title: Plasma vasopressin, neurophysin, renin and aldosterone during a 4-day head-down bed rest with and without exercise.
abstract: The purpose of this study was to investigate the main renal and hormonal responses to head-down bed rest, which is currently considered a reliable experimental model for the simulation of weightlessness. Urinary output and electrolytes, plasma renin activity (PRA), aldosterone (PA), antidiuretic hormone (ADH) and immunoreactive neurophysin-I (Np) were measured in eight adult volunteers submitted to a 4-day head-down bed rest (-6 degrees) after a 24-h control period in the horizontal position (day 0). Four of the eight subjects were submitted to two 1-h periods of controlled muscular exercise (50% VO2max) from day 1 to day 4. Throughout the head-down bed rest period, urinary output remained stable, although lower than in the control period (day 0), but the urinary Na/K ratio decreased. Plasma electrolytes and osmolality, and creatinine clearance remained unchanged. There was no significant difference between exercising and non-exercising subjects. At the hormonal level, PRA and PA increased during the head-down bed rest. This increase was more pronounced in the group with exercise. At the end of the tilt period, PRA and PA were about 3 times higher than on day 1. No significant changes could be observed for ADH and Np. It is concluded that a 4-day head-down bed rest results in no apparent changes in neurohypophyseal secretory activity, and in a progressive secondary hyperaldosteronism.
mesh_terms: D000328:Adult; D000450:Aldosterone / Q000097:blood; D001510:Bed Rest / Q000379:methods*; D002320:Cardiovascular Physiological Phenomena; D006728:Hormones / Q000097:blood*; D006801:Humans; D008297:Male; D009481:Neurophysins / Q000097:blood; D005082:Physical Exertion; D011187:Posture; D011188:Potassium / Q000652:urine; D012083:Renin / Q000097:blood; D012964:Sodium / Q000652:urine; D013997:Time Factors; D014667:Vasopressins / Q000097:blood; D014893:Weightlessness
chemical_list: D006728:Hormones; D009481:Neurophysins; D014667:Vasopressins; D000450:Aldosterone; D012964:Sodium; D012083:Renin; D011188:Potassium