted to basal levels when the second stimulus was applied. ACTH-induced cortisol peaks depressed the subsequent meal-related peaks, the exercise-induced peaks, and the spontaneous secretory episodes at the end of the night, and thus had a strong depressor capacity. When exercise was the prior stimulus, the subsequent meal-related peaks were depressed, but the response to later exercise was not affected. Meal-related peaks and the spontaneous diurnal or nocturnal peaks did not depress the subsequent secretory episodes. These quantitatively comparable cortisol episodes were preceded by ACTH rises whose amplitude and duration were not identical: spontaneous and meal-related ACTH peaks were smaller than the provoked one; exercise-induced ACTH peaks were of longer duration than those after ACTH1-24 injection. The different depressor capacities of similar sized cortisol episodes and the lack of proportionality between spontaneous and provoked ACTH and cortisol peaks suggest that there are separate adrenocortical activation channels, which depend on the origin of the stimulation.

Adrenocorticotropic Hormone↗

PubMed1977

Failure of noise exposure to modify temporal patterns of plasma cortisol in man.

The purpose of this investigation was to assess the modification in the temporal pattern of plasma cortisol levels during exposure to noises of different intensities, frequencies and durations. Plasma cortisol concentrations were measured from 08.00 h to 15.00 h at 10 min intervals in eight subjects on a control day and one or two exposure days. Noise exposures induced no significant increase in plasma cortisol concentration. It is concluded that noise, at "safe" levels for human hearing conservation, when not associated with other potentially noxious stimuli does not cause hyperactivity of the pituitary-adrenocortical system. These results do not tally with those from animal studies where noise is known to activate corticotrophin (ACTH) secretion.

Adult↗