5 Vivarium, 5 Synchronous

Cosmos 936 Russian Hardware Suite

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.

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.

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.

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