Stress-induced changes in the cyclic nucleotide concentrations and phosphorylase activity in the myocardium

Restraint stress was produced by immobilizing rats in supine position for 6, 12 and 24h. Control rats were deprived of food and water for the same time intervals. Concentrations of cyclic AMP and cyclic GMP and activity of glycogen phosphorylase were studied in the ventricle myocardium of the animals. The cAMP concentrations in the myocardium of immobilized rats were significantly lower after 6 and 12h, but were higher after 24 h compared with control values. The cyclic GMP concentrations showed the same tendency though the differences were not significant. The concentrations of cAMP and cGMP in both restrained and control rats increased in the 12-hour experiment but decreased in the 24-hour experiment as compared to the 6 h values. Phosphorylase "a" and total phosphorylase activities were higher after 12-hour immobilization, but were lower after 24-hour restraint compared with control group. In the 6-hour experiment there were no differences between restrained and control rat. The percentage of phosphorylase "a" of the total activity was equal in immobilized and control animals. time related changes were also observed in the phosphorylase activity. The present results suggest that cyclic nucleotides and glycogen phosphorylase may improve myocardial metabolism by diminution of energy consumption and activation of glycogenolysis under trees conditions.