Summary
The purpose of this study was to investigate the main renal and hormonal responses to head-down bed rest, which is curently 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‡) 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% \(V_{O_{2{\text{max}}} } \)) 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.
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Annat, G., Güell, A., Gauquelin, G. et al. Plasma vasopressin, neurophysin, renin and aldosterone during a 4-day head-down bed rest with and without exercise. Europ. J. Appl. Physiol. 55, 59–63 (1986). https://doi.org/10.1007/BF00422894
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DOI: https://doi.org/10.1007/BF00422894