Effect of PDE4 inhibitors on fibroblastic colony formation by whole bone marrow. Whole bone marrow was prepared and cultured in the CFU-f assay as described in the text and treated with varying concentrations of the PDE4 inhibitors EMD 273316, EMD95833, EMD249615 or EMD219906. Medium changes, fixation and staining were as in Fig. 1. 10-7 M PGE2 was used as a positive control in these experiments. Data presented are mean colony numbers per Petri dish ± S.D. * Denotes significant difference from control cultures, p < 0.05.