5 Vivarium, 5 Synchronous
Key Flight Hardware
Cosmos 936 Russian Hardware Suite
Objectives/Hypothesis
Whether a muscle fiber employs an oxidative or glycolytic energy mechanism is
not immutably fixed, but can be influenced by external factors. Since space
flight drastically alters the stimulus patterns to which skeletal muscle is
exposed, it is relevant to investigate the changes which take place, not only
in the muscle fiber size, but also in the energy mechanism. Rather than sampling
each muscle only at a few positions along its length, this experiment seeks
a quantitative total ascer- tainment of fiber size, number, and type.
Approach or Method
Muscle fiber size and type distribution were studied in the extensor digitorum
longus (EDL) muscle of space-flown rats and controls, using histochemical prepar-
ation techniques and computer image analysis to quantify the space-flight-induced
changes in muscle fiber size, number, and energy metabolism. The computer program
produces a scatter plot showing how the fibers are distributed in diameter and
optical density.
Results
Average fiber diameter was largest in the vivarium control animals and smallest
in the flight animals. Flight muscles appeared to be shorter than those of other
groups. If this length difference is not an artifact of dissection, it could
be the result of chronic extension of the foot and/or toes during space flight.
Fiber num- ber showed no significant difference. The "slow" fiber percentage
was quite vari- able, and no statistically significant fiber type conversion
was noted. There were no major cytoarchitectural changes, and necrotic changes
and "moth eaten" fibers were not seen. The grouped grand mean fiber diameters
show 17% and 7% reduc- tions for the flight and synchronous groups, respectively,
when compared to the vivarium group, strongly supporting the contention that
hypogravity aggravates the atrophic effects of hypokinesis. While reduced activity
may be the major cause of fiber atrophy in space flight, other factors may contribute.
For example, the stress of negotiating the microgravity environment could produce
an ACTH-corti- sol response, a possible contributor to reduced fiber size.
Publications
Experiment Reference Number: C936-3
Castleman, K.R. and L.A. Chui: Spaceflight Effects on Muscle Fibers. Final
Reports of U.S. Experiments Flown on the Soviet Satellite Cosmos 936. S.N. Rosenzweig
and K.A. Souza, eds., NASA TM-78526, 1978, pp. 274-289.
Castleman, K.R. et al.: Quantitative Muscle Biopsy Analysis. Proceedings of
the SPIE, vol. 89, 1976, p. 119.¥
Van Der Meulen, J.P. et al.: Computer Assisted Quantitative Analysis of Muscle
Biopsy: Preliminary Observations. Neurology, vol. 274, 1977, p. 355.¥
¥ = publication of related ground-based study