Differential Effects of Lumenal L-arginine and NG-nitro L-arginine on Blood Flow and Water Fluxes in Rat Ileum

1. The role of endogenous mucosal nitric oxide (NO) in the local regulation of H2O absorption and blood flow in rat ileum was studied by perfusing L-arginine (L-Arg) (0.1-1.0 mM) and NG-nitro L-arginine (L-NOARG) (0.01-1.0 mM) through the lumen. D-Arginine (D-Arg) or L-Arg (1 mM), combined with L-NOARG, were used to determine if any of the measured intestinal effects of L-NOARG were exerted through NO formation. 2. Net and unidirectional H2O fluxes and effective mucosal blood flow were measured using 3H2O and [14C]-inulin in the perfusate. Mucosal NO formation was measured as the appearance of lumenal NO2-. 3. L-NOARG, beginning at a concentration of 0.1 mM, decreased net H2O absorption, but had only minor effects on unidirectional H2O fluxes or on blood flow. L-NOARG increased blood pressure, beginning at a concentration of 0.5 mM. 4. L-Arg had no significant effects on net H2O absorption or blood pressure, and only minor effects on unidirectional H2O fluxes and blood flow. 5. NO appearance in the lumen was marginally decreased by 1.0 mM L-NOARG, but not increased by L-Arg. 6. Mucosal blood flow resistance paralleled systemic blood pressure suggesting that vascular effects on the mucosa were exerted only after L-NOARG had reached the general circulation. 7. Lumenal L-Arg reversed the effects of lumenal L-NOARG on net H2O absorption and blood pressure, but D-Arg did not. 8. It was concluded that there is tonic NO production by the rat intestinal mucosa that promotes H20 absorption, but does not affect blood flow resistance. Mucosal NO production was not related to the observed effects on mucosal function.