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The study was designed to test the hypothesis that nitric oxide (NO)‐releasing compounds increase guanosine 3′:5′‐cyclic monophosphate (cyclic GMP) production in human polymorphonuclear leucocytes (PMNs) and concomitantly inhibit PMN functions, i.e. leukotriene B4 (LTB4) synthesis, degranulation, chemotaxis and superoxide anion (O2−) release. The effects of two new NO‐releasing compounds, GEA 3162 and GEA 5024 were compared to 3‐morpholino‐sydnonimine (SIN‐1) and S‐nitroso‐N‐acetyl‐penicillamine (SNAP). GEA 3162 and GEA 5024 (1–100 μm) inhibited Ca ionophore A23187‐induced LTB4 and β‐glucuronidase release, chemotactic peptide FMLP‐induced chemotaxis and opsonized zymosan‐triggered chemiluminescence dose‐dependently in human PMNs. SIN‐1 and SNAP were weaker inhibitors. Cellular cyclic GMP production was increased after exposure to NO‐donors concomitantly with the inhibition of PMN functions. No alterations in the levels of adenosine 3′:5′‐cylic monophosphate (cyclic AMP) were detected. The results suggest that NO, possibly through increased cyclic GMP, inhibits the activation of human PMNs and may thus act as a local modulator in inflammatory processes.

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