[Alterations in the cyclase system of skeletal muscles and in the content of cyclic nucleotides in blood plasma of rats after the administration of caffeine].

Concentration of cyclic nucleotide monophosphates was increased both in rat skeletal muscles and in blood plasma after enteral administration of caffeine. A decrease in content of cAMP and cGMP down to the initial level coincided with the activation of phosphodiesterase in skeletal muscles. A direct correlation was found between the alteration in cyclic nucleotides content in skeletal muscles and in blood plasma. Muscle tissue might serve as one of the main sources of cyclic nucleotides in blood plasma. The rate of alterations in concentration of blood plasma cyclic nucleotides was not apparently limited by their penetration across the cell membranes.