Neutrophil-derived relaxing factor relaxes vascular smooth muscle through a cGMP-mediated mechanism

Neutrophils harvested from the peritoneal cavities of rats have been shown to release a factor that relaxes precontracted aorta and has a pharmacologic profile similar to that previously reported for endothelium-derived relaxing factor (EDRF). The present study was designed to determine if this neutrophil-derived relaxing factor (NDRF) relaxes rat aortic smooth muscle by affecting the intracellular cGMP levels. Aortic sheets (endothelium removed) were incubated in organ chambers in a physiological salt solution containing phenylephrine (1 x 10(-7) M) and superoxide dismutase (10 or 100 U/ml). Basal cGMP levels (10-15 pmoles/g tissue) were not affected by the incubation reagents. Neutrophils (3 x 10(6) to 1 x 10(8) cells/10 ml) increased cGMP, but not cAMP, levels in a cell number-dependent manner. Peak induction occurred at 5 min of incubation. Methylene blue (1 x 10(-5) M) inhibited and zaprinast (1 x 10(-5) M) potentiated the neutrophil-induced increases in cGMP. The data thus support the hypothesis that neutrophil-induced vascular smooth muscle relaxation is mediated through a factor, NDRF, which increases intracellular cGMP levels.