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 orbita l MIR station, it organized simultaneously a ground simulation, called the Human Behaviour Study, of this manned space mission. The ground s imulation was a confinement experiment, and this paper describes the c hanges in volume-regulating hormones that occurred during and after 20 weeks of confinement. Methods: In a normobaric diving chamber, 3 subj ects were confined for 135 d. Arterial pressure, plasma concentrations of blood volume-regulating hormones (active renin and arginine-vasopr essin), 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 unt il week 15 of confinement, while heart rate was elevated from week 6 u ntil the end of the simulation. Plasma active renin was elevated throu ghout the confinement (after week 6). Urine volume increased transitiv ely on the first 2 d of confinement. Conclusions: The results obtained during this long-term confinement experiment have major importance re garding concerns about spaceflight and bed rest data, because we obser ved hormonal changes during the experiment that normally are assigned to the fluid shift that occurs in weightlessness or in the head-down t ilt position (i.e., an increase of renin, an increase of urinary volum e during the first two days, and a decreased urinary cyclic guanosine monophosphate; Maillet A, et al. Acta Astronaut 1995; 35:547-52).