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

Abstract

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 Ca 2+. Cyclic AMP, superoxide production and elastase release were measured by radioimmunoassay, lucigenin-enhanced chemiluminescence, and a colorimetric procedure respectively. Cytosolic Ca 2+ 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 β 1-, α 1- or α 2-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 Ca 2+ 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 Ca 2+. These effects of epinephrine on the clearance of Ca 2+ from the cytosol of FMLP-activated neutrophils were attenuated by propranolol, and are compatible with enhancement of the activity of the cAMP-dependent Ca 2+ sequestering/resequestering endo-membrane Ca 2+-ATPase. We conclude that epinephrine down-regulates the pro-inflammatory activities of neutrophils by cAMP-mediated enhancement of the clearance of cytosolic Ca 2+.