Carrasco, M., M. Del Rio, A. Hernanz and M. De La Fuente. Inhibition of human neutrophil functions by sulfated and nonsulfated cholecystokinin octapeptides. Peptides 18(3) 415–422, 1997.—The effects of CCK-8s and desulfated CCK-8 at concentrations ranging from 10−14 to 10−6M were studied in vitro on several functions of human peripheral neutrophils: adherence to substrate, mobility (spontaneous and directed by a chemical gradient or chemotaxis), ingestion of inert particles (latex beads) or cells (Candida albicans), and production of superoxide anion measured by the nitroblue tetrazolium reduction test. The effect of CCK-8s on intracellular levels of cAMP was investigated as well as the implication of calcium in the action of CCK-8s on phagocytic function using stimulants and inhibitors of both intracellular and extracellular calcium channels. The two peptides, at concentrations from 10−12 to 10−8M, inhibited significantly both mobility and ingestion capacities and increased adherence to substrate. A dose-response relationship was observed with a maximum inhibition of neutrophil functions at 10−10M. CCK-8s and desulfated CCK-8 induced in these cells a significant, but transient, increase of cAMP levels at 60 s. Moreover, CCK-8s was found to inhibit completely the stimulation of latex bead phagocytosis in neutrophils produced by the calcium ionophore A23187. These results suggest that CCK-8 is a negative modulator of several neutrophil functions and that the inhibition of these activities could be carried out through an increase of the intracellular cAMP levels and a decrease of the extracellular calcium input.