Dynamics of the changes in the tissular levels of cyclic AMP after cobalt-60 gamma-irradiation.

The total amounts of cyclic AMP in liver, brain and intestinal mucosa have been measured in rats, at constant intervals, up to 18 days after whole body exposure to either a unique moderate dose (500 rd) or a unique lethal dose (750 rd) of cobalt-60 gamma-radiation. This radiation, even in a lethal dose, was found to induce no significant changes in the hepatic levels of cAMP. In contrast, an abrupt short-lasting increase in the levels of cAMP was observed in brain and intestinal mucosa after a 500-rd-irradiation, and a progressive long-lasting increase in its levels in the intestinal mucosa and, especially, in the brain was found after a 750-rd-irradiation. It is concluded that these organs contain different cAMP systems, which would explain, at least in part, their dissimilar responses to the ionizing rays.