Cyclic nucleotide levels in mouse mammary epithelial cells during growth arrest and growth initiation in culture

Intracellular levels of cyclic AMP (cAMP) and cyclic GMP (cGMP) were measured in high and low tumorigenic mouse mammary epithelial cells during growth arrest in 1% fetal bovine serum and during the first 60 minutes after serum stimulation of cell proliferation in arrested cultures. Stationary MCG-T14 cells, which are highly tumorigenic and grow to high densities in 1% serum, exhibited lower levels of cAMP, higher levels of cGMP, and a lower ratio of cAMP to cGMP than quiescent MCG-V14 cells, which have low tumorigenicity and achieve low cell densities in 1% serum. Within 5-10 minutes after cell growth was initiated in arrested cultures by the addition of serum, both cell lines responded with a fourfold to fivefold increase in cGMP and a concomitant 50% decrease in cAMP. MCG-T14 cells exhibited the highest intracellular levels of cGMP and the lowest cAMP to cGMP ratio within 10 minutes after serum addition.