Human skeletal muscle protein breakdown during spaceflight.
Stein, T. P., and M. D. Schluter.
Department of Surgery, University of Medicine and Dentistry of New
Jersey, School of Osteopathic Medicine, Stratford, NJ, 08084 and the
Human Research Facility of the National Aeronautics and Space
Administration - Ames Research Center, Moffett Field, CA 94035
APStracts 3:0252E, 1996.
Human space flight is associated with a loss of body protein.
Excretion of 3-methylhistidine (3-MeH) in the urine is a useful
measurement of myofibrillar protein breakdown. Bed rest, particularly
with 6o head down tilt, is an accepted ground based model for human
spaceflight. The objectives of this report were to compare 3-MeH
excretion from two Life Sciences Shuttle missions (duration 9.5 and
15 d, n=9) against 17 days of bed rest (n=7) with 6o head down tilt.
The bed rest study was designed to mimic an actual Life Sciences
spaceflight and so incorporated an extensive battery of physiological
tests focused on the musculo-skeletal system. Results: Data are mean
+ SEM with the number of subjects in (). Nitrogen retention based on
excretion of nitrogen in the urine was reduced during both bed rest
from 22 + 1 (7) to 1 + 5 (7) mg N. kg-1.d-1, (p<0.05) for bed
rest and spaceflight (from 57 + 9 (9) to 19 + 3 (9) mg N. kg-1.d-1,
(p<0.05). 3-MeH excretion was unchanged with either bed rest,
(pre bed rest 5.30 + 0.29 (7) vs bed rest 5.71 + 0.30 (7) [mu]mol 3
-MeH. kg-1.d-1, p=ns) or spaceflight, (preflight 4.98 + 0.37 (9) vs
4.59 + 0.39 (9) [mu]mol 3-MeH. kg-1.d-1 inflight p=ns). Conclusions:
(i) 3-MeH excretion was unaffected by spaceflight on the Shuttle or
bed rest plus exercise. (ii) Since protein breakdown (elevated 3-MeH)
was increased on Skylab but not on Shuttle, it follows that muscle
protein breakdown is not an inevitable consequence of space flight.
Received 30 July 1996; accepted in final form 5 December 1996.
APS Manuscript Number E369-6.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996