The influence of inhibiting the nitric oxide (NO) synthetase on tissue perfusion as indicated by tissue oxygen tensions was determined. Tissue oxygen probes were placed subcutaneously and on serosal and mucosal surfaces of colon of anesthetized adult rats. After a control period, the inhibitor of NO formation, N(G)-nitro-L-arginine methyl ester (L-NMMA), was given intravenously and followed 20 min later by infusion of substrate for NO synthetase, L-arginine. Mean arterial blood pressure (MAP), subcutaneous tissue oxygen tension (P(SQ)O2), serosal tissue oxygen tension (P SO(2)), and mucosal tissue oxygen tension (P(M)O2) were simultaneously measured. Baseline values for the measured parameters were MAP = 95 + or - 9 mmHg, P(SQ)O2 = 61 + or - 7 mmHg, P(S)O2 65 + or - 7 mmHg, and P(M)02 = 9 + or - 2 mmHg. The infusion of L-NMMA induced a significant increase in MAP to 123 + or - 7 mmHg (p < .001) and P(SQ)O2 to 72 + or - 7 mmHg (p < .001). P(S)O2 did not change significantly from baseline after L-NMMA infusion. A significant decrease in P(M)O2 to 4 + or - 2 mmHg was noted after L-NMMA infusion (p < .001). The administration of L-arginine promptly returned all measured parameters to baseline levels within 10 min of infusion. A transmural P(O2) gradient exists across the colon with P(M)O2 far lower than P(S)O2. P(SQ)O2 approximates P(S)O2 at baseline and P(S)O2 is not altered by inhibition of the NO synthetase. The 45% reduction in mucosal PO2 after L-NMMA, which was reversed by L-arginine infusion, suggests that nitric oxide participates in splanchnic vasomotor control with a preferential effect in the mucosal vasculature. The observed decrease in mucosal PO2 observed after inhibition of NO production is similar to the worsened hypoxia previously measured during hemorrhagic shock. Further work clarifying the local control mechanisms of gut tissue P02 can direct therapies to increase gut tissue oxygenation.