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1 Department of Surgery, University of Medicine and Dentistry of New Jersey, School of Osteopathic Medicine, Stratford, New Jersey 08084; and 2 Department of Surgery, University of Florida College of Medicine, Gainesville, Florida 32610
Human spaceflight is associated with a chronic
loss of protein from muscle. The objective of this study was to
determine whether changes in urinary hormone excretion could identify a
hormonal role for this loss. Urine samples were collected from the
crews of two Life Sciences Space Shuttle missions before and during spaceflight. Data are means ± SE with the number of subjects in parentheses. The first value is the mean preflight measurement, and the
second value is the mean inflight measurement. Adrenocorticotropic hormone (ACTH) [27.7 ± 4.4 (9) vs. 25.1 ± 3.4 (9)
ng/day], growth hormone [724 ± 251 (9) vs. 710 ± 206 (9) ng/day], insulin-like growth factor I [6.81 ± 0.62 vs. 6.04 ± 0.51 (8) nM/day], and C-peptide [44.9 ± 8.3 (9) vs. 50.7 ± 10.3 (9) µg/day] were unchanged with spaceflight. In contrast, free
3,5,3'-triiodothyronine [791 ± 159 (9) vs.
371 ± 41 (9) pg/day,
P < 0.05], prostaglandin
E2 (PGE2) [1,064 ± 391 (8) vs. 465 ± 146 (8) ng/day,
P < 0.05], and its metabolite
PGE-M [1,015 ± 98 (9) vs. 678 ± 105 (9) ng/day, P < 0.05] were decreased
inflight. The urinary excretion of most hormones returned
to their preflight levels during the postflight period, with the
exception of ACTH [47.5 ± 10.3 (9) ng/day],
PGE2 [1,433 ± 327 (8)
ng/day], PGF2
,
[2,786 ± 313 (8) ng/day], and its metabolite PGF-M
[4,814 ± 402 (9) ng/day], which were all increased
compared with the preflight measurement
(P < 0.05). There was a trend for
urinary cortisol to be elevated inflight [55.3 ± 5.9 (9) vs.
72.5 ± 11.1 µg/day, P = 0.27] and postflight [82.7 ± 8.6 (8) µg/day,
P = 0.13]. The inflight human
data support ground-based in vitro work showing that prostaglandins
have a major role in modulating the changes in muscle protein content in response to tension or the lack thereof.
cortisol; shuttle; urinary hormone excretion
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