Substance P primes the formation of hydrogen peroxide and nitric oxide in human neutrophils

Substance P (SP), a neurotransmitter of the central and peripheral nervous system, has been implicated as a mediator of the pulmonary inflammatory res ponse through its stimulatory effects on neutrophils. We investigated the r ole of SP in priming the production of reactive oxygen species by human neu trophils with the cytochrome c reduction assay and by flow cytometry using the intracellular oxidizable probe dichlorofluorescein. We also investigate d SP-induced formation of nitrite and nitrate as an index of nitric oxide ( NO) production, Our results indicate that SP primes two distinct pathways w ith respect to the induction of reactive oxygen species in the human neutro phil: the production of superoxide anion and hydrogen peroxide by the calmo dulin-dependent NADPH oxidase, and the generation of NO by a constitutive N O synthase. Preincubation of neutrophils with inhibitors of calmodulin and NO synthase diminished the oxidative response in an additive fashion, These results give insight into distinct signal transduction pathways in the SP- primed neutrophil with respect to the formation of superoxide anion, hydrog en peroxide, and NO.