[The stimulating effect of cyclic AMP, glucagon and insulin on guanidine acetate-N-methyltransferase activity in rat liver and pancreas].

N6,O2'-dibutyrylcyclo-3',5'-AMP injected to intact rats alone or in combination with theophylline increases the activity of guanidine acetate methyltransferase (GAMT) in liver and pancreas. Cyclic 3',5'-AMP and its dibutyryl analog administered immediately or two hours after the suturing of common bile duct (SCBD) stimulate the increase of pancreatic GAMT activity 2-3 fold. Glucagon, injected intraabdominally simultaneously with SCBD and administration of theophylline, dramatically increases the theophylline effect on the GAMT activity. The freezing of rat pancreas pretreated witn secretin, a hormone structurally similar to glucagon, results in a 1.5-2-fold increase of creatine synthesis from S-adenosylmethionine and guanidinacetic acid. An hour after glucagon administration to intact rats the GAMT activity of liver increases 9 times. The effect of glucagon is enhanced by insulin. Cycloheximide inhibits the increase of GAMT activity, induced by glucagon or a combination of glucagon and insulin. Experiments on tissue homogenates demonstrate that 3',5'-AMP in concentrations of 10(-8) --10(-2) M does not affect the GAMT activity or to some extent inhibits the enzyme. The homogenate incubation in a medium containing 10(-5) M epinephrine or 10(-7) M caffeine and 5 mM Mg2+ leads to an increase in the GAMT activity. Oligomycin removes the stimulating effects of caffeine and Mg2+ on the enzyme activation. This is probably due to the presence of 3',5'-AMP-dependent protein kinase in the mechanism of GAMT activation by cyclic AMP.