Plasma amino acids during human spaceflight

Background: The plasma amino acid distribution patterns were measured before, during and after flight on the Space Shuttle. The plasma samples were collected from the four payload crewmembers of the 1993 SLS-2 Columbia Shuttle mission. Samples were taken 45, 15 and 8 d before flight; inflight on days 2, 8 and 12 after launch; post-flight on the day of landing; and again 6, 14 and 45 d after landing. Results: Most of the changes found pertained to the essential amino acids, particularly the branched chain amino acids (BCAA). The principle findings were: a) The plasma aminograms for inflight days 8 and 12 were very similar and both aminograms were very different from that of flight day 2. Flight day 2 was not different from the preflight ground control. b) With increasing time in space, there was an increase in the concentration of leucine and isoleucine in the plasma (p < 0.05). This increase occurred even though dietary BCAA intake was not increased inflight. c) The concentrations of the total essential amino acids and the branched chain amino acids (BCAA) in particular were decreased on the day of landing (p < 0.05).