Table 1.

Twenty-four-hour pretreatment with PGE₂ desensitizes PGE₂ responses in a concentration-dependent manner

Pretreatment condition	Log EC50
Vehicle	− 7.40 ±0.16
1 nM PGE2	− 7.10 ± 0.25
10 nM PGE2	− 6.79 ± 0.20
100 nM PGE2	− 6.09 ±0.15

HFL-1 cells were treated with vehicle and 1 nM, 10 nM, or 100 nM PGE₂ for 24 h and washed, then acute cAMP responses to PGE₂ were measured using the cADDis assay. Various concentrations of PGE₂ ranging from 0.1 to 10 μM were added and responses measured as the change in fluorescence normalized to the change in fluorescence of maximal response stimulated by 1 μM forskolin plus 200 μM IBMX. The log EC₅₀ was then calculated for PGE₂ in each pretreatment condition. Data are mean ± SEM of n = 3–10