Glycogen cycle enzymes and cyclic nucleotides in avian muscular dystrophy

Fast-frozen pectoralis muscle samples were taken from normal chickens (lines 200 and 412) and chickens having hereditary muscular dystrophy (line 304). The glycogen phosphorylase activity ratio (activity without AMP/activity with AMP) was significantly greater in dystrophic muscles (0.306 +/- 0.046) than it was in normal muscles (0.090 +/- 0.023). Glucagon treatment did not cause any changes in phosphorylase activity ratios. Isoproterenol treatment of both normal and dystrophic muscles raised the phosphorylase activity ratio of normal muscles to 0.446 +/- 0.054, which was not significantly different from that of the dystrophic muscles. The dystrophic muscles had significantly less glycogen than normal muscles (23.3 +/- 2.8 compared with 36.8 +/- 2.8 mumoles glucosyl units/g of muscle). There was no relationship of muscular dystrophy to total phosphorylase activity (measured in the presence of 1 mM AMP) and to glycogen synthase activities measured without and with glucose 6-phosphate. Normal muscles had 28% less cAMP and 49% less cGMP than dystrophic muscles, but these differences were eliminated by treatment of the chickens with glucagon.