cAMP-treated bovine adrenocortical cells are arrested in the G1 phase of the cell cycle. Removal of serum also arrests bovine adrenocortical cells in G1. In the presence of cAMP, serum and fibroblast growth factor stimulate increases in medium cell volume, but DNA synthesis is not initiated. Under these conditions cAMP increases steroidogenic capacity 7- to 10-fold as assessed by metabolism of pregnenolone to fluorogenic steroids. When the kinetics of entry of cells into S phase are quantitated, serum- and FGF-treated cells initiate DNA synthesis at an exponential rate after a 12-h lag. In contrast when cAMP is removed, cells immediately initiate DNA synthesis without a lag at a similar exponential rate (6.3 and 5.3% of the cells entering S/h). In the presence of growth factors, cAMP-treated bovine adrenocortical cells are thus hypertrophied with increased steroidogenic capacity, but are reversibly arrested at the G1/S boundary. These findings suggest that cAMP arrests cell replication by mechanisms distinct from those of serum deprivation.
8-Bromo Cyclic Adenosine Monophosphate Adrenal Cortex