Hormonal changes during a 20-week confinement

BACKGROUND: When the European Space Agency planned the EUROMIR'95 long-duration flight with a European astronaut on board the Russian orbital MIR station, it organized simultaneously a ground simulation, called the Human Behaviour Study, of this manned space mission. The ground simulation was a confinement experiment, and this paper describes the changes in volume-regulating hormones that occurred during and after 20 weeks of confinement. METHODS: In a normobaric diving chamber, 3 subjects were confined for 135 d. Arterial pressure, plasma concentrations of blood volume-regulating hormones (active renin and arginine-vasopressin), and urinary variables (aldosterone, arginine-vasopressin, and metabolites of catecholamines) were measured before, during, and after confinement. RESULTS: Arterial pressure was increased from week 1 until week 15 of confinement, while heart rate was elevated from week 6 until the end of the simulation. Plasma active renin was elevated throughout the confinement (after week 6). Urine volume increased transitively on the first 2 d of confinement. CONCLUSIONS: The results obtained during this long-term confinement experiment have major importance regarding concerns about spaceflight and bed rest data, because we observed hormonal changes during the experiment that normally are assigned to the fluid shift that occurs in weightlessness or in the head-down tilt position (i.e., an increase of renin, an increase of urinary volume during the first two days, and a decreased urinary cyclic guanosine monophosphate.