TY - JOUR T1 - Regulation of cyclic nucleotide levels and glycogen phosphorylase activity by acetylcholine and epinephrine in perfused rat hearts. JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 412 LP - 419 VL - 198 IS - 2 AU - R M Gardner AU - D O Allen Y1 - 1976/08/01 UR - http://jpet.aspetjournals.org/content/198/2/412.abstract N2 - Acetylcholine (ACh) produced a time and dose-dependent increase in cyclic 3',5'-guanosine monophosphate (cyclic GMP) levels in perfused rat hearts without any significant (P greater than .05) change in cyclic 3',5'-adensoine monophosphate (cyclic AMP) level or glycogen phosphorylase activity. Epinephrine produced a dose-dependent increase in both cyclin AMP and phosphorylase activity but no significant (P greater than .05) change in cyclic GMP levels. When ACh (10(-6) M) was infused into hearts during the infusion of epinephrine (10(-6) M), a time-dependent increase in cyclic GMP and decrease in cyclic AMP occurred, both of which preceded a significant (P less than .05) decrease in glycogen phosphorylase activity. In epinephrine-stimulated hearts, ACh produced a dose-dependent increase in cyclic GMP levels. Similar concentrations produced a fall in cyclic AMP levels and phosphorylase activity. No condition tested resulted in a significant (P greater than .05) change in glycogen synthase activity. It is concluded that ACh can reduce cyclic AMP levels and phosphorylase activity only when they have been elevated above basal values. These changes are associated with an increase in cyclic GMP. The reduction in phosphorylase produced by ACh may be the result of either or both of the changes in cyclic nucleotide levels. ER -