Nitric oxide (NO) synthesis occurs during wound healing, but its role has not been defined. To study the effect of NO on
wound repair, S-methyl
isothiouronium (MITU, a competitive inhibitor of
NO synthase) was administered at a dose of 10, 50, and 100 mg/kg
body weight/day, using intraperitoneally implanted miniosmotic pumps. Groups of 10 male Balb/C mice underwent a dorsal skin incision and
polyvinyl alcohol sponges were inserted subcutaneously. The animals were sacrificed 10 days postwounding and
wound breaking strength and
hydroxyproline content of sponges, an index of reparative
collagen deposition, were determined. Some sponges were used to harvest
wound fluid and infiltrating cells, which were then incubated overnight with or without 1 mM MITU.
Nitrite and
nitrate, stable end products of NO, were measured in
wound fluid and in
wound cell culture supernatants. Continuous
intraperitoneal infusion of MITU significantly decreased
wound fluid
nitrite/
nitrate concentrations in a dose dependent manner (P < 0.01). Inhibition of
wound NO synthesis by 100 mg MITU/kg/day was paralleled by lowered
wound collagen accumulation (P < 0.01) and
wound breaking strength (P < 0.01). In vitro NO synthesis by
wound cells obtained from animals treated with 100 mg MITU/kg/day was not significantly different from controls (12.6 +/- 1.2 vs 10.7 +/- 0.6 nmole NO2 + NO3/microgram
DNA), reflecting the reversible inhibition of
NO synthase by MITU. However, NO production was equally inhibited in
wound infiltrating cells by the in vitro addition of MITU (83% vs 85%, respectively). These data suggest that
nitric oxide synthesis is critical to
wound collagen accumulation and acquisition of mechanical strength.