S49.1 Lymphoma cells were arrested in GI phase of the cell cycle when treated with either 1 pM dexamethasone (Dex) or 0.5 mM N6,02-dibutyryl cyclic adenosine 3':5'-monophosphate (Bt,cAMP) plus 0.2 mM theophylline. However, the two agents had markedly different effects on aspects of polyamine and cyclic nucleotide metabolism within the arrested cells. Bt,cAMP had a n early and pronounced inhibitory effect on ornithine decarboxylase (ODC) activity causing a decrease to 40% of control within 1 h. However, there was no significant inhibition of ODC activity in the Dex-treated cells until 4 h of exposure, at which time ODC activity was reduced to approximately 60% of the control value. Sadenosyl-L-methionine decarboxylase (SAMD) activity was reduced by both agents, Bt,cAMP having the more pronounced inhibitory effect. The activity of SAMD was reduced to 40% of control after 10 h of Dex, whereas Bt,cAMP reduced the activity to approximately 25% of control within 4 h. Intracellular polyamine pools were decreased rapidly in Dex-treated cells but not in those exposed to Bt,cAMP. Bt,cAMP decreased the amount of type I (PK,) and type I1 (PK,,) cyclic AMP-dependent protein kinase (CAMP-PK) activity to 30% of control or less within 2 h. In contrast, Dex had very little effect on either PK, or PK, until 24 h, when cell viability was affected. The specific activity of both PK, and PK,, remained significantly decreased in cells exposed to Bt,cAMP for 6 h and then resuspended in fresh medium. The rapid decrease in ODC activity in response to Bt,cAMP and the slow recovery after washout may be due to the marked decreases in total PK, and PK,, activities. Dex, which had no effect on PK, and PK,, specific activities, only slowly inhibited ODC activity and recovery of enzyme activity was rapid upon resuspension in fresh medium. These data further stress the importance of the maintenance of the cellular protein kinase pools in the regulation of the recovery time to growth inhibition in response to naturally occurring steroids and second messengers.