Molecular and metabolic evidence for the restricted expression of inducible nitric oxide synthase in healing wounds

Tissue injury initiates a temporally ordered sequence of local cellular and metabolic responses presumably necessary for successful repair. Previous i nvestigations demonstrated that metabolic evidence for nitric oxide synthas e (NOS) activity is detectable in wounds only during the initial 48 to 72 h ours of the repair process. Present results identify the cell types contrib uting inducible NOS (iNOS) to experimental wounds in rats. iNOS antigen was expressed in most macrophages present in wounds 6 to 24 hours after injury , and these cells exhibited NAPDH diaphorase and NOS activity. Polymorphonu clear leukocytes contained little iNOS antigen and no NADPH diaphorase acti vity and were minimally able to convert L-arginine to L-citrulline. The fre quency of iNOS-positive macrophages declined on days 3 and 5 after wounding . By day 10, most macrophages in the wound were negative for iNOS. These ce lls, however, acquired iNOS antigen and activity in culture. Wound fluids, but not normal rat serum, suppressed the induction of iNOS during culture. Findings indicate that the expression of iNOS in healing wounds is restrict ed to macrophages present during the early phases of repair and that compon ents of wound fluid suppress the induction of iNOS in macrophages in late w ounds. Polymorphonuclear leukocytes contribute little iNOS activity to the healing wound.