2.9 Materials
Selective PDE-4 inhibitors tested in this study were: roflumilast-N-Oxide (RNO), the active metabolite of roflumilast (Bundschuh et al., 2001), kindly provided by Nycomed-Takeda (Konstanz, Germany), roflumilast for in vivo experiments by Aurogene (Rome, Italy) and rolipram by Calbiochem (Milan, Italy).