Increases in rat liver cyclic AMP concentrations prior to the initiation of DNA synthesis following partial hepatectomy or hormone infusion

Abstract

In rat liver following partial hepatectomy an unprecedented biphasic increase in cyclic AMP concentration was observed. After a lag period of 1 1 2 hr , the cyclic AMP content rose to a peak at 2 1 2 hr . The cyclic AMP level fell to normal at 8 hr, and then rose again to a second peak at 12 hr. DNA synthesis started at 18 hr, by which time the cyclic AMP level was approaching control values. A biphasic increase in cyclic AMP concentration was also observed to precede the initiation of DNA synthesis in intact liver following the infusion of a mixture of tri-iodothyronine, amino acids, glucagon and heparin. The relationship between these biphasic changes in cyclic AMP levels and the initiation of DNA synthesis in liver is discussed.