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Hormonal changes during 17 days of head-down bed-rest
Marc-Antoine Custaud1, Sara B Arnaud, Timothy H Monk
1Laboratoire de Physiologie de l'Environnement (GIP exercice), Faculté de Médecine Lyon Grange-Blanche, 8 Avenue Rockefeller, F-69373 Lyon Cedex 08, France. mcustaud@club-internet.fr
Life Sciences
|December 24, 2002
Summary
Head-down bed rest, mimicking space flight, altered daily hormone rhythms in men. Nighttime cortisol and normetadrenaline excretion decreased, while melatonin rhythms remained stable.
Area of Science:
- Endocrinology
- Chronobiology
- Space Physiology
Background:
- Hydroelectrolytic balance is crucial for human health.
- Space flight disrupts physiological rhythms and fluid regulation.
- Head-down bed rest (HDBR) is a model for microgravity effects.
Purpose of the Study:
- To investigate the impact of HDBR on daily hormone rhythms.
- To assess changes in hormones regulating hydroelectrolytic balance during simulated space flight.
Main Methods:
- Six men underwent 17 days of HDBR.
- Urine samples collected before, during, and after HDBR.
- Urinary excretion of Growth Hormone (GH), Cortisol, 6 Sulfatoxymelatonin (aMT6s), Normetadrenaline (NMN), and Metadrenaline (NM) measured.
Main Results:
- Decreased nocturnal urinary cortisol excretion during HDBR.
- Stable daily rhythm of Growth Hormone (GH) before and during HDBR.
- Persistent melatonin rhythm (measured via aMT6s) without phase shift.
- Reduced nocturnal normetadrenaline (NMN) excretion during HDBR.
Conclusions:
- HDBR significantly alters daily rhythms of cortisol and normetadrenaline.
- Melatonin and GH rhythms show resilience during simulated microgravity.
- These findings inform countermeasures for space travel's physiological effects.