β-Adrenoceptor stimulation up-regulates phosphodiesterase 4 activity and reduces prostaglandin E₂-inhibitory effects in human neutrophils

Abstract.

Human neutrophils were treated for 4 h with a combination of salbutamol (1 µM), a β₂-adrenoceptor agonist, and rolipram (30 µM), a selective phosphodiesterase 4 inhibitor, to investigate whether this treatment produces up-regulation of phosphodiesterase activity with functional consequences. Anion-exchange chromatography coupled with the use of selective activators and inhibitors demonstrated that a phosphodiesterase activity with characteristics of the isoenzyme type 4 was increased in drug-treated cells. Kinetic analysis showed a ~1.5-fold increase in V _max without alteration of K _m values. The augmented phosphodiesterase activity in drug-treated cells was abolished by actinomycin D. Cyclic AMP content in drug-treated cells was higher than resting values (27.28±2.79 pmol/10⁶ cells vs. 0.34±0.03 pmol/10⁶ cells). Reverse transcriptase-polymerase chain reaction showed increased expression of mRNA transcripts for PDE4B and PDE4A in drug-treated cells. Functionally, up-regulation of phosphodiesterase 4 reduced the inhibition by prostaglandin E₂ of zymosan-induced superoxide generation.