Revised hypothesis and future perspectives

Results from space have been unexpected and not predictable from the result s of ground-based simulations. Therefore, the concept of how weightlessness and gravity modulates the regulation of body fluids must be revised and a new simulation model developed. The main questions to ask in the future are the following: Does weightlessness induce a diuresis and natriuresis durin g the initial hours of space flight leading to an extracellular and intrava scular fluid volume deficit? Can sodium in excess be stored in a hitherto u nknown way, particularly during space flight? Why are fluid and sodium reta ining systems activated by spaceflight? Why are the renal responses to sali ne and water stimuli in space attenuated compared with those of ground simu lations? How can the effects of weightlessness on fluid and electrolyte reg ulation be correctly simulated on the ground? The information obtained from space may be of relevance to fluid and electrolyte balance in edematous pa tients. (C) 2001 by the National Kidney Foundation, Inc.