In rabbit muscles, glycolytic enzymes become poorer and respiratory enzymes become richer in the following order: back muscle, gastrocnemius, soleus, diaphragma, and heart1-3). This aspect seems to be stationary even with changes in nutritional environment.
The present studies are undertaken in an attempt to elucidate the behavior of key enzymes in carbohydrate metabolism for differentiation of these enzyme patterns and also of contraction-relaxation of muscles.
One group of rabbits were anesthetized by intravenous injection of a relaxant-3-
o-toloxy-1, 2-propanediol and then bled thoroughly. The other group of the animals were killed by decapitation. The five kinds of muscles stated above in both groups of rabbits were removed, and immediately frozen by liquid nitrogen, and then activities of phosphorylase with or without AMP and of glycogen synthetase with or without G6P were measured. The results were that the total activities of phosphorylase and the amount of active form of glycogen synthetase in both groups of animals were poorer in the above mentioned order of five muscles, and the ratio of active form to the total of both enzymes also decreased in the same order by the relaxant.
Activities of glycogen synthetase in liver and those in muscle of rat were compared under various nutritional environments. Liver enzyme decreased on starvation and increased on feeding protein free diet. But even under the same conditions, the muscle enzymes hardly showed any change. By denervation, the changes in enzyme activities in muscle could be observed and seemed to respond what were the diet. In rat whose ischiadic nerve of one side was partly excised, aldolase in gastrocnemius of the side of excision decreased and that of the opposite side was not modified. Phosphorylase of the side of excision decreased and that of the opposite side increased. Phosphofructokinase of the excision side was hardly modified and that of the opposite side decreased.
These facts may indicate that innervation would protect the changes in muscle enzyme activities, and that an especially close interrelationship would exist between nerve ending and key enzyme in view of the interesting changes in key enzymes upon injection of a relaxant and after denervation.
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