Changes in enzymes and potassium content of the neuromuscular systems of albino rats during prolonged exposure to simulated hypogravics.

With respect to neuromuscular function, aldosterone activity, enzymatic and potassium (K) metabolism of organ tissues were investigated during the stress and adaptation stabilized phases of hypodynamically stressed rats. During adaptation, muscle tissue enzymes, such as aldolase, showed no change until the 35th day. The decrease of succinic dehydrogenase (SDH) was evident at 7 days. Lactic dehydrogenase (LDH) and creatine phosphokinase (CPK) serum levels increased transiently on the 18th day; this implied the development of muscular atrophy. A decrease in the 42K uptake of muscle was found from the 18th day onward. In the brain, a progressive decrease of aldolase was observed. 42K uptake showed no change in the brain, but the K content increased at both 7 and 18 days of exposure. The increase of cholinesterase (ChE) was more remarkable in the brain than in muscle, although transient. We suggest that the brain plays an important part in the adaptation process, through increasing or maintaining the functions of the neuromuscular excitation system during the 7-18 days of hypodynamic exposure.