Nitric Oxide

Abstract

Summary: Rat serosal mast cells were tested for their ability to generate a nitric oxide (NO)-like factor by two bioassay systems: inhibition of platelet aggregation and stimulation of mast cell guanylate cyclase. The relationship between histamine release and NO-like activity from these cells was also investigated. Incubation with human washed platelets of rat serosal mast cells treated with indomethacin resulted in an inhibition of thrombin-induced platelet aggregation proportional to the number of cells. The inhibition was potentiated by superoxide dismutase (SOD, 60 U/ml) and reversed by oxyhemoglobin (oxyHb, 10 μM). The inhibitory activity of mast cells was also prevented by NG-monomethyl-l-arginine (MeArg, 300 μM), an effect reversed by coincubation with l-Arg (100 μM) but not d-Arg (100 μM). When mast cells alone were exposed for 10 min to either stirring (1,000 rpm), E. coli lipopolysaccharide (LPS, 20 μg/ml), or sodium nitro-prusside (NaNp, 80 μM) an increase in the levels of their guanosine-3′,5′-cyclic monophosphate (cyclic GMP) was observed. The increase promoted by stirring or LPS but not that by NaNp was reduced by pretreatment with MeArg. The inhibitory effect of MeArg was reversed by l-Arg but not d-Arg. The increase in cyclic GMP after pretreatment with MeArg (300 μM) was accompanied by a marked increase in histamine release from these cells. The effect of MeArg was reversed by l-Arg but not d-Arg both at 200 μM. The release of histamine by the calcium ionophore A23187 (1 μM), compound 48/80 (0.5 μg/ml), or paracetamol (10 μM)-prostaglandin synthase (500 mU/ml) was prevented by coincubation with NaNp (0.1-100 μM), an effect reversed by oxyHb (10 μM). However, the release of histamine by superoxide anions generated by xanthine (100 μM)-xanthine oxidase (20 mU/ml) was not altered by NaNp. These results demonstrate that rat serosal mast cells release a NO-like factor derived from l-arginine that (a) inhibits platelet function and (b) through a stimulation of the soluble guanylate cyclase modulates the release of histamine. These effects are also shared by drugs such as NaNp that release NO.