NITRIC-OXIDE METABOLISM IN WOUNDS

Arginine can be metabolized in wounds to nitric oxide and citrulline b y nitric oxide synthase or to urea and ornithine by arginase, We inves tigated the expression of these arginine metabolic pathways over a 3-w eek, period, Groups of 8-10 male Balb/C mice underwent a dorsal skin i ncision and subcutaneous polyvinyl alcohol sponge implantation. The an imals were sacrificed at various times, and sponges were harvested to obtain wound fluid and wound cells. Cells or whole sponges were incuba ted with L-[2,3-H-3]arginine, with or without N-G-L-monomethyl-arginin e (NMMA, a competitive inhibitor of nitric oxide synthase). Nitrite an d nitrate (both stable end products of nitric oxide metabolism) and am ino acids were measured in wound fluid and wound cell culture supernat ants, Increasing concentrations of nitrite and nitrate were noted in w ound fluid and in whole sponge cultures until the second week postwoun ding, indicating sustained wound nitric oxide synthesis. In wound flui d arginine levels were undetectable at all times, suggesting sustained utilization. Wound fluid citrulline levels showed an early peak and t hen a gradual decrease, suggesting that recycling for continued nitric oxide production may occur. Wound fluid ornithine levels increased un til Day 10 and remained elevated, indicative of continued arginase act ivity, In vitro production of nitrite/nitrate and citrulline by cells and whole sponges was inhibitable by NMMA, Inducible nitric oxide synt hase expression was confirmed by immunoblotting, while immunohistochem istry demonstrated that macrophages are a major source of wound nitric oxide. The data show that nitric oxide synthesis occurs for prolonged periods after injury and macrophages appear to be a major cellular so urce. (C) 1997 Academic Press.