[Reaction between cGMP and cAMP in their effect on muscle carbohydrate metabolism]

cGMP (10(-4)-10(-7) M) did not affect the activity of phosphorylase and glycogen synthetase from chicken sceletal muscles; but the cGMP prevented completely an effect of cAMP on the enzymes. This blocking effect was specific for cGMP (GMP did not exhibit the effect) and for cAMP (influence of calcium on the enzyme was not eliminated by cAMP). Possible mechanisms of the cGMP effects studied are considered: 1) stimulation of cAMP hydrolysis, 2) antagonism at the level of proteinkinase system. cGMP (10(-4)-10(-7) M) did not stimulate the phosphodiesterase activity at millimolar concentration of its substrate--cAMP.