Epinephrine effect on glycogen phosphorylase activity in catfish liver and muscles

In catfish, the percentage of the active (a) form of glycogen phosphorylase with respect to the total (a + b) form varied in control slices from about 90% to 65% and 20%, respectively for liver, red, and white muscles. Epinephrine added to the incubation medium of liver and white muscle slices caused a significant increase in the specific activity of phosphorylase a in liver and white muscle, but not in red muscle. In liver slices epinephrine showed its effect from the concentration of 3.5 X 10(-8) M. The increase of enzyme activity explains the lowering of the glycogen level in liver and white muscle induced by epinephrine.