MEDICAL BASE-LINE DATA-COLLECTION ON BONE AND MUSCLE CHANGE WITH SPACE-FLIGHT

It has been documented that astronauts suffer from a progressive and c ontinuous negative calcium balance in space flight. The National Space Development Agency of Japan (NASDA) discussed the experimental protoc ols with the National Aeronautics and Space Agency's (NASA's) Johnson Space Center (JSC) and has started a medical baseline collection on bo ne and calcium metabolism, and muscle changes with space flight. The s ubjects were two astronauts, a 42-year-old female and a 32-year-old ma le, who experienced real space flights. Fractional excretion of calciu m (FECa) increased in both subjects just after the space flight. There was a negative calcium balance with urinary calcium leak even after a short flight. We also noticed a decrease (-3.0%) of bone mineral dens ity (BMD) of the lumbar spine (L2-4), a weight bearing bone. These bon e changes may be due to a negative calcium balance. However, the BMD o f the skull, a nonweight bearing bone, increased after the flight. Thi s indicates that the effect of weightlessness on bone is different in respective bones, depending on the weight loading, Our data of the bon e metabolic marker clearly indicate that bone resorption is stimulated , shown by an elevation of urinary pyridinolinks and plasma tartrate-r esistant acid phosphate (TRACP) activity. Bone specific alkaline phosp hatase, a bone formation marker, was elevated in both subjects, but no t intact osteocalcin, Whether this pathophysiological phenomenon is du e to an accelerated bone resorption or suppressed bone formation is st ill obscure. In addition, the physiological cross-sectional area (PCSA ) of muscle in the legs greatly decreased (from -10% to -15%) after th e flight, and it took over a month to be recovered in both subjects. H owever, the muscle volume loss in the legs seemed to be reversible. To examine bone and muscle metabolism with space flight, further investi gations and international standardization of experimental protocols ar e necessary. (C) 1998 by Elsevier Science Inc. All rights reserved.