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 muM) on superoxide production by, and release of elastase from human neutrophil s activated with the chemotactic tripeptide, N-formyl-L-methionyl-L-leucyl- L-phenylalanine (FMLP)(1 muM) in vitro, and to relate alterations in these responses to changes in adenosine 3,5' cyclic monophosphate (cAMP) and cyto solic free Ca2+. Cyclic AMP, superoxide production and elastase release wer e measured by radioimmunoassay, lucigenin-enhanced chemiluminescence, and a colorimetric procedure respectively. Cytosolic Ca2+ fluxes were measured b y fura-2 spectrofluorimetry in combination with radiometric procedures that enable distinction between net efflux and influx of the cation. Epinephrin e Treatment of neutrophils resulted in increased cAMP and dose-related inhi bition of both superoxide production and elastase release, which was potent iated by the type 4 phosphodiesterase inhibitor, rolipram, and attenuated b y propranolol, but not by selective beta (1)-, alpha (1)- or alpha (2)-adre noreceptor antagonists. Although epinephrine did not affect the FMLP-activa ted abruptly-occurring increase in fura-2 fluorescence intensity, indicatin g no effects on the release of Ca2+ from neutrophil intracellular stores, t his agent accelerated the rate of decline in fluorescence in the setting of decreased efflux and a reduction in store-operated influx of Ca2+. These e ffects of epinephrine on the clearance of Ca2+ from the cytosol of FMLP-act ivated neutrophils were attenuated by propranolol, and are compatible with enhancement of the activity of the cAMP-dependent Ca2+ sequestering/reseque stering endo-membrane Ca2+-ATPase. We conclude that epinephrine down-regula tes the pro-inflammatory activities of neutrophils by cAMP-mediated enhance ment of the clearance of cytosolic Ca2+. (C) 2001 Elsevier Science Inc. All rights reserved.