Focal degenerative changes of skeletal muscle fibers (decrease in mean diameter, excessive axonal branching and a decrease in the mean diameter of motor end-plates together with a reduction of their acetylcholinesterase levels) were found by means of the experimental model thyrotoxic myopathy in mice compared to controls. A decrease in protein kinase affinity to cAMP and an increase in the number of nucleotide binding sites were revealed with a simultaneous decrease in cAMP level. The weakening of hormonal control of cAMP-dependent processes is probably the basic cause of muscular weakness and structural changes in skeletal muscles in thyrotoxic myopathy.
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