Interaction between PDE4 inhibitors and PGE2. CFU-f cultures were carried out as described in Fig. 1 and the cells treated with 1 μM EMD273316, EMD95833, EMD249615 or EMD219906 in the presence or absence of 1 nM PGE2. Data presented are mean colony numbers per Petri dish ± S.D. * Denotes significant difference from control cultures, p < 0.05; # denotes significant difference from corresponding PGE2-free cultures, p < 0.05.