A new relaxing factor in supernatant of incubated rat peritoneal neutrophils

It was found that when rat peritoneal neutrophils were added to an organ bath, they released an unstable vasoactive substance designated as neutrophil-derived relaxing factor (NDRF), which is similar to endothelium-derived relaxing factor. Besides NDRF, a more stable (activity maintained for at least 7 days at -80 degrees C) relaxing factor was found to be generated in the supernatant after the incubation of rat peritoneal neutrophils in buffer. This supernatant relaxing factor (SRF) induced an increase in the guanosine 3',5'-cyclic monophosphate content of aortic strips. Its relaxing activity was potentiated by superoxide dismutase. It was inhibited by hemoglobin, hydroquinone, or methylene blue but not by catalase or mannitol. Preincubation of polymorphonuclear neutrophils with aspirin, quinacrine, metyrapone, or AA-861 had no effect on the relaxing activity of SRF. L-Arginine dose dependently increased the relaxing activity of SRF, whereas NG-monomethyl-L-arginine (L-NMMA) decreased it, and this decrease was reversed by L-arginine. In contrast, neither L-arginine nor L-NMMA affected the relaxing activity of NDRF. These data suggest that SRF may represent a relaxing factor that is synthesized de novo from L-arginine.