Induction of a transient elevation in intracellular levels of adenosine-3',5'-cyclic monophosphate by chemotactic factors: an early event in human neutrophil activation.

Abstract The chemotaetic factors N-formyl-methionyl-leucylphenylalanine (FMLP) and the complement-derived fragment C5a were observed to induce a transient elevation of intracellular levels of adenosine-3’,5’-cyclic monophosphate (cAMP) in human neutrophils. The kinetics of the FMLP- and C5a-induced cAMP changes were similar: a 2- to 3-fold increase was observed at 5 to 15 sec after the addition of optimal doses of the stimuli; the response had declined by 1 min and approached control levels by 5 min of incubation at 37°C. The changes in cAMP levels were not associated with significant changes in levels of guanosine-3’,5’-cyclic monophosphate (cGMP), even with incubations up to 1 hr. Both FMLP and C5a caused the generation of superoxide radicals (O2-), which was initiated after a lag period of about 20 sec and promoted granule enzyme release from cytochalasin B-treated cells. The dose-responsiveness of the FMLP- (10-8 M - 10-7 M) and C5a- (1 to 10 μl/ml) induced O2- generation, exocytosis, and cAMP elevations was similar. As the peak elevations in cAMP occurred during the latency period of O2- generation, these studies suggest that the rise in intracellular cAMP may represent an early event in the sequence of neutrophil activation and may be responsible for subsequent metabolic events. In an attempt to further characterize the significance of this cAMP rise, the effects of preincubation of the cells with cAMP agonists on the FMLP-induced cAMP response, O2- generation, granule enzyme release, and 22Na+ uptake were investigated. Preincubation of the cells with prostaglandin E1 (PGE1, 0.01 to 10 Ug/ml), 3-isobutyl-1-methylxanthine (IBMX 2.5 × 10-5 M to 4 × 10-4 M), and dibutyryl-cAMP (3.3 × 10-5 M to 10-3 M), agents that cause comparable though sustained increases in cAMP levels, did not stimulate O2- release or exocytosis, but resulted in dose-dependent inhibition of FMLP-induced O2- production and enzyme release. IBMX preincubation resulted in blunting of the early (5 to 15 sec) FMLP-induced cAMP response, but potentiated later (1 to 5 min) FMLP effects. In contrast, the PGE1-and FMLP-stimulated cAMP responses were additive. These drugs had no effect on the magnitude of the FMLP-induced 22Na+ uptake. These data suggest that the inhibitory effects of the cAMP agonists on O2- generation and granule enzyme release occur at point(s) distal to ion influxes.