BLOOD-VOLUME REGULATING HORMONES RESPONSE DURING 2 SPACE RELATED SIMULATION PROTOCOLS - 4-WEEK CONFINEMENT AND HEAD-DOWN BED-REST

The volume of regulating hormones (renin, aldosterone, arginine vasopr essin and atrial natriuretic factor), electrolytes and creatinine conc entrations, and blood pressure were measured in two different four-wee k experimental protocols: respectively -6 degrees head-down bed-rest ( 5 subjects) and confinement (6 subjects). We observed a significant in crease (P < 0.01 at D2 vs D-5) of systolic blood pressure during confi nement and a different level of response for some hormones, especially for arginine vasopressin (300% increase during confinement instead of 50% during bed-rest). The renin-angiotensin-aldosterone system was en hanced during confinement and head-down bed-rest. In both conditions, we obtained a similar pattern of response for blood volume regulating hormones. During confinement, two main factors were inactivity and str ess activation of the sympathetic nervous system. In the bed-rest stud y the response is principally due to the fluid shift and blood volume adaptation but it is not possible to exclude the role of inactivity an d stress.