Histamine up-regulates phosphodiesterase 4 activity and reduces prostaglandin E2-inhibitory effects in human neutrophils

Abstract:

Objective: To investigate whether histamine produces up-regulation of phosphodiesterase (PDE) activity with functional consequences in human peripheral blood neutrophils.¶Methods: PDE activity was studied by a radioisotopic method following anion-exchange chromatography. Reverse transcriptase-polymerase chain reaction (RT-PCR) was used for detection of mRNA transcripts of PDE4 subtypes. Cyclic AMP (cAMP) levels were measured by enzyme-immunoassay, and superoxide generation by cytochrome c reduction.¶Treatment: Neutrophils were incubated for 4 h with histamine (1 μM).¶Results: PDE4 was the only isoenzyme activity increased in treated neutrophils. Kinetic analysis showed a ∼1.5-fold increase in V _max without alteration of K _m values. cAMP content in treated cells was higher than resting values (0.52 ± 0.07 vs. 2.75 ± 0.31 pmol/10⁶ cells). RT-PCR showed increased expression of mRNA transcripts for PDE4B in histamine-treated cells. Functionally, up-regulation of PDE4 reduced the inhibition by prostaglandin E₂ of zymosan-induced superoxide generation.¶Conclusion: Histamine up-regulates PDE4 activity and produces heterologous desensitisation of human neutrophils.