title: Influence of head-down bed rest on the circadian rhythms of hormones and electrolytes involved in hydroelectrolytic regulation.
abstract: We investigated in six men the impact of a 17-day head-down bed rest (HDBR) on the circadian rhythms of the hormones and electrolytes involved in hydroelectrolytic regulation. This HDBR study was designed to mimic an actual spaceflight. Urine samples were collected at each voiding before, during and after HDBR. Urinary excretion of aldosterone, arginine vasopressin (AVP), cyclic guanosine monophosphate (cGMP), cortisol, electrolytes (Na+ and K+) and creatinine were determined. HDBR resulted in a significant reduction of body mass (P < 0.01) and of caloric intake [mean (SEM) 2,778 (37) kcal.24 h(-1) to 2,450 (36) kcal.24 h(-1), where 1 kcal.h(-1) = 1.163 J.s(-1); P< 0.01]. There was a significant increase in diastolic blood pressure [71.8 (0.7) mmHg vs 75.6 (0.91) mmHg], with no significant changes in either systolic blood pressure or heart rate. The nocturnal hormonal decrease of aldosterone was clearly evident only before and after HDBR, but the day/night difference did not appear during HDBR. The rhythm of K+ excretion was unchanged during HDBR, whereas for Na+ excretion, a large decrease was shown during the night as compared to the day. The circadian rhythm of cortisol persisted. These data suggest that exposure to a 17-day HDBR could induce an exaggeration of the amplitude of the Na+ rhythm and abolition of the aldosterone rhythm.
authors.affiliation: Laboratoire de Physiologie de l'Environnement (GIP Exercise and EA 645), Faculté de Médecine, Lyon Grange-Blanche, France.
authors.forename: C
authors.initials: C
authors.lastname: Millet
authors.forename: M A
authors.initials: MA
authors.lastname: Custaud
authors.forename: A M
authors.initials: AM
authors.lastname: Allevard
authors.forename: M
authors.initials: M
authors.lastname: Zaouali-Ajina
authors.forename: T H
authors.initials: TH
authors.lastname: Monk
authors.forename: S B
authors.initials: SB
authors.lastname: Arnaud
authors.forename: B
authors.initials: B
authors.lastname: Claustrat
authors.forename: C
authors.initials: C
authors.lastname: Gharib
authors.forename: G
authors.initials: G
authors.lastname: Gauquelin-Koch
mesh_terms: D000328:Adult; D000450:Aldosterone / Q000652:urine*; D001127:Arginine Vasopressin / Q000652:urine; D001794:Blood Pressure / Q000502:physiology; D015992:Body Mass Index; D002940:Circadian Rhythm / Q000502:physiology*; D003404:Creatinine / Q000652:urine; D006152:Cyclic GMP / Q000652:urine; D004231:Diuresis / Q000502:physiology; D002149:Energy Intake / Q000502:physiology; D018475:Head-Down Tilt; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D006854:Hydrocortisone / Q000652:urine; D008297:Male; D008875:Middle Aged; D011187:Posture / Q000502:physiology; D011188:Potassium / Q000652:urine*; D012964:Sodium / Q000652:urine*; D013312:Stress, Physiological / Q000503:physiopathology; D014882:Water-Electrolyte Balance / Q000502:physiology*
chemical_list: D001127:Arginine Vasopressin; D000450:Aldosterone; D012964:Sodium; D003404:Creatinine; D006152:Cyclic GMP; D011188:Potassium; D006854:Hydrocortisone