The anti-inflammatory interactions of epinephrine with human neutrophils in vitro are achieved by cyclic AMP-mediated accelerated resequestration of cytosolic calcium

This study was designed to evaluate the effects of epinephrine (0.01-1 μM) on superoxide production by, and release of elastase from human neutrophils activated with the chemotactic tripeptide, N-formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP) (1 μM) in vitro, and to relate alterations in these responses to changes in adenosine 3,5′ cyclic monophosphate (cAMP) and cytosolic free Ca2+. Cyclic AMP, superoxide production and elastase release were measured by radioimmunoassay, lucigenin-enhanced chemiluminescence, and a colorimetric procedure respectively. Cytosolic Ca2+ fluxes were measured by fura-2 spectrofluorimetry in combination with radiometric procedures that enable distinction between net efflux and influx of the cation. Epinephrine treatment of neutrophils resulted in increased cAMP and dose-related inhibition of both superoxide production and elastase release, which was potentiated by the type 4 phosphodiesterase inhibitor, rolipram, and attenuated by propranolol, but not by selective β1-, α1- or α2-adrenoreceptor antagonists. Although epinephrine did not affect the FMLP-activated abruptly-occurring increase in fura-2 fluorescence intensity, indicating no effects on the release of Ca2+ from neutrophil intracellular stores, this agent accelerated the rate of decline in fluorescence in the setting of decreased efflux and a reduction in store-operated influx of Ca2+. These effects of epinephrine on the clearance of Ca2+ from the cytosol of FMLP-activated neutrophils were attenuated by propranolol, and are compatible with enhancement of the activity of the cAMP-dependent Ca2+ sequestering/resequestering endo-membrane Ca2+-ATPase. We conclude that epinephrine down-regulates the pro-inflammatory activities of neutrophils by cAMP-mediated enhancement of the clearance of cytosolic Ca2+. © 2001 Elsevier Science Inc.