During a 25-day space mission of French cosmonaut on board Mir station, the joint Soviet-French Czecho-Slovak experiment "Minilab" has been conducted in order to evaluate a fluid-electrolyte metabolism status and its hormonal control at different flight stages and early postflight. In cosmonaut venous blood was drawn twice, and 24-hour urine samples were collected on mission Days 5 and 19. With the aid of Plasma-02 equipment the blood plasma and urinary samples were treated, frozen and maintained aboard the station. Postflight, frozen samples were delivered to the laboratory for further analyses. In-flight, urinary excretion of fluid and sodium decreased by 25-35%. On mission Day 9, the blood plasma levels of vasopressin increased by 450% and on Day 20 by 700% as opposed to the baseline levels, blood aldosterone content was also elevated with an increased renal excretion of both hormones. Blood plasma renin activity elevated two-fold, and atrio-natriuretic factor (ANF) content practically did not differ from a baseline value. In-flight circulating plasma volume (CPV) decreased by 20%. Postflight, there occurred the body hypohydration and activation of the hormonal systems providing a retention of body fluids and electrolytes to restore an adequate CPV and fluid-electrolyte homeostatic as a whole.

Water-salt metabolism and its hormonal regulation studied in the 2nd joint Soviet-French space flight