The content of cyclic nucleotides (3',5'-cGMP and 3',5'-cAMP) in cat skeletal muscle during sympathetic cholinergic vasodilatation.

Phosphorylase activity and content of cyclic GMP and AMP were investigated in the gastrocnemius muscle of the cat during the development of cholinergic vasodilatation evoked by stimulation of the hypothalamus. Samples of muscle tissue were taken during an early stage of the vascular effect. One of the hindlimbs was denervated and served as control. With the development of the dilator response the conductance in the bed of the femoral artery increased by 143 +/- 12%, phosphorylase "a" activity reached 76.1 +/- 2.1% of the total phosphorylase activity as compared with 49.2 +/- 1.9% in the control, the content of cGMP increased approximately 2-fold. The content of cAMP remained unchanged. All these effects - the increase in blood flow, phosphorylase activation and the increase in cGMP content - were abolished by atropine. It is suggested that acetylcholine, released by sympathetic endings during hypothalamic stimulation, has the effect of increasing the level of intracellular cGMP and that the vasodilatation is secondary to the metabolic changes.