The cGMP system in irradiated animals. Changes in cGMP content and activities of guanylate cyclase and cyclic nucleotide phosphodiesterase.

Changes in the functioning of the cGMP system of the thymocytes and liver of mice subjected to 8 Gy roentgen irradiation were found. Within one hour after irradiation an increase in the cGMP level in thymocytes was noted; two rises in the cGMP concentration in the liver were established, at 0.5 and 24 hours after irradiation. These changes in the cGMP level were correlated to an increase in the guanylate cyclase activities in the thymocytes and liver of the mice subjected to irradiation, and to a lesser extent to changes in the activities of cGMP phosphodiesterase in these tissues. A post-irradiation increase in the rat liver guanylate cyclase activity was also observed. A decrease in cGMP phosphodiesterase activity in the liver of the irradiated mice was followed by a change in the enzymatic kinetics and an increase in cGMP phosphodiesterase thermolability. The post-irradiation rise in guanylate cyclase activity was produced by activation of the enzyme.