The experimental data on the role of the cyclic nucleotides (cAMP, cGMP) in the mammalian integrating systems and their significance in the processes of adaptation and radiosensitivity change of animals are analysed. The changes in the system of cyclic nucleotides (CN) are reported for a number of morbid conditions at the subunit level. The CN system changes as a body response to the extreme action including ionizing radiation are revealed. A concept on a phase correlation between adrenergic and cholinergic system activity in development of adaptive reaction of a cell and a body on the whole during radiation or the action of some other factors is emphasized. The significance of cAMP/cGMP ratio calculation (coefficient K) is underlined for the analysis and prediction of the morbid state outcome.